Two of the Milky Way's earliest building blocks identified

Astronomers have identified what could be two of the Milky Way's earliest building blocks: Named "Shakti" and "Shiva," these appear to be the remnants of two galaxies that merged between 12 and 13 billion years ago with an early version of the Milky Way, contributing to our home galaxy's initial growth. The new find is the astronomical equivalent of archeologists identifying traces of an initial settlement that grew into a large present-day city. It required combining data for nearly 6 million stars from ESA's Gaia mission with measurements from the SDSS survey. The results have been published in the Astrophysical Journal.

The early history of our home galaxy, the Milky Way, is one of joining smaller galaxies, which makes for fairly large building blocks. Now, Khyati Malhan and Hans-Walter Rix of the Max Planck Institute for Astronomy have succeeded in identifying what could be two of the earliest building blocks that can still be recognized as such today: proto-galactic fragments that merged with an early version of our Milky Way between 12 and 13 billion years ago, at the very beginning of the era of galaxy formation in the Universe. The components, which the astronomers have named Shakti and Shiva, were identified by combining data from ESA's astrometry satellite Gaia with data from the SDSS survey. For astronomers, the result is the equivalent of finding traces of an initial settlement that grew into a large present-day city.

Tracing the origins of stars that came from other galaxies

When galaxies collide and merge, several processes happen in parallel. Each galaxy carries along its own reservoir of hydrogen gas. Upon collision, those hydrogen gas clouds are destabilized, and numerous new stars are formed inside. Of course, the incoming galaxies also already have their own stars, and in a merger, stars from the galaxies will mingle. In the long run, such "accreted stars" will also account for some of the stellar population of the newly-formed combined galaxy. Once the merger is completed, it might seem hopeless to identify which stars came from which predecessor galaxy. But in fact, at least some ways of tracing back stellar ancestry exist.

Help comes from basic physics. When galaxies collide and their stellar populations mingle, most of the stars retain very basic properties, which are directly linked to the speed and direction of the galaxy in which they originated. Stars from the same pre-merger galaxy share similar values for both their energy and what physicists call angular momentum -- the momentum associated with orbital motion or rotation. For stars moving in a galaxy's gravitational field, both energy and angular momentum are conserved: they remain the same over time. Look for large groups of stars with similar, unusual values for energy and angular momentum -- and chances are, you might find a merger remnant.

Additional pointers can assist identification. Stars that formed more recently contain more heavier elements, what astronomers call "metals," than stars that formed a long time ago. The lower the metal content ("metallicity"), the earlier the star presumably formed. When trying to identify stars that already existed 13 billion years ago, one should look for stars with very low metal content ("metal-poor").

Virtual excavations in a large data set

Identifying the stars that joined our Milky Way as parts of another galaxy has only become possible comparatively recently. It requires large, high-quality data sets, and the analysis involves sifting the data in clever ways so as to identify the searched-for class of objects. This kind of data set has only been available for a few years. The ESA astrometry satellite Gaia provides an ideal data set for this kind of big-data galactic archeology. Launched in 2013, it has produced an increasingly accurate data set over the past decade, which by now includes positions, changes in position and distances for almost 1.5 billion stars within our galaxy.

Gaia data revolutionized studies of the dynamics of stars in our home galaxy, and has already led to the discovery of previously unknown substructures. This includes the so-called Gaia Enceladus/Sausage stream, a remnant of the most recent larger merger our home galaxy has undergone, between 8 and 11 billion years ago. It also includes two structures identified in 2022: the Pontus stream identified by Malhan and colleagues and the "poor old heart" of the Milky Way identified by Rix and colleagues. The latter is a population of stars that newly formed during the initial mergers that created the proto-Milky Way, and continue to reside in our galaxy's central region.

Traces of Shakti and Shiva

For their present search, Malhan and Rix used Gaia data combined with detailed stellar spectra from the Sloan Digital Sky Survey (DR17). The latter provide detailed information about the stars' chemical composition. Malhan says: "We observed that, for a certain range of metal-poor stars, stars were crowded around two specific combinations of energy and angular momentum."

In contrast with the "poor old heart," which was also visible in those plots, the two groups of like-minded stars had comparatively large angular momentum, consistent with groups of stars that had been part of separate galaxies which had merged with the Milky Way. Malhan has named these two structures Shakti and Shiva, the latter one of the principal deities of Hinduism and the former a female cosmic force often portrayed as Shiva's consort.

