Russia is stepping in to save a long-standing European Space Agency plan for a two-legged mission to Mars launching in 2016 and 2018 that had looked to be doomed because of NASA budget problems.
The original ExoMars plan was for NASA to provide the Earth-to-Mars transportation for an ESA-built orbiter and descent module demonstrator in 2016 and an ESA-built rover in 2018. But while the US Congress is willing to provide NASA with $700-800 million for its own - as yet undefined - mission in 2018, no other money is forthcoming from Washington for Mars exploration after NASA's planned 2013 launch of an atmospheric monitor.
However, after the ESA's governing council gave the go-ahead for ExoMars in March, the Paris-based agency met Roscosmos this month in Moscow and the two reached agreement for Russia to provide Proton launches for both legs of the mission. ESA and Roscosmos expect to sign a formal agreement before year-end.
According to ESA - which stresses that NASA is welcome to come back to the team - Russia's involvement will also enhance the scientific return of the 2016 trip, as Roscosmos wants to provide a couple of extra experiments.
The 2018 mission will also feature a Russian-majority entry, descent and landing module, and extra scientific instruments.
ESA's 2018 rover plans include a drill capable of giving its robotic laboratory access to subsurface locations, where organic molecules may be well preserved.
Recent discoveries suggest Mars had a wet past, so scientists are increasingly keen to investigate whether life arose on the Red Planet. NASA's own Curiosity rover, now halfway to Mars for an August 2012 landing, is also equipped to study Martian soil.
ESA also stresses that ExoMars is a test-bed for international collaboration on a future sample return mission.
Roscosmos will be keen to join ExoMars, as Soviet and Russian Mars missions have a long history of flops, most recently this year's failure of the Phobos Grunt sample return mission to get beyond Earth orbit.
ESA and Roscosmos have a fruitful history of collaboration, including on the Mars500 simulated mission, which concluded late in 2011, to evaluate the psychological and physical effects on a human crew of an 18-month trip to our nearest neighbour.