NASA's DART impact permanently changed the shape and orbit of asteroid moon

When NASA's Double Asteroid Redirection Test (DART) spacecraft collided with an asteroid moon called Dimorphos in 2022, the moon was significantly deformed -- creating a large crater and reshaping it so dramatically that the moon derailed from its original evolutionary progression -- according to a new study. The study's researchers believe that Dimorphos may start to "tumble" chaotically in its attempts to move back into gravitational equilibrium with its parent asteroid named Didymos.

"For the most part, our original pre-impact predictions about how DART would change the way Didymos and its moon move in space were correct," said Derek Richardson, a professor of astronomy at the University of Maryland and a DART investigation working group lead. "But there are some unexpected findings that help provide a better picture of how asteroids and other small bodies form and evolve over time."

The paper published in Planetary Science Journal on August 23, 2024 by a team led by Richardson detailed notable post-impact observations and described possible implications for future asteroid research.

One of the biggest surprises was how much the impact with DART changed the shape of Dimorphos. According to Richardson, the asteroid moon was originally oblate (shaped like a hamburger) but became more prolate (stretched out like a football) after the DART spacecraft collided with it.

"We were expecting Dimorphos to be prolate pre-impact simply because that's generally how we believed the central body of a moon would gradually accumulate material that's been shed off a primary body like Didymos. It would naturally tend to form an elongated body that would always point its long axis toward the main body," Richardson explained. "But this result contradicts that idea and indicates that something more complex is at work here. Furthermore, the impact-induced change in Dimorphos' shape likely changed how it interacts with Didymos."

Richardson noted that although DART only hit the moon, the moon and the main body are connected through gravity. The debris scattered by the spacecraft on impact also played a role in the disturbed equilibrium between the moon and its asteroid, shortening Dimorphos' orbit around Didymos. Interestingly, Didymos' shape remained the same -- a finding that indicates that the larger asteroid's body is firm and rigid enough to maintain its form even after losing mass to create its moon.

According to Richardson, Dimorphos' changes have important implications for future exploration efforts, including the European Space Agency's follow-up mission to the Didymos system slated for October 2024.

"Originally, Dimorphos was probably in a very relaxed state and had one side pointing toward the main body, Didymos, just like how Earth's moon always has one face pointing toward our planet," Richardson explained. "Now, it's knocked out of alignment, which means it may wobble back and forth in its orientation. Dimorphos might also be 'tumbling,' meaning that we may have caused it to rotate chaotically and unpredictably."

The team is now waiting to find out when the ejected debris will clear from the system, whether Dimorphos is still tumbling in space and when it will eventually regain its previous stability.

"One of our biggest questions now is if Dimorphos is stable enough for spacecraft to land and install more research equipment on it," he said. "It could take a hundred years to see noticeable changes in the system, but it's only been a few years since the impact. Learning about how long it takes Dimorphos to regain its stability tells us important things about its internal structure, which in turn informs future attempts to deflect hazardous asteroids."

Richardson and his team hope that Hera will provide more information about DART's impact. By late 2026, Hera will arrive at the binary asteroid system containing Dimorphos and Didymos to assess the internal properties of both asteroids for the first time, providing a more detailed analysis of the DART mission and its implications for the future.

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Tracking down the asteroid that sealed the fate of the dinosaurs

Geoscientists from the University of Cologne have led an international study to determine the origin of the huge piece of rock that hit the Earth around 66 million years ago and permanently changed the climate. The scientists analysed samples of the rock layer that marks the boundary between the Cretaceous and Paleogene periods. This period also saw the last major mass extinction event on Earth, in which around 70 percent of all animal species became extinct. The results of the study published in Science indicate that the asteroid formed outside Jupiter's orbit during the early development of our solar system.

According to a widely accepted theory, the mass extinction at the Cretaceous-Paleogene boundary was triggered by the impact of an asteroid at least 10 kilometres in diameter near Chicxulub on the Yucatán Peninsula in Mexico.

On impact, the asteroid and large quantities of earth rock vaporized.

Fine dust particles spread into the stratosphere and obscured the sun.

This led to dramatic changes in the living conditions on the planet and brought photosynthetic activity to a halt for several years.

The dust particles released by the impact formed a layer of sediment around the entire globe.

This is why the Cretaceous-Paleogene boundary can be identified and sampled in many places on Earth.

It contains high concentrations of platinum-group metals, which come from the asteroid and are otherwise extremely rare in the rock that forms the Earth's crust.

By analysing the isotopic composition of the platinum metal ruthenium in the cleanroom laboratory of the University of Cologne's Institute of Geology and Mineralogy, the scientists discovered that the asteroid originally came from the outer solar system.

"The asteroid's composition is consistent with that of carbonaceous asteroids that formed outside of Jupiter's orbit during the formation of the solar system," said Dr Mario Fischer-Gödde, first author of the study.

The ruthenium isotope compositions were also determined for other craters and impact structures of different ages on Earth for comparison. This data shows that within the last 500 million years, almost exclusively fragments of S-type asteroids have hit the Earth. In contrast to the impact at the Cretaceous-Paleogene boundary, these asteroids originate from the inner solar system. Well over 80 percent of all asteroid fragments that hit the Earth in the form of meteorites come from the inner solar system. Professor Dr Carsten Münker, co-author of the study, added: "We found that the impact of an asteroid like the one at Chicxulub is a very rare and unique event in geological time. The fate of the dinosaurs and many other species was sealed by this projectile from the outer reaches of the solar system."

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Probing the effects of interplanetary space on asteroid Ryugu

Samples reveal evidence of changes experienced by the surface of asteroid Ryugu, some probably due to micrometeoroid bombardment.

Analyzing samples retrieved from the asteroid Ryugu by the Japanese Space Agency's Hayabusa2 spacecraft has revealed new insights into the magnetic and physical bombardment environment of interplanetary space. The results of the study, carried out by Professor Yuki Kimura at Hokkaido University and co-workers at 13 other institutions in Japan, are published in the journal Nature Communications.

The investigations used electron waves penetrating the samples to reveal details of their structure and magnetic and electric properties, a technique called electron holography.

Hayabusa2 reached asteroid Ryugu on 27 June 2018, collected samples during two delicate touchdowns, and then returned the jettisoned samples to Earth in December 2020. The spacecraft is now continuing its journey through space, with plans for it to observe two other asteroids in 2029 and 2031.

One advantage of collecting samples directly from an asteroid is that it allows researchers to examine long-term effects of its exposure to the environment of space. The 'solar wind' of high energy particles from the sun and bombardment by micrometeoroids cause changes known as space-weathering. It is impossible to study these changes precisely using most of the meteorite samples that land naturally on Earth, partly due to their origin from the internal parts of an asteroid, and also due to the effects of their fiery descent through the atmosphere.

"The signatures of space weathering we have detected directly will give us a better understanding of some of the phenomena occurring in the Solar System," says Kimura. He explains that the strength of the magnetic field in the early solar system decreased as planets formed, and measuring the remnant magnetization on asteroids can reveal information about the magnetic field in the very early stages of the solar system.

Kimura adds, "In future work, our results could also help to reveal the relative ages of surfaces on airless bodies and assist in the accurate interpretation of remote sensing data obtained from these bodies."

One particularly interesting finding was that small mineral grains called framboids, composed of magnetite, a form of iron oxide, had completely lost their normal magnetic properties. The researchers suggest this was due to collision with high velocity micrometeoroids between 2 and 20 micrometers in diameter. The framboids were surrounded by thousands of metallic iron nanoparticles. Future studies of these nanoparticles will hopefully reveal insights into the magnetic field that the asteroid has experienced over long periods of time.

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Metal scar found on cannibal star

When a star like our Sun reaches the end of its life, it can ingest the surrounding planets and asteroids that were born with it. Now, using the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile, researchers have found a unique signature of this process for the first time -- a scar imprinted on the surface of a white dwarf star. The results are published today in The Astrophysical Journal Letters.

"It is well known that some white dwarfs -- slowly cooling embers of stars like our Sun -- are cannibalising pieces of their planetary systems. Now we have discovered that the star's magnetic field plays a key role in this process, resulting in a scar on the white dwarf's surface," says Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium in Northern Ireland, UK, and lead author of the study.

