Does the organic material of comets predate our solar system?

The nucleus of comet 67P Churyumov-Gerasimenko (“Chury") as seen by the European Rosetta space probe.

The ESA's Rosetta mission, which ended in September 2016, found that organic matter made up 40% (by mass) of the nucleus of comet 67P Churyumov-Gerasimenko, a.k.a. Chury. Organic compounds, combining carbon, hydrogen, nitrogen, and oxygen, are building blocks of life on Earth. Yet, according to Jean-Loup Bertaux and Rosine Lallement -- from the Laboratoire Atmosphères, Milieux, Observations Spatiales (CNRS / UPMC / Université de Versailles Saint-Quentin-en-Yvelines) and the Galaxies, Étoiles, Physique et Instrumentation department of the Paris Observatory (Observatoire de Paris / CNRS / Université Paris Diderot), respectively -- these organic molecules were produced in interstellar space, well before the formation of the Solar System. Bertaux and Lallement further assert that astronomers are already familiar with much of this matter.

For 70 years, scientists have known that analysis of stellar spectra indicates unknown absorptions, throughout interstellar space, at specific wavelengths called the diffuse interstellar bands (DIBs). DIBs are attributed to complex organic molecules that US astrophysicist Theodore Snow believes may constitute the largest known reservoir of organic matter in the Universe. This interstellar organic material is usually found in the same proportions. However, very dense clouds of matter like presolar nebulae are exceptions. In the middle of these nebulae, where matter is even denser, DIB absorptions plateau or even drop. This is because the organic molecules responsible for DIBs clump together there. The clumped matter absorbs less radiation than when it floated freely in space.

Such primitive nebulae end up contracting to form a solar system like our own, with planets . . . and comets. The Rosetta mission taught us that comet nuclei form by gentle accretion of grains progressively greater in size. First, small particles stick together into larger grains. These in turn combine into larger chunks, and so on, until they form a comet nucleus a few kilometers wide.

Thus, the organic molecules that formerly populated the primitive nebulae -- and that are responsible for DIBs -- were probably not destroyed, but instead incorporated into the grains making up cometary nuclei. And there they have remained for 4.6 billion years. A sample-return mission would allow laboratory analysis of cometary organic material and finally reveal the identity of the mysterious interstellar matter underlying observed absorption lines in stellar spectra.

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Surprising dunes on comet Chury

Left, an image of comet Chury showing outgassing of water vapor, which entrains dust (© ESA/Rosetta/NAVCAM). Right, the neck region, between the comet's two lobes. Various types of relief can be seen, including the dunes, at bottom left (circled in red), in the sandy region.

Surprising images from the Rosetta spacecraft show the presence of dune-like patterns on the surface of comet Chury. Researchers at the Laboratoire de Physique et Mécanique des Milieux Hétérogènes (CNRS/ESPCI Paris/UPMC/Université Paris Diderot) studied the available images and modeled the outgassing of vapor to try to explain the phenomenon. They show that the strong pressure difference between the sunlit side of the comet and that in shadow generates winds able to transport grains and form dunes. Their work is published on 21 February 2017 in the journal PNAS.

The formation of sedimentary dunes requires the presence of grains and of winds that are strong enough to transport them along the ground. However, comets do not have a dense, permanent atmosphere as on Earth. Nonetheless, the OSIRIS camera on board the Rosetta spacecraft showed the presence of dune-like forms approximately ten meters apart on 67P/Churyumov-Gerasimenko. They are found on the lobes of the comet as well as on the neck that connects them. Comparison of two images of the same spot taken 16 months apart provides evidence that the dunes moved and are therefore active.

Faced with this unexpected finding, the researchers show that there is in fact a wind blowing along the comet's surface. It is caused by the pressure difference between the sunlit side, where the surface ice can sublimate due to the energy provided by the sunlight, and the night side. This transient atmosphere is still extremely tenuous, with a maximum pressure at perihelion, when the comet is closest to the Sun, 100,000 times lower than on Earth. However, gravity on the comet is also very weak, and an analysis of the forces exerted on the grains at the comet's surface shows that these thermal winds can transport centimeter-scale grains, whose presence has been confirmed by images of the ground. The conditions required to allow the formation of dunes, namely winds able to transport the grains along the ground, are thus met on Chury's surface.

This work represents a step forward in understanding the various processes at work on cometary surfaces. It also shows that the Rosetta mission still has many surprises and discoveries in store.