Their energy and angular momentum values, plus their overall low metallicity on par with that of the "poor old heart," makes Shakti and Shiva good candidates for some of the earliest ancestors of our Milky Way. Rix says: "Shakti and Shiva might be the first two additions to the 'poor old heart' of our Milky Way, initiating its growth towards a large galaxy."

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'Bouncing' comets could deliver building blocks for life to exoplanets

How did the molecular building blocks for life end up on Earth? One long-standing theory is that they could have been delivered by comets. Now, researchers from the University of Cambridge have shown how comets could deposit similar building blocks to other planets in the galaxy.

In order to deliver organic material, comets need to be travelling relatively slowly -- at speeds below 15 kilometres per second. At higher speeds, the essential molecules would not survive -- the speed and temperature of impact would cause them to break apart.

The most likely place where comets can travel at the right speed are 'peas in a pod' systems, where a group of planets orbit closely together. In such a system, the comet could essentially be passed or 'bounced' from the orbit of one planet to another, slowing it down.

At slow enough speeds, the comet would crash on a planet's surface, delivering the intact molecules that researchers believe are the precursors for life. The results, reported in the Proceedings of the Royal Society A, suggest that such systems would be promising places to search for life outside our Solar System if cometary delivery is important for the origins of life.

Comets are known to contain a range of the building blocks for life, known as prebiotic molecules. For example, samples from the Ryugu asteroid, analysed in 2022, showed that it carried intact amino acids and vitamin B3. Comets also contain large amounts of hydrogen cyanide (HCN), another important prebiotic molecule. The strong carbon-nitrogen bonds of HCN make it more durable to high temperatures, meaning it could potentially survive atmospheric entry and remain intact.

"We're learning more about the atmospheres of exoplanets all the time, so we wanted to see if there are planets where complex molecules could also be delivered by comets," said first author Richard Anslow from Cambridge's Institute of Astronomy. "It's possible that the molecules that led to life on Earth came from comets, so the same could be true for planets elsewhere in the galaxy."

The researchers do not claim that comets are necessary to the origin of life on Earth or any other planet, but instead they wanted to place some limits on the types of planets where complex molecules, such as HCN, could be successfully delivered by comets.

Most of the comets in our Solar System sit beyond the orbit of Neptune, in what is known as the Kuiper Belt. When comets or other Kuiper Belt objects (KBOs) collide, they can be pushed by Neptune's gravity toward the Sun, eventually getting pulled in by Jupiter's gravity. Some of these comets make their way past the Asteroid Belt and into the inner Solar System.

"We wanted to test our theories on planets that are similar to our own, as Earth is currently our only example of a planet that supports life," said Anslow. "What kinds of comets, travelling at what kinds of speed, could deliver intact prebiotic molecules?"

Using a variety of mathematical modelling techniques, the researchers determined that it is possible for comets to deliver the precursor molecules for life, but only in certain scenarios. For planets orbiting a star similar to our own Sun, the planet needs to be low mass and it is helpful for the planet to be in close orbit to other planets in the system. The researchers found that nearby planets on close orbits are much more important for planets around lower-mass stars, where the typical speeds are much higher.

In such a system, a comet could be pulled in by the gravitational pull of one planet, then passed to another planet before impact. If this 'comet-passing' happened enough times, the comet would slow down enough so that some prebiotic molecules could survive atmospheric entry.

"In these tightly-packed systems, each planet has a chance to interact with and trap a comet," said Anslow. "It's possible that this mechanism could be how prebiotic molecules end up on planets."

For planets in orbit around lower-mass stars, such as M-dwarfs, it would be more difficult for complex molecules to be delivered by comets, especially if the planets are loosely packed. Rocky planets in these systems also suffer significantly more high-velocity impacts, potentially posing unique challenges for life on these planets.

The researchers say their results could be useful when determining where to look for life outside the Solar System.

"It's exciting that we can start identifying the type of systems we can use to test different origin scenarios," said Anslow. "It's a different way to look at the great work that's already been done on Earth. What molecular pathways led to the enormous variety of life we see around us? Are there other planets where the same pathways exist? It's an exciting time, being able to combine advances in astronomy and chemistry to study some of the most fundamental questions of all."

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Self-healing plastic becomes biodegradable

Imagine a plastic like this: harder than common plastics, non-flammable, and even with self-healing properties. But that is not all! It can be produced at room temperature in water, which is very energy-efficient and does not require toxic solvents. Before hardening, you can shape the plastic in any way you want -- like chewing gum. By adding water, it can also be converted back to its "chewing gum" form at any time, reshaped and thus recycled as often as desired.