The scar the team observed is a concentration of metals imprinted on the surface of the white dwarf WD 0816-310, the Earth-sized remnant of a star similar to, but somewhat larger than, our Sun.

"We have demonstrated that these metals originate from a planetary fragment as large as or possibly larger than Vesta, which is about 500 kilometres across and the second-largest asteroid in the Solar System," says Jay Farihi, a professor at University College London, UK, and co-author on the study.

The observations also provided clues to how the star got its metal scar.

The team noticed that the strength of the metal detection changed as the star rotated, suggesting that the metals are concentrated on a specific area on the white dwarf's surface, rather than smoothly spread across it. They also found that these changes were synchronised with changes in the white dwarf's magnetic field, indicating that this metal scar is located on one of its magnetic poles.

Put together, these clues indicate that the magnetic field funneled metals onto the star, creating the scar.*

"Surprisingly, the material was not evenly mixed over the surface of the star, as predicted by theory. Instead, this scar is a concentrated patch of planetary material, held in place by the same magnetic field that has guided the infalling fragments," says co-author John Landstreet, a professor at Western University, Canada, who is also affiliated with the Armagh Observatory and Planetarium.

"Nothing like this has been seen before."

To reach these conclusions, the team used a 'Swiss-army knife' instrument on the VLT called FORS2, which allowed them to detect the metal scar and connect it to the star's magnetic field.

"ESO has the unique combination of capabilities needed to observe faint objects such as white dwarfs, and sensitively measure stellar magnetic fields," says Bagnulo.

In their study, the team also relied on archival data from the VLT's X-shooter instrument to confirm their findings.

Harnessing the power of observations like these, astronomers can reveal the bulk composition of exoplanets, planets orbiting other stars outside the Solar System.

This unique study also shows how planetary systems can remain dynamically active, even after 'death'.

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Records of cometary dust hitting the asteroid Ryugu

Ryugu is a near-Earth asteroid that gained significant attention when the Japanese Hayabusa2 mission collected samples and returned them to Earth. These samples have proven to offer a treasure trove of insights into the solar systems, including the possible role of asteroids in delivering organic molecules to earth.

Now, a team of scientists have performed an intensive investigation of Ryugu samples, discovering evidence that points to cometary organic matter being transported from space to the near-Earth region.

The team included Megumi Matsumoto, an assistant professor from the Earth Science Department at Tohoku University Graduate School of Science.

Details of their findings were published in the journal Science Advances on January 19, 2024.

Asteroid Ryugu has no protective atmospheres, and its surface layer is directly exposed to space.

Small interplanetary dust in space can hit the asteroid surface, causing changes to the composition of the asteroid surface materials.

Matsumoto and her colleagues revealed that the sample surfaces contain small 'melt splashes,' ranging in size from 5 to 20 micrometers.

These melt splashes were created when micrometeoroids of cometary dust bombarded Ryugu.

"Our 3D CT imaging and chemical analyses showed that the melt splashes consist mainly of silicate glasses with voids and small inclusions of spherical iron sulfides," says Matsumoto.

"The chemical compositions of the melt splashes suggest that Ryugu's hydrous silicates mixed with cometary dust."

The mixing and melting of Ryugu's surface materials and cometary dust during impact induced heating and rapid cooling formed the melt splashes.

The voids correspond to the water vapor released from the Ryugu's hydrous silicates and subsequently captured in the melt splashes.

Analysis also revealed small carbonaceous materials with abundant nano-pores and iron sulfide inclusions in the melt splashes.

The carbonaceous materials are texturally similar to primitive organic matter in cometary dust, though they lack nitrogen and oxygen, making them chemically different from organic matter.

"We propose that the carbonaceous materials formed from cometary organic matter via the evaporation of volatiles, such as nitrogen and oxygen, during the impact-induced heating. This suggests that cometary matter was transported to the near-Earth region from the outer solar system," adds Matsumoto.

"This organic matter might be the small seeds of life once delivered from space to Earth."

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NASA's Webb discovers dusty 'cat's tail' in Beta Pictoris System

Beta Pictoris, a young planetary system located just 63 light-years away, continues to intrigue scientists even after decades of in-depth study. It possesses the first dust disk imaged around another star — a disk of debris produced by collisions between asteroids, comets, and planetesimals. Observations from NASA’s Hubble Space Telescope revealed a second debris disk in this system, inclined with respect to the outer disk, which was seen first. Now, a team of astronomers using NASA’s James Webb Space Telescope to image the Beta Pictoris system (Beta Pic) has discovered a new, previously unseen structure.

The team, led by Isabel Rebollido of the Astrobiology Center in Spain, used Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) to investigate the composition of Beta Pic’s previously detected main and secondary debris disks. The results exceeded their expectations, revealing a sharply inclined branch of dust, shaped like a cat’s tail, that extends from the southwest portion of the secondary debris disk.

“Beta Pictoris is the debris disk that has it all: It has a really bright, close star that we can study very well, and a complex cirumstellar environment with a multi-component disk, exocomets, and two imaged exoplanets,” said Rebollido, lead author of the study. “While there have been previous observations from the ground in this wavelength range, they did not have the sensitivity and the spatial resolution that we now have with Webb, so they didn’t detect this feature.”

A Star’s Portrait Improved with Webb

Even with Webb or JWST, peering at Beta Pic in the right wavelength range — in this case, the mid-infrared — was crucial to detect the cat’s tail, as it only appeared in the MIRI data. Webb’s mid-infrared data also revealed differences in temperature between Beta Pic’s two disks, which likely is due to differences in composition.

“We didn’t expect Webb to reveal that there are two different types of material around Beta Pic, but MIRI clearly showed us that the material of the secondary disk and cat’s tail is hotter than the main disk,” said Christopher Stark, a co-author of the study at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The dust that forms that disk and tail must be very dark, so we don’t easily see it at visible wavelengths — but in the mid-infrared, it’s glowing.”

To explain the hotter temperature, the team deduced that the dust may be highly porous “organic refractory material,” similar to the matter found on the surfaces of comets and asteroids in our solar system. For example, a preliminary analysis of material sampled from asteroid Bennu by NASA’s OSIRIS-REx mission found it to be very dark and carbon-rich, much like what MIRI detected at Beta Pic.

The Tail’s Puzzling Beginning Warrants Future Research

However, a major lingering question remains: What could explain the shape of the cat’s tail, a uniquely curved feature unlike what is seen in disks around other stars?

Rebollido and the team modeled various scenarios in an attempt to emulate the cat’s tail and unravel its origins. Though further research and testing is required, the team presents a strong hypothesis that the cat’s tail is the result of a dust production event that occurred a mere one hundred years ago.

“Something happens — like a collision — and a lot of dust is produced,” shared Marshall Perrin, a co-author of the study at the Space Telescope Science Institute in Baltimore, Maryland. “At first, the dust goes in the same orbital direction as its source, but then it also starts to spread out. The light from the star pushes the smallest, fluffiest dust particles away from the star faster, while the bigger grains do not move as much, creating a long tendril of dust.”

“The cat’s tail feature is highly unusual, and reproducing the curvature with a dynamical model was difficult,” explained Stark. “Our model requires dust that can be pushed out of the system extremely rapidly, which again suggests it’s made of organic refractory material.”

The team’s preferred model explains the sharp angle of the tail away from the disk as a simple optical illusion. Our perspective combined with the curved shape of the tail creates the observed angle of the tail, while in fact, the arc of material is only departing from the disk at a five-degree incline. Taking into consideration the tail’s brightness, the team estimates the amount of dust within the cat’s tail to be equivalent to a large main belt asteroid spread out across 10 billion miles.

A recent dust production event within Beta Pic’s debris disks could also explain a newly-seen asymmetric extension of the inclined inner disk, as shown in the MIRI data and seen only on the side opposite of the tail. Recent collisional dust production could also account for a feature previously spotted by the Atacama Large Millimeter/submillimeter Array in 2014: a clump of carbon monoxide (CO) located near the cat’s tail. Since the star’s radiation should break down CO within roughly one hundred years, this still-present concentration of gas could be lingering evidence of the same event.

“Our research suggests that Beta Pic may be even more active and chaotic than we had previously thought,” said Stark. “JWST continues to surprise us, even when looking at the most well-studied objects. We have a completely new window into these planetary systems.”

