Meteorite Tells Us That Mars Had A Dense Atmosphere 4 Billion Years Ago

Exploration missions have suggested that Mars once had a warm climate, which sustained oceans on its surface. To keep Mars warm requires a dense atmosphere with a sufficient greenhouse effect, while the present-day Mars has a thin atmosphere whose surface pressure is only 0.006 bar, resulting in the cold climate it has today. It has been a big mystery as to when and how Mars lost its dense atmosphere.

An old meteorite has been known to contain the ancient Martian atmosphere. The researchers simulated how the composition of the Martian atmosphere changed throughout history under various conditions. By comparing the results to the isotopic composition of the trapped gas, the researchers revealed how dense the Martian atmosphere was at the time when the gas became trapped in the meteorite.

The research team concluded that Mars had a dense atmosphere 4 billion years ago. The surface air pressure at the time was at least 0.5 bar and could have been much higher. Because Mars had its magnetic field about 4 billion years ago and lost it, the result suggests that stripping by the solar wind is responsible for transforming Mars from a warm wet world into a cold desert world.

NASA’s MAVEN spacecraft is orbiting Mars to explore the processes that removed the Martian atmosphere. The Japan Aerospace Exploration Agency (JAXA) is planning to further observe the removal processes by the Martian Moons eXploration (MMX) spacecraft. These missions will reveal how the dense atmosphere on ancient Mars predicted in this study was removed over time.

New Light Shed On How Earth And Mars Were Created

Analysing a mixture of earth samples and meteorites, scientists from the University of Bristol have shed new light on the sequence of events that led to the creation of the planets Earth and Mars.

Planets grow by a process of accretion — a gradual accumulation of additional material — in which they collisionally combine with their neighbours.

This is often a chaotic process and material gets lost as well as gained.

Massive planetary bodies impacting at several kilometres per second generate substantial heat which, in turn, produces magma oceans and temporary atmospheres of vaporised rock.

Before planets get to approximately the size of Mars, gravitational attraction is too weak to hold onto this inclement silicate atmosphere.

Repeated loss of this vapour envelope during continued collisional growth causes the planet’s composition to change substantially.

Dr Remco Hin from the University of Bristol’s School of Earth Sciences, led the research which is published today in Nature.

He said: “We have provided evidence that such a sequence of events occurred in the formation of the Earth and Mars, using high precision measurements of their magnesium isotope compositions.

“Magnesium isotope ratios change as a result of silicate vapour loss, which preferentially contains the lighter isotopes. In this way, we estimated that more than 40 per cent of the Earth’s mass was lost during its construction.

“This cowboy building job, as one of my co-authors described it, was also responsible for creating the Earth’s unique composition.”

The research was carried out in an effort to resolve a decades long debate in Earth and planetary sciences about the origin of distinctive, volatile poor compositions of planets.

Did this result from processes that acted in the mixture of gas and dust in the nebula of the earliest solar system or is it consequence of their violent growth?

Researchers analysed samples of the Earth together with meteorites from Mars and the asteroid Vesta, using a new technique to get higher quality (more accurate and more precise) measurements of magnesium isotope ratios than previously obtained.

The main findings are three-fold:

Earth, Mars and asteroid Vesta have distinct magnesium isotope ratios from any plausible nebula starting materials

The isotopically heavy magnesium isotope compositions of planets identify substantial (~40 per cent) mass loss following repeated episodes of vaporisation during their accretion

This slipshod construction process results in other chemical changes during growth that generate the unique chemical characteristics of Earth.

Dr Hin added: “Our work changes our views on how planets attain their physical and chemical characteristics.

“While it was previously known that building planets is a violent process and that the compositions of planets such as Earth are distinct, it was not clear that these features were linked.

“We now show that vapour loss during the high energy collisions of planetary accretion has a profound effect on a planet’s composition.

“This process seems common to planet building in general, not just for Earth and Mars, but for all planets in our Solar System and probably beyond, but differences in the collision histories of planets will create a diversity in their compositions.”

