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The rock-strewn surface of asteroid Bennu, now being mapped at close range by NASA’s OSIRIS-REx spacecraft before an attempt to collect samples next summer. Image: NASA/Goddard/University of Arizona

Got a bit of spare time?

Managers with NASA’s OSIRIS-REx mission are looking for citizen scientists to help count and characterise rocks – lots of rocks – on the surface of the asteroid Bennu to aid in selecting a safe site for an attempt in July 2020 to collect samples for return to Earth.

“For the safety of the spacecraft, the mission team needs a comprehensive catalog of all the boulders near the potential sample collection sites,” said said Dante Lauretta, OSIRIS-REx principal investigator. “I invite members of the public to assist the OSIRIS-REx mission team in accomplishing this essential task.”

NASA and CosmoQuest, a project operated by the Planetary Science Institute, have set up an interactive web interface where interested citizen scientists can map rocks, boulders and other interesting features. All that is required by the mapping app is a computer with a relatively large screen and a precision mouse or trackpad.

And time. Plenty of time. That’s because Bennu’s crust appears to be made up of a blanket of rocks and boulders giving it the appearance of a rubble pile.

“We are very pleased and excited to make OSIRIS-REx images available for this important citizen science endeavour,” said Rich Burns, OSIRIS-REx project manager at NASA Goddard Space Flight Center. “Bennu has surprised us with an abundance of boulders. We ask for citizen scientists’ help to evaluate this rugged terrain so that we can keep our spacecraft safe during sample collection operations.”

The OSIRIS-REx spacecraft is currently mapping Bennu’s surface in close-range detail. The mapping phase will continue through 10 July when mission planners will begin the sample site selection process. After primary and secondary sites are selected, the spacecraft will move in to map both ares at sub-centimetre resolution.

If all goes well, OSIRIS-REx will attempt to snag samples in July 2020, returning them to Earth in September 2023.

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In this view of Mars’ north polar ice cap, the vertical scale has been exaggerated to highlight elevation changes. New research indicates enough water is locked up in buried remnants of polar ice sheets to cover the red planet to a depth of 1.5 meters (5 feet). Image: SA/DLR/FU Berlin; NASA MGS MOLA Science Team

Scientists have discovered remnants of ancient ice sheets buried in sand a mile beneath Mars’s north pole, they report in a new study. The findings show conclusive evidence of the waxing and waning of polar ice on the red planet due to changes in its orbit and tilt, according to the study’s authors.

Researchers at the University of Texas at Austin and the University of Arizona made the discovery using measurements gathered by the Shallow Radar (SHARAD) instrument on NASA’s Mars Reconnaissance Orbiter. SHARAD emits radar waves that can penetrate up to a mile and a half beneath Mars’s surface.

The new findings, published today in AGU’s journal 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, according to the researchers. Studying the geometry and composition of these layers could tell scientists whether climate conditions were previously favourable for life.

The team found layers of sand and ice that were as much as 90 percent water in some places. If melted, the newly discovered ice would be equivalent to a global layer of water around Mars at least 1.5 meters (5 feet) deep, which could be one of the largest water reservoirs on the planet, according to the researchers.

“We didn’t expect to find this much water ice here,” said Stefano Nerozzi, a graduate research assistant at the University of Texas Institute for Geophysics (UTIG) and lead author of the new study. “That likely makes it the third largest water reservoir on Mars after the polar ice caps.”

A composite image of alternating layers of ice and sand captured by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter. The image was processed to show water ice as light-coloured layers with sandy layers a darker blue. Thin patches of frost show up as white. Image: NASA/JPL/University of Arizona

The findings were corroborated by an independent study using gravity data instead of radar, led by researchers at Johns Hopkins University and also published today in Geophysical Research Letters, of which Nerozzi is a co-author.

The authors suspect 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 the ancient ice caps were lost. The new findings show 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.

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An artist’s impression of two large planetary bodies colliding. New research suggests a dwarf planet colliding with the Moon early in the solar system’s history best explains major differences between the lunar near and farside. Image: NASA/JPL-Caltech

New research supports theories that a collision with a wayward dwarf planet early in the history of the solar system best explains why the Moon’s farside features heavily cratered terrain compared to the nearside with its lower-lying basins.

