EARLY MARS WAS COVERED IN ICE SHEETS
University of British Columbia
A large number of the valley networks scarring Mars's surface were carved by water melting beneath glacial ice, not by free-flowing rivers as previously thought, according to new research. The findings effectively throw cold water on the dominant "warm and wet ancient Mars" hypothesis, which postulates that rivers, rainfall and oceans once existed on the red planet. To reach this conclusion, astronomers developed and used new techniques to examine thousands of Martian valleys. They also compared the Martian valleys to the subglacial channels in the Canadian Arctic Archipelago and uncovered striking similarities. The similarity between many Martian valleys and the subglacial channels on Devon Island in the Canadian Arctic motivated the authors to conduct their comparative study. Devon Island is one of the best analogues we have for Mars here on Earth -- it is a cold, dry, polar desert, and the glaciation is largely cold-based. In total, the researchers analyzed more than 10,000 Martian valleys, using a novel algorithm to infer their underlying erosion processes. The findings demonstrate that only a fraction of valley networks match patterns typical of surface water erosion, which is in marked contrast to the conventional view. Using the geomorphology of Mars' surface to rigorously reconstruct the character and evolution of the planet in a statistically meaningful way is, frankly, revolutionary.
The theory also helps explain how the valleys would have formed 3.8 billion years ago on a planet that is further away from the Sun than Earth, during a time when the Sun was less intense. Climate modelling predicts that Mars' ancient climate was much cooler during the time of valley network formation. These environments would also support better survival conditions for possible ancient life on Mars. A sheet of ice would lend more protection and stability of underlying water, as well as providing shelter from solar radiation in the absence of a magnetic field -- something Mars once had, but which disappeared billions of years ago.
A PIECE OF MARS IS GOING HOME
NASA
A piece of a meteorite called Sayh al Uhaymir 008 (SaU008) will be carried on board NASA's Mars 2020 rover mission, now being built at the agency's Jet Propulsion Laboratory in Pasadena, California. This chunk will serve as target practice for a high-precision laser on the rover's arm. Mars 2020's goal is ambitious: collect samples from the Red Planet's surface that a future mission could potentially return to Earth. One of the rover's many tools will be a laser designed to illuminate rock features as fine as a human hair. That level of precision requires a calibration target to help tweak the laser's settings. Previous NASA rovers have included calibration targets as well. Depending on the instrument, the target material can include things like rock, metal or glass, and can often look like a painter's palette. But working on this particular instrument sparked an idea among JPL scientists: why not use an actual piece of Mars? Earth has a limited supply of Martian meteorites, which scientists determined were blasted off Mars' surface millions of years ago. These meteorites aren't as unique as the geologically diverse samples 2020 will collect. But they're still scientifically interesting -- and perfect for target practice. SHERLOC will be the first instrument on Mars to use Raman and fluorescence spectroscopies, scientific techniques familiar to forensics experts. Whenever an ultraviolet light shines over certain carbon-based chemicals, they give off the same characteristic glow that you see under a black light. Scientists can use this glow to detect chemicals that form in the presence of life. SHERLOC will photograph the rocks it studies, then map the chemicals it detects across those images. That adds a spatial context to the layers of data Mars 2020 will collect. Martian meteorites are precious in their rarity. Only about 200 have been confirmed by The Meteoritical Society, which has a database listing these vetted meteorites.
POSSIBILITY OF LIFE BELOW SURFACE OF MARS
New York University
Although no life has been detected on the Martian surface, a new study finds that conditions below the surface could potentially support it. The subsurface -- which is less harsh and has traces of water -- has never been explored. According to the study, the steady bombardment of penetrating Galactic Cosmic Rays (GCRs) might provide the energy needed to catalyze organic activity there. There is growing evidence suggesting the presence of an aqueous environment on ancient Mars, raising the question of the possibility of a life-supporting environment. The erosion of the Martian atmosphere resulted in drastic changes in its climate, surface water disappeared, shrinking habitable spaces on the planet, with only a limited amount of water remaining near the surface in form of brines and water-ice deposits. Life, if it ever existed, would have had to adapt to harsh modern conditions, which include
low temperatures and surface pressure, and high radiation dose. The subsurface of Mars has traces of water in the form of water-ice and brines, and undergoes radiation-driven redox chemistry. Using a combination of numerical models, space mission data, and studies of deep-cave ecosystems on Earth for research, the study proposes mechanisms through which life, if it ever existed on Mars, could survive and be detected with the upcoming ExoMars mission (2022) by the European Space Agency and Roscosmos. It hypothesizes that galactic cosmic radiation, which can penetrate several meters below the surface, will induce chemical reactions that can be used for metabolic energy by extant life, and host organisms using mechanisms seen in similar chemical and radiation environments on Earth.
