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‘Halos’ discovered on Mars widen time frame for potential life

Curiosity takes a self-portrait at "Murray Buttes" in September 2016. Photo Credit: NASA / JPL

Curiosity takes a self-portrait at “Murray Buttes” in September 2016. Photo Credit: NASA / JPL

A paper released recently indicates that a habitable environment may have existed on Mars for far longer than previously believed. The paper, which was published in Geophysical Research Letters, looked at halos, or light areas, surrounding fractures in areas of Gale Crater on Mars.

Using data from the Mars Science Laboratory “Curiosity” rover, the group at Los Alamos National Laboratory in Los Alamos, New Mexico, was able to determine that Gale Crater once contained a lake of water that was likely drinkable. Moreover, even after the surface water of the lake disappeared, a significant amount of remained beneath the surface, and for a much longer period of time than previously understood.

“What this finding tells us is that, even when the lake eventually evaporated, substantial amounts of groundwater were present for much longer than we previously thought – thus further expanding the window for when life might have existed on Mars,” said Jens Frydenvang, a scientist and the lead author of the paper at Los Alamos National Laboratory and the University of Copenhagen.

In this image taken by NASA's Curiosity Mars rover, pale zones called "halos" border bedrock fractures. This photo was taken in 2015. The measurements offer a sense of scale. Photo Credit: NASA / JPL

In this image taken by NASA’s Curiosity Mars rover, pale zones called “halos” border bedrock fractures. This photo was taken in 2015. The measurements offer a sense of scale. Photo Credit: NASA / JPL

Using the laser-shooting Chemistry Camera (ChemCam) instrument, the Alpha-Particle X-ray Spectrometer (APXS), and cameras, as well as the Chemistry and Mineralogy Instrument (CheMin), scientists looked at samples observed and collected on sols 1,112, 1,119, and 1,126 near the lower north slope of Aeolis Mons, more commonly known as Mount Sharp.

What they found was the Stimson formation, a sedimentary mudstone rock, which is normally a plain dark stone, took on lighter tones along fracture lines. The closer to the fracture, the lighter the appearance of the rock was, which was similar to other haloed areas observed at Maria’s Pass and Williams and Bridger Basin.

Curiosity obtained samples from two areas within Bridger Basin, referred to as “Greenhorn” and “Big Sky”. The Greenhorn drill samples were taken from within the halo region of the Stimson formation, and the Big Sky drill samples were taken from outside of the halo area.

CheMin revealed the Greenhorn samples taken within the halo were greater than 40 percent elevated in amorphous silica as compared to the Big Sky samples taken outside of the halo areas. They also had increased amounts of feldspar compared to pyroxene.

The ChemCam indicated that within the halo regions, the silica content is between 60 to 80 weight percent, whereas outside of the bright halo regions, the average is 45 weight percent of silica. At the center-most area of the halo regions, the silica content was greater than 80 weight percent.

Additionally, scientists have been able to trace the haloed areas back following the fractures to areas with previous evidence of water. The halo regions Curiosity observed and sampled are at elevations of 65 to 100 feet (20 to 30 meters) from the floor of Gale Crater, which indicates the significant abundance of water that must have once existed there.

Mount Sharp is a three-mile (five-kilometer) high mountain at the center of the 71.5-mile (115-kilometer) wide Gale Crater. Since arriving at Mount Sharp in 2012, Curiosity has found evidence of hematite, sulfate-bearing layers of regolith, and mud clays. All of these indicate a period in Mars’ past when an abundance of water not only had existed but also persisted for some length of time.

It is thought that Gale Crater likely experienced one or more episodes of burial and erosion. When and how long these had lasted is still to be determined, but experts have suggested that it could have existed from 4.1 billion years ago, during the Noachian Era, through to the early Hesperian Era that began 3.7 billion to 3.0 billion years ago.

The Hesperian Era coincides with the point when Mars’ environment is believed to have changed radically from a warmer, wetter environment, to the cold, dry one seen today, whereas the earlier Noachian Era coincides with the time on Earth that Archea, or the very first life, was beginning to form.

One thing that has, again, been confirmed is that none of the evidence has pointed to hydrothermal environments. Rather, the samples and observations indicate sedimentary rocks formed at lower temperatures (less than 176 degrees Fahrenheit, or 80 degrees Celsius).

These results, along with two other recently released papers on findings regarding Mars’ habitability, have caused scientists to broaden their models as well as their understanding of the geologic history of the Red Planet and the possibility of the development of Martian life.



A native of the Greater Los Angeles area, Ocean McIntyre's writing is focused primarily on science (STEM and STEAM) education and public outreach. McIntyre is a NASA/JPL Solar System Ambassador as well as holding memberships with The Planetary Society, Los Angeles Astronomical Society, and is a founding member of McIntyre is currently studying astrophysics and planetary science with additional interests in astrobiology, cosmology and directed energy propulsion technology. With SpaceFlight Insider seeking to expand the amount of science articles it produces, McIntyre was a welcomed addition to our growing team.

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