Methane detected on Mars
The NASA robot rover Curiosity has detected methane on Mars while exploring the Gale crater, fuelling speculation that life might be its source. Animals and other organisms on Earth produce methane as a waste gas.
But astrobiologist Michael New is being more cautious. Speaking at NASA's Washington headquarters he said: "You need to know what is going on right at the source. You need to know the context. It's very hard to look at the methane alone and say it came from life."
NASA first detected methane on Mars in 2009, when telescopes revealed methane plumes on the planet's northern hemisphere. The finding suggested Mars had a replenishing supply of the gas because methane molecules would last for an average of 340 years in the Martian atmosphere before being broken down by sunlight.
Methane can also be made in a number of non-organic ways, including as a reaction between cosmic dust and ultraviolet rays from the sun.
The latest results from Curiosity confirm the 2009 finding. They show methane is present in the Martian atmosphere at one part per billion, or at concentrations 4,000 times less than on Earth.
The Curiosity Rover was sent to Mars in order to ascertain whether life once existed, or could exist there. During its mission it will analyse the planet's soil and rocks.
The rover detected a 10-fold rise in methane in the atmosphere around it as well as organic molecules in powdered rocks collected by its drill. This was the first time organics have been detected on surface material on the planet. It is believed they could have formed on the planet itself or landed there on a meteorite. The methane levels dropped when Curiosity moved about a kilometre away, suggesting the methane was produced by a local source.
The findings have been published in Science. The NASA authors cautiously suggest that microbial bugs known as methanogens might be a possible source of the methane.
"In the best of all possible worlds you would crack open a Martian rock and there would be eyes staring back at you," said New. "Or at least endolithic communities [organisms such as moss or lichen that live in rock cracks], which you can find living inside rocks in the desert and in Antarctica. The rocks can provide protection, but sometimes they are using the chemistry of rocks for energy as well. So if you cracked open a rock and saw a band of green or orange, that could mean life. That would be great, but we can't expect it to happen," said New.
Gale Crater was formed by a meteor impact 3.5 billion to 3.8 billion years ago. Mount Sharp lies at its centre, and it is believed flowing water once carved channels into the mountain and crater walls. Curiosity has discovered that water is bound to the soil within the crater.