The stark difference between the two hemispheres was first noticed when spacecraft began beaming back images of the farside for the first time. NASA’s Gravity Recovery and Interior Laboratory – GRAIL – mission in 2012 revealed the crust on the farside is thicker than its nearside counterpart and includes an extra layer of material.

Planetary scientists have debated several theories for the asymmetry over the years, including the merger of two moons very early in the solar system’s evolution or an impact with a dwarf planet later, after the Moon’s crust solidified.

Carrying out a new study based on GRAIL gravity measurements, Meng Hua Zhu of the Space Science Institute at Macau University of Science and Technology and a team of researchers ran 360 computer simulations to test a variety of lunar impact scenarios in an attempt to reproduce the crust seen on the Moon today.

“The detailed gravity data obtained by GRAIL has given new insight into the structure of the lunar crust underneath the surface,” said Zhu, lead author of a paper describing the research in the American Geophysical Union’s Journal of Geophysical Research: Planets.

The best candidate to explain the GRAIL observations is an impact by a large body about 780 kilometres (480 miles) across that slammed into the Moon’s nearside at some 22,500 kilometres per hour (14,000 mph). That’s equivalent to a body slightly smaller than the dwarf planet Ceres hitting the Moon at a quarter of the speed of shooting stars in Earth’s atmosphere.

Another good fit was obtained using a slightly smaller impactor moving slightly faster at some 24,500 kph (15,000 mph).

Either way, according to Zhu, huge amounts of material would have rained back down, burying the farside under 5 to 10 kilometres (3 to 6 miles) of debris, explaining the extra layer of crust detected by the GRAIL spacecraft. The research indicates the impactor probably was not a second moon, but an independent body on an intersecting trajectory.

The modelling also provides an explanation for different levels of isotopes of potassium, phosphorus and other elements on the Moon compared to Earth thanks to material being added to the lunar crust after the Moon’s formation.

“This is a paper that will be very provocative,” said Steve Hauck, a professor of planetary geodynamics at Case Western Reserve University and editor of the AGU’s Journal of Geophysical Research: Planets. “Understanding the origin of the differences between the nearside and the farside of the Moon is a fundamental issue in lunar science.

“Several planets have hemispherical dichotomies, yet for the Moon we have a lot of data to be able to test models and hypotheses with, so the implications of the work could likely be broader than just the Moon.”

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Galaxy NGC 4485, located some 25 million light years from Earth in the constellation Canes Venatici, apparently avoided a direct hit during an encounter with a larger galaxy millions of years ago, a glancing blow that triggered a firestorm of chaotic starbirth on one side and leaving the other side relatively intact. Even so, the seemingly intact region shows signs of a previous spiral structure, an indication the galaxy was evolving normally in the past. The offending galaxy in the apparent hit and run is NGC 4490, out of view in this image. The two galaxies are now separated by about 24,000 light years.

NGC 4485. Image: NASA and ESA; Acknowledgment: T. Roberts (Durham University, UK), D. Calzetti (University of Massachusetts) and the LEGUS Team, R. Tully (University of Hawaii), and R. Chandar (University of Toledo)

For context, here is a wide view of the two galaxies:

In this ground-based view, NGC 4485 is the smaller galaxy of the central pair. The larger galaxy is NGC 4490. Image: NASA, ESA, Digitized Sky Survey 2 (Acknowledgement: Davide De Martin)

And here is a view of NGC 4490 from the Hubble Space Telescope:

The Hubble Space Telescope captured this view of NGC 4490’s central region. Image: ESA/Hubble & NASA
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A view of the Moon between 80 degrees south latitude and the south pole based on data from the Lunar Reconnaissance Orbiter’s laser altimeter. Permanently shadowed areas that never receive sunlight – possible sources of ice – are shown in red outlines with black fill. Image: Stopar J. and Meyer H./Lunar and Planetary Institute Regional Planetary Image Facility

The Trump administration has directed NASA to send astronauts back to the surface of the Moon by the end of 2024. The agency’s target is the Moon’s south polar region, where permanently shadowed craters provide the constant low temperatures needed to trap vast reservoirs of ice – a potential source of rocket fuel, air and water.