Supersonic Gas Streams Left Over From The Big Bang Drive Massive Black Hole Formation

An international team of researchers has successfully used a super-computer simulation to recreate the formation of a massive black hole from supersonic gas streams left over from the Big Bang. Their study, published in this week’s Science, shows this black hole could be the source of the birth and development of the largest and oldest super-massive black holes recorded in our Universe.

“This is significant progress. The origin of the monstrous black holes has been a long-standing mystery and now we have a solution to it,” said author and Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Principal Investigator Naoki Yoshida.

Recent discoveries of these super-massive black holes located 13 billion light years away, corresponding to when the universe was just five per cent of its present age, pose a serious challenge to the theory of black hole formation and evolution. The physical mechanisms that form black holes and drive their growth are poorly understood.

Theoretical studies have suggested these black holes formed from remnants of the first generation of stars, or from a direct gravitational collapse of a massive primordial gas cloud. However, these theories either have difficulty in forming super-massive black holes fast enough, or require very particular conditions.

Yoshida and JSPS Overseas Research Fellow Shingo Hirano, currently at the University of Texas at Austin, identified a promising physical process through which a massive black hole could form fast enough. The key was incorporating the effect of supersonic gas motions with respect to dark matter. The team’s super-computer simulations showed a massive clump of dark matter had formed when the universe was 100 million years old. Supersonic gas streams generated by the Big Bang were caught by dark matter to form a dense, turbulent gas cloud. Inside, a protostar started to form, and because the surrounding gas provided more than enough material for it to feed on, the star was able to grow extremely big in a short amount of time without releasing a lot of radiation.

“Once reaching the mass of 34,000 times that of our Sun, the star collapsed by its own gravity, leaving a massive black hole. These massive black holes born in the early universe continued to grow and merge together to become a supermassive black hole,” said Yoshida.

“The number density of massive black holes is derived to be approximately one per a volume of three billion light-years on a side — remarkably close to the observed number density of supermassive black holes,” said Hirano.

The result from this study will be important for future research into the growth of massive black holes. Especially with the increased number of black hole observations in the far universe that are expected to be made when NASA’s James Webb Space Telescope is launched next year.

Farthest Active Inbound Comet Yet Seen

NASA’s Hubble Space Telescope has photographed the farthest active inbound comet ever seen, at a whopping distance of 1.5 billion miles from the Sun (beyond Saturn’s orbit). Slightly warmed by the remote Sun, it has already begun to develop an 80,000-mile-wide fuzzy cloud of dust, called a coma, enveloping a tiny, solid nucleus of frozen gas and dust. These observations represent the earliest signs of activity ever seen from a comet entering the solar system’s planetary zone for the first time.

The comet, called C/2017 K2 (PANSTARRS) or “K2,” has been travelling for millions of years from its home in the frigid outer reaches of the solar system, where the temperature is about minus 440 degrees Fahrenheit. The comet’s orbit indicates that it came from the Oort Cloud, a spherical region almost a light-year in diameter and thought to contain hundreds of billions of comets. Comets are the icy leftovers from the formation of the solar system 4.6 billion years ago and therefore pristine in icy composition.

“K2 is so far from the Sun and so cold, we know for sure that the activity — all the fuzzy stuff making it look like a comet — is not produced, as in other comets, by the evaporation of water ice,” said lead researcher David Jewitt of the University of California, Los Angeles. “Instead, we think the activity is due to the sublimation [a solid changing directly into a gas] of super-volatiles as K2 makes its maiden entry into the solar system’s planetary zone. That’s why it’s special. This comet is so far away and so incredibly cold that water ice there is frozen like a rock.”

Based on the Hubble observations of K2’s coma, Jewitt suggests that sunlight is heating frozen volatile gases — such as oxygen, nitrogen, carbon dioxide, and carbon monoxide — that coat the comet’s frigid surface. These icy volatiles lift off from the comet and release dust, forming the coma. Past studies of the composition of comets near the Sun have revealed the same mixture of volatile ices.