From Science Daily

Final descent image from Rosetta spacecraft

The OSIRIS narrow-angle camera aboard the Space Agency's Rosetta spacecraft captured this image of comet 67P/Churyumov-Gerasimenko on September 30, 2016, from an altitude of about 10 miles (16 kilometers) above the surface during the spacecraft's controlled descent. The image scale is about 12 inches (30 centimeters) per pixel and the image itself measures about 2,000 feet (614 meters) across.

A new image of comet 67P/Churyumov-Gerasimenko was taken by the European Space Agency's (ESA) Rosetta spacecraft shortly before its controlled impact into the comet's surface on Sept. 30, 2016. Confirmation of the end of the mission arrived at ESA's European Space Operations Center in Darmstadt, Germany, at 4:19 a.m. PDT (7:19 a.m. EDT / 1:19 p.m. CEST) with the loss of signal upon impact.

The final descent gave Rosetta the opportunity to study the comet's gas, dust and plasma environment very close to its surface, as well as take very high-resolution images.

The image was taken from an altitude of 167 feet (51 meters) above the comet's surface by the spacecraft's OSIRIS wide-angle camera on Sept. 30.?The image scale is about two-tenths of an inch (5 millimeters) per pixel. The image measures about 9 feet (2.4 meters) across.

The decision to end the mission on the surface is a result of Rosetta and the comet heading out beyond the orbit of Jupiter again. Farther from the sun than Rosetta had ever journeyed before, there would be little power to operate the craft. Mission operators were also faced with an imminent month-long period when the sun is close to the line-of-sight between Earth and Rosetta, meaning communications with the craft would have become increasingly more difficult.

The European Space Agency's Rosetta mission was launched in 2004 and arrived at comet 67P/Churyumov-Gerasimenko on Aug. 6, 2014. It is the first mission in history to rendezvous with a comet and escort it as it orbits the sun. On Nov. 4, 2014, a smaller lander name Philae, which had been deployed from the Rosetta mothership, touched down on the comet and bounced several times before finally alighting on the surface. Philae obtained the first images taken from a comet's surface and sent back valuable scientific data for several days.

U.S. contributions aboard the Rosetta spacecraft are the Microwave Instrument for Rosetta Orbiter (MIRO); the Alice spectrograph; the Ion and Electron Sensor (IES), part of the Rosetta Plasma Consortium Suite; and the Double Focusing Mass Spectrometer (DFMS) electronics package for the Rosetta Orbiter Spectrometer for Ion Neutral Analysis (ROSINA). They are part of a suite of 11 total science instruments aboard Rosetta.

Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta is the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun's radiation. Observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in the formation of planets.

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The End Is Nigh for Rosetta's Comet Mission

There is no nice way to kill a space probe, particularly one as scientifically productive and endearing as Rosetta, the first comet orbiter. But its demise will come on Sept. 30, assuming it doesn't crash into the comet sooner.

After more than two years circling the Comet 67P/Churyumov-Gerasimenko, Rosetta will drop to its icy surface and shut down, ending communications with Earth.

This time, ground controllers expect Rosetta's landing will stick -- unlike sidekick Philae's bouncing touchdown on Nov. 12, 2014. And unlike Philae, which ran through a two-day series of experiments after landing, Rosetta will not attempt any surface science.

Even though Rosetta will free-fall into the comet at the speed of a sedate walk, it is not designed to withstand the impact. Particularly vulnerable are Rosetta's 105-foot long solar array wings.

The European Space Agency is ending the mission because 67P is racing toward the outer solar system, making charging of Rosetta's batteries increasingly challenging. The spacecraft also has been subjected to the harsh radiation and extreme temperatures of space since launching in March 2004 and is unlikely to last too much longer.

Rosetta will take a last look around as it descends to the comet's surface. Scientists have selected a landing spot on the smaller lobe of the duck-shaped comet, a region that contains many large, active pits. Lumpy structures known as "goosebumps," line the pit walls. Scientists suspect they may be remnants of primordial mini-comets that melded together to form 67P during the solar system's early days.

Rosetta will take close-up images of the pits and collect data about the dust, gas and plasma around them, its final contribution to an ongoing quest to learn more about the origins of the solar system and the development of life on Earth, and perhaps elsewhere.

"Rosetta has been a great mission and it will be sad when its telecommunications signal will soon be lost," said University of Washington astronomer Donald Brownlee, who led NASA's Stardust comet sample return mission.

Read more at Discovery News

Stardust Brought Back Comet Pieces 10 Years Ago

On a January morning 10 years ago, tiny pieces of a comet landed on Earth inside of a spacecraft. NASA’s Stardust return-sample capsule arrived in Utah with its precious cargo on board, and ever since, principal investigator Don Brownlee (University of Washington) has been combing through the samples to see what it collected after seven years in space.