To help mission planners better understand the region, the Lunar and Planetary Institute, or LPI, is providing a new atlas of sorts covering the south polar region at varying scales complete with colour-coded elevations that clearly highlight areas where ice might be found, along with lighted areas where future crews could generate solar power to extract it.

The new atlas features 14 topographic maps based on high-resolution data from the Lunar Reconnaissance Orbiter, including digital elevation models derived from the spacecraft’s Lunar Orbiter Laser Altimeter.

“There are many exciting places to explore on the Moon, but the south pole has long held promise for a sustainable human presence,” said Julie Stopar, director of the Regional Planetary Image Facility at the LPI. “This collection can assist mission planners in this new era of south pole exploration.”

A closeup of the Moon’s south pole. Image: Stopar J. and Meyer H./Lunar and Planetary Institute Regional Planetary Image Facility

At the Moon’s poles, the Sun never climbs much higher that about a degree above the horizon. Over the course of a year, the Sun’s position along the horizon changes and while the angles and lengths of shadows reflect that changing position, the depths of some craters and other low-elevation areas never receive any sunlight. The resulting constant low temperatures can trap water ice that otherwise would sublimate away.

While it would not be easy, future astronauts may be able to use solar-powered electrolysis to break ice down into hydrogen and oxygen, allowing them, in a sense, to live off the land.

“Water-ice trapped near the lunar poles is particularly of interest for future explorers, as it may serve as a ready source of breathable air, drinkable water and spacecraft propellant,” the LPI noted when announcing the south pole atlas. “The new south pole maps can be used to identify and characterise topographically elevated (and illuminated) areas as well as permanently shadowed areas.”

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Observers in the UK with clear skies around 1am BST on Tuesday, 21 May can see Jupiter, the solar system’s largest planet, just 4 degrees from the waning gibbous Moon low in the south-southeast. At this time both the Moon and Jupiter fit within the same field of view of binoculars magnifying less than 10×, seen against the constellation backdrop of Ophiuchus, the Serpent Bearer. Look for first-magnitude star Antares in the adjacent constellation of Scorpius just 13 degrees to the right of Jupiter. AN graphic by Ade Ashford.Keen skywatchers in Western Europe and the British Isles will already be aware of a bright ‘star’ low in the southeast shortly after local midnight. The object is, of course, a planet – none other than the solar system’s largest, Jupiter. Any potential confusion as to its identity is resolved in the small hours of Tuesday, 21 May when the waning gibbous Moon lies nearby.

Shining conspicuously at magnitude -2.6, Jupiter is already brighter than any star visible in the nighttime sky, the planet fast approaching its closest approach to Earth for the year. Opposition to the Sun occurs on 10 June, but Jupiter and Earth are nearest two days later at a distance of 4.284 astronomical units or 641 million kilometres (398 million miles). More on that nearer the time.

At 1am BST on 21 May, Jupiter lies almost 652 million kilometres from Earth and appears slightly larger than 45 arcseconds in diameter. While the gibbous Moon and Jupiter may appear close together, it is merely a line of sight effect: the solar system’s largest planet is actually 1685 times farther away than our lunar neighbour.Jupiter’s Great Red Spot transits at 12:20am on 21 May and remains on show for a further hour for observers using 7.6-cm (3-inch) and larger telescopes at magnifications of 100× and more (seeing permitting). Jupiter’s innermost Galilean moon, Io, is eclipsed by the planet’s shadow at 12:22am, hence only the other three – Europa, Ganymede and Callisto – remain on show at 1am (all times given in British Summer Time). AN graphic by Ade Ashford.

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Before-and-after images show the impact site of the Israeli Beresheet lunar lander after it crashed to the moon in April. The before picture was taken by the Lunar Reconnaissance Orbiter when lighting conditions matched those on the day Beresheet crashed. Image: NASA/GSFC/Arizona State University

Executing an erroneous command sequence during its historic descent to the moon 11 April, the Israeli Beresheet robotic lander slammed into the surface at some 3,600 km/h (2,200 mph) at an angle of about 8.4 degrees, disintegrating on impact and creating a dark, elongated smudge about 10 metres (32 feet) across.

