Massive Martian ice discovery opens a window into red planet's history

Newly discovered layers of ice buried a mile beneath Mars' north pole are the remnants of ancient polar ice sheets and could be one of the largest water reservoirs on the planet, according to scientists at The University of Texas at Austin and the University of Arizona. The team made the discovery using measurements gathered by the Shallow Radar (SHARAD) on NASA's Mars Reconnaissance Orbiter (MRO). SHARAD emits radar waves that can penetrate up to a mile and a half beneath the surface of Mars. The findings, published May 22 in Geophysical Research Letters, are important because the layers of ice are a record of past climate on Mars in much the same way that tree rings are a record of past climate on Earth. Studying the geometry and composition of these layers could tell scientists whether climate conditions were previously favorable for life, researchers said. The team found layers of sand and ice that were as much as 90% water in some places. If melted, the newly discovered polar ice would be equivalent to a global layer of water around Mars at least 1.5 meters (5 feet) deep. "We didn't expect to find this much water ice here," said lead author Stefano Nerozzi, a graduate research assistant at the University of Texas Institute for Geophysics (UTIG) who is completing his Ph.D. at the Jackson School of Geosciences. "That likely makes it the third largest water reservoir on Mars after the polar ice caps." The findings were corroborated by an independent study using gravity data instead of radar, led by researchers at Johns Hopkins University. Nerozzi was a co-author. The papers have been published simultaneously in Geophysical Research Letters.

The authors think that the layers formed when ice accumulated at the poles during past ice ages on Mars. Each time the planet warmed, a remnant of the ice caps became covered by sand, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.

Scientists have long known about glacial events on Mars, which are driven by variations in the planet's orbit and tilt. Over periods of about 50,000 years, Mars leans toward the sun before gradually returning to an upright position, like a wobbling spinning top. When the planet spins upright, the equator faces the sun, allowing the polar ice caps to grow. As the planet tilts, the ice caps retreat, perhaps vanishing entirely.

Until now, scientists thought that the ancient ice caps were lost. The paper shows that in fact significant ice sheet remnants have survived under the planet's surface, trapped in alternating bands of ice and sand, like layers on a cake.

Co-author Jack Holt, a professor at the Lunar and Planetary Laboratory of the University of Arizona, said that the study provides new, important insights into the exchange of water ice between the poles and the midlatitudes, where his research group previously confirmed the presence of widespread glaciers, also using the SHARAD instrument.

"Surprisingly, the total volume of water locked up in these buried polar deposits is roughly the same as all the water ice known to exist in glaciers and buried ice layers at lower latitudes on Mars, and they are approximately the same age," he said.

Holt, who was a UTIG scientist and research professor for 19 years before joining the University of Arizona in 2018, has been a co-investigator with SHARAD since the spacecraft arrived at Mars in 2006.

Nerozzi said that studying this record of past polar glaciation could help determine whether Mars was ever habitable.

"Understanding how much water was available globally versus what's trapped in the poles is important if you're going to have liquid water on Mars," Nerozzi said. "You can have all the right conditions for life, but if most of the water is locked up at the poles, then it becomes difficult to have sufficient amounts of liquid water near the equator."

Chinese lunar rover's "lucky" find could unlock secrets of moon and earth

China's Yutu-2, the first rover on the far side of the moon, has found materials from deep inside the moon that could help unravel the mystery of the lunar mantle composition and the formation and evolution of the moon and the earth. Using data obtained by the visible and near infrared spectrometer installed on Yutu-2, a research team led by Li Chunlai, with the National Astronomical Observatories of China under the Chinese Academy of Sciences, found that the lunar soil in the landing area of the Chang'e-4 probe contains olivine and pyroxene which came from the lunar mantle deep inside the moon. The first important scientific discovery of the Chang'e-4 probe since it made the first-ever soft landing on the far side of the moon was published online in the latest issue of the academic journal Nature. The moon comprises a core, mantle and crust, like the earth. With the evolution of lunar magma, the light plagioclase rose to the upper layer to form the lunar crust, while the heavier olivine and pyroxene sank to form the lunar mantle, Li said. "But since the lunar crust is very thick, and there has been no volcanic activity and plate movement on the moon for billions of years, it's hard to find materials from the lunar mantle on the surface," Li said. The composition of the lunar mantle has long been the subject of theory. Neither the lunar samples from missions by the United States and Soviet Union, nor the remote sensing probes orbiting the moon have provided direct evidence of the accurate composition of the lunar mantle. Chinese scientists focused on a special area on the far side of the moon - the South Pole-Aitken (SPA) Basin, which was formed by a celestial collision over 4 billion years ago. With a diameter of 2,500 km and a depth of about 13 km, the basin is the oldest and largest impact crater on the moon.

