More evidence of water on Mars

River deposits exist across the surface of Mars and record a surface environment from over 3.5 billion years ago that was able to support liquid water at the surface. A region of Mars named Aeolis Dorsa contains some of the most spectacular and densely packed river deposits seen on Mars.

The dotted white arrow points to curved strata recording point bar growth and river migration. The boundaries of 
ancient valley walls are defined by textural and albedo changes and are also associated with lateral river migration. 
Stacked above the point bars and completely confined within the dotted white and black lines are topographically
 inverted river deposits outcropping as ridges (e.g., black arrow). In places (e.g., south of the dotted white arrow),
 the ridges run against the dotted boundaries, suggesting flow was once redirected along a valley wall 
[Credit: B.T. Cardenas et al., Geological Society of America Bulletin]

These deposits are observable with satellite images because they have undergone a process called "topographic inversion." where the deposits filling once topographically low river channels have been exhumed in such a way that they now exist as ridges at the surface of the planet.

With the use of high-resolution images and topographic data from cameras on orbiting satellites, B.T. Cardenas and colleagues from the Jackson School of Geosciences identify fluvial deposit stacking patterns and changes in sedimentation styles controlled by a migratory coastline. They also develop a method to measure river paleo-transport direction for a subset of these ridges.

Together, these measurements demonstrate that the studied river deposits once filled incised valleys. On Earth, incised valleys are commonly cut and filled during falling and rising eustatic sea level, respectively.

Cardenas and colleagues conclude that similar falling and rising water levels in a large water body forced the formation of the paleo-valleys in their study area. Cross-cutting relationships are observed at the valley-scale, indicating multiple episodes of water level fall and rise, each well over 50 meters, a similar scale to eustatic sea level changes on Earth.

The conclusion that such large water level fluctuations and coastline movements were recorded by these river deposits suggests some long-term stability in the controlling, downstream water body, which would not be expected from catastrophic hydrologic events.

The findings are published in the GSA Bulletin.

Source: Geological Society of America [September 18, 2017]

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Splashdown! Crashing into martian mud

An impactor smashing into an ice-rich surface gave rise to the complex flow features around this ancient crater on Mars.

Perspective view of a 32 km-wide impact crater north of the Hellas basin that formed at time when the 
martian environment was much wetter, as seen in the fluidised nature of the debris excavated from it 
[Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

Impacts of comets and asteroids have shaped the surfaces of rocky planets and moons over the Solar System's 4.6 billion year history, and can reveal environmental conditions at the time of their formation.

During an impact, the energy transferred to the ground goes into melting and vapourising the impactor and parts of the surface, as well as excavating vast amounts of material from the ground, throwing it out onto the surrounding terrain as a blanket of debris.

The characteristics of the ejected material can provide clues as to the conditions of the planet's surface and its general environment.

Colour view of crater north of the Hellas basin. The crater is 32 km-wide and was formed at time when the
 martian environment was much wetter, as seen in the fluidised nature of the debris excavated from it 
[Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

The 32 km-wide crater seen centre-stage in this image clearly formed at a time when water or ice was present near the surface. The energy of the impact heated up the water-rich sub-surface, allowing it to flow more easily, leading to the 'fluidised' nature of the ejecta blanket.

The periphery of the lobes of excavated material often displays a raised ridge: as the flow slowed, the debris behind it piled up, pushing up the material at its periphery into ramparts.

Many craters on Mars show this pattern, sometimes with multiple layers of ejecta. Here, up to three layers of ejecta lobes can be identified, some of them terminating in ramparts. Multiple layer ejecta deposits can result from a combination of impact into a buried layer of water-rich ground, and interaction of ejected material with the atmosphere.

This image shows the relative heights of a cratered region north of the Hellas Basin on Mars. As indicated in 
the key at top right, whites and browns/reds represent the highest terrain, while blue/purple is the lowest 
[Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

The scene is located north of the Hellas impact basin, one of the largest in the entire Solar System at 2300 km. The region is in an area that is suspected to be the former drainage basin of a lake.

Small channels can also be seen to the south in the main image (left), providing more evidence of the region's watery past.

Source: European Space Agency [September 15, 2017]

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Curiosity Mars rover climbing toward ridge top

NASA's Mars rover Curiosity has begun the steep ascent of an iron-oxide-bearing ridge that's grabbed scientists' attention since before the car-sized rover's 2012 landing.

Researchers used the Mastcam on NASA's Curiosity Mars rover to gain this detailed view of layers 
in "Vera Rubin Ridge" from just below the ridge [Credit: NASA/JPL-Caltech/MSSS]

"We're on the climb now, driving up a route where we can access the layers we've studied from below," said Abigail Fraeman, a Curiosity science-team member at NASA's Jet Propulsion Laboratory in Pasadena, California.

"Vera Rubin Ridge" stands prominently on the northwestern flank of Mount Sharp, resisting erosion better than the less-steep portions of the mountain below and above it. The ridge, also called "Hematite Ridge," was informally named earlier this year in honor of pioneering astrophysicist Vera Rubin.

"Vera Rubin Ridge," a favored destination for NASA's Curiosity Mars rover even before the rover landed in 2012,
 rises near the rover nearly five years later in this panorama from Curiosity's Mastcam 
[Credit: NASA/JPL-Caltech/MSSS]

"As we skirted around the base of the ridge this summer, we had the opportunity to observe the large vertical exposure of rock layers that make up the bottom part of the ridge," said Fraeman, who organized the rover's ridge campaign. "But even though steep cliffs are great for exposing the stratifications, they're not so good for driving up."