Eleven days after the crash, NASA’s Lunar Reconnaissance Orbiter flew overhead and captured an image of the impact site, allowing a before-and-after comparison and calculations to help researchers determine what happened in the privately-developed landers final moments.

The LRO was 90 kilometres (56 miles) above the crash site when snapped the images and was unable to detect any signs of a crater. It’s possible a crater was excavated that’s too small for the orbiter’s camera system to resolve, or it may be that Beresheet simply gouged the surface thanks to the spacecraft’s shallow impact angle, fragility and velocity.

The left frame shows the Beresheet impact site. The right frame was processed to highlight the white impact halo around the central smudge where the lander hit the surface. The scale bar represents 100 metres (328 feet). Image: NASA/GSFC/Arizona State University

“The smudge is likely a roughened surface (more micro-shadows) due to the impact and disintegration of the lander,” the LRO Camera team said on the instrument’s web site. “Surrounding the smudge is an area of increased reflectance (up to 20% higher). This ragged zone spans 30 to 50 meters from the smudge and includes a ray that extends southward about 100 meters.

“The higher reflectance was likely caused by gases or very fine high-speed particles rapidly moving away from the impact site, which smoothed the upper layer of regolith and redistributed fine soil particles, which in turn increased reflectance.”

The team compared the Beresheet crash site to impacts of other small spacecraft – LADEE, Ranger and GRAIL – that hit the moon at roughly the same speed.

“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,” NASA said in a release.

SpaceIL, the non-profit behind the Beresheet project, said in a Twitter posting the halo “was likely formed by soil particles blown outward” during the lander’s descent, adding “it was traveling faster than most speeding bullets when it hit the Moon’s surface.”

The Royal Observatory tweeted best wishes for a softer landing when Beresheet 2 eventually heads for the Moon.

“Thanks,” SpaceIL replied. “We’re working on it.”

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A composite image from ESO’s VLT Survey Telescope showing the position of the European Space Agency’s Gaia spacecraft. Such precise tracking improves the accuracy of Gaia’s sky maps. Image: ESO

Gaia, operated by the European Space Agency (ESA), surveys the sky from orbit to create the largest, most precise three-dimensional map of our galaxy. One year ago, the Gaia mission produced its much-awaited second data release, which included high-precision measurements — positions, distance and proper motions — of more than one billion stars in our Milky Way galaxy. This catalogue has enabled transformational studies in many fields of astronomy, addressing the structure, origin and evolution the Milky Way and generating more than 1700 scientific publications since its launch in 2013.

In order to reach the accuracy necessary for Gaia’s sky maps, it is crucial to pinpoint the position of the spacecraft from Earth. Therefore, while Gaia scans the sky, gathering data for its stellar census, astronomers regularly monitor its position using a global network of optical telescopes, including the VST at ESO’s Paranal Observatory. The VST is currently the largest survey telescope observing the sky in visible light, and records Gaia’s position in the sky every second night throughout the year.

“Gaia observations require a special observing procedure,” explained Monika Petr-Gotzens, who has coordinated the execution of ESO’s observations of Gaia since 2013. “The spacecraft is what we call a ‘moving target’, as it is moving quickly relative to background stars — tracking Gaia is quite the challenge.”

An artist’s impression of the European Space Agency’s Gaia spacecraft. Image: ESA/ATG medialab; background image: ESO/S. Brunier

The VST observations are used by ESA’s flight dynamics experts to track Gaia and refine the knowledge of the spacecraft’s orbit. Painstaking calibration is required to transform the observations, in which Gaia is just a speck of light among the bright stars, into meaningful orbital information. Data from Gaia’s second release was used to identify each of the stars in the field of view, and allowed the position of the spacecraft to be calculated with astonishing precision — up to 20 milliarcseconds.

“This is a challenging process: we are using Gaia’s measurements of the stars to calibrate the position of the Gaia spacecraft and ultimately improve its measurements of the stars,” explains Timo Prusti, Gaia project scientist at ESA.