After Chang'e-4 successfully landed on the Von Karman Crater in SPA Basin on Jan. 3 this year, the Yutu-2 rover obtained good quality spectral data at two sites.

"The data, unlike that obtained by Yutu on the near side of the moon, gave us a pleasant surprise," said Li.

Analysis showed the lunar soil in the landing area contains a large amount of olivine, low-calcium pyroxene and a small amount of high-calcium pyroxene, which are very likely from the lunar mantle, Li said.

So how did the materials from deep inside the moon get there?

After analyzing the high-resolution remote sensing images and the hyperspectral data, the researchers believed the materials were ejected from a 72-km-wide crater named Finsen to the northeast of the Von Karman Crater.

Li explained that after the SPA Basin was formed, more small asteroids crashed into the area, leading to more small craters. The collision that caused the Finsen Crater might have been so violent that the materials were knocked into the Von Karman Crater.

When scientists were selecting the landing site for Chang'e-4, flat areas were given priority. However, most of the flat areas on the moon are basalt formed as magma solidified.

It was lucky that Chang'e-4 probe landed in a region where the basalt is covered by lunar mantle debris.

"Furthermore, the rover is driving at the edge of the ejecta. According to our calculation, it might reach the basalt area in another 2 km or so. When it reaches the basalt area, we can compare the composition of the different lunar soils," Li said.

He said the study could provide a reference for a future mission to collect and return with samples and even the construction of a lunar base.

If the planned Chang'e-6 probe can go to that area, it would not only get the first-ever sample from the far side of the moon, but also have the chance to collect samples of materials coming from deep inside the moon, Li said.

"Most of the evolution of the moon happened about 3 billion years ago, while the early history of Earth before 3 billion years ago has been erased by geological activities. The moon is like a fossil that gives a glimpse of the early history of Earth," Li added.

Beresheet Impact Site Spotted

The photo above shows the landing site of the Israeli Beresheet spacecraft on a region of the Moon called Sea of Serenity, or Mare Serenitatis in Latin. On April 11, 2019, SpaceIL, a non-profit organization, attempted to land its spacecraft in this ancient volcanic field on the nearside of the Moon. After a smooth initial descent, Beresheet made a hard landing on the surface. As soon as its orbit placed NASA's Lunar Reconnaissance Orbiter (LRO) over the landing site on April 22, 2019, LRO imaged Beresheet's impact site. The LRO Camera (LROC) consists of three imagers: a seven-color Wide Angle Camera (WAC) and two black-and-white Narrow Angle Cameras (NAC) mounted on the LRO, which has been studying the Moon from orbit for a decade. NAC captured the Beresheet impact photo. LROC took this image from 56 miles (90 kilometers) above the surface. The cameras captured a dark smudge, about 10 meters wide, that indicates the point of impact. The dark tone suggests a surface roughened by the hard landing, which is less reflective than a clean, smooth surface. From so far away, LROC could not detect whether Beresheet formed a surface crater upon impact. It's possible the crater is just too small to show up in photos. Another possibility is that Beresheet formed a small indent instead of a crater, given its low angle of approach (around 8.4 degrees relative to the surface), light mass (compared to a dense meteoroid of the same size), and low velocity (again, relative to a meteoroid of the same size; Beresheet's speed was still faster than most speeding bullets).

The light halo around the smudge could have formed from gas associated with the impact or from fine soil particles blown outward during Beresheet's descent, which smoothed out the soil around the landing site, making it highly reflective.

There are many clues that we're actually looking at a man-made crater instead of a meteoroid-caused one. This is an important consideration, since the Moon, having no atmosphere, is constantly bombarded by space rocks that leave craters.

Most importantly, we knew the coordinates of the landing site within a few miles thanks to radio tracking of Beresheet, and we have 11 "before" images of the area, spanning a decade, and three "after" images. In all of these images, including one taken 16 days before the landing, we saw only one new feature of the size Beresheet would have created.

Existing mathematical models helped us estimate the size and shape of the crater that would have formed if an object of Beresheet's mass and velocity struck the surface. We also referenced craters created by similar-size spacecraft (GRAIL, LADEE, Ranger) that have struck the Moon at about the same speed, and we saw that the white tail stretching from the landing halo towards the south is a shape that's consistent with Beresheet's southward descent trajectory and angle of approach.

For the before image above, we used a photo from December 16, 2016. This is because the lighting conditions that day, based on the angle at which the Sun would have illuminated the Moon at that particular time in its orbit, were the most similar to the April 22 image.