Is that impossible? No, it is not! In 2016, the research team around Konstanz chemist Helmut Cölfen presented just such a material -- a mineral plastic. However, even though the plastic, with its novel manufacturing process and outstanding material properties, has since attracted great interest from industry, it still had a crucial shortcoming from the Konstanz chemists' point of view: due to its chemical composition, it was difficult to biodegrade.

A new ingredient for greater environmental compatibility

"Previously, we used polyacrylic acid to produce our mineral plastic. Chemically, this acid has the same backbone as polyethylene, which is known to cause major problems in the environment because it is hardly biodegradable," explains Cölfen. The research team led by Cölfen and Ilesha Avasthi, a postdoc in Cölfen's lab, therefore set to work looking for an alternative basic building block to develop an environmentally compatible mineral plastic that retains the intriguing properties of the original material. And they found what they were looking for.

In their current publication in the journal Small Methods, the Konstanz chemists present the next generation of their mineral plastic. Instead of petroleum-based ingredients such as polyacrylic acid, they now use polyglutamic acid. This natural biopolymer is readily available in large quantities and can even be obtained sustainably, for example from biotechnological production using microorganisms. A variety of microorganisms that already exist in the environment can degrade polyglutamic acid.

"Our new mineral plastic has the same positive properties as the previous one, but has the decisive advantage that its basic building block -- polyglutamic acid -- can be produced with the help of microorganisms and is completely biodegradable," says Helmut Cölfen.

Support from biologists

In order to prove that this biodegradability also applies to the new mineral plastic itself and not just to its individual components, the chemists enlisted the support of David Schleheck and postdoc Harry Lerner from the Department of Biology at the University of Konstanz. "Helmut Cölfen has created a new type of mineral plastic in his laboratory, and our task now was to make it disappear again with the help of microorganisms," says Schleheck with a smile.

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Earth formed from dry, rocky building blocks

Billions of years ago, in the giant disk of dust, gas, and rocky material that orbited our young sun, larger and larger bodies coalesced to eventually give rise to the planets, moons, and asteroids we see today. Scientists are still trying to understand the processes by which planets, including our home planet, were formed. One way researchers can study how Earth formed is to examine the magmas that flow up from deep within the planet's interior. The chemical signatures from these samples contain a record of the timing and the nature of the materials that came together to form Earth -- analogous to how fossils give us clues about Earth's biological past.

Now, a study from Caltech shows that the early Earth accreted from hot and dry materials, indicating that our planet's water -- the crucial component for the evolution of life -- must have arrived late in the history of Earth's formation.

The study, involving an international team of researchers, was conducted in the laboratories of Francois Tissot, assistant professor of geochemistry and Heritage Medical Research Institute Investigator; and Yigang Zhang of the University of Chinese Academy of Sciences. A paper describing the research appears in the journal Science Advances. Caltech graduate student Weiyi Liu is the paper's first author.

Though humans do not have a way to journey into the interior of our planet, the rocks deep within the earth can naturally make their way to the surface in the form of lavas. The parental magmas of these lavas can originate from different depths within Earth, such as the upper mantle, which begins around 15 kilometers under the surface and extends for about 680 kilometers; or the lower mantle, which spans from a depth of 680 kilometers all the way to the core-mantle boundary at about 2,900 kilometers below our feet. Like sampling different layers of a cake -- the frosting, the filling, the sponge -- scientists can study magmas originating from different depths to understand the different "flavors" of Earth's layers: the chemicals found within and their ratios with respect to one another.

Because the formation of Earth was not instantaneous and instead involved materials accreting over time, samples from the lower mantle and upper mantle give different clues to what was happening over time during Earth's accretion. In the new study, the team found that the early Earth was primarily composed of dry, rocky materials: chemical signatures from deep within the planet showed a lack of so-called volatiles, which are easily evaporated materials like water and iodine. In contrast, samples of the upper mantle revealed a higher proportion of volatiles, three times of those found in the lower mantle. Based on these chemical ratios, Liu created a model that showed Earth formed from hot, dry, rocky materials, and that a major addition of life-essential volatiles, including water, only occurred during the last 15 percent (or less) of Earth's formation.

The study is a crucial contribution to theories of planet formation, a field which has undergone several paradigm shifts in recent decades and is still characterized by vigorous scientific debate. In this context, the new study makes important predictions for the nature of the building blocks of other terrestrial planets -- Mercury and Venus -- which would be expected to have formed from similarly dry materials.