PLANET FOUND ORBITING SMALL, COOL STAR
National Radio Astronomy Observatory
Using the National Science Foundation's continent-wide Very Long Baseline Array (VLBA), astronomers have discovered a Saturn-sized planet closely orbiting a small, cool star 35 light-years from Earth. This is the first discovery of an extrasolar planet with a radio telescope using a technique that requires extremely precise measurements of a star's position in the sky, and only the second planet discovery for that technique and for radio telescopes. The technique has long been known, but has proven difficult to use. It involves tracking the star's actual motion in space, then detecting a minuscule "wobble" in that motion caused by the gravitational effect of the planet. The star and the planet orbit a location that represents the centre of mass for both combined. The planet is revealed indirectly if that location, called the barycentre, is far enough from the star's centre to cause a wobble detectable by a telescope. This technique, called the astrometric technique, is expected to be particularly good for detecting Jupiter-like planets in orbits distant from the star. This is because when a massive planet orbits a star, the wobble produced in the star increases with a larger separation between the planet and the star, and at a given distance from the star, the more massive the planet, the larger the wobble produced. Starting in June of 2018 and continuing for a year and a half, the astronomers tracked a star called TVLM 513-46546, a cool dwarf with less than a tenth the mass of our Sun. In addition, they used data from nine previous VLBA observations of the star between March 2010 and August 2011.
Extensive analysis of the data from those time periods revealed a telltale wobble in the star's motion indicating the presence of a planet comparable in mass to Saturn, orbiting the star once every 221 days. This planet is closer to the star than Mercury is to the Sun. Small, cool stars like TVLM 513-46546 are the most numerous stellar type in our Milky Way Galaxy, and many of them have been found to have smaller planets, comparable to Earth and Mars. Giant planets, like Jupiter and Saturn, are expected to be rare around small stars like this one, and the astrometric technique is best at finding Jupiter-like planets in wide orbits, so we were surprised to find a lower mass, Saturn-like planet in a relatively compact orbit. More than 4,200 planets have been discovered orbiting stars other than the Sun, but the planet around TVLM 513-46546 is only the second to be found using the astrometric technique. Another, very successful method, called the radial velocity technique, also relies on the gravitational effect of the planet upon the star. That technique detects the slight acceleration of the star, either toward or away from Earth, caused by the star's motion around the barycenter. A third technique, called the transit method, also very successful, detects the slight dimming of the star's light when a planet passes in front of it, as seen from Earth. The astrometric method has been successful for detecting nearby binary star systems, and was recognized as early as the 19th Century as a potential means of discovering extrasolar planets. Over the years, a number of such discoveries were announced, then failed to survive further scrutiny. The difficulty has been that the stellar wobble produced by a planet is so small when seen from Earth that it requires extraordinary precision in the positional measurements.
CLOSEST STAR CLUSTER DISINTEGRATING
Science News
The closest cluster of stars to Earth is falling apart and will soon die, astronomers say. Using the Gaia spacecraft to measure velocities of stars in the Hyades cluster and those escaping from it, researchers have predicted the cluster’s demise. Astronomers at the University of Cambridge find that there’s only around 30 million years left for the cluster to lose its mass completely. The star cluster, just 150 light-years away and visible to the naked eye in the constellation Taurus, formed about 680 million years ago from a large cloud of gas and dust in the Milky Way. Stellar gatherings such as the Hyades, known as open star clusters, are born with hundreds or thousands of stars that are held close to one another by their mutual gravitational pull. But numerous forces try to tear them apart: Supernova explosions from the most massive stars eject material that had been binding the cluster together; large
clouds of gas pass near the cluster and yank stars out of it; the stars themselves interact with one another and jettison the least massive ones; and the gravitational pull of the whole Milky Way galaxy lures stars away too. As a result, open star clusters rarely reach their billionth birthday.
The Hyades has survived longer than many of its peers. But astronomers first saw signs of trouble there in 2018, when teams in Germany and Austria independently used the European Space Agency’s Gaia space observatory to find numerous stars that had escaped the cluster. These departing stars form two long tails on opposite sides of the Hyades — the first ever seen near an open star cluster. Each stellar tail stretches hundreds of light-years and dwarfs the cluster itself, which is about 65 light-years across. In the new work, astronomers analysed how the cluster has lost stars over its life. It was born with about 1,200 solar masses but now has only 300 solar masses left. In fact, the two tails of escapees possess more stars than does the cluster. And the more stars the cluster loses, the less gravity it has to hold on to its remaining members, which leads to the escape of additional stars, exacerbating the cluster’s predicament. The Hyades star cluster had long been predicted to be losing stars in two tails but astronomers first spotted the escaping stars only in 2018. Some of the escaping stars lead and other stars trail the cluster as it revolves around the Milky Way’s centre. The main culprit behind the cluster’s coming demise is the Milky Way. Just as the Moon causes tides on Earth, lifting the seas on both the side facing the Moon and the side facing away, so the Galaxy exerts tides on the
Hyades: The Milky Way pulls stars out of the side of the cluster that faces the galactic centre as well as the cluster’s far side. Even millions of years after the cluster disintegrates, its stars will continue to drift through space with similar positions and velocities. It’s still probably going to be detectable as a coherent structure in position-velocity space but the stars will be so spread out from one another that they will no longer constitute a star cluster.
