Topic: Late February Astronomy Bulletin

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HOW LIFE CAME TO EARTH
Friedrich-Schiller-Universitaet Jena

Researchers have discovered a new clue in the search for the origin of life by showing that peptides can form on dust under conditions such as those prevailing in outer space. These molecules, which are one of the basic building blocks of all life, may therefore not have originated on our planet at all, but possibly in cosmic molecular clouds. All life as we know it consists of the same chemical building blocks. These include peptides, which perform various completely different functions in the body -- transporting substances, accelerating reactions or forming stabilising scaffolds in cells. Peptides consist of individual amino acids arranged in a specific order. The exact order determines a peptide's eventual properties. How these versatile biomolecules came into being is one of the questions about the origin of life. Amino acids, nucleobases and various sugars found in meteoroids, for example, show that this origin could be extraterrestrial in nature. However, for a peptide to be formed from individual amino acid molecules, very special conditions are required that were previously assumed to be more likely to exist on Earth. Water plays an important role in the conventional way in which peptides are created. In this process, individual amino acids combine to form a chain. For this to happen, one water molecule must be removed each time. Calculations have now shown that the amino acid glycine can be formed through a chemical precursor -- called an amino ketene -- combining with a water molecule. Put simply: in this case, water must be added for the first reaction step, and water must be removed for the second. With this knowledge, the team has now been able to demonstrate a reaction pathway that can take place under cosmic conditions and does not require water.

Instead of taking the chemical detour in which amino acids are formed, researchers wanted to find out whether amino ketene molecules could not be formed instead and combine directly to form peptides. This was done under the conditions that prevail in cosmic molecular clouds, that is to say on dust particles in a vacuum, where the corresponding chemicals are present in abundance: carbon, ammonia and carbon monoxide. In an ultra-high vacuum chamber, substrates that serve as a model for the surface of dust particles were brought together with carbon, ammonia and carbon monoxide at about one quadrillionth of normal air pressure and minus 263 degrees Celsius. Investigations showed that under these conditions, the peptide polyglycine was formed from the simple chemicals. These are therefore chains of the very simple amino acid glycine, and the team observed different lengths. The longest specimens consisted of eleven units of the amino acid. n this experiment, the German team was also able to detect the suspected amino ketene. The fact that the reaction can take place at such low temperatures at all is due to the amino ketene molecules being extremely reactive. They combine with each other in an effective polymerisation. The product of this is polyglycine. It was nevertheless surprising to us that the polymerisation of amino ketene could happen so easily under such conditions. This is because an energy barrier actually has to be overcome for this to happen. However, it may be that we are helped in this by a special effect of quantum mechanics. In this special reaction step, a hydrogen atom changes its place. However, it is so small that, as a quantum particle, it could not overcome the barrier but was simply able to cross it, so to speak, through the tunnelling effect. Now that it is clear that not only amino acids, but also peptide chains, can be created under cosmic conditions, we may have to look not only to Earth but also more into space when researching the origin of life.


PSYCHE MAY CONTAIN LESS IRON THAN PREVIOUSLY THOUGHT
Brown University

The asteroid 16 Psyche, which NASA intends to visit with a spacecraft in 2026, may be less heavy metal and more hard rock than scientists have surmised. Psyche, which orbits the Sun in the asteroid belt between Mars and Jupiter, is the largest of the M-type asteroids, which are composed chiefly of iron and nickel as opposed to the silicate rocks that make up most other asteroids. But when viewed from Earth, Psyche sends mixed signals about its composition. The light it reflects tells scientists that the surface is indeed mostly metal. That has led to conjecture that Psyche may be the exposed iron core of a primordial planetary body -- one whose rocky crust and mantle were blasted away by an ancient collision. However, measurements of Psyche's mass and density tell a different story. The way its gravity tugs on neighbouring bodies suggests that Psyche is far less dense than a giant hunk of iron should be. So if Psyche is indeed all metal, it would have to be highly porous -- a bit like a giant ball of steel wool with nearly equal parts void space and solid metal. Scientists wanted to see whether it was possible for an iron body the size of Psyche to maintain that near-50% porosity. For the study, the team created a computer model, based on known thermal properties of metallic iron, to estimate how the porosity of a large iron body would evolve over time. The model shows that to remain highly porous, Psyche's internal temperature would have to cool below 800 Kelvin very shortly after its formation. At temperatures above that, iron would have been so malleable that Psyche's own gravity would have collapsed most of the pore space within its bulk. Based on what is known about conditions in the early solar system, the researchers say, it's extremely unlikely that a body of Psyche's size -- about 140 miles in diameter -- could have cooled so quickly. In addition, any event that may have added porosity to Psyche after its formation -- a massive impact, for example -- would likely have also heated Psyche back up above 800 K. So any newly introduced porosity would have been unlikely to last.

