December 13, 2013
Curiosity Performs First Rock-Dating Analysis On Mars
Brett Smith for redOrbit.com - Your Universe Online
While scientists have analyzed the age of rock samples from other planetary bodies before, the work has always been performed on Earth. Now, an international team of scientists has announced the first-ever geological analysis of a rock sample performed on another celestial body – Mars.
According to a report in the journal Science Express, the on-planet analysis could lead to a greater understanding of Mars’ geologic history and the potential for life to have existed on the Red Planet. The paper is part of a series of articles in the journal based on data gathered by NASA’s Mars Curiosity rover during its stay at a geologic feature called Yellowknife Bay.
The milestone analysis was the result of NASA’s pre-mission-launch call for scientists from around the world to submit ideas for experiments that could be performed with the Curiosity rover’s Mars Science Laboratory (MSL). The geochemical analysis performed on Mars is similar to a technique that has been used on Earth for decades.
The analysis involved a technique known as potassium-argon dating, which determines the age of a rock sample by finding out how much argon gas it contains. The noble gas is created by the radioactive decay of potassium-40 within a rock. Because the decay occurs at a known rate, scientists can calculate a rock sample’s age by measuring its amount of argon.
Using Curiosity’s Sample Analysis on Mars (SAM) instrument, NASA was able to heat a Martian rock sample to a high enough temperature that gasses within the dust and rocks were released and could be captured by an onboard mass spectrometer.
The research team determined the age of the mudstone in Yellowknife Bay to be between 3.8 and 4.5 billion years old.
"In one sense, this is an utterly unsurprising result—it's the number that everybody expected," said study author Ken Farley, a geologist at the California Institute of Technology.
The finding matches the age of Yellowknife Bay determined by a technique called crater counting. The method is based on the idea that planetary surfaces are constantly being hit with objects that create impact craters. Therefore, a planetary surface with many impact craters is said to be older than one with fewer craters.
"What was surprising was that our result—from a technique that was implemented on Mars with little planning on Earth—got a number that is exactly what crater counting predicted," Farley says. "MSL instruments weren't designed for this purpose, and we weren't sure if the experiment was going to work, but the fact that our number is consistent with previous estimates suggests that the technique works, and it works quite well."
The researchers also investigated changes to Yellowknife Bay’s landscape over time through a technique called surface exposure dating.
"The surface of Mars, the surface of Earth, and basically all surfaces in the solar system are being bombarded by cosmic rays," Farley explained.
When these rays hit an atom, they break the atom's nucleus and create isotopes of other elements. Because the rays only penetrate two to three meters below the surface, the abundance of cosmic-ray-generated isotopes indicates how long a sample has been on the surface.
Using measurements of three different isotopes, helium-3, neon-21, and argon-36, the researchers determined that the current surface of Yellowknife Bay has been exposed for approximately 80 million years.
"All three of the isotopes give exactly the same answer,” Farley said. “That is probably the most remarkable thing I've ever seen as a scientist, given the difficulty of the analyses.”
The Caltech scientist added that the surface’s relatively short exposure time bodes well for the discovery of fossilized lifeforms in Yellowknife Bay and the prospects of such a discovery are “better than many people had guessed.”