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Ryugu samples illuminate terrestrial weathering effects on primitive meteorites

A groundbreaking study conducted by a team of international scientists has unveiled unprecedented insights into the nature of the asteroid Ryugu and shed light on the composition of water- and carbon-rich small bodies in the solar system.

Asteroids like Ryugu are remnants of planetary embryos that never reached larger sizes, making them invaluable windows into materials that formed in the early solar system.

The study centered on laboratory measurements of the samples brought back to the Earth by the Hayabusa2 spacecraft in 2020.

Led by the Japan Aerospace Exploration Agency (JAXA), Hayabusa2 aimed to uncover the true nature of Ryugu and explore how astrologists can use knowledge from meteorites to interpret telescopic observations of other hydrous asteroids.

Unlike meteorites derived from similar hydrous asteroids, the Ryugu samples avoided terrestrial alteration -- the interaction with oxygen and water in the Earth's atmosphere.

Reflectance spectroscopy, a primary technique linking laboratory analyses of meteorites to asteroid observations, was employed to compare fresh Ryugu samples with meteorites altered in terrestrial environments.

The team successfully developed analytical procedures that avoided exposing the samples to Earth's atmosphere, ensuring the preservation of their original conditions.

Previous studies suggested that Ryugu's sample mineralogy resembled CI chondrites, the most primitive meteorites chemically.

However, other studies have contradicted this by revealing a significant difference in reflectance spectra between Ryugu samples and CI chondrites.

Further investigations in the new study indicated that heating CI samples under reducing conditions at 300 °C reproduced Ryugu's sample mineralogy well, resulting in spectra closely matching those of Ryugu samples.

The findings challenge previous assumptions about the parent bodies of CI chondrites and underscore the susceptibility of primitive meteorite spectra to terrestrial weathering.

The study suggests that actual CI chondrite parent bodies likely exhibit darker and flatter reflectance spectra than previously thought.

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New algorithm ensnares its first 'potentially hazardous' asteroid

An asteroid discovery algorithm -- designed to uncover near-Earth asteroids for the Vera C. Rubin Observatory's upcoming 10-year survey of the night sky -- has identified its first "potentially hazardous" asteroid, a term for space rocks in Earth's vicinity that scientists like to keep an eye on. The roughly 600-foot-long asteroid, designated 2022 SF289, was discovered during a test drive of the algorithm with the ATLAS survey in Hawaii. Finding 2022 SF289, which poses no risk to Earth for the foreseeable future, confirms that the next-generation algorithm, known as HelioLinc3D, can identify near-Earth asteroids with fewer and more dispersed observations than required by today's methods.

"By demonstrating the real-world effectiveness of the software that Rubin will use to look for thousands of yet-unknown potentially hazardous asteroids, the discovery of 2022 SF289 makes us all safer," said Rubin scientist Ari Heinze, the principal developer of HelioLinc3D and a researcher at the University of Washington.

The solar system is home to tens of millions of rocky bodies ranging from small asteroids not larger than a few feet, to dwarf planets the size of our moon. These objects remain from an era over four billion years ago, when the planets in our system formed and took their present-day positions.

Most of these bodies are distant, but a number orbit close to the Earth, and are known as near-Earth objects, or NEOs. The closest of these -- those with a trajectory that takes them within about 5 million miles of Earth's orbit, or about 20 times the distance from Earth to the moon -- warrant special attention. Such "potentially hazardous asteroids," or PHAs, are systematically searched for and monitored to ensure they won't collide with Earth, a potentially devastating event.

Scientists search for PHAs using specialized telescope systems like the NASA-funded ATLAS survey, run by a team at the University of Hawaii's Institute for Astronomy. They do so by taking images of parts of the sky at least four times every night. A discovery is made when they notice a point of light moving unambiguously in a straight line over the image series. Scientists have discovered about 2,350 PHAs using this method, but estimate that at least as many more await discovery.

From its peak in the Chilean Andes, the Vera C. Rubin Observatory is set to join the hunt for these objects in early 2025. Funded primarily by the U.S. National Science Foundation and the U.S. Department of Energy, Rubin's observations will dramatically increase the discovery rate of PHAs. Rubin will scan the sky unprecedentedly quickly with its 8.4-meter mirror and massive 3,200-megapixel camera, visiting spots on the sky twice per night rather than the four times needed by present telescopes. But with this novel observing "cadence," researchers need a new type of discovery algorithm to reliably spot space rocks.

Rubin's solar system software team at the University of Washington's DiRAC Institute has been working to just develop such codes. Working with Smithsonian senior astrophysicist and Harvard University lecturer Matthew Holman, who in 2018 pioneered a new class of heliocentric asteroid search algorithms, Heinze and Siegfried Eggl, a former University of Washington researcher who is now an assistant professor at the University of Illinois at Urbana-Champaign, developed HelioLinc3D: a code that could find asteroids in Rubin's dataset. With Rubin still under construction, Heinze and Eggl wanted to test HelioLinc3D to see if it could discover a new asteroid in existing data, one with too few observations to be discovered by today's conventional algorithms.

John Tonry and Larry Denneau, lead ATLAS astronomers, offered their data for a test. The Rubin team set HelioLinc3D to search through this data and on July 18, 2023 it spotted its first PHA: 2022 SF289, initially imaged by ATLAS on September 19, 2022 at a distance of 13 million miles from Earth.

In retrospect, ATLAS had observed 2022 SF289 three times on four separate nights, but never the requisite four times on one night to be identified as a new NEO. But these are just the occasions where HelioLinc3D excels: It successfully combined fragments of data from all four nights and made the discovery.

"Any survey will have difficulty discovering objects like 2022 SF289 that are near its sensitivity limit, but HelioLinc3D shows that it is possible to recover these faint objects as long as they are visible over several nights," said Denneau. "This in effect gives us a 'bigger, better' telescope."

Other surveys had also missed 2022 SF289, because it was passing in front of the rich starfields of the Milky Way. But by now knowing where to look, additional observations from Pan-STARRS and Catalina Sky Survey quickly confirmed the discovery. The team used B612 Asteroid Institute's ADAM platform to recover further unrecognized observations by the NSF-supported Zwicky Transient Facility telescope.

2022 SF289 is classified as an Apollo-type NEO. Its closest approach brings it within 140,000 miles of Earth's orbit, closer than the moon. Its diameter of 600ft is large enough to be classified as "potentially hazardous." But despite its proximity, projections indicate that it poses no danger of hitting Earth for the foreseeable future. Its discovery has been announced in the International Astronomical Union's Minor Planet Electronic Circular MPEC 2023-O26.

Currently, scientists know of 2,350 PHAs but expect there are more than 3,000 yet to be found.

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Sun 'umbrella' tethered to asteroid might help mitigate climate change

Earth is rapidly warming and scientists are developing a variety of approaches to reduce the effects of climate change. István Szapudi, an astronomer at the University of Hawaiʻi Institute for Astronomy, has proposed a novel approach -- a solar shield to reduce the amount of sunlight hitting Earth, combined with a tethered, captured asteroid as a counterweight. Engineering studies using this approach could start now to create a workable design that could mitigate climate change within decades.

The paper, "Solar radiation management with a tethered sun shield," is published in Proceedings of the National Academy of Sciences.

One of the simplest approaches to reducing the global temperature is to shade the Earth from a fraction of the Sun's light. This idea, called a solar shield, has been proposed before, but the large amount of weight needed to make a shield massive enough to balance gravitational forces and prevent solar radiation pressure from blowing it away makes even the lightest materials prohibitively expensive. Szapudi's creative solution consists of two innovations: a tethered counterweight instead of just a massive shield, resulting in making the total mass more than 100 times less, and the use of a captured asteroid as the counterweight to avoid launching most of the mass from Earth.

"In Hawaiʻi, many use an umbrella to block the sunlight as they walk about during the day. I was thinking, could we do the same for Earth and thereby mitigate the impending catastrophe of climate change?" Szapudi said.

Szapudi began with the goal of reducing solar radiation by 1.7%, an estimate of the amount needed to prevent a catastrophic rise in global temperatures. He found that placing a tethered counterbalance toward the Sun could reduce the weight of the shield and counterweight to approximately 3.5 million tons, about one hundred times lighter than previous estimates for an untethered shield.

