A Russian rocket has lifted off from Kazakhstan in a new mission to find life on Mars.
ExoMars is a joint project between the European and Russian space agencies.
The rocket will launch two unmanned probes which will travel across space for seven months.
The Trace Gas Orbiter will hunt for methane gas in the Martian atmosphere and show if it was generated by geology or biological processes.
Methane is a gas largely produced by living organisms and could prove life once existed on the planet.
The second probe, Schiaparelli, is a trial lander which will test technology ahead of the later mission.
ExoMars 2018 will send another rover built in the UK to drill below the planet’s surface to look for signs of life.
The two missions will cost over £900m, but if traces of life are found this could be one of the biggest discoveries of all time.
Planetary scientist Dr Peter Grindrod, from Birkbeck, University of London, who is funded by the UK Space Agency, said: “It’s incredibly exciting.
“This is a series of missions that’s trying to address one of the fundamental questions in science: is there life anywhere else besides the Earth?
“Finding that life exists elsewhere in the solar system would be a huge discovery, so the evidence has to be strong.
“As they say, extraordinary claims require extraordinary evidence.”