Washington: The laser-shooting ChemCam instrument aboard the Curiosity rover currently searching the surface of Mars for signs of habitability has shown what appears to be a common feature on the surface of some very different Martian rocks during Curiosity`s first 90 days on the Red Planet.
But exactly what that common feature is remains an intriguing mystery.
The ChemCam instrument uses an extremely powerful laser to vaporize a pinpoint of rock surface.
The instrument then reads the chemical composition of the vaporized sample with a spectrometer.
The highly accurate laser can fire multiple pulses in the same spot, providing scientists with an opportunity to gently interrogate a rock sample, even up to a millimeter in depth.
Many rocks are zapped 30 to 50 times in a single location, and one rock was zapped 600 times.
Members of the ChemCam team generally discard results from the first five laser blasts because of a belief that after the first five blasts, the laser has penetrated to a depth that provides a true representative sample of rock chemistry.
Instead of tossing out those data, however, Los Alamos National Laboratory postdoctoral researcher Nina Lanza looked at them specifically across a diverse set of Martian rocks.
She found that the first five shots had chemical similarities regardless the rock type.
What`s more, after five shots, like other scientists had noticed, the spectrum from the vaporized rock stabilized into a representative sample of the rock type below.
Lanza is quick to point out that she`s making no concrete claim as to the identity or origin of whatever is being seen during the first five shots of each ChemCam sampling.
The common signature from the first five blasts could indeed be entirely surface dust, or it could be a rock coating or a rind formed by natural weathering processes.
As the mission progresses, Lanza hopes that integrating other instruments aboard Curiosity with ChemCam sampling activities could help rule out unknowns such as surface dust, while careful experiments here on Earth could provide crucial clues for solving the Martian mystery of the first five shots.