Taken together, the results suggest that Psyche probably isn't a porous, all-iron body, the researchers conclude. More likely, it's harbouring a hidden rocky component that drives its density down. But if Psyche does have a rocky component, why does its surface look so metallic when viewed from Earth? There are few possible explanations, the researchers say. One of those possibilities is ferrovolcanism -- iron-spewing volcanoes. It's possible, the researchers say, that Psyche is actually a differentiated body with a rocky mantle and an iron core. But widespread ferrovolcanic activity may have brought large amounts of Psyche's core up to the surface, putting an iron coating atop its rocky mantle. Prior research by Johnson and Evans has shown that ferrovolcanism is possible on a body like Psyche. Whatever the case, scientists will soon get a much clearer picture of this mysterious asteroid. Later this year, NASA plans to launch a spacecraft that will rendezvous with Psyche after a four-year journey to the asteroid belt.


 300 YEAR-OLD ASTEROIDS DISCOVERED
UC Berkeley/SETI Institute

An international team of astronomers has discovered the youngest pair of asteroids ever recorded in our solar system, beating the previous record by a factor of ten. Astronomers believe that planets and even our Sun were formed by the clumping of dense objects in a giant cloud of dust and gas. Objects that did not clump together remain in the Universe as comets and asteroids and hold vital clues about the early years of our solar system. Astronomers use large telescopes, such as one housed at Lowell Observatory, to study asteroids and other celestial objects. During routine observations conducted in 2019, the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) telescope in Hawaii and Catalina Sky Survey in Arizona observed a near-earth asteroid (NEA) each that had very similar orbits around the Sun. Termed 2019 PR2 and 2019 QR6, these asteroids were dubbed a pair, two asteroids separated from a single parent. Further observations of the pair conducted using several telescopes revealed that the larger of the asteroid is about a kilometre wide while the other is about half the size. Although they are over one million km away in their orbits, the two asteroids display very similar surface properties further confirming their common origin.
The multinational research team used mathematical modelling and accessed previously unnoticed detections of the asteroids made by the Catalina Sky Survey, a good decade and a half prior to their recorded observation to determine that the pair had split from its parent body only 300 years ago, making them the youngest known asteroids in the solar system. Conventionally asteroid origins are explained by rotational fission, where the rotational speed of the parent asteroid reaches a critical speed, after which debris flies off from it while still maintaining an orbit similar to the parent body. The standard model, however, could not completely explain the origins of the asteroid duo, the press release said. Therefore, the research team has hypothesized a new origin theory for them. According to the new model, the parent body for the asteroid pair was likely a comet, whose jets of gas sent the asteroids to the positions they are in today. However, the asteroids do not show comet-like properties, which raises further questions about how their journeys so far. Astronomers are hopeful that at least some of these questions will be answered when the asteroid duo will fly past Earth again in 2033 and be within the reach of the giant telescopes peering at the skies, the press release said.


ANOTHER TRANS-NEPTUNIAN OBJECT FOUND
Vatican Observatory

Astronomers have found a new member of the solar system orbiting beyond the planet Neptune. This “trans-Neptunian object,” or “TNO,” is currently is designated “2021 XD7.” It was first observed on December 3, 2021, using the Vatican Advanced Technology Telescope (VATT) on Mt. Graham in Arizona (USA). The first TNO, Pluto (originally classified as a planet but now considered a dwarf planet), was discovered in 1930. Like Pluto, TNO 2021 XD7 has an eccentric orbit that is significantly tilted with respect to the orbits of Earth and the solar system’s other planets. That orbit brings the object no closer to the Sun than the distance of Neptune (which is 30 times the Earth’s distance from the Sun) yet carries it more than twice that far out from the Sun. 2021 XD7 takes roughly three centuries to complete one orbit around the Sun. Because of its great distance, little is currently known about the object, but it is certainly much smaller even than Pluto, which itself is but a fraction of the size of Earth’s Moon. The Vatican Advanced Technology Telescope, also known as the Alice P. Lennon Telescope, was built in the 1990s under Pope St. John Paul II. The Vatican Observatory’s older telescopes, located at Castel Gandolfo, had become less useful for astronomical research, owing to light pollution from Rome.


