Category: Asteroids & Comets

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.

Cosmic Magnifying Lens Reveals Inner Jets Of Black Holes

Astronomers using Caltech’s Owens Valley Radio Observatory (OVRO) have found evidence for a bizarre lensing system in space, in which a large assemblage of stars is magnifying a much more distant galaxy containing a jet-spewing supermassive black hole. The discovery provides the best view yet of blobs of hot gas that shoot out from supermassive black holes.

“We have known about the existence of these clumps of material streaming along black hole jets, and that they move close to the speed of light, but not much is known about their internal structure or how they are launched,” says Harish Vedantham, a Caltech Millikan Postdoctoral Scholar. “With lensing systems like this one, we can see the clumps closer to the central engine of the black hole and in much more detail than before.” Vedantham is lead author of two new studies describing the results in the Aug. 15 issue of The Astrophysical Journal. The international project is led by Anthony Readhead, the Robinson Professor of Astronomy, Emeritus, and director of the OVRO.

Many supermassive black holes at the centers of galaxies blast out jets of gas traveling near the speed of light. The gravity of black holes pulls material toward them, but some of that material ends up ejected away from the black hole in jets. The jets are active for one to 10 million years — every few years, they spit out additional clumps of hot material. With the new gravitational lensing system, these clumps can be seen at scales about 100 times smaller than before.

“The clumps we’re seeing are very close to the central black hole and are tiny — only a few light-days across. We think these tiny components moving at close to the speed of light are being magnified by a gravitational lens in the foreground spiral galaxy,” says Readhead. “This provides exquisite resolution of a millionth of a second of arc, which is equivalent to viewing a grain of salt on the moon from Earth.”

A critical element of this lensing system is the lens itself. The scientists think that this could be the first lens of intermediate mass — which means that it is bigger than previously observed “micro” lenses consisting of single stars and smaller than the well-studied massive lenses as big as galaxies. The lens described in the new paper, dubbed a “milli-lens,” is thought to be about 10,000 solar masses, and most likely consists of a cluster of stars. An advantage of a milli-sized lens is that it is small enough not to block the entire source, which allows the jet clumps to be magnified and viewed as they travel, one by one, behind the lens. What’s more, the researchers say the lens itself is of scientific interest because not much is known about objects of this intermediate-mass range.

“This system could provide a superb cosmic laboratory for both the study of gravitational milli-lensing and the inner workings of the nuclear jet in an active galaxy,” says Readhead.

The new findings are part of an OVRO program to obtain twice-weekly observations of 1,800 active supermassive black holes and their host galaxies, using OVRO’s 40-meter telescope, which detects radio emissions from celestial objects. The program has been running since 2008 in support of NASA’s Fermi mission, which observes the same galaxies in higher-energy gamma rays.

In 2010, the OVRO researchers noticed something unusual happening with the galaxy in the study, an active galaxy called PKS 1413+ 135. Its radio emission had brightened, faded, and then brightened again in a very symmetrical fashion over the course of a year. The same type of event happened again in 2015. After a careful analysis that ruled out other scenarios, the researchers concluded that the overall brightening of the galaxy is most likely due to two successive high-speed clumps ejected by the galaxy’s black hole a few years apart. The clumps traveled along the jet and became magnified when they passed behind the milli-lens.

“It has taken observations of a huge number of galaxies to find this one object with the symmetrical dips in brightness that point to the presence of a gravitational lens,” says coauthor Timothy Pearson, a senior research scientist at Caltech who helped discover in 1981 that the jet clumps travel at close to the speed of light. “We are now looking hard at all our other data to try to find similar objects that can give a magnified view of galactic nuclei.”

The next step to confirm the PKS 1413+ 135 results is to observe the galaxy with a technique called very-long-baseline interferometry (VLBI), in which radio telescopes across the globe work together to image cosmic objects in detail. The researchers plan to use this technique beginning this fall to look at the galaxy and its supermassive black hole, which is expected to shoot out another clump of jet material in the next few years. With the VLBI technique, they should be able to see the clump smeared out into an arc across the sky via the light-bending effects of the milli-lens. Identifying an arc would confirm that indeed a milli-lens is magnifying the ultra-fast jet clumps spewing from a supermassive black hole.

“We couldn’t do studies like these without a university observatory like the Owens Valley Radio Observatory, where we have the time to dedicate a large telescope exclusively to a single program,” said Readhead.