While this number is still far beyond current launch capabilities, only 1% of the weight -- about 35,000 tons -- would be the shield itself, and that is the only part that needs to be launched from Earth. With newer, lighter materials, the mass of the shield can be reduced even further. The remaining 99% of the total mass would be asteroids or lunar dust used as a counterweight. Such a tethered structure would be faster and cheaper to build and deploy than other shield designs.

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Researchers demystify the unusual origin of the Geminids meteor shower

The Geminids meteoroids light up the sky as they race past Earth each winter, producing one of the most intense meteor showers in our night sky.

Mysteries surrounding the origin of this meteoroid stream have long fascinated scientists because, while most meteor showers are created when a comet emits a tail of ice and dust, the Geminids stem from an asteroid -- a chunk of rock that normally does not produce a tail. Until recently, the Geminids had only been studied from Earth.

Now, Princeton researchers used observations from NASA's Parker Solar Probe mission to deduce that it was likely a violent, catastrophic event -- such as a high-speed collision with another body or a gaseous explosion -- that created the Geminids. The findings, which were published in the Planetary Science Journal on June 15, narrow down hypotheses about this asteroid's composition and history that would explain its unconventional behavior.

"Asteroids are like little time capsules for the formation of our solar system," said Jamey Szalay, research scholar at the Princeton University space physics laboratory and co-author on the paper. "They were formed when our solar system was formed, and understanding their composition gives us another piece of the story."

An unusual asteroid

Unlike most known meteor showers that come from comets, which are made of ice and dust, the Geminids stream seems to originate from an asteroid -- a chunk of rock and metal -- called 3200 Phaethon.

"Most meteoroid streams are formed via a cometary mechanism, it's unusual that this one seems to be from an asteroid," said Wolf Cukier, undergraduate class of 2024 at Princeton and lead author on the paper.

"Additionally, the stream is orbiting slightly outside of its parent body when it's closest to the sun, which isn't obvious to explain just by looking at it," he added, referring to a recent study with Parker Solar Probe images of the Geminids led by Karl Battams of the Naval Research Laboratory.

When a comet travels close to the Sun it gets hotter, causing the ice on the surface to release a tail of gas, which in turn drags with it little pieces of ice and dust. This material continues to trail behind the comet as it stays within the Sun's gravitational pull. Over time, this repeated process fills the orbit of the parent body with material to form a meteoroid stream.

But because asteroids like 3200 Phaethon are made of rock and metal, they are not typically affected by the Sun's heat the way comets are, leaving scientists to wonder what causes the formation of 3200 Phaethon's stream across the night sky.

"What's really weird is that we know that 3200 Phaethon is an asteroid, but as it flies by the Sun, it seems to have some kind of temperature-driven activity," Szalay said. "Most asteroids don't do that."

Some researchers have suggested that 3200 Phaethon may actually be a comet that lost all of its snow, leaving only a rocky core resembling an asteroid. But the new Parker Solar Probe data show that although some of 3200 Phaethon's activity is related to temperature, the creation of the Geminids stream was likely not caused by a cometary mechanism, but by something much more catastrophic.

Opening the time capsule

To learn about the origin of the Geminids stream, Cukier and Szalay used the new Parker Solar Probe data to model three possible formation scenarios, then compared these models to existing models created from Earth-based observations.

"There are what's called the 'basic' model of formation of a meteoroid stream, and the 'violent' creation model," Cukier said. "It's called 'basic' because it's the most straight-forward thing to model, but really these processes are both violent, just different degrees of violence."

These different models reflect the chain of events that would transpire according to the laws of physics based on different scenarios. For example, Cukier used the basic model to simulate all of the chunks of material releasing from the asteroid with zero relative velocity -- or with no speed or direction relative to 3200 Phaethon -- to see what the resulting orbit would look like and compare it to the orbit shown by the Parker Solar Probe probe data.

He then used the violent creation model to simulate the material releasing from the asteroid with a relative velocity of up to one kilometer per hour, as if the pieces were knocked loose by a sudden, violent event.

He also simulated the cometary model -- the mechanism behind the formation of most meteoroid streams. The resulting simulated orbit matched the least with the way the Geminids orbit actually appears according to the Parker Solar Probe data, so they ruled out this scenario.

In comparing the simulated orbits from each of the models, the team found that the violent models were most consistent with the Parker Solar Probe data, meaning it's likely that a sudden, violent event -- such as a high-speed collision with another body or a gaseous explosion, among other possibilities -- created the Geminids stream.

The research builds on the work of Szalay and several colleagues of the Parker Solar Probe mission, built and assembled at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, to assemble a picture of the structure and behavior of the large cloud of dust that swirls through the innermost solar system.

They took advantage of Parker's flight path -- an orbit that swings it just millions of miles from the Sun, closer than any spacecraft in history -- to get the best direct look at the dusty cloud of grains shed from passing comets and asteroids.

Although the probe doesn't measure dust particles directly, it can track dust grains in a clever way: as dust grains pelt the spacecraft along its path, the high-velocity impacts create plasma clouds. These impact clouds produce unique signals in electric potential that are picked up by several sensors on the probe's FIELDS instrument, which is designed to measure the electric and magnetic fields near the Sun.

"The first-of-its-kind data our spacecraft is gathering now will be analyzed for decades to come," said Nour Raouafi, Parker Solar Probe project scientist at APL. "And it's exciting to see scientists of all levels and skills digging into it to shed light on the Sun, the solar system and the universe beyond."

Reaching for the stars

Cukier said his passion for learning about outer space combined with departmental support are what motivated him to pursue this project.

After taking a hands-on lab class offered by the Princeton space physics laboratory -- where he gained practical experience building space instruments, like those currently sampling the Sun's environment aboard Parker Solar Probe -- and serving as treasurer for the undergraduate astronomy club, he decided he wanted to pursue extracurricular research.

He was met with enthusiasm when he reached out to scientists in the Princeton Space Physics group. "Everyone is very supportive of undergraduate research, especially in astrophysics, because it's really part of the departmental culture," he said.

"It's always wonderful when our students like Wolf can contribute so strongly to this sort of space research," said David McComas, head of the Space Physics group and vice president for the Princeton Plasma Physics Laboratory (PPPL). "Many of us have been in awe of the Geminids meteor displays for years and it is awesome to finally have the data and research to show how they likely formed."

Cukier said that he's been drawn to watching the sky since he was a kid. "Planetary science is surprisingly accessible," he said. "For the Geminids, for instance, anyone can go outside on December 14 this year at night and look up. It's visible from Princeton, and some of the meteors are really bright. I'd highly recommend seeing it."

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Pass the salt: This space rock holds clues as to how Earth got its water

Sodium chloride, better known as table salt, isn't exactly the type of mineral that captures the imagination of scientists. However, a smattering of tiny salt crystals discovered in a sample from an asteroid has researchers at the University of Arizona Lunar and Planetary Laboratory excited, because these crystals can only have formed in the presence of liquid water.

Even more intriguing, according to the research team, is the fact that the sample comes from an S-type asteroid, a category known to mostly lack hydrated, or water-bearing, minerals. The discovery strongly suggests that a large population of asteroids hurtling through the solar system may not be as dry as previously thought. The finding, published in Nature Astronomy, gives renewed push to the hypothesis that most, if not all, water on Earth may have arrived by way of asteroids during the planet's tumultuous infancy.

Tom Zega, the study's senior author and a professor of planetary sciences at the UArizona Lunar and Planetary Laboratory, and Shaofan Che, lead study author and a postdoctoral fellow at the Lunar and Planetary Laboratory, performed a detailed analysis of samples collected from asteroid Itokawa in 2005 by the Japanese Hayabusa mission and brought to Earth in 2010.

The study is the first to demonstrate that the salt crystals originated on the asteroid's parent body, ruling out any possibility they might have formed as a consequence of contamination after the sample reached Earth, a question that had plagued previous studies that found sodium chloride in meteorites of a similar origin.

"The grains look exactly like what you would see if you took table salt at home and placed it under an electron microscope," Zega said. "They're these nice, square crystals. It was funny, too, because we had many spirited group meeting conversations about them, because it was just so unreal."

Zega said the samples represent a type of extraterrestrial rock known as an ordinary chondrite. Derived from so-called S-type asteroids such as Itokawa, this type makes up about 87% of meteorites collected on Earth. Very few of them have been found to contain water-bearing minerals.

