If there ever was (or is) life on Mars, it likely would have been composed of tiny microbes that left behind wisps of methane gas as minute signs of their existence. The gas might have accumulated in rocks and the atmosphere over the ages, just waiting for Earthlings to come along and find it.
Controversial studies have reported that methane exists in Mars’ atmosphere, giving scientists hope that they would find more evidence once more sophisticated research instruments arrived. Then, last November, surface data from the Curiosity rover indicated that the methane concentration on Mars did not exceed 5 ppb (parts per billion). In July, it was reduced to 2.7 ppb. Newly analyzed data, published today in Science, is even grimmer: Scientists now believe the concentration is at most 1.3 ppb, making it unlikely that bacteria ever lived below the surface. In comparison, Earth’s atmosphere contains 1,800 ppb.
Scientists have always been skeptical of reports of methane in Mars’ atmosphere. Previous measurements were made from Earth’s surface or by a NASA satellite orbiting Mars, both of which produced inconsistencies in their data.
It’s possible that sunlight and harsh characteristics of Mars’ atmosphere tear apart methane molecules as soon as they are formed. But Curiosity will keep sniffing for the gas, as will future missions. The European Space Agency plans to send a satellite in 2016 specially equipped to map out gases in the Martian atmosphere, paving the way for a rover in 2018.