Following the Martian Yellowknife Road

Posted by Thomas Anderson

An international team of researchers from Los Alamos National Laboratory and the French Space Agency say they have managed to track a trail of minerals that point to the prior presence of water at the Curiosity rover site on Mars.

Indeed, researchers from the Mars Science Laboratory’s ChemCam team recently described how the laser instrument aboard NASA's Curiosity Rover has detected veins of gypsum running through an area known as Yellowknife Bay, located some 700 meters away from where the Curiosity Rover first touched down some five months ago.

"These veins are composed mainly of hydrated calcium sulfate, such as bassinite or gypsum," explained ChemCam team member Nicolas Mangold, of the Laboratoire de Planétologie et Géodynamique de Nantes, in Nantes, France. "On Earth, forming veins like these requires water circulating in fractures."

According to ChemCam team member Sam Clegg of Los Alamos National Laboratory, gypsum and certain other related minerals can be formed when water reacts with other rocks and minerals. The presence of gypsum and its cousin, bassinite, along with physical evidence of alluvial flow patterns previously seen during the Mars Science Laboratory mission, could indicate that the Yellowknife Bay area once was home to ponds created by runoff or subsurface water that had percolated to the surface.

Clegg and his colleagues first noticed the possibility of a gypsum signature weeks ago when ChemCam’s spectrometer recorded an increasing amount of calcium and a corresponding decrease in the silicon composition of a sample. Gypsum, a sedimentary rock, is made of calcium sulfate with bound water, while most of the rocks sampled so far on Mars are primarily composed of silicon. The change in composition indicated to the team that they were seeing something new in Martian geology.

The ChemCam instrument fires a powerful laser to vaporize rocks and then uses its spectrometer to analyze the samples. Because the laser can fire several pulses to sample rock situated below layers of surface dust, the ChemCam team was able to catch its first signs of calcium before anyone could actually see it. However, the instrument’s camera subsequently recorded the pale veins of mineral after the rock surface had been dusted off by laser blasts.

“Being able to see what we are sampling has been tremendously useful to the team and to the mission,” said ChemCam team leader Roger Wiens of Los Alamos National Laboratory.

As the rover moved down into Yellowknife Bay, ChemCam’s cameras as well as others aboard Curiosity have documented the increasing presence of light-colored veins of minerals that could be telltale signs that Mars was once a wet planet.

"Since the Mars Science Laboratory mission is focused on whether Mars is or was habitable, this new evidence of water on or below the planet’s surface is very exciting,... We should be able to learn more about what we’re seeing once mission scientists can use Curiosity’s drill to sample some of these larger portions of material and analyze them using the CheMin instrument," Wiens added.