“I think these volatiles are spread all through K2, and in the beginning billions of years ago, they were probably all through every comet presently in the Oort Cloud,” Jewitt said. “But the volatiles on the surface are the ones that absorb the heat from the Sun, so, in a sense, the comet is shedding its outer skin. Most comets are discovered much closer to the Sun, near Jupiter’s orbit, so by the time we see them, these surface volatiles have already been baked off. That’s why I think K2 is the most primitive comet we’ve seen.”

K2 was discovered in May 2017 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii, a survey project of NASA’s Near-Earth Object Observations Program. Jewitt used Hubble’s Wide Field Camera 3 at the end of June to take a closer look at the icy visitor.

Hubble’s sharp “eye” revealed the extent of the coma and also helped Jewitt estimate the size of the nucleus — less than 12 miles across — though the tenuous coma is 10 Earth diameters across.

This vast coma must have formed when the comet was even farther away from the Sun. Digging through archival images, Jewitt’s team uncovered views of K2 and its fuzzy coma taken in 2013 by the Canada-France-Hawaii Telescope (CFHT) in Hawaii. But the object was then so faint that no one noticed it.

“We think the comet has been continuously active for at least four years,” Jewitt said. “In the CFHT data, K2 had a coma already at 2 billion miles from the Sun, when it was between the orbits of Uranus and Neptune. It was already active, and I think it has been continuously active coming in. As it approaches the Sun, it’s getting warmer and warmer, and the activity is ramping up.”

But, curiously, the Hubble images do not show a tail flowing from K2, which is a signature of comets. The absence of such a feature indicates that particles lifting off the comet are too large for radiation pressure from the Sun to sweep them back into a tail.

Astronomers will have plenty of time to conduct detailed studies of K2. For the next five years, the comet will continue its journey into the inner solar system before it reaches its closest approach to the Sun in 2022 just beyond Mars’ orbit. “We will be able to monitor for the first time the developing activity of a comet falling in from the Oort Cloud over an extraordinary range of distances,” Jewitt said. “It should become more and more active as it nears the Sun and presumably will form a tail.”

Jewitt said that NASA’s James Webb Space Telescope, an infrared observatory scheduled to launch in 2018, could measure the heat from the nucleus, which would give astronomers a more accurate estimate of its size.

The team’s results will appear in the September 28 issue of The Astrophysical Journal Letters.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

Small Collisions Make Big Impact On Mercury’s Thin Atmosphere

Mercury, our smallest planetary neighbor, has very little to call an atmosphere, but it does have a strange weather pattern: morning micro-meteor showers.

Recent modeling along with previously published results from NASA’s MESSENGER spacecraft — short for Mercury Surface, Space Environment, Geochemistry and Ranging, a mission that observed Mercury from 2011 to 2015 — has shed new light on how certain types of comets influence the lopsided bombardment of Mercury’s surface by tiny dust particles called micrometeoroids. This study also gave new insight into how these micrometeoroid showers can shape Mercury’s very thin atmosphere, called an exosphere.

The research, led by Petr Pokorný, Menelaos Sarantos and Diego Janches of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, simulated the variations in meteoroid impacts, revealing surprising patterns in the time of day impacts occur. These findings were reported in the Astrophysical Journal Letters on June 19, 2017.

“Observations by MESSENGER indicated that dust must predominantly arrive at Mercury from specific directions, so we set out to prove this with models,” Pokorný said. This is the first such simulation of meteoroid impacts on Mercury. “We simulated meteoroids in the solar system, particularly those originating from comets, and let them evolve over time.”

Earlier findings based on data from MESSENGER’s Ultraviolet and Visible Spectrometer revealed the effect of meteoroid impacts on Mercury’s surface throughout the planet’s day. The presence of magnesium and calcium in the exosphere is higher at Mercury’s dawn — indicating that meteoroid impacts are more frequent on whatever part of the planet is experiencing dawn at a given time.