Because LRO was beyond the horizon during Beresheet's descent and landing, it couldn't capture a photo until its orbit brought it nearby 11 days later. LRO passes over the lunar poles with each revolution. Meanwhile, the Moon rotates on its axis below the spacecraft, allowing LRO to pass over every part of the Moon twice a month (once during lunar night and once during lunar day). LROC may take more images of the landing site when it passes the same area again on May 19.

Efforts are ongoing to bounce laser pulses from the Lunar Orbiter Laser Altimeter, also on board LRO, to measure the return from the Laser Retroreflector Array of small corner cube mirrors. This instrument was provided by NASA's Goddard Space Flight Center and was installed on the top deck of the Beresheet spacecraft. Attempts are ongoing to examine if the retroreflector may have survived the impact.

What a dying star's ashes tell us about the birth of our solar system

A grain of dust forged in the death throes of a long-gone star was discovered by a team of researchers led by the University of Arizona. The discovery challenges some of the current theories about how dying stars seed the universe with raw materials for the formation of planets and, ultimately, the precursor molecules of life. Tucked inside a chondritic meteorite collected in Antarctica, the tiny speck represents actual stardust, most likely hurled into space by an exploding star before our own sun existed. Although such grains are believed to provide important raw materials contributing to the mix from which the sun and our planets formed, they rarely survive the turmoil that goes with the birth of a solar system. "As actual dust from stars, such presolar grains give us insight into the building blocks from which our solar system formed," said Pierre Haenecour, lead author of the paper, which is scheduled for advance online publication on Nature Astronomy's website on Apr. 29. "They also provide us with a direct snapshot of the conditions in a star at the time when this grain was formed." Dubbed LAP-149, the dust grain represents the only known assemblage of graphite and silicate grains that can be traced to a specific type of stellar explosion called a nova. Remarkably, it survived the journey through interstellar space and traveled to the region that would become our solar system some 4.5 billion years ago, perhaps earlier, where it became embedded in a primitive meteorite. Novae are binary star systems in which a core remnant of a star, called a white dwarf, is on its way to fading out of the universe, while its companion is either a low-mass main sequence star or a red giant. The white dwarf then begins syphoning material off its bloated companion. Once it accretes enough new stellar material, the white dwarf re-ignites in periodic outbursts violent enough to forge new chemical elements from the stellar fuel and spew them deep into space, where they can travel to new stellar systems and become incorporated in their raw materials.

Since shortly after the Big Bang, when the universe consisted of only hydrogen, helium and traces of lithium, stellar explosions have contributed to the chemical enrichment of the cosmos, resulting in the plethora of elements we see today.

Taking advantage of sophisticated ion and electron microscopy facilities at the UA's Lunar and Planetary Laboratory, a research team led by Haenecour analyzed the microbe-sized dust grain down to the atomic level. The tiny messenger from outer space turned out to be truly alien - highly enriched in a carbon isotope called 13C.

"The carbon isotopic compositions in anything we have ever sampled that came from any planet or body in our solar system varies typically by a factor on the order of 50," said Haenecour, who will join the Lunar and Planetary Laboratory as an assistant professor in the fall. "The 13C we found in LAP-149 is enriched more than 50,000-fold. These results provide further laboratory evidence that both carbon- and oxygen-rich grains from novae contributed to the building blocks of our solar system."

Although their parent stars no longer exist, the isotopic and chemical compositions and microstructure of individual stardust grains identified in meteorites provide unique constraints on dust formation and thermodynamic conditions in stellar outflows, the authors wrote.

Detailed analysis revealed even more unexpected secrets: Unlike similar dust grains thought to have been forged in dying stars, LAP-149 is the first known grain consisting of graphite that contains an oxygen-rich silicate inclusion.

"Our find provides us with a glimpse into a process we could never witness on Earth," Haenecour added. "It tells us about how dust grains form and move around inside as they are expelled by the nova. We now know that carbonaceous and silicate dust grains can form in the same nova ejecta, and they get transported across chemically distinct clumps of dust within the ejecta, something that was predicted by models of novae but never found in a specimen."

Unfortunately, LAP-149 does not contain enough atoms to determine its exact age, so researchers hope to find similar, larger specimens in the future.

"If we could date these objects someday, we could get a better idea of what our galaxy looked like in our region and what triggered the formation of the solar system," said Tom Zega, scientific director of the UA's Kuiper Materials Imaging and Characterization Facility and associate professor in the Lunar and Planetary Laboratory and UA Department of Materials Science and Engineering.

"Perhaps we owe our existence to a nearby supernova explosion, compressing clouds of gas and dust with its shockwave, igniting stars and creating stellar nurseries, similar to what we see in Hubble's famous 'Pillars of Creation' picture."

