Curiosity rover may be 'burping' methane out of Mars' subsurface 

  A new theory suggests that NASA's Curiosity rover is "burping" the surface of the Red Planet, releasing methane trapped beneath a salty crust. 

https://cdn.mos.cms.futurecdn.net/ByTi42ffHtMS5fH9Y9hA9Y.png

https://www.space.com/mars-methane-mystery-salt-crust-curiosity-rover