"Space exploration to the outer planets is really important because a water world is probably the best place to look for extraterrestrial life," Tissot says. "But the inner solar system shouldn't be forgotten. There hasn't been a mission that's touched Venus's surface for nearly 40 years, and there has never been a mission to the surface of Mercury. We need to be able to study those worlds to better understand how terrestrial planets such as Earth formed."

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Webb locates dust reservoirs in two supernovae

Researchers using NASA's James Webb Space Telescope have made major strides in confirming the source of dust in early galaxies. Observations of two Type II supernovae, Supernova 2004et (SN 2004et) and Supernova 2017eaw (SN 2017eaw), have revealed large amounts of dust within the ejecta of each of these objects. The mass found by researchers supports the theory that supernovae played a key role in supplying dust to the early universe.

Dust is a building block for many things in our universe -- planets in particular. As dust from dying stars spreads through space, it carries essential elements to help give birth to the next generation of stars and their planets. Where that dust comes from has puzzled astronomers for decades. One significant source of cosmic dust could be supernovae -- after the dying star explodes, its leftover gas expands and cools to create dust.

"Direct evidence of this phenomenon has been slim up to this point, with our capabilities only allowing us to study the dust population in one relatively nearby supernova to date -- Supernova 1987A, 170,000 light-years away from Earth," said lead author Melissa Shahbandeh of Johns Hopkins University and the Space Telescope Science Institute in Baltimore, Maryland. "When the gas cools enough to form dust, that dust is only detectable at mid-infrared wavelengths provided you have enough sensitivity."

For supernovae more distant than SN 1987A like SN 2004et and SN 2017eaw, both in NGC 6946 about 22 million light-years away, that combination of wavelength coverage and exquisite sensitivity can only be obtained with Webb's MIRI (Mid-Infrared Instrument).

The Webb observations are the first breakthrough in the study of dust production from supernovae since the detection of newly formed dust in SN 1987A with the Atacama Large Millimeter/submillimeter Array (ALMA) telescope nearly a decade ago.

Another particularly intriguing result of their study isn't just the detection of dust, but the amount of dust detected at this early stage in the supernova's life. In SN 2004et, the researchers found more than 5,000 Earth masses of dust.

"When you look at the calculation of how much dust we're seeing in SN 2004et especially, it rivals the measurements in SN 1987A, and it's only a fraction of the age," added program lead Ori Fox of the Space Telescope Science Institute. "It's the highest dust mass detected in supernovae since SN 1987A."

Observations have shown astronomers that young, distant galaxies are full of dust, but these galaxies are not old enough for intermediate mass stars, like the Sun, to have supplied the dust as they age. More massive, short-lived stars could have died soon enough and in large enough numbers to create that much dust.

While astronomers have confirmed that supernovae produce dust, the question has lingered about how much of that dust can survive the internal shocks reverberating in the aftermath of the explosion. Seeing this amount of dust at this stage in the lifetimes of SN 2004et and SN 2017eaw suggests that dust can survive the shockwave -- evidence that supernovae really are important dust factories after all.

Researchers also note that the current estimations of the mass may be the tip of the iceberg. While Webb has allowed researchers to measure dust cooler than ever before, there may be undetected, colder dust radiating even farther into the electromagnetic spectrum that remains obscured by the outermost layers of dust.

The researchers emphasized that the new findings are also just a hint at newfound research capabilities into supernovae and their dust production using Webb, and what that can tell us about the stars from which they came.

"There's a growing excitement to understand what this dust also implies about the core of the star that exploded," Fox said. "After looking at these particular findings, I think our fellow researchers are going to be thinking of innovative ways to work with these dusty supernovae in the future."

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Better understanding the physics of our universe

For the last six years, Indiana University researchers and collaborators from around the world have sought to answer important questions about the most basic laws of physics that govern our universe. Their experiment, the Majorana Demonstrator, has helped to push the horizons on research concerning one of the fundamental building blocks of the universe: neutrinos.

The experiment's final report was published in Physical Review Letters in February.

Neutrinos -- subatomic particles similar to an electron but that have no electric charge -- are the second most abundant particles in the universe after light. However, they are some of the hardest particles to measure because they do not interact the way other particles do.

"Neutrinos have a profound impact on the universe and physics at every imaginable scale, surprising us down at the particle interaction level and having broad impact up through the cosmic scales," said Walter Pettus, an assistant professor of physics in the IU College of Arts and Sciences. "But they are also the most frustrating to study because we know so much about them, yet we have so many gaps."

