Recent findings concerning a meteorite found 30 years ago in Antarctica suggest that too little water was present on Mars when the matter was dislodged four billion years ago to make life on the planet sustainable. The discovery was made by UCSD researchers in collaboration with the National Aeronautics and Space Administration and the Smithsonian Institution.
In a report published on Dec. 22, 2014 in the online version of the Proceedings of the National Academy of Sciences, lead author and project scientist at UCSD’s department of chemistry, Robina Shaheen, described how the new measurements of isotopes — atoms which contain more or less neutrons than protons — within the carbonate formation of the rock led to this conclusion.
Named Allan Hills 84001 after the region in Antarctica where it was found, the meteorite spent years floating in space before being pulled into Earth’s gravity and landing 13,000 years ago. ALH84001 was originally collected and analyzed by NASA, and in 1996, it was announced that bacteria found in the meteorite might be evidence of microbiological life on Mars.
Shaheen was asked to study ALH84001 in 2010 after the publication of a paper detailing how she and other UCSD researchers used a technique to demonstrate how isotopically anomalous carbonates may form naturally on aerosols without the presence of bacteria.
Carbonate formation varies based on its carbon and oxygen isotopes, which are either heavier or lighter than normal atoms depending on their source. Using the previously mentioned technique, Shaheen and her team were able to analyze the relative abundance of isotopes within ALH84001 to determine the meteorite’s chemical signature.
The isotopic weirdness, the variation of isotopes now within the carbonates of the meteorite, depends on how much water and carbon dioxide were present to interact four billion years ago before the rock was dislodged.
Furthermore, the interaction of carbon dioxide and ozone in Mars’ atmosphere also left behind a specific signature to be analyzed. When both measurements are taken into consideration, the degree of isotopic weirdness can be used to determine how much water and ozone were present at the time the carbonate formed.
In 1996, it was believed that the bacteria found in the meteorite implied that Mars had a relatively warm surface with large oceans, but the recently published findings suggest otherwise.
“Our data suggests that these microscopic structures can be produced by abiotic processes and that the amount of water present four billion years ago was not like earth with huge oceans,” Shaheen told the UCSD Guardian. “Oxygen isotopes of the carbonates indicate that there might be a small lake or sea. The water might have exchanged isotopically with ozone.”
Researchers were also able to identify simultaneous measurements of carbon isotopes on the same samples of the meteorite, suggesting that different minerals within the meteorite had separate origins.
Using a combination of two techniques, Isotope Ratio Mass Spectrometer at UCSD and Microprobe analysis at NASA Johnson Space Center, the carbonates were divided and categorized as belonging to two separate generations. The calcium rich carbonates found were indicative of a more recent Martian atmosphere, while the iron rich carbonates were determined to have originated 3.9 billion years ago.
Both carbonate phases had similar weirdness in oxygen isotopes acquired from the ozone, which supports the idea that the amount of water present almost four billion years ago was not enough to wash off the ozone signal from these carbonates.