"It has long been thought that ordinary chondrites are an unlikely source of water on Earth," said Zega who is the director of the Lunar and Planetary Laboratory's Kuiper Materials Imaging & Characterization Facility. "Our discovery of sodium chloride tells us this asteroid population could harbor much more water than we thought."

Today, scientists largely agree that Earth, along with other rocky planets such as Venus and Mars, formed in the inner region of the roiling, swirling cloud of gas and dust around the young sun, known as the solar nebula, where temperatures were very high -- too high for water vapor to condense from the gas, according to Che.

"In other words, the water here on Earth had to be delivered from the outer reaches of the solar nebula, where temperatures were much colder and allowed water to exist, most likely in the form of ice," Che said. "The most likely scenario is that comets or another type of asteroid known as C-type asteroids, which resided farther out in the solar nebula, migrated inward and delivered their watery cargo by impacting the young Earth."

The discovery that water could have been present in ordinary chondrites, and therefore been sourced from much closer to the sun than their "wetter" kin, has implications for any scenario attempting to explain the delivery of water to the early Earth.

The sample used in the study is a tiny dust particle spanning about 150 micrometers, or roughly twice the diameter of a human hair, from which the team cut a small section about 5 microns wide -- just large enough to cover a single yeast cell -- for the analysis.

Using a variety of techniques, Che was able to rule out that the sodium chloride was the result of contamination from sources such as human sweat, the sample preparation process or exposure to laboratory moisture.

Because the sample had been stored for five years, the team took before and after photos and compared them. The photos showed that the distribution of sodium chloride grains inside the sample had not changed, ruling out the possibility that any of the grains were deposited into the sample during that time. In addition, Che performed a control experiment by treating a set of terrestrial rock samples the same as the Itokawa sample and examining them with an electron microscope.

"The terrestrial samples did not contain any sodium chloride, so that convinced us the salt in our sample is native to the asteroid Itokawa," he said. "We ruled out every possible source of contamination."

Zega said tons of extraterrestrial matter is raining down on Earth every day, but most of it burns up in the atmosphere and never makes it to the surface.

"You need a large enough rock to survive entry and deliver that water," he said.

Previous work led by the late Michael Drake, a former director of the Lunar and Planetary Lab, in the 1990s proposed a mechanism by which water molecules in the early solar system could become trapped in asteroid minerals and even survive an impact on Earth.

"Those studies suggest several oceans worth of water could be delivered just by this mechanism," Zega said. "If it now turns out that the most common asteroids may be much 'wetter' than we thought, that will make the water delivery hypothesis by asteroids even more plausible."

Itokawa is a peanut-shaped near-Earth asteroid about 2,000 feet long and 750 feet in diameter and is believed to have broken off from a much larger parent body. According to Che and Zega, it is conceivable that frozen water and frozen hydrogen chloride could have accumulated there, and that naturally occurring decay of radioactive elements and frequent bombardment by meteorites during the solar system's early days could have provided enough heat to sustain hydrothermal processes involving liquid water. Ultimately, the parent body would have succumbed to the pummeling and broken up into smaller fragments, leading to the formation of Itokawa.

"Once these ingredients come together to form asteroids, there is a potential for liquid water to form," Zega said. "And once you have liquids form, you can think of them as occupying cavities in the asteroid, and potentially do water chemistry."

The evidence pointing at the salt crystals in the Itokawa sample as being there since the beginning of the solar system does not end here, however. The researchers found a vein of plagioclase, a sodium-rich silicate mineral, running through the sample, enriched with sodium chloride.

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DART impact provided real-time data on evolution of asteroid's debris

When asteroids suffer natural impacts in space, debris flies off from the point of impact. The tail of particles that form can help determine the physical characteristics of the asteroid. NASA's Double Asteroid Redirection Test mission in September 2022 gave a team of scientists including Rahil Makadia, a Ph.D. student in the Department of Aerospace Engineering at the University of Illinois Urbana-Champaign, a unique opportunity -- to observe the evolution of an asteroid's ejecta as it happened for the first time.

"My work on this mission so far has been to study the heliocentric changes to the orbit of Didymos and its smaller moon Dimorphos -- the target of the DART spacecraft," said Makadia. "Even though it hit the secondary, there are still some changes in the entire system's orbit around the sun because the entire system feels the consequences of the impact. The ejecta that escapes the system provides an extra boost in addition to the impact. So, to accurately determine where the system will be in 100 years, you need to know the contribution of the ejecta that escaped the system."

The team observed a 33-minute change in the orbit after DART's impact. Makadia said, if there were no ejecta, the period change would have been less than 33 minutes. But because some ejecta escaped the gravitational pull of Dimorphos, the orbit period change is higher than if there were no ejecta at all.

These three panels capture the breakup of the asteroid Dimorphos when it was deliberately hit by NASA's 1,200-pound Double Asteroid Redirection Test mission spacecraft on September 26, 2022. Hubble Space Telescope had a ringside view of the space demolition derby. The top panel, taken 2 hours after impact, shows an ejecta cone of an estimated 1,000 tons of dust. The center frame shows the dynamic interaction within the asteroid's binary system that starts to distort the cone shape of the ejecta pattern about 17 hours after the impact. The most prominent structures are rotating, pinwheel-shaped features. The pinwheel is tied to the gravitational pull of the companion asteroid, Didymos. In the bottom frame Hubble next captures the debris being swept back into a comet-like tail by the pressure of sunlight on the tiny dust particles. This stretches out into a debris train where the lightest particles travel the fastest and farthest from the asteroid. The mystery is compounded when Hubble records the tail splitting in two for a few days.

The study, published in the journal Nature, focused on the Hubble Space Telescope's measurements of the ejecta, beginning 15 minutes after the impact to 18 ½ days after the impact. The images showed the exact evolution of the tail and how it evolved over time.

"After a few days, the primary force acting on these ejecta particles becomes solar radiation pressure," Makadia said. "The photons emitted from the sun exert an acceleration on these small particles, and they evolve into a straight tail in an anti-solar direction.

"There have been cases in which it was determined that a natural impact caused the observed active asteroid. But because this one was very much intended, we could have telescopes pointed at it before and after the impact and study its evolution."

He said they'll use the data about how this ejecta evolves to understand how the entire system's orbit changes as well.

"Now that we have this treasure trove of data, we can make educated guesses about other tails we might observe," Makadia said. "Depending on what kind of particles are in the tail and their sizes, we can figure out how long ago that impact happened. And we'll be able to understand the ejecta that escape the system and change the entire system's heliocentric orbit."

Makadia, who earned his B.S. in 2020 from UIUC, said almost all of his work is computational.

"To calculate where an asteroid will be on a given date, we need to propagate all the possible locations that the asteroid could be at an initial time, not just one nominal solution. That requires a lot of computational power and understanding of how orbits are affected by small forces, like solar radiation pressure as well as gravity from all kinds of sources within the solar system.

"I developed simulations to study the heliocentric changes when I first started working on my Ph.D. to make sure we have a propagator that can impart all these impulses that are coming from the escaping ejecta. Now I'm developing an orbit determination tool so once we do have enough observations, we can extract this information about the heliocentric change to the system."

About the project, Makadia said, "This is 100 percent the most exciting thing in my life. It's absolutely real but so astonishing. Even now, whenever people ask about it, it sounds like I'm talking about a movie plot rather than an actual thing that happened."

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New NASA DART data prove viability of asteroid deflection as planetary defense strategy

NASA's Double Asteroid Redirection Test (DART) was Earth's first attempt at launching a spacecraft to intentionally collide with and deflect an asteroid as a planetary defense technique. On September 26, 2022, the DART spacecraft collided with a small asteroid moon called Dimorphos, which orbits a larger asteroid called Didymos. Neither asteroid posed a threat to Earth, but they represented similar celestial bodies that could one day approach and endanger the planet.

In four papers published in the journal Nature on March 1, 2023, the DART team -- which includes University of Maryland astronomers -- detailed DART's successful impact, the possible physics behind the collision, observations of the resulting debris ejected from the asteroid and calculations of Dimorphos' orbital changes. The findings confirm the feasibility of redirecting near-Earth objects like asteroids as a planetary defense measure.