The Majorana Demonstrator, a collaboration of 60 researchers from 24 institutions, was designed to fill many of those gaps at the same time, probing into the most fundamental properties of neutrinos.

One aspect they hoped to observe was whether the neutrino could be its own antiparticle -- a subatomic particle of the same mass but with the opposite electric charge. Since the neutrino is uncharged, it is the only particle in the universe that could be its own antiparticle. Understanding that would provide insight into why the neutrino has mass in the first place -- information which would have wide-spread impacts in understanding how the universe was formed.

To determine if the neutrino is its own antiparticle, the researchers needed to observe a rare occurrence called neutrinoless double-beta decay. However, this process takes a single atom at least 1026 years -- significantly longer than the age of the universe. Instead, they chose to observe nearly 1026 atoms over the course of six years.

To observe this incredibly rare decay, the researchers needed the perfect environment. In the Sanford Underground Research Facility in the Black Hills of South Dakota, located a mile underground, they built one of the cleanest and quietest environments on Earth. Extremely sensitive detectors were made of a high-purity germanium and were packed in a 50-ton lead shield and surrounded by materials of unprecedented cleanliness. Even the copper used was grown underground in their lab with impurity levels so low they couldn't be measured.

Pettus and a team of IU students were responsible primarily for analyzing data from the experiment. Graduate student Nafis Fuad, undergraduate senior Isaac Baker, sophomore Abby Kickbush and Jennifer James, a student with the Research Experiences for Undergraduates Program, have been involved in the project. Their focus has been on understanding the stability of the experiment, analyzing details of the recorded waveforms and characterizing backgrounds.

"It's like looking for a tiny needle in a very, very, very big haystack -- you have to carefully get rid of all the hays (a.k.a. backgrounds) possible, and you don't even know if there's actually a needle in there in the first place or not," Fuad said. "It's very exciting to be a part of that search."

While the researchers ultimately did not observe the decay they hoped for, they did discover that the neutrino's scale for decay is longer than the limit they placed on it, which they will test further during the next phase of the experiment. In addition, they recorded other scientific results -- ranging from dark matter to quantum mechanics -- that helps provide a better understanding of the universe.

Through the project, the researchers proved that the techniques they utilized could be used at a much larger scale in a potentially game-changing search that could help explain the existence of matter in the universe.

"We didn't see the decay we were looking for, but we have raised the bar on where to look for the physics we're going after," Pettus said. "True to its name, the Demonstrator advanced critical technologies that we are already leveraging for the next phase of the experiment in Italy. We may not have broken our picture of physics yet, but we've certainly pushed the horizons, and I am very excited about what we have accomplished."

The next phase of the project, called LEGEND-200, has already begun taking data in Italy, with plans to run over the next five years. Researchers aim to observe the decay happening at a magnitude higher sensitivity than the Majorana Demonstrator. Beyond that, thanks to support from the U.S. Department of Energy, the team is already designing the successor experiment, LEGEND-1000.

Pettus is excited about the future of this work and looks forward to involving more students on the project, both in data analysis and hardware development for LEGEND-1000.

"If we discover the neutrino is its own antiparticle, there will still be ground under our feet and stars in the sky, and our understanding of physics doesn't change the reality of the physical laws that always have and continue to govern our universe," Pettus said. "But knowing what's down there at the most fundamental level and how the universe works gives us a richer, more beautiful world to live in -- or possibly just weirder -- and that pursuit is fundamentally human."

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Drying process could be key step in the development of life

One-hundred fifty years ago, Charles Darwin speculated that life likely originated in a warm little pond. There, Darwin supposed, chemical reactions and the odd lightning strike might have led to chains of amino acids that, over time, became more and more complex until the beginnings of life emerged.

Ever since, researchers have investigated this type of pre-life or "prebiotic" chemistry, trying to figure out the chemical pathways that could have led from a pool filled with simple amino acids to bacteria, redwood trees and people. After a series of experiments, University of Wisconsin-Madison chemical engineering PhD student Hayley Boigenzahn and John Yin, a professor of chemical and biological engineering and a founding faculty member of the Wisconsin Institute for Discovery, can explain how one of the potentially crucial early steps on the path of life could have happened. They published their findings in the Dec. 2022 issue of the journal Origins of Life and Evolution of Biospheres.