NEW PLANET DETECTED AROUND PROXIMA CENTAURI
ESO

A team of astronomers using the Very Large Telescope (ESO’s VLT) in Chile have found evidence of another planet orbiting Proxima Centauri, the closest star to our Solar System. This candidate planet is the third detected in the system and the lightest yet discovered orbiting this star. At just a quarter of Earth’s mass, the planet is also one of the lightest exoplanets ever found. The newly discovered planet, named Proxima d, orbits Proxima Centauri at a distance of about four million kilometres, less than a tenth of Mercury’s distance from the Sun. It orbits between the star and the habitable zone — the area around a star where liquid water can exist at the surface of a planet — and takes just five days to complete one orbit around Proxima Centauri. The star is already known to host two other planets: Proxima b, a planet with a mass comparable to that of Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star. Proxima b was discovered a few years ago using the HARPS instrument on ESO’s 3.6-metre telescope. The discovery was confirmed in 2020 when scientists observed the Proxima system with a new instrument on ESO’s VLT that had greater precision, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO). It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. As the signal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet, and not simply a result of changes in the star itself. At just a quarter of the mass of Earth, Proxima d is the lightest exoplanet ever measured using the radial velocity technique, surpassing a planet recently discovered in the L 98-59 planetary system. The technique works by picking up tiny wobbles in the motion of a star created by an orbiting planet’s gravitational pull. The effect of Proxima d’s gravity is so small that it only causes Proxima Centauri to move back and forth at around 1.44 kilometres per hour.


EVIDENCE OF PLANETS IN HABITABLE ZONE OF DEAD STAR
RAS

A ring of planetary debris studded with moon-sized structures has been observed orbiting close to a white dwarf star. Researchers observed WD1054–226, a white dwarf 117 light years away, recording changes in its light over 18 nights using the ULTRACAM high-speed camera on the ESO 3.5m New Technology Telescope (NTT) at the La Silla Observatory in Chile. In order to better interpret the changes in light, the researchers also looked at data from the NASA Transiting Exoplanet Survey Satellite (TESS). They found pronounced dips in light corresponding to 65 evenly spaced clouds of planetary debris orbiting the star every 25 hours. The researchers concluded that the regularity of the transiting structures suggests they are kept in such a precise arrangement by a nearby planet. The planet is thought to be similar in size to that of the terrestrial planets in our solar system. The approximate distance between the planet and WD1054–226 is around 1.7% of the Earth-Sun distance (roughly 2.5 million kilometres). They found that the light from WD1054–226 was always somewhat obscured by enormous clouds of orbiting material passing in front of it, suggesting a ring of planetary debris orbiting the star. The habitable zone, sometimes called the Goldilocks zone, is the area where the temperature would theoretically allow liquid water to exist on the surface of a planet. Compared to a star like the Sun, the habitable zone of a white dwarf will be smaller and closer to the star as white dwarfs give off less light and heat. This is because they are small, dense stars, gradually cooling down in space for the remainder of their lifetimes.

The structures observed in the study orbit in an area that would have been enveloped by the star while it was a red giant, so are likely to have formed or arrived relatively recently, rather than survived from the birth of the star and its planetary system.
It is expected that this orbit around the white dwarf was swept clear during the giant star phase of its life, and thus any planet that can potentially host water and hence, life, would be a recent development. The area would be habitable for at least two billion years, including at least one billion years into the future. More than 95% of all stars will eventually become white dwarfs. The exceptions are the largest stars that explode and become either black holes or neutron stars. When stars begin running out of hydrogen, they expand and cool, becoming red giants. The Sun will enter this phase in four to five billion years, swallowing Mercury, Venus, and possibly Earth. Once the outer material has gently blown away and hydrogen is exhausted, the hot core of the star remains, slowly cooling over billions of years – this is the star’s white dwarf phase.

