The "Rock Hall" drill site is located on Vera Rubin Ridge and is where the selfie was taken. The team reported that the carbon 13 in the drill hole was very low. The selfies were taken by the MAHLI camera on the end of the rover's robotic arm. The credit is NASA/Caltech-JPL/MSSS.
Since landing on Mars in August of 2012 NASA's rover has been roaming the crater taking samples and sending them back home to be analyzed. Researchers have three plausible explanations for the carbon's origin, based on the analysis of carbon isotopes in samples taken from half a dozen exposed locations.
The researchers note that all three of the scenarios are unconventional.
There are two stable isotopes of carbon. Researchers can determine details about the carbon cycle even if it happened a long time ago by looking at the amounts of each substance.
Christopher H. House, professor of geosciences, Penn State, said that the amounts of carbon 12 and carbon 13 in our solar system are the amounts that existed at the formation of the solar system. Carbon 12 reacts more quickly than carbon 13 so it's possible to see the carbon cycle by looking at the relative amounts of each in samples.
In the last nine years, NASA's Jet Propulsion Laboratory in Southern California has led the exploration of an area of Gale Crater that has exposed layers of ancient rock. The samples were recovered from the buried layers. The samples were heated in the absence of oxygen. A wide range of carbon 12 and carbon 13 amounts can be found in the analysis of a portion of the reduced carbon produced by this pyrolysis. Some carbon was enriched while other carbon was not.
The samples that are very low in carbon 13 are very similar to the samples from Australia that were 2.7 billion years old. The samples were caused by biological activity when methane was consumed by ancient mats, but we can't say that on Mars because it's a planet that may have formed out of different materials and processes than Earth.
The researchers suggest three possible explanations for the samples being extremely low in carbon dioxide and methane.
The solar system passes through a cloud of particles every couple of hundred million years.
House said that it doesn't deposit a lot of dust. It is difficult to see any of the deposition events in the Earth record.
The temperature on Mars would have been lowered by the dust cloud if it had still water. After the glacier melted, the dust would have deposited on top of the ice and left behind a layer of dirt.
There is not much evidence of glaciers on Mars. The explanation is plausible, but more research is needed.
The ultraviolet conversion of carbon dioxide to organic compounds is a possible explanation for the lower amounts of carbon 13
The drill hole is on Vera Rubin Ridge. The drill powder from this hole showed a carbon cycle that included either the atmosphere or Interstellar dust. The image was taken by a hand lens. The credit is NASA/Caltech-JPL/MSSS.
There are papers that say that UV could cause this type of fractionation. We need more experimental results to rule out this explanation.
There are three possible ways to produce carbon 13 deplete samples.
A strong carbon 13 signature from a paleo surface would indicate that past microbes consumed methane. Methane may have been released from the ground on Ancient Mars. The methane would either be consumed by surface microbes or deposited directly on the surface.
According to the researchers, there is currently no evidence of surface microbes on the past Mars landscape, and so the biological explanation highlighted in the paper relies on ultraviolet light to place the carbon 13 signal onto the ground.
"All three possibilities point to an unusual carbon cycle unlike anything on Earth today," said House. We need more data to figure out which of these is the correct explanation. It would be great if the rover could detect a large methane plume and measure the carbon isotopes from that, but there are not many large enough samples to do that, and most are small.
The remains of microbial mats or evidence of glaciers could clear things up a bit.
House said that it was the best course of study when studying another world.
Some of the samples it found in the study will be returned to the pediment in about a month.
House said that the research accomplished a long-standing goal for Mars exploration. One of the most important geology tools is to measure different carbon isotopes from the same place on another planet.
Gregory M. Wong is a recent graduate of Penn State.
There arepleted carbon isotope compositions observed at the crater on Mars.
The National Academy of Sciences has a journal.
The carbon was retrieved from the ocean on January 17th, 2022, and may yield clues to ancient Mars.
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