In a famous 1952 study called the Miller-Urey experiment, researchers simulated the conditions thought to be present on the prebiotic Earth, including certain ratios of water, methane, hydrogen and other elements. When zapped with electricity to simulate lightning, the researchers found that the reaction produced amino acids, suggesting that these molecules were widely present on the prebiotic Earth.

"We know amino acids are the building blocks of proteins and proteins are essential for life," says Yin. "In prebiotic chemistry, it's long been a question of how we could we get these things to form bonds and strings in a manner that might eventually lead to a living cell. The question is hard because the particular chemistry involved is one that tends to fail in the presence of water."

In her experiment, Boigenzahn investigated whether it's possible these amino acids could have come together during periods of environmental change -- for instance, as a pool of water evaporated. In the presence of a chemical activator, these amino acids could bond together into peptides, or short chains of amino acids.

To study how amino acids might form bonds during the drying process, Boigenzahn created solutions of the amino acid glycine and trimetaphosphate, an activator that is naturally created during volcanic processes. Using a heater to evaporate the solution, Boigenzahn watched what happened to the amino acids over 24 hours.

What she found was a two-stage process. In the first stage, when the pH of the solution was alkaline, the glycine combined into two-molecule units called dimers, which are also produced protons, making the pH of the solution neutral. In the second stage, as evaporation took place, the dimers began to bond together to form longer peptide chains, called oligoglycine.

It's easy to imagine a scenario in which amino acids in a volcanically warmed hot spring containing an activator first combine into dimers. Then, as the water evaporates and its chemistry changes, the dimers bond and begin to form into longer chains of amino acids.

"What we're showing here is that that it doesn't necessarily have to be the same environment throughout all the reactions," says Boigenzahn. "They can occur in different environments, provided that the reactions that are occurring help create an environment that's beneficial for the next steps."

Through multiple wet-dry cycles, it's possible the peptide chains grew longer and longer. Eventually, they could have begun to fold in on themselves, forming enzymes, or proteins that catalyze chemical reactions. That could set the stage for more complex proteins and the beginnings of metabolism.

Boigenzahn and Yin both say it will be a long time before researchers figure out a possible path from Darwin's warm little pond to the beginnings of life. But, especially for chemical engineers, the effort of studying prebiotic chemistry could have big payoffs.

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Scientist helps identify new evidence for habitability in Enceladus's ocean

The search for extraterrestrial life just got more interesting as a team of scientists including Southwest Research Institute's Dr. Christopher Glein has discovered new evidence for a key building block for life in the subsurface ocean of Saturn's moon Enceladus. New modeling indicates that Enceladus's ocean should be relatively rich in dissolved phosphorus, an essential ingredient for life.

"Enceladus is one of the prime targets in humanity's search for life in our solar system," said Glein, a leading expert in extraterrestrial oceanography. He is a co-author of a paper in the Proceedings of the National Academy of Sciences (PNAS) describing this research. "In the years since NASA's Cassini spacecraft visited the Saturn system, we have been repeatedly blown away by the discoveries made possible by the collected data."

The Cassini spacecraft discovered Enceladus's subsurface liquid water and analyzed samples as plumes of ice grains and water vapor erupted into space from cracks in the moon's icy surface.

"What we have learned is that the plume contains almost all the basic requirements of life as we know it," Glein said. "While the bioessential element phosphorus has yet to be identified directly, our team discovered evidence for its availability in the ocean beneath the moon's icy crust."

One of the most profound discoveries in planetary science over the past 25 years is that worlds with oceans beneath a surface layer of ice are common in our solar system. Such worlds include the icy satellites of the giant planets, such as Europa, Titan and Enceladus, as well as more distant bodies like Pluto. Worlds like Earth with surface oceans must reside within a narrow range of distances from their host stars to maintain the temperatures that support surface liquid water. Interior water ocean worlds, however, can occur over a much wider range of distances, greatly expanding the number of habitable worlds likely to exist across the galaxy.

"The quest for extraterrestrial habitability in the solar system has shifted focus, as we now look for the building blocks for life, including organic molecules, ammonia, sulfur-bearing compounds as well as the chemical energy needed to support life," Glein said. "Phosphorus presents an interesting case because previous work suggested that it might be scarce in the ocean of Enceladus, which would dim the prospects for life."

Phosphorus in the form of phosphates is vital for all life on Earth. It is essential for the creation of DNA and RNA, energy-carrying molecules, cell membranes, bones and teeth in people and animals, and even the sea's microbiome of plankton.