Even years later, surprises have emerged. In 2014, Brownlee’s team announced that probable interstellar particle tracks were found in the aerogel and aluminum foil particle detectors. A newer paper (by another team) submitted to the Lunar and Planetary Science Conference in Houston suggests this interplanetary dust is also made up in part of glass, which is a rare element in meteoroids.

“We’re constantly learning new things using better and better techniques,” Brownlee told Discovery News. “The more you look at these, how to deal with them, the more you can refine the techniques.”

Stardust collected samples from Comet Wild-2 in 2004, about two years before a part of the spacecraft came back to Earth with samples on board. The spacecraft was a pioneer in sample collection, with only one spacecraft (Japan’s Hayabusa, in 2010) doing it since on an asteroid. Hayabusa-2 (in flight now) and NASA’s OSIRIS-REx (yet to be launched) plan asteroid sample returns in the coming years.

One of the biggest surprises of the mission, Brownlee recalled, was finding that at least half the rocky material in the comet was made of materials that were “white-hot” when they were formed. This suggested that the rocky stuff was almost all formed in closer to the sun, and then transported out to the region where Pluto was, where ices formed. It gave a new understanding of our solar system’s history.

Another comet mission has been on the mind of the public lately. The European Rosetta mission has been orbiting Comet 67P/Churyumov–Gerasimenko for more than a year, and delivered a lander (Philae) that worked for a few days on the surface. Brownlee said he was sad Philae didn’t function for as long as planned, because that was the best way to do direct comparison with Stardust’s findings. But Rosetta’s gas analysis of 67P is “complementary” to the solids that Stardust brought back to Earth for analysis, he added.

Read more at Discovery News

Rosetta's Comet Spews Molecular Oxygen Surprise

The comet being studied by Europe’s Rosetta spacecraft contains molecular oxygen, a surprising discovery that will force scientists to rethink details of how the solar system formed.

Scientists expected that the highly reactive gas would have long ago combined with hydrogen, but they found molecular oxygen (abbreviated O2) consistently outgassing from comet 67P/Churyumov-Gerasimenko.

“It is the most surprising discovery we have made so far in 67P,” said Rosetta scientist Kathrin Altwegg, with the Physics Institute and Center for Space and Habitability at the University of Bern in Germany.

“The first time we really saw it I think we all went a little bit into denial because ... oxygen was not among the molecules suspected in a cometary coma,” Altwegg said. “All models show that molecular oxygen will react with the hydrogen and will no longer be present.”

The discovery also may complicate an evolving strategy to look for signs of extraterrestrial life by scanning the atmospheres of distant planets for telltale chemical signatures. Molecular oxygen, along with methane, is a key bio-signature of life on Earth.

“If we look at exoplanets, our goal of course will be to detect biosignatures, to see if the planet contains life. And as far as I know, so far the combination of methane and O2 was a hint that you have life underneath it. On the comet, we have both methane and O2, but we don’t have life. So it’s probably not a very good biosignature,” Altwegg said.

Scientists measured the amounts of O2 coming from 67P for months before publishing their results this week in Nature. They found that the levels of O2, relative to water, remained stable as solar heating made the comet more active. That was the proverbial smoking gun that 67P’s molecular oxygen was more than skin deep.

“This oxygen has to be present in the whole body. If it were only on the top surface, we would see a decrease over time of the oxygen-to-H20 (water) ratio,” said André Bieler, a research fellow and Rosetta scientist at the University of Michigan’s Department of Atmospheric, Oceanic and Space Sciences.

Read more at Discovery News

Sublime Surprise: Rosetta's Comet Cycles its Ice

Scientists have discovered an unexpectedly regular cycle of ice formation and depletion on the surface of a comet, a pattern tied to an orbital dance of shadow and sunlight.

Measurements taken by the European Space Agency’s Rosetta spacecraft, currently orbiting comet 67P/Churyumov-Gerasimenko, show that ice builds up when a particular region of the comet is in shadow. The ice then transitions, or sublimates, to gaseous water vapor when that region shifts into sunlight.

“We observed this cycle for several comet rotations … We were surprised to see so clearly the appearance and disappearance of the ice due to temperature and illumination conditions,” planetary scientist Maria Cristina De Sanctis, with the Institute for Space Astrophysics and Planetology in Rome, wrote in an email to Discovery News.