DISMEMBERED GLOBULAR FOUND AT GALAXY’S EDGE
University of Sydney
An international team of astronomers has discovered the remnant of an ancient collection of stars that was torn apart by our own galaxy, the Milky Way, more than two billion years ago. The discovery of this shredded 'globular cluster' is surprising, as the stars in this galactic archaeological find have much lower quantities of heavier elements than in other such clusters. The evidence strongly suggests the original structure was the last of its kind, a globular cluster whose birth and life were different to those remaining today. Our Galaxy is home to about 150 globular clusters, each a ball of a million or so stars that orbit in the Galaxy's tenuous stellar halo. These globular clusters are old and have witnessed the growth of the Milky Way over billions of years. Using the Anglo-Australian Telescope in outback New South Wales, this collaboration measured the speeds of a stream of stars in the Phoenix constellation, revealing them to be remnants of a globular cluster that was pulled apart by the gravity of the Milky Way about two billion years ago. Once the team knew which stars belonged to the stream, it measured their abundance of elements heavier than hydrogen and helium; something astronomers refer to as metallicity. It was really surprised to find that the Phoenix Stream has a very low metallicity, making it distinctly different to all of the other globular clusters in the Galaxy.
After the Big Bang, only hydrogen and helium existed in any substantial amount in the Universe. These elements formed the first generation of stars many billions of years ago. It is within these and later stellar generations that heavier elements were formed, such as the calcium, oxygen and phosphorus that in part make up your bones. Observations of other globular clusters have found that their stars are enriched with heavier elements forged in earlier generations of stars. Current formation theories suggest that this dependence on previous stars means that no globular cluster should be found unenriched and that there is a minimum metallicity 'floor' below which no cluster can form. But the metallicity of the Phoenix Stream progenitor sits well below this minimum, posing a significant problem for our ideas of globular cluster origins. One possible explanation is that the Phoenix Stream represents the last of its kind, the remnant of a population of globular clusters that was born in radically different environments to those we see today. While potentially numerous in the past, this population of globular clusters was steadily depleted by the gravitational forces of the Galaxy, which tore them to pieces, absorbing their stars into the main body of the galactic system. This means that the stream is a relatively temporary phenomenon, which will dissipate in time. Remains of this cluster were found before it faded forever into the Galaxy's halo. As yet, there is no clear explanation for the origins of the Phoenix Stream progenitor cluster and where it sits in the evolution of galaxies remains unclear. The next question to ask is whether there are more ancient remnants out there, the leftovers of a population that no longer exists. Finding more such streams will give us a new view of what was going on in the early Universe.
MAMMAL CELLS MAY NOT FIGHT SPACE GERMS
University of Exeter
The immune systems of mammals -- including humans -- might struggle to detect and respond to germs from other planets, new research suggests. Microorganisms (such as bacteria and viruses) could exist beyond Earth, and there are plans to search for signs of them on Mars and some of Saturn and Jupiter's moons. Such organisms might be based on different amino acids (key building blocks of all life) than lifeforms on Earth. Scientists from the universities of Aberdeen and Exeter tested how mammal immune cells responded to peptides (combinations of amino acids) containing two amino acids that are rare on Earth but are commonly found on response to these "alien" peptides was "less efficient" than the reaction to those common on Earth. The study -- conducted in mice, whose immune cells function in
a similar way to those of humans -- suggests extra-terrestrial microorganisms could pose a threat to space missions, and on Earth if they were brought back. The world is now only too aware of the immune challenge posed by the emergence of brand new pathogens and scientists wondered what would happen if we were to be exposed to a microorganism that had been retrieved from another planet or moon where life had evolved. Some very unusual organic building blocks exist outside of the planet Earth, and these could be used to make up the cells of such alien microbes. Would our immune system be able to detect proteins made from these non-terrestrial building blocks if such organisms were discovered and were brought back to Earth and then accidently escaped? Researchers examined the reaction of T cells, which are key to immune responses, to peptides containing amino acids commonly found on meteorites: isovaline and aminoisobutyric acid. The response was less efficient, with activation levels of 15% and 61% -- compared to 82% and 91% when exposed to peptides made entirely of amino acids that are common on Earth.
Life on Earth relies on essential 22 amino acids and scientists hypothesised that lifeforms that evolved in an environment of different amino acids might contain them in their structure. They chemically synthetised 'exo-peptides' containing amino acids that are rare on Earth, and tested whether a mammal immune system could detect them. The investigation showed that these exo-peptides were still processed, and T cells were still activated, but these responses were less efficient than for 'ordinary'
Earth peptides. They therefore speculate that contact with extra-terrestrial microorganisms might pose an immunological risk for space missions aiming to retrieve organisms from exoplanets and moons. The discovery of liquid water at several locations in the solar system raises the possibility that microbial life may have evolved outside Earth, and could therefore be accidentaly introduced into the Earth's ecosystem.
Topic: Mid August Astronomy Bulletin (Read 1345 times)