Stardust Hitches A Ride On Meteorites More Often Than Previously Thought

 

Even tiny dust particles have stories to tell − especially when they come from outer space. Meteorites contain tiny amounts of what is popularly known as stardust, matter originating from dying stars. Such stardust is part of the raw material from which some 4.6 billion years ago our planets and the meteorite parent bodies, the so-called asteroids, emerged. Peter Hoppe and his team at the Max Planck Institute for Chemistry in Mainz have now discovered that many of the silicate stardust particles in meteorites are much smaller than was previously thought. To date, many of them have therefore probably been overlooked in studies, leading the scientists to believe that the mass of the silicate stardust particles in meteorites is at least twice as large as previously assumed.

The Max Planck scientists obtained the new findings by changing their investigational methods. Using the NanoSIMS ion probe, the researchers in Mainz produced “maps” of thinly sectioned meteorite samples. Such maps show the abundance distribution of specific isotopes in the submicrometre range. The sample is first scanned with a focused ion beam. The particles knocked out of the sample in the process are then analyzed by mass spectrometry. However, even the usual 100-nanometre-wide ion beam was too wide for the latest discovery. “Until now, it was only possible to reliably find stardust grains measuring at least about 200 nanometres. We’ve narrowed the ion beam for our investigations, which means that we’re able to detect many smaller stardust grains,” Peter Hoppe, Group Leader at the MPI for Chemistry, explains. This method was always thought to be too ineffective for sampling, he continues. “Using the conventional, coarser method, you can scan an area ten times greater in the same amount of time.” The researchers were rewarded for their patience and found an unexpectedly high number of “hotspots” with anomalous isotopic abundances in the images of the meteoritic thin sections, indicating the presence of silicate stardust. “Evidently, many of the silicate stardust grains are smaller than was previously thought. With the conventional method, meteoritic stardust grains measuring less than about 200 nanometres have for the most part gone undiscovered,” Peter Hoppe concludes.

Based on the new findings, it is suspected that silicate stardust makes up several percent of the dust in the interstellar proto-mass of our solar system. The discovery by the researchers at the MPI for Chemistry therefore suggests that silicate stardust was a more important component in the birth of our solar system than had been assumed.

A chief component of silicates is oxygen. Unlike silicon carbide stardust, for example, silicate stardust grains cannot be separated from meteorites by chemical methods. Because of this, they remained undetected for a long time. It was only with the help of the NanoSIMS ion probe that the first silicate stardust particle was identified as a “hotspot” in oxygen isotope abundance maps in 2002. The NanoSIMS ion probe is a secondary ion mass spectrometer that is able to measure isotopes on the nanoscale.

Hotspots are areas with unusual isotopic abundances – the fingerprints of the parent stars, which can be clearly identified in the isotope abundance images obtained by measuring the samples. Isotopes of a chemical element have the same number of protons but a different number of neutrons in the nucleus.

Meteoroids are fragments of asteroids (rocky and metal-containing small planets), which circle around the sun as celestial bodies. If meteoroids reach the Earth and survive atmospheric entry, they are called meteorites. A distinction is made between stony, stony-iron and iron meteorites. The Queen Alexandra Range (QUE) 99177, Meteorite Hills (MET) 00426 and Acfer 094 meteorites surveyed by the MPI for Chemistry researchers are a so-called carbonaceous chondrites, which belong to the group of stony meteorites.

Primordial Black Holes May Have Helped To Forge Heavy Elements

Astronomers like to say we are the byproducts of stars, stellar furnaces that long ago fused hydrogen and helium into the elements needed for life through the process of stellar nucleosynthesis.

As the late Carl Sagan once put it: “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.”

But what about the heavier elements in the periodic chart, elements such as gold, platinum and uranium?

Astronomers believe most of these “r-process elements” — elements much heavier than iron — were created, either in the aftermath of the collapse of massive stars and the associated supernova explosions, or in the merging of binary neutron star systems.

“A different kind of furnace was needed to forge gold, platinum, uranium and most other elements heavier than iron,” explained George Fuller, a theoretical astrophysicist and professor of physics who directs UC San Diego’s Center for Astrophysics and Space Sciences. “These elements most likely formed in an environment rich with neutrons.”

In a paper published August 7 in the journal Physical Review Letters, he and two other theoretical astrophysicists at UCLA — Alex Kusenko and Volodymyr Takhistov — offer another means by which stars could have produced these heavy elements: tiny black holes that came into contact with and are captured by neutron stars, and then destroy them.

Neutron stars are the smallest and densest stars known to exist, so dense that a spoonful of their surface has an equivalent mass of three billion tons.

Tiny black holes are more speculative, but many astronomers believe they could be a byproduct of the Big Bang and that they could now make up some fraction of the “dark matter” — the unseen, nearly non-interacting stuff that observations reveal exists in the universe.