The meteorite containing the speck of stardust is one of the most pristine meteorites in the Lunar and Planetary Laboratory's collection. Classified as a carbonaceous chondrite, it is believed to be analogous to the material on Bennu, the target asteroid of the UA-led OSIRIS-REx mission. By taking a sample of Bennu and bringing it back to Earth, the OSIRIS-REx mission team hopes to provide scientists with material that has seen little, if any, alteration since the formation of our solar system.

Until then, researchers depend on rare finds like LAP-149, which survived being blasted from an exploding star, caught in a collapsing cloud of gas and dust that would become our solar system and baked into an asteroid before falling to the earth.

"It's remarkable when you think about all the ways along the way that should have killed this grain," Zega said.

Rare-Earth metals in the atmosphere of a glowing-hot exoplanet

KELT-9 b is the hottest exoplanet known to date. In the summer of 2018, a joint team of astronomers from the universities of Bern and Geneva found signatures of gaseous iron and titanium in its atmosphere. Now these researchers have also been able to detect traces of vaporized sodium, magnesium, chromium, and the rare-Earth metals scandium and yttrium. Exoplanets are planets outside our solar system that orbit around stars other than the Sun. Since the discovery of the first exoplanets in the mid-90's, well over 3'000 exoplanets have been discovered. Many of these planets are extreme compared to the planets in our solar system: Hot gas giants that orbit incredibly close to their host stars, sometimes within periods of less than a few days. Such planets do not exist in our solar system, and their existence has defied predictions of how and why planets form. For the past 20 years, astronomers from all over the world have been working to understand where these planets come from, what they are made of, and what their climates are like. An extremely hot gas giant KELT-9 is a star located 650 light years from the Earth in the constellation Cygnus. Its exoplanet KELT-9 b exemplifies the most extreme of these so-called hot-Jupiters because it orbits very closely around its star that is almost twice as hot as the Sun. Therefore, its atmosphere reaches temperatures of around 4'000 C. In such heat, all elements are almost completely vaporized and molecules are broken apart into their constituent atoms - much like is the case in the outer layers of stars. This means that the atmosphere contains no clouds or aerosols and the sky is clear, mostly transparent to light from its star.

The atoms that make up the gas of the atmosphere absorb light at very specific colors in the spectrum, and each atom has a unique "fingerprint" of colors that it absorbs. These fingerprints can be measured with a sensitive spectrograph mounted on a large telescope, allowing astronomers to discern the chemical composition of the atmospheres of planets that are many light-years away.

The exoplanet as a treasure trove

A team of researchers from the Universities of Bern and Geneva collaborated to use this technique, and made an interesting discovery: "Using the HARPS-North spectrograph on the Italian National Telescope on the island of La Palma, we found iron and titanium atoms in the hot atmosphere of KELT-9 b", explains Kevin Heng, Director and Professor at the Center for Space and Habitabilty (CSH) at the University of Bern and a member of the National Centre of Competence in Research PlanetS.

The team observed the KELT-9 system for a second time last summer, with the goal of confirming their previous detections, but also to proceed to search for additional elements that could be present in the data as well. Their survey included 73 atoms, among which some so-called rare-Earth metals. These substances are less common on Earth, but are applied in advanced materials and devices.

Jens Hoeijmakers, who is the first author of the study which is now published in the Journal Astronomy and Astrophysics and who is a Postdoc at the CSH in Bern and at Geneva Observatory, says: "Our team predicted that the spectrum of this planet could well be a treasure trove where a multitude of species can be detected that have not been observed in the atmosphere of any other planet before."

After careful analysis, the researchers indeed found strong signals of vaporized sodium, magnesium, chromium and the rare-Earth metals scandium and yttrium in the spectrum of the planet. The latter three of these have never been detected robustly in the atmosphere of an exoplanet before.

"The team also advanced their interpretation of this data, and were able to use these signals to estimate at what altitude in the planet's atmosphere these atoms are absorbing", says Jens Hoeijmakers. What is more, the researchers also know more about strong global wind patterns high up in the atmosphere that blow the material from one hemisphere to the other.

"With further observations, many more elements may well be discovered by using the same technique in the atmosphere of this planet in the future, and perhaps also on other planets that are heated to similarly high temperatures", explains Jens Hoeijmakers.

Kevin Heng adds: "The chances are good that one day we will find so-called biosignatures, i.e. signs of life, on an exoplanet, using the same techniques that we are applying today. Ultimately, we want to use our research to fathom the origin and development of the solar system as well as the origin of life."