“After careful and lengthy data processing, we have now achieved the accuracy required for the ground-based observations of Gaia to be implemented as part of the orbit determination,” says Martin Altmann, lead of the Ground Based Optical Tracking (GBOT) campaign at the Centre for Astronomy of Heidelberg University, Germany.

The GBOT information will be used to improve our knowledge of Gaia’s orbit not only in observations to come, but also for all the data that have been gathered from Earth in the previous years, leading to improvements in the data products that will be included in future releases.

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The High Resolution Imaging Science Experiment, or HiRISE, instrument aboard the Mars Reconnaissance Orbiter sends back a steady stream of spectacular images revealing subtle and not-so-subtle surface features on the red planet’s surface. In this view, late winter sunlight, striking the martian surface at a very low angle, contributed to a striking HiRISE image of sand dunes dusted with carbon dioxide frost and dust. Dark spots could be areas where underlying sand is exposed thanks to earlier defrosting activity. In a tweet about the photo, the HiRISE team wrote “It was hard not to title this ‘The Duck of Mars.'” The image is the first in a new series of observations designed to track seasonal processes.

Image: NASA/JPL/University of Arizona
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A thrust fault (indicated by arrows) crosses the Taurus-Littrow valley where the Apollo 17 mission landed (asterisk) in 1971. Moonquake indicators include material from a landslide visible at one end of the fault (1); boulder tracks on a nearby slope (2); and areas where fresh soil has been exposed (3). Image: NASA/GSFC/Arizona State University/Smithsonian

Data from seismometers left on the Moon by Apollo astronauts, a new technique for analysing the data they produced and detailed images captured by NASA’s Lunar Reconnaissance Orbiter show the moon is still shrinking as its interior slowly cools, triggering thrust faults where one section of crust is pushed over another.

In a paper published in Nature Geoscience, researchers conclude the Moon has shrunk by about 50 metres (150 feet) over the past several hundred million years.

“Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink,” said Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington. “Some of these quakes can be fairly strong, around five on the Richter scale.”

Five Apollo crews – missions 11, 12, 14, 15 and 16 – placed seismometers on the Moon between 1969 and 1971. The Apollo 11 instrument operated for just three weeks, but the other four recorded 28 shallow moonquakes through 1977, ranging from about 2 to 5 on the Richter scale.

Watters’ team re-examined the Apollo data using a new algorithm that helped them more accurately determine the locations of the 28 observed moonquakes. Eight of them were within 30 kilometres (18.6 miles) of thrust faults visible from orbit, well within the range where strong shaking could be expected based on the size of the fault scarps.

In addition, six of the eight moonquakes happened when the Moon was near its farthest point from Earth where tidal stresses reach a peak.

“We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking Moon and the Moon is still tectonically active,” said Watters.

To make sure, the team ran 10,000 simulations and found just a 4 percent chance of a coincidence that could produce the same results.

Astronaut Buzz Aldrin places a seismometer on the moon during the Apollo 11 mission in July 1969. Image: NASA

Additional evidence comes from the Lunar Reconnaissance Orbiter, which has imaged more than 3,500 fault scarps, the low step-like cliffs produced by such faults. Some of those images show landslides and boulders at the bottom of relatively bright areas on the slopes of fault scarps. Because solar and space radiation gradually darken the moon’s surface, bright areas indicate soil that has been recently exposed to space. Visible tracks of boulders are another indication of seismic activity.

One of the moonquakes occurred just 13 kilometres (8 miles) from the Taurus-Littro valley where Apollo 17 astronauts Gene Cernan and Harrison Schmitt landed in 1971. The astronauts drove their lunar rover over the cliff face of the Lee-Lincoln fault scarp and examined boulders and boulder tracks indicative of quake activity. A landslide covering the southern section of the scarp provides additional evidence.

“Establishing a new network of seismometers on the lunar surface should be a priority for human exploration of the Moon, both to learn more about the Moon’s interior and to determine how much of a hazard moonquakes present,” said co-author Renee Weber, a planetary seismologist at NASA’s Marshall Space Flight Center.

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