Team members performed thermodynamic and kinetic modeling that simulates the geochemistry of phosphorus based on insights from Cassini about the ocean-seafloor system on Enceladus. In the course of their research, they developed the most detailed geochemical model to date of how seafloor minerals dissolve into Enceladus's ocean and predicted that phosphate minerals would be unusually soluble there.

"The underlying geochemistry has an elegant simplicity that makes the presence of dissolved phosphorus inevitable, reaching levels close to or even higher than those in modern Earth seawater," Glein said. "What this means for astrobiology is that we can be more confident than before that the ocean of Enceladus is habitable."

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How to catch a perfect wave: Scientists take a closer look inside the perfect fluid

Scientists have reported new clues to solving a cosmic conundrum: How the quark-gluon plasma -- nature's perfect fluid -- evolved into matter.

A few millionths of a second after the Big Bang, the early universe took on a strange new state: a subatomic soup called the quark-gluon plasma.

And just 15 years ago, an international team including researchers from the Relativistic Nuclear Collisions (RNC) group at Lawrence Berkeley National Laboratory (Berkeley Lab) discovered that this quark-gluon plasma is a perfect fluid -- in which quarks and gluons, the building blocks of protons and neutrons, are so strongly coupled that they flow almost friction-free.

Scientists postulated that highly energetic jets of particles fly through the quark-gluon plasma -- a droplet the size of an atom's nucleus -- at speeds faster than the velocity of sound, and that like a fast-flying jet, emit a supersonic boom called a Mach wave. To study the properties of these jet particles, in 2014 a team led by Berkeley Lab scientists pioneered an atomic X-ray imaging technique called jet tomography. Results from those seminal studies revealed that these jets scatter and lose energy as they propagate through the quark-gluon plasma.

But where did the jet particles' journey begin within the quark-gluon plasma? A smaller Mach wave signal called the diffusion wake, scientists predicted, would tell you where to look. But while the energy loss was easy to observe, the Mach wave and accompanying diffusion wake remained elusive.

Now, in a study published recently in the journal Physical Review Letters, the Berkeley Lab scientists report new results from model simulations showing that another technique they invented called 2D jet tomography can help researchers locate the diffusion wake's ghostly signal.

"Its signal is so tiny, it's like looking for a needle in a haystack of 10,000 particles. For the first time, our simulations show one can use 2D jet tomography to pick up the tiny signals of the diffusion wake in the quark-gluon plasma," said study leader Xin-Nian Wang, a senior scientist in Berkeley Lab's Nuclear Science Division who was part of the international team that invented the 2D jet tomography technique.

To find that supersonic needle in the quark-gluon haystack, the Berkeley Lab team culled through hundreds of thousands of lead-nuclei collision events simulated at the Large Hadron Collider (LHC) at CERN, and gold-nuclei collision events at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. Some of the computer simulations for the current study were performed at Berkeley Lab's NERSC supercomputer user facility.

Wang says that their unique approach "will help you get rid of all this hay in your stack -- help you focus on this needle." The jet particles' supersonic signal has a unique shape that looks like a cone -- with a diffusion wake trailing behind, like ripples of water in the wake of a fast-moving boat. Scientists have searched for evidence of this supersonic "wakelet" because it tells you that there is a depletion of particles. Once the diffusion wake is located in the quark-gluon plasma, you can distinguish its signal from the other particles in the background.

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Discovery boosts theory that life on Earth arose from RNA-DNA mix

 Chemists at Scripps Research have made a discovery that supports a surprising new view of how life originated on our planet.

In a study published in the chemistry journal Angewandte Chemie, they demonstrated that a simple compound called diamidophosphate (DAP), which was plausibly present on Earth before life arose, could have chemically knitted together tiny DNA building blocks called deoxynucleosides into strands of primordial DNA.

The finding is the latest in a series of discoveries, over the past several years, pointing to the possibility that DNA and its close chemical cousin RNA arose together as products of similar chemical reactions, and that the first self-replicating molecules -- the first life forms on Earth -- were mixes of the two.

The discovery may also lead to new practical applications in chemistry and biology, but its main significance is that it addresses the age-old question of how life on Earth first arose. In particular, it paves the way for more extensive studies of how self-replicating DNA-RNA mixes could have evolved and spread on the primordial Earth and ultimately seeded the more mature biology of modern organisms.

"This finding is an important step toward the development of a detailed chemical model of how the first life forms originated on Earth," says study senior author Ramanarayanan Krishnamurthy, PhD, associate professor of chemistry at Scripps Research.