This dawn-dusk asymmetry is created by a combination of Mercury’s long day, in comparison to its year, and the fact that many meteroids in the solar system travel around the Sun in the direction opposite the planets. Because Mercury rotates so slowly — once every 58 Earth days, compared to a Mercury year, a complete trip around the Sun, lasting only 88 Earth days — the part of the planet at dawn spends a disproportionately long time in the path of one of the solar system’s primary populations of micrometeoroids. This population, called retrograde meteoroids, orbits the Sun in the direction opposite the planets and comprises pieces from disintegrated long-period comets. These retrograde meteroids are traveling against the flow of planetary traffic in our solar system, so their collisions with planets — Mercury, in this case — hit much harder than if they were traveling in the same direction.

These harder collisions helped the team further key in on the source of the micrometeoroids pummeling Mercury’s surface. Meteroids that originally came from asteroids wouldn’t be moving fast enough to create the observed impacts. Only meteoroids created from two certain types of comets — Jupiter-family and Halley-type — had the speed necessary to match the obseravations.

“The velocity of cometary meteoroids, like Halley-type, can exceed 224,000 miles per hour,” Pokorný said. “Meteoroids from asteroids only impact Mercury at a fraction of that speed.”

Jupiter-family comets, which are primarily influenced by our largest planet’s gravity, have a relatively short orbit of less than 20 years. These comets are thought to be small pieces of objects originating in the Kuiper Belt, where Pluto orbits. The other contributor, Halley-type comets, have a longer orbit lasting upwards of 200 years. They come from the Oort Cloud, the most distant objects of our solar system — more than a thousand times farther from the Sun than Earth.

The orbital distributions of both types of comets make them ideal candidates to produce the tiny meteoroids that influence Mercury’s exosphere.

Pokorný and his team hope that their initial findings will improve our understanding of the rate at which comet-based micrometeoroids impact Mercury, further improving the accuracy of models of Mercury and its exosphere.

A Fresh Look At Older Data Yields A Surprise Near The Martian Equator

Scientists taking a new look at older data from NASA’s longest-operating Mars orbiter have discovered evidence of significant hydration near the Martian equator — a mysterious signature in a region of the Red Planet where planetary scientists figure ice shouldn’t exist.

Jack Wilson, a post-doctoral researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, led a team that reprocessed data collected from 2002 to 2009 by the neutron spectrometer instrument on NASA’s Mars Odyssey spacecraft. In bringing the lower-resolution compositional data into sharper focus, the scientists spotted unexpectedly high amounts of hydrogen — which at high latitudes is a sign of buried water ice — around sections of the Martian equator.

An accessible supply of water ice near the equator would be of interest in planning astronaut exploration of Mars. The amount of delivered mass needed for human exploration could be greatly reduced by using Martian natural resources for a water supply and as raw material for producing hydrogen fuel.

By applying image-reconstruction techniques often used to reduce blurring and remove “noise” from medical or spacecraft imaging data, Wilson’s team improved the spatial resolution of the data from around 320 miles to 180 miles (520 kilometers to 290 kilometers). “It was as if we’d cut the spacecraft’s orbital altitude in half,” Wilson said, “and it gave us a much better view of what’s happening on the surface.”

The neutron spectrometer can’t directly detect water, but by measuring neutrons, it can help scientists calculate the abundance of hydrogen — and infer the presence of water or other hydrogen-bearing substances. Mars Odyssey’s first major discovery, in 2002, was abundant hydrogen just beneath the surface at high latitudes. In 2008, NASA’s Phoenix Mars Lander confirmed that the hydrogen was in the form of water ice. But at lower latitudes on Mars, water ice is not thought to be thermodynamically stable at any depth. The traces of excess hydrogen that Odyssey’s original data showed at lower latitudes were initially explained as hydrated minerals, which other spacecraft and instruments have since observed.

Wilson’s team concentrated on those equatorial areas, particularly with a 600-mile (1,000-kilometer) stretch of loose, easily erodible material between the northern lowlands and southern highlands along the Medusae Fossae Formation. Radar-sounding scans of the area have suggested the presence of low-density volcanic deposits or water ice below the surface, “but if the detected hydrogen were buried ice within the top meter of the surface, there would be more than would fit into pore space in soil,” Wilson said. The radar data came from both the Shallow Radar on NASA’s Mars Reconnaissance Orbiter and the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the European Space Agency’s Mars Express orbiter and would be consistent with no subsurface water ice near the equator.