"We can't stop hurricanes or earthquakes yet, but we ultimately learned that we can prevent an asteroid impact with sufficient time, warning and resources," said Derek Richardson, a professor of astronomy at UMD and a DART investigation working group lead. "With sufficient time, a relatively small change in an asteroid's orbit would cause it to miss the Earth, preventing large-scale destruction from occurring on our planet."

DART mission more successful than expected

Richardson and his UMD Department of Astronomy colleagues Professor Jessica Sunshine and Principal Research Scientist Tony Farnham played critical roles in studying the effectiveness of the DART mission to deflect an asteroid from an Earth-bound path.

Farnham was instrumental in computing the geometrical conditions and dimensions needed to interpret observations of the event accurately. Using data from spacecraft engineers and from the Didymos Reconnaissance and Asteroid Camera for Optical Navigation (DRACO), Farnham helped determine what the DART spacecraft was looking at as it approached Dimorphos.

"When dealing with observations from a spacecraft, we need to understand where in space the spacecraft is located with respect to the asteroid, the sun and Earth and where it's facing at any given time," Farnham explained. "With this information, we have the context to make our conjectures and evaluate our work."

Thanks to Farnham's work, the DART team gained important information about the general timeline of the impact, the location and nature of the impact site, and the size and shape of Dimorphos. To the team's surprise, they found the small asteroid to be an oblate spheroid, or a slightly squashed sphere-like body, instead of a more elongated shape expected from theoretical predictions.

"Both Didymos and Dimorphos are more squishy in shape -- looking more like peanut butter M&Ms and less like peanut M&Ms -- than we expected," Sunshine said. "This shape also challenges some of our preconceptions about how such asteroids form and complicates the physics behind DART because it prompts us to rethink our current models of binary asteroids."

In addition to Dimorphos' irregular shape, the scientists also noticed that the asteroid's surface was noticeably bouldery and blocky. This geomorphic quality likely influenced crater formation, the amount and physical properties of ejecta (debris expelled from impacts), and the momentum of a DART-like impact.

Sunshine, who previously served as the deputy principal investigator for the UMD-led NASA Deep Impact mission, observed that these different textural qualities led to different impact outcomes -- critical in evaluating how successfully the DART spacecraft redirected Dimorphos from its original orbit.

"The Deep Impact mission collided with a comet whose surface is made up of small, mostly uniform grains," Sunshine explained. "Deep Impact resulted in a more uniform fan of debris than the filamentary structures seen after DART's impact into bouldery terrain. As it turns out, the movement of DART-caused ejecta really had a profound effect on the success of DART's mission."

Extra push from impact debris shortened Dimorphos' orbit

The DART spacecraft was not the sole provider of momentum in the impact with Dimorphos; an additional shove was caused by violent spews of debris when the spacecraft slammed into the diminutive asteroid moon.

"There was so much debris ejected from the impact that Dimorphos was pushed approximately 3.5 times more effectively compared to being hit by the DART spacecraft alone," explained Richardson, who helped compute and verify the momentum transferred between the DART spacecraft and Dimorphos.

According to Farnham, who calculated the direction of the asteroid's ejecta, this finding was confirmed when the team measured the asteroid's orbit had changed more than the team's more conservative expectations. The difference in orbital periods, or the length of time it takes for a celestial object to complete one rotation around another object, indicates that the orbit of Dimorphos around Didymos had changed.

"Pre-impact, we expected the impact to shorten Dimorphos' orbit by only about 10 minutes,'' Farnham said. "But after the impact, we learned that the orbital period was shortened even more, reducing an ordinarily 12-hour orbit by slightly more than 30 minutes. In other words, the ejected material acted as a jet to push the moon even further out of its original orbit."

Following up with Hera mission

The DART mission represents a major first step to developing appropriate planetary defense strategies against near-Earth objects like asteroids.

The DART team anticipates that the upcoming European Space Agency Hera mission launching in October 2024 will unravel more information about the DART impact site. By 2026-27, the Hera spacecraft will revisit the binary asteroid system containing Dimorphos and Didymos and assess the internal properties of both asteroids for the first time, providing a more detailed analysis of the DART impact's effects on the system and the geophysics behind solar system formation.

"We still don't know a lot about Dimorphos and Didymos because we have only seen the outsides," Sunshine said. "What is their internal structure like? Are there differences in porosity between the two? Those are the types of questions we need to answer to really see how effective our deflections are and how celestial bodies like those asteroids form and evolve."

While the Hera mission is still in the construction phase, research from both DART and its predecessors like Deep Impact still offer a wealth of information on how humans can develop additional ways to defend Earth from approaching asteroids and comets. Thanks to a legacy of kinetic impact testing initiatives and planetary defense research led by the late Distinguished University Professor of Astronomy Mike A'Hearn, UMD astronomers are uniquely equipped to evaluate and advance planetary scale impact experimentation. Richardson, Sunshine, Farnham and their colleagues hope to honor the work that led up to DART by continuing to help pioneer new methods of asteroid threat mitigation.

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A star is born: Nearby galaxies provide clues about star formation

It is a popular notion that aside from large celestial objects like planets, stars and asteroids, outer space is empty. In fact, galaxies are filled with something called the interstellar medium (ISM) -- that is, the gas and dust that permeate the space in between those large objects. Importantly, under the right conditions, it is from the ISM that new stars are formed.

Now researchers from the University of California San Diego, in collaboration with a worldwide project team, have released their findings in a special issue of The Astrophysical Journal Letters dedicated to their work using advanced telescope images through the JWST Cycle 1 Treasury Program.

"With JWST, you can make incredible maps of nearby galaxies at very high resolution that provide amazingly detailed images of the interstellar medium," stated Associate Professor of Physics Karin Sandstrom who is a co-principal investigator on the project.

Although JWST can look at very distant galaxies, the ones Sandstrom's group studied are relatively close at about 30 million light years away, including one known as the Phantom Galaxy. Also known as M74 or NGC 628, astronomers have known of the Phantom Galaxy's existence since at least the 18th century.

Sandstrom, along with postdoctoral scholar Jessica Sutter and former postdoctoral scholar Jeremy Chastenet (now at University of Ghent), focused on a specific component of the ISM called polycyclic aromatic hydrocarbons (PAHs). PAHs are small particles of dust -- the size of a molecule -- and it's their small size that makes them so valuable to researchers.

When PAHs absorb a photon from a star, they vibrate and produce emission features that can be detected in the mid-infrared electromagnetic spectrum -- something that typically doesn't happen with larger dust grains from the ISM. The vibrational features of PAHs allow researchers to observe many important characteristics including size, ionization and structure.

This is something Sandstrom has been interested in since graduate school. "The Spitzer Space Telescope looked at the mid-infrared and that's what I used in my Ph.D. thesis. Since Spitzer was retired, we haven't had much access to the mid-infrared spectrum, but JWST is incredible," she stated. "Spitzer had a mirror that was 0.8 meters; JWST's mirror is 6.5 meters. It's a huge telescope and it has amazing instruments. I've been waiting a very long time for this."

Even though PAHs are not by mass a big fraction of the overall ISM, they're important because they're easily ionized -- a process that can produce photoelectrons which heat the rest of the gas in the ISM. A better understanding of PAHs will lead to a better understanding of the physics of the ISM and how it operates. Astrophysicists are hopeful JWST can provide a view into how PAHs are formed, how they change and how they're destroyed.

Because PAHs are evenly distributed throughout the ISM, they allow researchers to see not just the PAHs themselves, but everything around them as well. Previous maps, such as ones taken by Spitzer, contained much less detail -- they essentially looked like galactic blobs. With the clarity JWST provides, astrophysicists can now see gas filaments and even "bubbles" blown by newly formed stars, whose intense radiation fields and resulting supernova evaporate the gas clouds around them.

To get observation time on JWST, the Cycle 1 Treasury Program team had to design observations that included details such as exposure length and filters. Once their submission was accepted, Space Telescope Science Institute, which is responsible for the science and mission operations for JWST, captures and processes the data. This program includes data from 19 galaxies in total.

The Cycle 1 Treasury Program is part of a bigger project called PHANGS (Physics at High Angular Resolution in Nearby GalaxieS). PHANGS studies star formation and the ISM using multi-wavelength images from the Atacama Large Millimeter Array (ALMA) and the Very Large Telescope, both in Chile. However, because the dense clouds in which star formation happens contain a lot of dust, it is difficult for optical light to penetrate to see what's happening inside. Using the mid-infrared spectrum allows researchers to use that same dust and its bright emission to get high-resolution, detailed images.

