[meteorite-list] NASA Finds Evidence of Diverse Environments in Curiosity Samples

[Ron Baalke]

https://www.jpl.nasa.gov/news/news.php?feature=6870

NASA Finds Evidence of Diverse Environments in Curiosity Samples
Jet Propulsion Laboratory
June 9, 2017

NASA scientists have found a wide diversity of minerals in the initial 
samples of rocks collected by the Curiosity rover in the lowermost layers 
of Mount Sharp on Mars, suggesting that conditions changed in the water 
environments on the planet over time.

Curiosity landed near Mount Sharp in Gale Crater in August 2012. It reached 
the base of the mountain in 2014. Layers of rocks at the base of Mount 
Sharp accumulated as sediment within ancient lakes around 3.5 billion 
years ago. Orbital infrared spectroscopy had shown that the mountain's 
lowermost layers have variations in minerals that suggest changes in the 
area have occurred.

In a paper published recently in Earth and Planetary Science Letters, 
scientists in the Astromaterials Research and Exploration Science (ARES) 
Division at NASA's Johnson Space Center in Houston report on the first 
four samples collected from the lower layers of Mount Sharp.

"We went to Gale Crater to investigate these lower layers of Mount Sharp 
that have these minerals that precipitated from water and suggest different 
environments," said Elizabeth Rampe, the first author of the study and 
a NASA exploration mission scientist at Johnson. "These layers were deposited 
about 3.5 billion years ago, coinciding with a time on Earth when life 
was beginning to take hold. We think early Mars may have been similar 
to early Earth, and so these environments might have been habitable."

The minerals found in the four samples drilled near the base of Mount 
Sharp suggest several different environments were present in ancient Gale 
Crater. There is evidence for waters with different pH and variably oxidizing 
conditions. The minerals also show that there were multiple source regions 
for the rocks in "Pahrump Hills" and "Marias Pass."

The paper primarily reports on three samples from the Pahrump Hills region. 
This is an outcrop at the base of Mount Sharp that contains sedimentary 
rocks scientists believe formed in the presence of water. The other sample, 
called "Buckskin," was reported last year, but those data are incorporated 
into the paper.

Studying such rock layers can yield information about Mars' past habitability, 
and determining minerals found in the layers of sedimentary rock yields 
much data about the environment in which they formed. Data collected at 
Mount Sharp with the Chemistry and Mineralogy (CheMin) instrument on Curiosity 
showed a wide diversity of minerals.

At the base are minerals from a primitive magma source; they are rich 
in iron and magnesium, similar to basalts in Hawaii. Moving higher in 
the section, scientists saw more silica-rich minerals. In the "Telegraph 
Peak" sample, scientists found minerals similar to quartz. In the "Buckskin" 
sample, scientists found tridymite. Tridymite is found on Earth, for example, 
in rocks that formed from partial melting of Earth's crust or in the continental 
crust -- a strange finding because Mars never had plate tectonics.

In the "Confidence Hills" and "Mojave 2" samples, scientists found clay 
minerals, which generally form in the presence of liquid water with a 
near-neutral pH, and therefore could be good indicators of past environments 
that were conducive to life. The other mineral discovered here was jarosite, 
a salt that forms in acidic solutions. The jarosite finding indicates 
that there were acidic fluids at some point in time in this region.

There are different iron-oxide minerals in the samples as well. Hematite 
was found near the base; only magnetite was found at the top. Hematite 
contains oxidized iron, whereas magnetite contains both oxidized and reduced 
forms of iron. The type of iron-oxide mineral present may tell scientists 
about the oxidation potential of the ancient waters.

The authors discuss two hypotheses to explain this mineralogical diversity. 
The lake waters themselves at the base were oxidizing, so either there 
was more oxygen in the atmosphere or other factors encouraged oxidation. 
Another hypothesis -- the one put forward in the paper -- is that later-stage 
fluids arose. After the rock sediments were deposited, some acidic, oxidizing 
groundwater moved into the area, leading to precipitation of the jarosite 
and hematite. In this scenario, the environmental conditions present in 
the lake and in later groundwater were quite different, but both offered 
liquid water and a chemical diversity that could have been exploited by 
microbial life.

"We have all this evidence that Mars was once really wet but now is dry 
and cold," Rampe said. "Today, much of the water is locked up in the poles 
and in the ground at high latitudes as ice. We think that the rocks Curiosity 
has studied reveal ancient environmental changes that occurred as Mars 
started to lose its atmosphere and water was lost to space."

In the paper, the authors discuss whether this specific area on Mars is 
a mark of this event happening or just a natural drying of this area. 
Scientists will search for answers to these questions as the rover moves 
up the mountain.

To view the paper, go to:

https://www.sciencedirect.com/science/article/pii/S0012821X17302005

To learn more about ARES, go to:

https://ares.jsc.nasa.gov

For more information about the Curiosity rover mission, visit:

https://www.nasa.gov/curiosity

https://mars.nasa.gov/msl/

News Media Contact
William P. Jeffs
Johnson Space Center, Houston
281-483-5111
william.p.jeffs at nasa.gov

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

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo at nasa.gov / dwayne.c.brown at nasa.gov

2017-165