The finding helps resolve a puzzle about why a comet’s surface can be relatively free of ice, such as what has been observed on 67P and other comets, even though the bodies are outgassing water. The cycle of condensation and sublimation shows how water ice can be transported from the interior of the comet to the surface.

“This water cycle appears to be an important process in the evolution of the comet,” researchers wrote in an article published in this week’s Nature.

The cycle also helps explain why comets stay active. “In some way, it can prolong the comet’s life,” De Sanctis added.

Scientists are not yet sure if the water cycle accounts for 67Ps’ odd twin-lobed, duck shape. One theory is that 67P originally was two comets that melded together over time. The other idea is that the region between the comet’s lobes, informally referred to as “the neck”, has been especially active over time, causing a gradual reshaping of what was once a rounder (and single) body.

“There is a strong debate about this issue,” De Sanctis said. “Personally, I think that the neck region can be the result of an evolution of the comet that experienced different thermal regimes at different distance from the sun."

"Rosetta sees that at relatively large distances from the sun, the neck region is the most active and thus it is also the one that is most largely affected by the condensation and sublimation phenomena," she said.

Read more at Discovery News

Philae's Comet May Host Alien 'Life': Astronomers

Astronomers proposed a novel explanation Monday for the strange appearance of the comet carrying Europe’s robot probe Philae through outer space: alien microscopic life.

Many of the frozen dust ball’s features, which include a black crust over lakes of ice, flat-bottomed craters and mega-boulders scattered on the surface, were “consistent” with the presence of microbes, they said.

Observations by the European Space Agency’s Rosetta comet orbiter has shown that 67P/Churyumov-Gerasimenko “is not to be seen as a deep-frozen inactive body, but supports geological processes,” Max Wallis of the University of Cardiff said in a statement issued by the Royal Astronomical Society (RAS).

In fact, the comet racing towards the sun at a speed of 32.9 kilometers (20.4 miles) per second, “could be more hospitable to micro-life than our Arctic and Antarctic regions.”

Wallis and his colleague Chandra Wickramasinghe of the Buckingham Center for Astrobiology, presented their theory Monday to a meeting of the RAS in Llandudno, Wales.

They pointed to Rosetta’s detection of complex organic material, which gave the comet its surprisingly super-dark and low-reflecting surface, as “evidence for life.”

Furthermore, Wickramasinghe said that 67P’s gas ejections started “at distances from the Sun too far away to trigger surface sublimation”.

This implied that micro-organisms under the comet’s surface had been “building pockets of high pressure gases that crack overlying ice and vent organic particles,” he said by email.

Wickramasinghe also cited a rugged surface with evidence of re-sealed cracks and displaced boulders, and a covering of organics which “need to be resupplied.”

The observed features “are all consistent with a mixture of ice and organic material that consolidate under the Sun’s warming during the comet’s orbiting in space, when active micro-organisms can be supported,” said the statement.

Micro-organisms could use liquid water to colonize the comet  – infiltrating cracks in the ice and “snow” during warmer periods when the cosmic wanderer is nearer the Sun, the duo said.

“Organisms containing anti-freeze salts are particularly good at adapting to these conditions and some could be active at temperatures as low as minus 40 degrees Celsius (minus 40 degrees Fahrenheit).”

Sunlit areas of the comet already approached this temperature last September, when it was about 500 million kilometers (310 million miles) from the Sun, and emitting weak jets of gas.

Comets follow elliptical orbits around the sun, and warm as they draw closer, causing a process of solid-to-gas transformation called sublimation, which is what gives them their spectacular tails.

As 67P approaches its closest point to the sun, about 185 million km on August 13, “the micro-organisms should become increasingly active,” the pair speculated.

Read more at Discovery News

Gigantic Sinkholes Dot Surface of Rosetta's Comet

Scientists have found gigantic sinkholes more than 200 yards (183 meters) in diameter -- twice the length of a football field -- and just about as deep breaking the surface of the comet being studied by the orbiting Rosetta spacecraft.

“The really cool thing about these sinkholes is that you can stare right into that comet. It’s just crazy. You can see a lot of features in the walls,” University of Maryland planetary scientist Dennis Bodewits told Discovery News.

The pits have near-circular openings, cylindrical shapes and steep walls. At least one of the 18 holes seems to be on a steep angle. Some are active, spewing out jets of dust from their walls or floors.

“Finding the pits was a total surprise,” said space physicist Paul Weissman, with NASA’s Jet Propulsion Laboratory in California.

Scientists suspect the pits are sinkholes that formed when material near the comet’s surface collapsed. The comet’s nucleus is only about half as dense as solid water ice, with an interior that is believed to be mostly empty space.