"One of the things I'm most excited about is now that we have this high-resolution tracer of the ISM, we can map all kinds of things, including the structure of the diffuse gas, which has to become denser and molecular for star formation to occur," said Sandstrom. "We can also map the gas surrounding newly formed stars where there is a lot of 'feedback' such as from supernova explosions. We really get to see the whole cycle of the ISM in a lot of detail. That is the core of how a galaxy is going to form stars."

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Asteroid findings from specks of space dust could save the planet

Curtin University-led research into the durability and age of an ancient asteroid made of rocky rubble and dust, revealed significant findings that could contribute to potentially saving the planet if one ever hurtled toward Earth.

The international team studied three tiny dust particles collected from the surface of ancient 500-metre-long rubble pile asteroid, Itokawa, returned to Earth by the Japanese Space Agency’s Hayabusa 1 probe.

The study’s results showed asteroid Itokawa, which is 2 million kilometres from Earth and around the size of Sydney Harbour Bridge, was hard to destroy and resistant to collision.

Lead author Professor Fred Jourdan, Director of the Western Australian Argon Isotope Facility, part of the John de Laeter Centre and the School of Earth and Planetary Sciences at Curtin, said the team also found Itokawa is almost as old as the solar system itself.

"Unlike monolithic asteroids, Itokawa is not a single lump of rock, but belongs to the rubble pile family which means it’s entirely made of loose boulders and rocks, with almost half of it being empty space,” Professor Jourdan said.

“The survival time of monolithic asteroids the size of Itokawa is predicted to be only several hundreds of thousands of years in the asteroid belt.

“The huge impact that destroyed Itokawa’s monolithic parent asteroid and formed Itokawa happened at least 4.2 billion years ago. Such an astonishingly long survival time for an asteroid the size of Itokawa is attributed to the shock-absorbent nature of rubble pile material.

“In short, we found that Itokawa is like a giant space cushion, and very hard to destroy.”

The Curtin-led team used two complementary techniques to analyse the three dust particles. The first one is called Electron Backscattered Diffraction and can measure if a rock has been shocked by any meteor impact. The second method - argon-argon dating - is used to date asteroid impacts.

Co-author Associate Professor Nick Timms, also from Curtin’s School of Earth and Planetary Sciences, said the durability of rubble pile asteroids was previously unknown, jeopardising the ability to design defence strategies in case one was hurtling toward Earth.

“We set out to answer whether rubble pile asteroids are resistant to being shocked or whether they fragment at the slightest knock,” Associate Professor Timms said.

“Now that we have found they can survive in the solar system for almost its entire history, they must be more abundant in the asteroid belt than previously thought, so there is more chance that if a big asteroid is hurtling toward Earth, it will be a rubble pile.

“The good news is that we can also use this information to our advantage - if an asteroid is detected too late for a kinetic push, we can then potentially use a more aggressive approach like using the shockwave of a close-by nuclear blast to push a rubble-pile asteroid off course without destroying it.”

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Ancient asteroid grains provide insight into the evolution of our solar system

The UK's national synchrotron facility, Diamond Light Source, was used by a large, international collaboration to study grains collected from a near-Earth asteroid to further our understanding of the evolution of our solar system.

Researchers from the University of Leicester brought a fragment of the Ryugu asteroid to Diamond's Nanoprobe beamline I14 where a special technique called X-ray Absorption Near Edge Spectroscopy (XANES) was used to map out the chemical states of the elements within the asteroid material, to examine its composition in fine detail. The team also studied the asteroid grains using an electron microscope at Diamond's electron Physical Science Imaging Centre (ePSIC).

Julia Parker is the Principal Beamline Scientist for I14 at Diamond. She said: "The X-ray Nanoprobe allows scientists to examine the chemical structure of their samples at micron to nano lengthscales, which is complemented by the nano to atomic resolution of the imaging at ePSIC. It's very exciting to be able to contribute to the understanding of these unique samples, and to work with the team at Leicester to demonstrate how the techniques at the beamline, and correlatively at ePSIC, can benefit future sample return missions."

The data collected at Diamond contributed to a wider study of the space weathering signatures on the asteroid. The pristine asteroid samples enabled the collaborators to explore how space weathering can alter the physical and chemical composition of the surface of carbonaceous asteroids like Ryugu.

The researchers discovered that the surface of Ryugu is dehydrated and that it is likely that space weathering is responsible. The findings of the study, published today in Nature Astronomy, have led the authors to conclude that asteroids that appear dry on the surface may be water-rich, potentially requiring revision of our understanding of the abundances of asteroid types and the formation history of the asteroid belt.

Ryugu is a near-Earth asteroid, around 900 metres in diameter, first discovered in 1999 within the asteroid belt between Mars and Jupiter. It is named after the undersea palace of the Dragon God in Japanese mythology. In 2014, the Japanese state space agency JAXA launched Hayabusa2, an asteroid sample-return mission, to rendezvous with the Ryugu asteroid and collect material samples from its surface and sub-surface. The spacecraft returned to Earth in 2020, releasing a capsule containing precious fragments of the asteroid. These small samples were distributed to labs around the world for scientific study, including the University of Leicester's School of Physics & Astronomy and Space Park where John Bridges, one of the authors on the paper, is a Professor of Planetary Science.

John said: "This unique mission to gather samples from the most primitive, carbonaceous, building blocks of the Solar System needs the world's most detailed microscopy, and thats why JAXA and the Fine Grained Mineralogy team wanted us to analyse samples at Diamond's X-ray nanoprobe beamline. We helped reveal the nature of space weathering on this asteroid with micrometeorite impacts and the solar wind creating dehydrated serpentine minerals, and an associated reduction from oxidised Fe3+ to more reduced Fe2+.

It's important to build up experience in studying samples returned from asteroids, as in the Hayabusa2 mission, because soon there will be new samples from other asteroid types, the Moon and within the next 10 years Mars, returned to Earth. The UK community will be able to perform some of the critical analyses due to our facilities at Diamond and the electron microscopes at ePSIC."

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Dinosaurs were on the up before asteroid downfall

The findings provide the strongest evidence yet that the dinosaurs were struck down in their prime and were not in decline, at the time the asteroid hit.

Scientists have long debated why non-bird dinosaurs, including Tyrannosaurus rex and Triceratops, became extinct -- whereas mammals and other species such as turtles and crocodiles survived.

The study, led by an international team of palaeontologists and ecologists, analysed 1,600 fossil records from North America. Researchers modelled the food chains and ecological habitats of land-living and freshwater animals during the last several million years of the Cretaceous, and the first few million years of the Paleogene period, after the asteroid hit.

Paleontologists have known for some time that many small mammals lived alongside the dinosaurs. But this research reveals that these mammals were diversifying their diets, adapting to their environments and becoming more important components of ecosystems as the Cretaceous unfolded. Meanwhile, the dinosaurs were entrenched in stable niches to which they were supremely well adapted.

Mammals didn't just take advantage of the dinosaurs dying, experts say. They were creating their own advantages through diversifying -- by occupying new ecological niches, evolving more varied diets and behaviours and enduring small shifts in climate, by rapidly adapting. These behaviours probably helped them to survive, as they were better able than the dinosaurs to cope with the radical and abrupt destruction caused by the asteroid.

First author, Jorge García-Girón, Geography Research Unit, University of Oulu, Finland and Department of Biodiversity and Environmental Management, University of León, Spain, said: "Our study provides a compelling picture of the ecological structure, food webs, and niches of the last dinosaur-dominated ecosystems of the Cretaceous period and the first mammal-dominated ecosystems after the asteroid hit. This helps us to understand one of the age-old mysteries of palaeontology: why all the non-bird dinosaurs died, but birds and mammals endured."

Co-lead author, Alfio Alessandro Chiarenza, Department of Ecology and Animal Biology, University of Vigo, Spain, said: "It seems that the stable ecology of the last dinosaurs actually hindered their survival in the wake of the asteroid impact, which abruptly changed the ecological rules of the time. Conversely, some birds, mammals, crocodilians, and turtles had previously been better adapted to unstable and rapid shifts in their environments, which might have made them better able to survive when things suddenly went bad when the asteroid hit."