The finding also nudges the field of origin-of-life chemistry away from the hypothesis that has dominated it in recent decades: The "RNA World" hypothesis posits that the first replicators were RNA-based, and that DNA arose only later as a product of RNA life forms.

Is RNA too sticky?

Krishnamurthy and others have doubted the RNA World hypothesis in part because RNA molecules may simply have been too "sticky" to serve as the first self-replicators.

A strand of RNA can attract other individual RNA building blocks, which stick to it to form a sort of mirror-image strand -- each building block in the new strand binding to its complementary building block on the original, "template" strand. If the new strand can detach from the template strand, and, by the same process, start templating other new strands, then it has achieved the feat of self-replication that underlies life.

But while RNA strands may be good at templating complementary strands, they are not so good at separating from these strands. Modern organisms make enzymes that can force twinned strands of RNA -- or DNA -- to go their separate ways, thus enabling replication, but it is unclear how this could have been done in a world where enzymes didn't yet exist.

A chimeric workaround

Krishnamurthy and colleagues have shown in recent studies that "chimeric" molecular strands that are part DNA and part RNA may have been able to get around this problem, because they can template complementary strands in a less-sticky way that permits them to separate relatively easily.

The chemists also have shown in widely cited papers in the past few years that the simple ribonucleoside and deoxynucleoside building blocks, of RNA and DNA respectively, could have arisen under very similar chemical conditions on the early Earth.

Moreover, in 2017 they reported that the organic compound DAP could have played the crucial role of modifying ribonucleosides and stringing them together into the first RNA strands. The new study shows that DAP under similar conditions could have done the same for DNA.

"We found, to our surprise, that using DAP to react with deoxynucleosides works better when the deoxynucleosides are not all the same but are instead mixes of different DNA 'letters' such as A and T, or G and C, like real DNA," says first author Eddy Jiménez, PhD, a postdoctoral research associate in the Krishnamurthy lab.

"Now that we understand better how a primordial chemistry could have made the first RNAs and DNAs, we can start using it on mixes of ribonucleoside and deoxynucleoside building blocks to see what chimeric molecules are formed -- and whether they can self-replicate and evolve," Krishnamurthy says.

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Key building block for organic molecules discovered in meteorites

 Scientists from Japan and the USA have confirmed the presence in meteorites of a key organic molecule which may have been used to build other organic molecules, including some used by life. The discovery validates theories of the formation of organic compounds in extraterrestrial environments.

The chemistry of life runs on organic compounds, molecules containing carbon and hydrogen, which also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life. An enduring mystery regarding the origin of life is how biology could have arisen from non-biological chemical processes, called prebiotic chemistry. Organic molecules from meteorites are one of the sources of organic compounds that lead to the formation of life on Earth.

Associate Professor Yasuhiro Oba from Hokkaido University led a team of researchers who discovered the presence of a prebiotic organic molecule called hexamethylenetetramine (HMT) in three different carbon-rich meteorites. Their discovery, published in the journal Nature Communications, validates models and theories that propose HMT as a key molecule in the formation of organic compounds in interstellar environments.

By confirming the presence of HMT in meteorites for the first time, this work supports the hypothesis that the compound was present in asteroids, the parent bodies of many meteorites. Early in the solar system's history, many asteroids could have been heated by collisions or the decay of radioactive elements. If some asteroids were warm enough and had liquid water, HMT could have broken down to provide building blocks that in turn reacted to make other important biological molecules which have been found in meteorites, including amino acids. Some types of amino acids are used by life to make proteins, which are used to build structures like hair and nails, or to speed up and regulate chemical reactions.

While the diversity of organic compounds in meteorites is well-documented, many questions remain about the processes by which these compounds were formed. The most important meteorites in this area of research are carbonaceous chondrites, stony meteorites that contain high percentages of water and organic compounds. Experimental models have shown that a combination of water, ammonia and methanol, when subjected to photochemical and thermal conditions common in extraterrestrial environments, give rise to a number or organic compounds, the most common of which is HMT. Interstellar ice is rich in methanol. Hypothetically, HMT should be common in water-containing extraterrestrial materials, but, until this study, it had not been detected.

HMT is susceptible to degradation when exposed to processes commonly used in the analysis of organic compounds in meteorites. The scientists developed a method that specifically extracted HMT from meteorites with minimal degradation. This method allowed them to isolate significant quantities of HMT and HMT derivatives from the meteorites Murchison, Murray and Tagish Lake.

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