If these tiny black holes follow the distribution of dark matter in space and co-exist with neutron stars, Fuller and his colleagues contend in their paper that some interesting physics would occur.

They calculate that, in rare instances, a neutron star will capture such a black hole and then devoured from the inside out by it. This violent process can lead to the ejection of some of the dense neutron star matter into space.

“Small black holes produced in the Big Bang can invade a neutron star and eat it from the inside,” Fuller explained. “In the last milliseconds of the neutron star’s demise, the amount of ejected neutron-rich material is sufficient to explain the observed abundances of heavy elements.”

“As the neutron stars are devoured,” he added, “they spin up and eject cold neutron matter, which decompresses, heats up and make these elements.”

This process of creating the periodic table’s heaviest elements would also provide explanations for a number of other unresolved puzzles in the universe and within our own Milky Way galaxy.

“Since these events happen rarely, one can understand why only one in ten dwarf galaxies is enriched with heavy elements,” said Fuller. “The systematic destruction of neutron stars by primordial black holes is consistent with the paucity of neutron stars in the galactic center and in dwarf galaxies, where the density of black holes should be very high.”

In addition, the scientists calculated that ejection of nuclear matter from the tiny black holes devouring neutron stars would produce three other unexplained phenomenon observed by astronomers.

“They are a distinctive display of infrared light (sometimes termed a “kilonova”), a radio emission that may explain the mysterious Fast Radio Bursts from unknown sources deep in the cosmos, and the positrons detected in the galactic center by X-ray observations,” said Fuller. “Each of these represent long-standing mysteries. It is indeed surprising that the solutions of these seemingly unrelated phenomena may be connected with the violent end of neutron stars at the hands of tiny black holes.”

Funding for this project was provided by the National Science Foundation (PHY-1614864) at UC San Diego and by the U.S. Department of Energy (DE-SC0009937) at UCLA. Alex Kusenko was also supported, in part, by the World Premier International Research Center Initiative (WPI), MEXT, Japan.

Primordial Asteroids Discovered

Southwest Research Institute (SwRI) was part of an international team that recently discovered a relatively unpopulated region of the main asteroid belt, where the few asteroids present are likely pristine relics from early in solar system history. The team used a new search technique that also identified the oldest known asteroid family, which extends throughout the inner region of the main asteroid belt.

The main belt contains vast numbers of irregularly shaped asteroids, also known as planetesimals, orbiting the Sun between Mars and Jupiter. As improved telescope technology finds smaller and more distant asteroids, astronomers have identified clusters of similar-looking bodies clumped in analogous orbits. These familial objects are likely fragments of catastrophic collisions between larger asteroids eons ago. Finding and studying asteroid families allows scientists to better understand the history of main belt asteroids.

“By identifying all the families in the main belt, we can figure out which asteroids have been formed by collisions and which might be some of the original members of the asteroid belt,” said SwRI Astronomer Dr. Kevin Walsh, a coauthor of the online Science paper detailing the findings. “We identified all known families and their members and discovered a gigantic void in the main belt, populated by only a handful of asteroids. These relics must be part of the original asteroid belt. That is the real prize, to know what the main belt looked like just after it formed.”

Identifying the very oldest asteroid families, those billions of years old, is challenging, because over time, a family spreads out. As asteroids rotate in orbit around the Sun, their surfaces heat up during the day and cool down at night. This creates radiation that can act as a sort of mini-thruster, causing asteroids to drift widely over time. After billions of years, family members would be almost impossible to identify, until now. The team used a novel technique, searching asteroid data from the inner region of the belt for old, dispersed families. They looked for the “edges” of families, those fragments that have drifted the furthest.

“Each family member drifts away from the center of the family in a way that depends on its size, with small guys drifting faster and further than the larger guys,” said team leader Marco Delbo, an astronomer from the Observatory of Cote d’Azur in Nice, France. “If you look for correlations of size and distance, you can see the shapes of old families.”

“The family we identified has no name, because it is not clear which asteroid is the parent,” Walsh said. “This family is so old that it appears to have formed over 4 billion years ago, before the gas giants in the outer solar system moved into their current orbits. The giant planet migration shook up the asteroid belt, removing many bodies, possibly including the parent of this family.”

The team plans to apply this new technique to the entire asteroid belt to reveal more about the history of the solar system by identifying the primordial asteroids versus fragments of collisions. This research was supported by the French National Program of Planetology and the National Science Foundation. The resulting paper, “Identification of a primordial asteroid family constrains the original planetesimal population,” appears in the August 3, 2017, online edition of Science.

Hubble Detects Exoplanet With Glowing Water Atmosphere

Scientists have found the strongest evidence to date for a stratosphere on an enormous planet outside our solar system, with an atmosphere hot enough to boil iron.