The comet, known as 67P/Churyumov-Gerasimenko, is is thought to be a "rubble pile" of boulder-sized chunks of silicates and organics that came together to form the comet’s body.

Once the pits form, newly exposed material escapes to space, causing the walls to slowly widen, scientists theorize.

“A fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother,” Jean-Baptiste Vincent, with Germany’s Max Planck Institute for Solar System Research, and colleagues write in this week’s Nature.

“I think they are sinkholes, but I don’t know that for certain,” Weissman, who was not involved in the research, told Discovery News.

“The mass we’ve seen in outbursts from this comet so far is not enough to empty one of these sinkholes,” he said. “Also, also if you look at the surface around the pits, there’s no evidence of debris having been thrown out and then falling back on to the comet. So that leaves us sinkholes. I don’t know that anyone has come up with any other explanation of how they may have formed. I think it’s a good explanation, but we don’t know for certain.”

Similar circular features were found on comets Wild-2 (pronounced “Vilt 2”) and Tempel-1, which were visited by NASA’s Stardust and Deep Impact space probes, respectively. Those depressions, however, were not nearly as deep as the cavities found on 67P, which Europe’s Rosetta spacecraft has been circling since August 2014.

“That suggested that these were older surfaces, older features that had been eroded and filled in,” Bodewits said.

Based in the size and location of 67P’s pits, scientists suspect some variation in materials or structure a few hundred yards beneath the surface.

Read more at Discovery News

Philae Rises! What's Next for Rosetta's Comet Lander?

Perched on the surface of a comet, the revived Philae lander should soon be able to resume -- and possibly expand -- an unprecedented examination of organic material believed to date back to the beginning of the solar system.

Released by the Rosetta mothership, Philae floated down to the surface of Comet 67P/Churyumov-Gerasimenko on Nov 12, but its anchoring harpoons failed and the 220-pound probe shot back into space. It landed a second time, bounced and finally came to rest about a half-mile away with two of its three legs on the ground and wedged next to a cliff wall.

Nevertheless, Philae ran through a 64-hour, pre-programmed series of experiments before its batteries died. The lander was supposed to set down in an area nearly always illuminated by the sun to recharge its batteries. Instead it ended up in shadow and fell silent.

Spacecraft controllers continued to use the orbiting Rosetta spacecraft to hunt for a signal from Philae while they waited for the comet to move closer to the sun, hoping the lander would recharge itself.

Over the weekend, Philae finally phoned home -- twice – rekindling scientists’ hopes that the mission could resume.

First, though, flight controllers need to figure out when Philae will be in regular position to communicate with Rosetta, which is used to relay the lander’s signals to Earth.

“It’s of utmost importance to see if we can get a stable communications pattern between the two machines,” Rosetta deputy flight director Elsa Montagnon, with the European Space Agency, told reporters during a webcast press conference at the Paris Air Show.

“If we can do that, then we can do the next step and resume the scientific operation of Philae,” she said.

Managers plan to reposition Rosetta a bit closer to the comet, which is becoming more active as it races toward the sun. The closest approach will be on Aug. 13. The comet is in a 6.5-year orbit around the sun that comes as close as between Earth and Mars and as far as beyond Jupiter.

Moving Rosetta is a bit risky because gas, dust and ice jetting from the comet can confuse the spacecraft’s navigational cameras.

“Imagine taking your car through a snowstorm -- you don’t see very much. It’s not very safe,” Montagnon said.

However, the potential for more science from Philae, particularly as the comet undergoes dramatic changes from heating, makes the risk worthwhile, project managers said.

Philae completed about 80 percent of the studies planned during its initial mission, including operating a small drill intended to dig out samples for chemical analysis.

Because of the lander’s angle, however, the drill didn’t reach down far enough to collect samples.

Scientists are keen to learn if the carbon-based material covering the comet’s surface is similar to organics found on Earth. One test, for example, would assess the molecular asymmetry to determine its chirality, or handedness.

“We are optimistic now that this analysis can be realized in the upcoming weeks. Temperature and energy of Philae seem sufficient and very promising,” Philae scientist Uwe Meierhenrich, an analytical chemist at the University of Nice Sophia Antipolis in France, wrote in an email to Discovery News.

Rotating Philae for drilling, however, will be among the last tasks ground control teams will attempt.

“We will start with something simple, not demanding too much power,” and no movement of the lander, before attempting activities that are more complex and higher risk,” said Barbara Cozzoni, with the German Aerospace Center’s Philae lander control center in Cologne.

Read more at Discovery News