Senior author, Professor Steve Brusatte, Personal Chair of Palaeontology and Evolution, School of GeoSciences, University of Edinburgh, said: "Dinosaurs were going strong, with stable ecosystems, right until the asteroid suddenly killed them off. Meanwhile, mammals were diversifying their diets, ecologies and behaviours while dinosaurs were still alive. So it wasn't simply that mammals took advantage of the dinosaurs dying, but they were making their own advantages, which ecologically preadapted them to survive the extinction and move into niches left vacant by the dead dinosaurs."

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Small asteroids are probably young

The Hayabusa2 spacecraft was developed in order to study the history of the asteroid Ryugu, and collected samples and returned them to earth for laboratory analysis. The project participants are Dr. Martin Jutzi and Dr. Sabina Raducan, both from the Physical Institute of the University of Bern, Department for Space Research and Planetology (WP), and are members of the National Center of Competence in Research (NCCR) PlanetS. Under their leadership, in a study which has recently been published in Nature Communications, the team has presented new findings on the formation and development of asteroids.

Rules on the development of craters help with dating asteroids

To explore the characteristics of asteroids, during the space mission Hayabusa2, a Small Carry-on Impactor was fired at the surface of the asteroid Ryugu. "The crater made by the impact was far larger than expected. We therefore tried to reproduce the results of the impact on Ryugu with the use of simulations, to ascertain the kind of characteristics the material is required to have on the surface of the asteroid," explains Martin Jutzi.

The nature and the size of an impact crater on an asteroid are influenced by various factors. Firstly, by the specific characteristics of the projectile, and secondly, by the characteristics of the asteroid -- its strength or gravity, for example. "The size and nature of the crater resulting from the impact can lead to a direct diagnosis of the material characteristics and the near-surface structure of the asteroid," explains Jutzi. The study of the crater formation process therefore has important implications for the understanding of the geological and geophysical development of asteroids.

"So far, the way in which the formation of craters works at low gravity has largely remained unexplored. This is because the conditions of the impact cannot be simulated in laboratory experiments on Earth," explains Sabina Raducan, who is managing the project together with Martin Jutzi. The researchers show that the asteroid probably has a very loose internal structure and is only held together by very small cohesive forces and gravitational interactions. "On the basis of these conditions, we are able to use our numerical simulations to reproduce the outcome of the impact on Ryugu," explains Raducan.

The relationships between the characteristics of the projectiles and the size of the crater derived from the results indicate that the surfaces of small asteroids must be very young. "Our results also show that low cohesion can have a significant impact on crater formation. On Ryugu, there are various geological surface units that have different ages. This may be attributable to the influence of cohesion," adds Jutzi.

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Mars was once covered by 300-meter deep oceans, study shows

Mars is called the red planet. But once, it was actually blue and covered in water, bringing us closer to finding out if Mars had ever harboured life.

Most researchers agree that there has been water on Mars, but just how much water is still debated.

Now a study from the University of Copenhagen shows that some 4.5 billion years ago, there was enough water for the entire planet to be covered in a 300-metre-deep ocean.

"At this time, Mars was bombarded with asteroids filled with ice. It happened in the first 100 million years of the planet's evolution. Another interesting angle is that the asteroids also carried organic molecules that are biologically important for life," says Professor Martin Bizzarro from the Centre for Star and Planet Formation.

In addition to water, the icy asteroids also brought biologically relevant molecules such as amino acids to the Red Planet. Amino acids are used when DNA and RNA form bases that contain everything a cell needs.

The study was published in the journal Science Advances.

Mars may have had the conditions for life before Earth

The new study indicates that the oceans that covered the entire planet in water were at least 300 metres deep. They may have been up to one kilometre deep. In comparison, there is actually very little water on Earth, explains Martin Bizzarro.

"This happened within Mars's first 100 million years. After this period, something catastrophic happened for potential life on Earth. It is believed that there was a gigantic collision between the Earth and another Mars-sized planet. It was an energetic collision that formed the Earth-Moon system and, as the same time, wiped out all potential life on Earth," says Martin Bizzarro.

Therefore, the researchers have really strong evidence that conditions allowing the emergence of life were present on Mars long before Earth.

Billion-year-old meteorite

It was by means of a meteorite that is billions of years old that the researchers have been able to look into Mars's past history. The meteorite was once part of Mars's original crust and offers a unique insight into what happened at the time when the solar system was formed.

The whole secret is hiding in the way Mars's surface has been created -- and of which the meteorite was once a part -- because it is a surface that does not move. On Earth it is opposite. The tectonic plates are in perpetual motion and recycled in the planet's interior.

Read more at Science Daily

Space probe's collision with asteroid: Study assesses ejecta momentum enhancement

On September 26, NASA's Double Asteroid Redirection Test (DART) spacecraft crashed into Dimorphos, a moonlet of the near-Earth asteroid Didymos, at 14,000 miles per hour. Prior to the impact, Southwest Research Institute engineers and scientists performed an experiment to study the cratering process that produces the mass of ejected materials and measures the subsequent momentum enhancement of the impact. The internally funded experiment, which used a more realistic target than those previously explored, is described in a new paper published in The Planetary Science Journal.

NASA not only tracks near-Earth asteroids (NEAs) that could pose a possible impact threat to our home planet but is also exploring technology to deflect the path of a small NEA. Only a small orbital change would be needed to change an object's trajectory so that it passes safely by Earth, as long as the change is applied sufficiently far in advance of the time of impact. Changing the momentum of an asteroid through a direct collision offers a one-two punch: the direct momentum transfer of the impacting projectile, pushing it forward, and the asteroid's recoil from the debris erupting from the impact crater, also known as crater ejecta. The ejecta transfers momentum, propelling the target away in an "action-reaction" fashion, much like a rocket launches when high-speed gas erupts from the rear of the vehicle.

"One big question we faced was what the asteroid would actually look like and what its composition would be. Whether we can learn something from small-scale laboratory experiments is an issue of major interest to us," said Dr. James D. Walker, director of SwRI's Engineering Dynamics department and the study's lead author.

Walker is a member of the DART Investigation Team alongside his co-authors, Dr. Sidney Chocron, Donald J. Grosch and Dr. Simone Marchi.

The DART mission spacecraft launched from Earth in November 2021. On September 26, it was deliberately crashed into the moonlet Dimorphos to assess whether a spacecraft could deflect an asteroid on a collision course with Earth. Dimorphos orbits the asteroid Didymos, a near-Earth object that has been classified as a potentially hazardous asteroid. DART is designed to nudge the orbit of the moonlet around Didymos.

SwRI's large two-stage light gas gun, which is capable of launching projectiles at speeds up to seven kilometers per second, was used to launch a projectile at an object representing the moonlet. Because Dimorphos was thought to be a "rubble pile" asteroid made up of pieces of rock bound together by gravity, the moonlet was represented by a collection of rocks and stones, in this case held together by cement.

"We fired an aluminum sphere, which represented the DART space probe, using the two-stage light gas gun at the target at 5.44 kilometers per second, which is approaching the expected 6.1 kilometers per second of the DART impact," Walker said. "Our experiment measured a momentum transfer to the target of 3.4 times the incoming momentum of the aluminum sphere projectile. The number 3.4 is referred to by scientists as the Greek letter beta of the impact. Hence the crater ejecta provided an additional 240% of momentum to deflect the body, beyond that provided by the projectile itself."

The experiment aimed to study the cratering process and measure the momentum enhancement that would result from the collision. Crucially, the rubble pile was not held in place but was hung vertically as a pendulum to measure the momentum enhancement, or recoil, created by the impact ejecta.

"It's important to understand the amount of recoil," co-author Dr. Simone Marchi said. "It all boils down to the amount of momentum that has been transferred to the target from the impact, and there was a significant amount of recoil and ejecta material."

By measuring the momentum, the SwRI team could then extract important information that could assess the difficulty of deflecting asteroids in space. In this latest experiment, the momentum enhancement was higher than what was witnessed in the team's prior experiments. A higher recoil suggests it would be easier to deflect the asteroid.

In the weeks following the impact, NASA announced that DART had been successful in nudging the moonlet. Walker is now looking forward to seeing what else can be learned from the mission, including the momentum transfer of the event in space.

Read more at Science Daily