[meteorite-list] Mars Rover Curiosoty's Next Stop Has Sandstone Variations

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2014-090

NASA Mars Rover's Next Stop Has Sandstone Variations
Jet Propulsion Laboratory
March 24, 2014

Variations in the stuff that cements grains together in sandstone have 
shaped the landscape surrounding NASA's Curiosity Mars rover and could 
be a study topic at the mission's next science waypoint.

On a journey with many months yet to go toward prime destinations on the 
lower slope of Mount Sharp, Curiosity is approaching a site called "the 
Kimberley." Scientists on the team picked this location last year as a 
likely place to pause for investigation. Its informal name comes from 
a northwestern Australia region known as the Kimberley. The Martian site's 
geological appeal, based on images taken from orbit, is that four types 
of terrain with different rock textures intersect there.

"The orbital images didn't tell us what those rocks are, but now that 
Curiosity is getting closer, we're seeing a preview," said Curiosity Deputy 
Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, 
Pasadena, Calif. "The contrasting textures and durabilities of sandstones 
in this area are fascinating. While superficially similar, the rocks likely 
formed and evolved quite differently from each other."

The rocks that the Curiosity mission has studied most intensively so far 
are finer-grain mudstone, rather than sandstone. The rover found evidence 
for an ancient lakebed environment favorable for microbial life when it 
analyzed sample powder drilled from mudstone last year in an area called 
"Yellowknife Bay."

The rover team is eager to inspect sandstone at the planned waypoint, 
now just 282 feet (86 meters) south of the rover. The pause for investigations 
at this site might include time for collecting rock-sample material with 
the rover's drill, for delivery to the laboratory instruments inside the 
vehicle.

Material filling the space between grains of sand in sandstone is called 
cement, whatever its composition. Characteristics of the cement can vary 
greatly, depending on the environmental history that affected the rock. 
Sandstones with some clay-mineral cements are quite soft. Tap them with 
a hammer and they crumble. Sandstones with quartz cement can be very hard. 
Hit them with a hammer and they ring.

"A major issue for us now is to understand why some rocks resist erosion 
more than other rocks, epecially when they are so close to each other 
and are both likely to be sandstones," said Michael Malin of Malin Space 
Science Systems, San Diego. He is the principal investigator for the Mast 
Camera and the Mars Descent Camera on Curiosity.

Malin said that variations in cement material of sandstones could provide 
clues to different types of wet environmental conditions in the area's 
history.

As in the southwestern United States, understanding why some sandstones 
are harder than others could help explain the major shapes of the landscape 
where Curiosity is working inside Gale Crater on Mars. Erosion-resistant 
sandstone forms a capping layer of mesas and buttes. It could even hold 
hints about why Gale Crater has a large layered mountain, Mount Sharp, 
at its center.

Erosion-resistant capping layers that Curiosity has sometimes driven across 
during the rover's traverse since leaving Yellowknife Bay have also presented 
an engineering challenge for the mission. Some rocks within those layers 
have sharp points that have punched holes in the rover's aluminum wheels. 
One of the strategies the rover team has used to reduce the pace of wheel 
damage is choosing routes that avoid crossing the hard caprock, where 
feasible.

"The wheel damage rate appears to have leveled off, thanks to a combination 
of route selection and careful driving," said JPL's Richard Rainen, mechanical 
engineering team leader for Curiosity. "We're optimistic that we're doing 
OK now, though we know there will be challenging terrain to cross in the 
future."

The pace at which new holes have appeared in the wheels during recent 
drives is less than one-tenth what it was a few months ago. Activities 
with a test rover at JPL this month show that wheels with much more extensive 
damage than has been sustained by any of Curiosity's six wheels can still 
perform well. The holes in Curiosity's wheels are all in the thin aluminum 
skin between much thicker treads. These tests on Earth are using wheels 
so damaged that many treads are broken, but they still provide traction.

NASA's Mars Science Laboratory Project is using Curiosity to assess ancient 
habitable environments and major changes in Martian environmental conditions. 
JPL, a division of the California Institute of Technology in Pasadena, 
built the rover and manages the project for NASA's Science Mission Directorate 
in Washington.

For more information about Curiosity, visit http://www.jpl.nasa.gov/msl 
, http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/. You can follow 
the mission on Facebook at http://www.facebook.com/marscuriosity and on 
Twitter at http://www.twitter.com/marscuriosity.

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov 

2014-090