The ascent to the top of the ridge from a transition in rock-layer appearance at the bottom of it will gain about 213 feet (65 meters) of elevation—about 20 stories. The climb requires a series of drives totaling a little more than a third of a mile (570 meters). Before starting this ascent in early September, Curiosity had gained a total of about 980 feet (about 300 meters) in elevation in drives totaling 10.76 miles (17.32 kilometers) from its landing site to the base of the ridge.

The Mastcam on NASA's Curiosity Mars rover captured this view of "Vera Rubin Ridge" about two weeks before
 the rover starting to ascend this steep ridge on lower Mount Sharp [Credit: NASA/JPL-Caltech/MSSS]

Curiosity's telephoto observations of the ridge from just beneath it show finer layering, with extensive bright veins of varying widths cutting through the layers.

"Now we'll have a chance to examine the layers up close as the rover climbs," Fraeman said.

This view of "Vera Rubin Ridge" from the ChemCam instrument on NASA's Curiosity Mars rover shows sedimentary 
layers and fracture-filling mineral deposits [Credit: NASA/JPL-Caltech/CNES/CNRS/LANL/IRAP/IAS/LPGN]

Curiosity Project Scientist Ashwin Vasavada of JPL said, "Using data from orbiters and our own approach imaging, the team has chosen places to pause for more extensive studies on the way up, such as where the rock layers show changes in appearance or composition. But the campaign plan will evolve as we examine the rocks in detail. As always, it's a mix of planning and discovery."

In orbital spectrometer observations, the iron-oxide mineral hematite shows up more strongly at the ridge top than elsewhere on lower Mount Sharp, including locations where Curiosity has already found hematite. Researchers seek to gain better understanding about why the ridge resists erosion, what concentrated its hematite, whether those factors are related, and what the rocks of the ridge can reveal about ancient Martian environmental conditions.

This view of "Vera Rubin Ridge" from the ChemCam instrument on NASA's Curiosity Mars rover shows sedimentary layers, 
mineral veins and effects of wind erosion [Credit: NASA/JPL-Caltech/CNES/CNRS/LANL/IRAP/IAS/LPGN]

"The team is excited to be exploring Vera Rubin Ridge, as this hematite ridge has been a go-to target for Curiosity ever since Gale Crater was selected as the landing site," said Michael Meyer, lead scientist of NASA's Mars Exploration Program at the agency's Washington headquarters.

During the first year after its landing near the base of Mount Sharp, the Curiosity mission accomplished a major goal by determining that billions of years ago, a Martian lake offered conditions that would have been favorable for microbial life. Curiosity has since traversed through a diversity of environments where both water and wind have left their imprint. Vera Rubin Ridge and layers above it that contain clay and sulfate minerals provide tempting opportunities to learn even more about the history and habitability of ancient Mars.

Source: Jet Propulsion Laboratory [September 14, 2017]

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Research provides evidence of ground-ice on asteroids

Research at the USC Viterbi School of Engineering has revealed new evidence for the occurrence of ground ice on the protoplanet Vesta.

Large, smooth areas on exoplanet Vesta correlated with higher concentrations of hydrogen 
[Credit: Elizabeth Palmer and Essam Heggy]

The work, under the sponsorship of NASA's Planetary Geology and Geophysics program, is part of ongoing efforts at USC Viterbi to improve water detectability techniques in terrestrial and planetary subsurfaces using radar and microwave imaging techniques.

The study, conducted at USC Viterbi in the Ming Hsieh Department of Electrical Engineering by research scientist Essam Heggy and graduate student Elizabeth Palmer from Western Michigan University, took over three years to complete.

Heggy is a member of the Ming Hsieh Department of Electrical Engineering's Mixil Lab, which is led by professor Mahta Moghaddam and specializes in radar and microwave imaging.

Vesta is located in the asteroid belt between Mars and Jupiter and, due to its large size, is believed to be a differentiated body with a core and a mantle just like our own planet.

Collisions between asteroids in the belt enable them to leave their orbits and travel great distances in the solar system, potentially colliding with other planetary bodies.

Finding ice on these bodies is of major importance to understanding the transport and evolution of water-rich materials in our solar system.

The team used a special technique called "bistatic radar" on the Dawn spacecraft to explore the surface texture of Vesta at the scale of a few inches. On some orbits, when the spacecraft was about to travel behind Vesta from Earth's perspective, its radio communications waves bounced off Vesta's surface, and mission personnel on the ground at NASA's Jet Propulsion Laboratory (JPL) received the signals back on Earth.

According to Heggy, this system of radar signaling was like "seeing a flame from a lighter in the middle of day from the opposite side of the United States."

Despite the challenges in measuring such a weak signal from the Dawn Spacecraft communication antenna from nearly 300 million miles away, the team assessed the occurrence of large, smooth areas on Vesta that correlated with the occurrence of higher concentration of hydrogen as measured by the gamma ray and neutron detector (GRaND) instrument onboard.

"I am excited that we were able to perform such an observation on Vesta. At USC we have been contributing to testing and developing several bistatic radar methods to explore water and ice on planetary surfaces and arid areas of Earth. As the largest research university located in an arid area of the planet, this effort is a natural outgrowth of our focus on understanding water evolution," Heggy said.

The USC researchers hope their work will get the public excited not just about water in space, but also about the importance of understanding water evolution in arid areas under changing climatic conditions.

The findings are published in Nature Communications.

Source: University of Southern California [September 13, 2017]

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