An international team of researchers, led by the University of Exeter, made the new discovery by observing glowing water molecules in the atmosphere of the exoplanet WASP-121b with NASA’s Hubble Space Telescope.
In order to study the gas giant’s stratosphere – a layer of atmosphere where temperature increases with higher altitudes – scientists used spectroscopy to analyse how the planet’s brightness changed at different wavelengths of light.

Water vapour in the planet’s atmosphere, for example, behaves in predictable ways in response to different wavelengths of light, depending on the temperature of the water. At cooler temperatures, water vapour in the planet’s upper atmosphere blocks light of specific wavelengths radiating from deeper layers towards space. But at higher temperatures, the water molecules in the upper atmosphere glow at these wavelengths instead.
The phenomenon is similar to what happens with fireworks, which get their colours from chemicals emitting light. When metallic substances are heated and vaporized, their electrons move into higher energy states. Depending on the material, these electrons will emit light at specific wavelengths as they lose energy: sodium produces orange-yellow and strontium produces red in this process, for example.

The water molecules in the atmosphere of WASP-121b similarly give off radiation as they lose energy, but it is in the form of infrared light, which the human eye is unable to detect.

The research is published in leading scientific journal Nature.

“Theoretical models have suggested that stratospheres may define a special class of ultra-hot exoplanets, with important implications for the atmospheric physics and chemistry,” said Dr Tom Evans, lead author and research fellow at the University of Exeter. “When we pointed Hubble at WASP-121b, we saw glowing water molecules, implying that the planet has a strong stratosphere.”

WASP-121b, located approximately 900 light years from Earth, is a gas giant exoplanet commonly referred to as a ‘hot Jupiter’, although with a greater mass and radius than Jupiter, making it much puffier. The exoplanet orbits its host star every 1.3 days, and is around the closest distance it could be before the star’s gravity would start ripping it apart.

This close proximity also means that the top of the atmosphere is heated to a blazing hot 2,500 degrees Celsius – the temperature at which iron exists in gas rather than solid form.

In Earth’s stratosphere, ozone traps ultraviolet radiation from the sun, which raises the temperature of this layer of atmosphere. Other solar system bodies have stratospheres, too – methane is responsible for heating in the stratospheres of Jupiter and Saturn’s moon Titan, for example. In solar system planets, the change in temperature within a stratosphere is typically less than 100 degrees Celsius. However, on WASP-121b, the temperature in the stratosphere rises by 1000 Celsius.

“We’ve measured a strong rise in the temperature of WASP-121b’s atmosphere at higher altitudes, but we don’t yet know what’s causing this dramatic heating,” says Nikolay Nikolov, co-author and research fellow at the University of Exeter. “We hope to address this mystery with upcoming observations at other wavelengths.”

Vanadium oxide and titanium oxide gases are candidate heat sources, as they strongly absorb starlight at visible wavelengths, similar to ozone absorbing UV radiation. These compounds are expected to be present in only the hottest of hot Jupiters, such as WASP-121b, as high temperatures are required to keep them in the gaseous state.

Indeed, vanadium oxide and titanium oxide are commonly seen in brown dwarfs, ‘failed stars’ that have some commonalities with exoplanets.

Previous research spanning the past decade has indicated possible evidence for stratospheres on other exoplanets, but this is the first time that glowing water molecules have been detected, the clearest signal yet for an exoplanet stratosphere.

It is one of the first results to come out of a new observing program being carried out by an international team of scientists, led by Associate Professor David Sing at the University of Exeter and Dr. Mercedes Lopez-Mórales at the Smithsonian Institution. The program has been awarded 800 hours to study and compare 20 different exoplanets, representing one of the largest time allocations for a single program in the entire 27 year history of Hubble.

“This new research is the smoking gun evidence scientists have been searching for when studying hot exoplanets. We have discovered this hot Jupiter has a stratosphere, a common feature seen in most of our solar system planets.” says Professor David Sing, co-author and Associate Professor of Astrophysics at the University of Exeter.

“It’s a truly exciting find as we’re seeing dramatic differences planet-to-planet which is giving valuable clues in figuring out how planets behave under different conditions, and we’re only just scratching the surface of all the new Hubble data.”

NASA’s forthcoming James Webb Space Telescope will be able to follow up on the atmospheres of planets like WASP-121b with higher sensitivity than any telescope currently in space.

“This super-hot exoplanet is going to be a benchmark for our atmospheric models, and will be a great observational target moving into the Webb era,” said Hannah Wakeford, co-author and Research Fellow at the University of Exeter.