Planets orbiting white dwarfs are challenging for astronomers to detect because the stars are much fainter than main-sequence stars such as the Sun. So far, astronomers have only found tentative evidence of a gas giant orbiting a white dwarf. This is the first time astronomers have detected any kind of planetary body in the habitable zone of a white dwarf. The moon-sized structures we have observed are irregular and dusty (e.g. comet-like) rather than solid, spherical bodies. Their absolute regularity is a mystery that cannot be currently explained.
“An exciting possibility is that these bodies are kept in such an evenly-spaced orbital pattern because of the gravitational influence of a nearby major planet. Without this influence, friction and collisions would cause the structures to disperse, losing the precise regularity that is observed. A precedent for this ‘shepherding’ is the way the gravitational pull of moons around Neptune and Saturn help to create stable ring structures orbiting these planets. The possibility of a major planet in the habitable zone is exciting and also unexpected; however, it is important to keep in mind that more evidence is necessary to confirm the presence of a planet. We cannot observe the planet directly so confirmation may come by comparing computer models with further observations of the star and orbiting debris.


SEVEN EARTH-SIZE PLANETS
Jet Propulsion Lab

Five years ago, astronomers revealed they had found that a red dwarf star called TRAPPIST-1 was home to a close-knit family of seven Earth-size planets. Using telescopes on the ground and in space, scientists revealed one of the most unusual planetary systems yet found beyond our Sun and opened the tantalizing question: Are any of these worlds habitable – a suitable home for life? Five years later, the planets are still enigmatic. Since the first announcement, subsequent studies have revealed that the TRAPPIST-1 planets are rocky, that they could be almost twice as old as our solar system, and that they are located 41 light-years from Earth. But a real game-changer will be the recently launched James Webb Space Telescope. Larger and more powerful than any previous space telescope, Webb will look for signs of atmospheres on the TRAPPIST-1 planets. A prime target for Webb is the fourth planet from the star, called TRAPPIST-1e. It’s right smack in the middle of what scientists call the habitable zone, also known as the Goldilocks zone. This is the orbital distance from a star where the amount of heating is right to allow liquid water on the surface of a planet. Though the planets are tightly packed around TRAPPIST-1, the red dwarf star is not only far cooler than our Sun, it is less than 10% its size. (In fact, if the entire system were placed in our own solar system, it would fit within the orbit of our innermost planet, Mercury.) The habitable zone is just a first cut. A potentially habitable planet also would require a suitable atmosphere, and Webb, especially in its early observations, is likely to gain only a partial indication of whether an atmosphere is present.

Measurements with the Hubble Space Telescope added more information about habitability. While Hubble does not have the power to determine whether the planets possess potentially habitable atmospheres, it did find that at least three of the planets – d, e, and f – do not appear to have the puffy, hydrogen-dominated atmospheres of gas giants, such as Neptune, in our solar system. Such planets are thought to be less likely to support life. That leaves open the possibility of “the atmospheres’ potential to support liquid water on the surface. The size of the TRAPPIST-1 planets also might help to strengthen the case for habitability, though the research is far from conclusive. They’re comparable to Earth not just in diameter but mass. Narrowing down the mass of the planets was possible, thanks to their tight bunching around TRAPPIST-1: Packed shoulder to shoulder, they jostle one another, enabling scientists to compute their likely range of mass from those gravitational effects. The densities suggest the planets might be composed of materials found in terrestrial planets like Earth. Scientists use computer models of possible planetary atmosphere formation and evolution to try to narrow down their possible composition, and these will be critical for the TRAPPIST-1 planets


MOST ACCURATE VIRTUAL REPRESENTATION OF UNIVERSE
Royal Astronomical Society

Scientists have produced the largest and most accurate virtual representation of the Universe to date. An international team of researchers, led by the University of Helsinki, and including members from Durham University in the UK, used supercomputer simulations to recreate the entire evolution of the cosmos, from the Big Bang to the present. The simulation, named SIBELIUS-DARK, is part of the “Simulations Beyond the Local Universe” (SIBELIUS) project, and is the largest and most comprehensive ‘constrained realisation’ simulation to date. The team meticulously compared the virtual Universe to a series of observational surveys to find the correct locations and properties for the virtual analogies of the familiar structures. It was found that our local patch of the Universe may be somewhat unusual as the simulation predicted a lower number of galaxies on average due to a local large-scale ‘underdensity’ of matter. While the level of this underdensity is not considered to be a challenge to the standard model of cosmology, it could have consequences for how we interpret information from observed galaxy surveys. The simulation covers a volume up to a distance of 600 million lightyears from Earth and is represented by over 130 billion simulated ‘particles’, requiring many thousands of computers working in tandem over several weeks and producing large amounts of data. The simulation was performed on the DiRAC COSmology MAchine (COSMA) operated by the Institute for Computational Cosmology at Durham University.

