Nasa's Curiosity rover has detected another methane "spike" on Mars, in what could be a sign of alien life on the red planet. According to the New York Times, which obtained an email about the discovery written by senior scientists at Nasa, the rover detected "startlingly high amounts of methane in the Martian air." The detection of methane hints at an even greater discovery - life on Mars - as the gas is often generated by microbes underground known as methanogens,which can survive without oxygen. "Given this surprising result, we’ve reorganized the weekend to run a follow-up experiment, " wrote scientist Ashwin R. Vasavada  in the email published by the New York Times. It is not the first time Nasa's robot has detected methane levels on the planet, and scientists are still not sure whether the gas is caused by living microbes.  This is because geothermal reactions, with no biological life involved, can also create methane.  When Curiosity landed on Mars in 2012 it could find barely any traces of methane, with less than one part per billion in the atmosphere.  Then in 2013 the rover detected a sudden increase in methane levels, with seven parts methane per billion, which endured for several months and then vanished.  The most recent discovery of Methane is 21 parts per billion, three times higher than the "spike" in 2013.  While increased methane levels measured by @MarsCuriosity are exciting, as possible indicators for life, it’s important to remember this is an early science result. To maintain scientific integrity, the science team will continue to analyze the data before confirming results. pic.twitter.com/zSrONQHuc5— Thomas Zurbuchen (@Dr_ThomasZ) June 22, 2019 Scientists are also not ruling out the possibility that the methane was not recent, having been trapped underground for millions of years, and only now is gradually emerging through cracks in the surface.  Thomas Zurbuchen, from Nasa's science mission directorate, advised people not to jump to any conclusions about the methane detection in a message on Twitter.  "While increased methane levels measured by Mars Curiosity are exciting, as possible indicators for life, it's important to remember this is an early science result," he wrote.  "To maintain scientific integrity, the science team will continue to analyse the data before confirming results."