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What happened to Mars’s methane? A strange mystery is afoot on Mars. Scientists detected traces of methane in the planet’s atmosphere years ago, but now the team collecting data from a satellite currently in orbit around Mars has reported that the orbiter has not found any evidence of methane in the atmosphere. The presence of methane is important because it is one of the foundational elements for life and it indicates the planet could once have been habitable.

Recently a mission called the ExoMars Trace Gas Orbiter (TGO) has been analyzing the atmosphere of Mars to see what gases, clouds, and dust it contains using an instrument called the NOMAD (Nadir and Occultation for MArs Discovery) spectrometer suite. In recently released findings, the NOMAD team confirmed that they have not found any methane down to a highly sensitive detection level of 50 parts per trillion, and that they had used observations covering almost the entire atmosphere down to the planet’s surface.

To add to the confusion, NASA’s Curiosity rover did find methane on Mars earlier in this year, although the findings were not consistent over time: the rover found “seasonally fluctuating levels” of the gas in the atmosphere. The leader of the Curiosity’s methane-sensing instrument, Dr. Chris Webster, told Science that he was sure that the findings would eventually be reconciled, as it took his team six months before they detected the methane spike as part of the planet’s methane cycle. “I’m confident that over time there will be a consistency between the two data sets,” he said.

The cycle of methane on Mars is believed to come from “microseeps” in the planet’s subsurface, in which small amounts of gases seep through the bedrock. It is thought that the methane originates from inside the planet due to living or geological sources, as opposed to originating from outside of the planet. This hypothesis is supported by data from the Trace Gas Orbiter that shows no methane falling through the atmosphere.

The TGO will continue collecting data until 2022, so perhaps more evidence about the methane cycles of Mars will be found in future years.

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