These ‘cosmological simulations’ developed by the team used relevant physics equations to describe how dark matter and cosmic gas evolve throughout the Universe’s lifetime. Dark matter is a hypothetical form of matter thought to account for a large amount of all matter in the Universe. First, the dark matter coalesces into small clumps, called haloes, and the surrounding gas is gravitationally attracted towards these clumps, eventually fragmenting into stars to form galaxies. Overtime, haloes grow large enough to host galaxies like our own Milky Way. Over the past 20 years, cosmologists have developed a ‘standard model’ of cosmology – the ‘Cold Dark Matter’ model – which can explain a plethora of observed astronomical data, from the properties of the heat left over from the Big Bang, to the number and spatial distribution of galaxies we observe around us today. When simulating a virtual cold dark matter universe, most cosmologists follow a ‘typical’, or random, patch, one that is similar to our own observed Universe, yet only in a statistical sense. The simulations carried out in this study are different. By using advanced generative algorithms (models how the data was generated in order to categorize a signal), the simulations are conditioned to reproduce our specific patch of Universe, thus containing the present day structures in the vicinity of our own galaxy that astronomers have observed over decades. This means that the familiar structures within our Local Universe, such as the Virgo, Coma and Perseus clusters of galaxies, the ‘Great Wall’ and the ‘Local Void’ – our cosmic habitat – are reproduced in the simulation. At the centre of the simulation is perhaps the most important structure, a pair of galaxies, the virtual counterparts of our own Milky Way and our nearby massive neighbour, the Andromeda galaxy.


FUTURE GRAVITATIONAL WAVE DETECTOR COULD UNCOVER SECRETS OF UNIVERSE
University of Nottingham

New research has shown that future gravitational wave detections from space will be capable of finding new fundamental fields and potentially shed new light on unexplained aspects of the Universe. Researchers suggest that LISA, the space-based gravitational-wave (GW) detector which is expected to be launched by ESA in 2037 will open up new possibilities for the exploration of the Universe. New fundamental fields, and in particular scalars, have been suggested in a variety of scenarios: as explanations for dark matter, as the cause for the accelerated expansion of the Universe, or as low-energy manifestations of a consistent and complete description of gravity and elementary particles. Observations of astrophysical objects with weak gravitational fields and small spacetime curvature have provided no evidence of such fields so far. However, there is reason to expect that deviations from General Relativity, or interactions between gravity and new fields, will be more prominent at large curvatures. For this reason, the detection of GWs -- which opened a novel window on the strong-field regime of gravity -- represents a unique opportunity to detect these fields. Extreme Mass Ratio Inspirals (EMRI) in which a stellar-mass compact object, either a black hole or a neutron star, inspirals into black hole up to millions of times the mass of the Sun, are among the target sources of LISA, and provide a golden arena to probe the strong-field regime of gravity. The smaller body performs tens of thousands of orbital cycles before it plunges into the supermassive black hole and this leads to long signals that can allow us to detect even the smallest deviations from the predictions of Einstein's theory and the Standard Model of Particle Physics.
The researchers have developed a new approach for modelling the signal and performed for the first time a rigorous estimate of LISA's capability to detect the existence of scalar fields coupled with the gravitational interaction, and to measure how much scalar field is carried by the small body of the EMRI. Remarkably, this approach is theory-agnostic, since it does not depend on the origin of the charge itself, or on the nature of the small body. The analysis also shows that such measurement can be mapped to strong bounds on the theoretical parameters that mark deviations from General Relativity or the Standard Model. LISA will be devoted to detect gravitational waves by astrophysical sources, will operate in a constellation of three satellites, orbiting around the Sun millions of kilometres far away each other. LISA will observe gravitational waves emitted at low frequency, within a band not available to terrestrial interferometers due to environmental noise. The visible spectrum for LISA will allow to study new families of astrophysical sources, different from those observed by Virgo and LIGO, as the EMRIs, opening a new window on the evolution of compact objects in a large variety of environments of our Universe.