How water ice could be preserved there is a mystery. A leading theory suggests an ice and dust mixture from the polar areas could be cycled through the atmosphere when Mars’ axial tilt was larger than it is today. But those conditions last occurred hundreds of thousands to millions of years ago. Water ice isn’t expected to be stable at any depth in that area today, Wilson said, and any ice deposited there should be long gone. Additional protection might come from a cover of dust and a hardened “duricrust” that traps the humidity below the surface, but this is unlikely to prevent ice loss over timescales of the axial tilt cycles.

“Perhaps the signature could be explained in terms of extensive deposits of hydrated salts, but how these hydrated salts came to be in the formation is also difficult to explain,” Wilson added. “So for now, the signature remains a mystery worthy of further study, and Mars continues to surprise us.”

Wilson led the research while at Durham University in the U.K. His team — which includes members from NASA Ames Research Center, the Planetary Science Institute and the Research Institute in Astrophysics and Planetology — published its findings this summer in the journal Icarus.

Nanosat Fleet Proposed For Voyage To 300 Asteroids

A fleet of tiny spacecraft could visit over 300 asteroids in just over three years, according to a mission study led by the Finnish Meteorological Institute. The Asteroid Touring Nanosat Fleet concept comprises 50 spacecraft propelled by innovative electric solar wind sails (E-sails) and equipped with instruments to take images and collect spectroscopic data on the composition of the asteroids. Each nanosat would visit six or seven asteroids before returning to Earth to deliver the data. The concept will be presented by Dr Pekka Janhunen at the European Planetary Science Congress (EPSC) 2017 in Riga on Tuesday 19th September.

“Asteroids are very diverse and, to date, we’ve only seen a small number at close range. To understand them better, we need to study a large number in situ. The only way to do this affordably is by using small spacecraft,” says Janhunen.

In the mission scenario, the nanosats flyby their target asteroids at a range of around 1000 kilometres. Each nanosat carries a 4-centimetre telescope capable of imaging the surface of asteroids with a resolution of 100 metres or better. An infrared spectrometer analyses spectral signatures in light reflected or emitted by the asteroid to determine its mineralogy. The instruments can be pointed at the target using two internal reaction wheels inside the nanosats.

“The nanosats could gather a great deal of information about the asteroids they encounter during their tour, including the overall size and shape, whether there are craters on the surface or dust, whether there are any moons, and whether the asteroids are primitive bodies or a rubble pile. They would also gather data on the chemical composition of surface features, such as whether the spectral signature of water is present,” says Janhunen.

E-sails make use of the solar wind – a stream of electrically charged particles emitted from the Sun – to generate efficient propulsion without need for propellant. Thrust is generated by the slow rotation of a tether, attached at one end to a main spacecraft carrying an electron emitter and a high-voltage source and at the other to a small remote unit. The spinning tether completes a rotation in about 50 minutes, tracing out a broad, shallow cone around a centre of mass close to the main spacecraft. By altering its orientation in relation to the solar wind, the nanosat can change thrust and direction.

The thrust generated by E-sails is small; a 5 kilogramme spacecraft with a 20-kilometre tether would give an acceleration of 1 millimetre per second at the distance of the Earth from the Sun. However, calculations show that, on top of the initial boost from launch, this is enough for the spacecraft to complete a tour through the asteroid belt and back to Earth in 3.2 years. Nanosatellites do not have the capacity for a large antenna, so the concept includes a final flyby of Earth to download the data. The overall mission would cost around 60 million Euros, including launch, giving a cost of about 200,000 Euros for each asteroid visited.

“The cost of a conventional, state-of-the-art mission to visit this number of asteroids could run into billions. This mission architecture, using a fleet of nanosats and innovative propulsion, would reduce the cost to just a few hundred thousand Euros per asteroid. Yet the value of the science gathered would be immense,” says Janhunen.