NASA has discovered traces of methane on Mars.
Methane has been identified on Mars
The Curiosity Rover has identified a steady stream of gas on the Red Planet coming from the Gale Crater, which appears at different times of the day and fluctuates depending on the season, raising hopes that there could be life elsewhere in the solar system.
Experts at the US space agency have suggested that the methane could be encased deep under solidified salt and only seeps out when temperatures rise on the planet.
On Earth, methane is a sign of life and is passed by animals when they digest food.
The erratic behaviour of the methane has left scientists perplexed and the situation is made even more complicated as spacecraft orbiting Mars have been unable to find any traces of the gas in the wider atmosphere.
Ashwin Vasavada, a scientist at NASA's Jet Propulsion Laboratory (JPL), said: "It's a story with a lot of plot twists."