The European Space Agency has announced a tentative agreement with Russia for an unmanned mission to explore signs of life on Mars.

The project, approved at a meeting in Naples Wednesday, calls for sending an orbital probe to Mars in 2016 that would look for traces of methane gas and other biological clues in the Red Planet's atmosphere. A six-wheeled rover would follow in 2018.

The ExoMars mission was born in December 2005 and more than $500 million has been spent on it so far.

When NASA pulled out in February due to budget constraints, Europe turned to Russia's Roscosmos space agency for help. Under a draft deal, Russia will provide heavy-lift Proton rockets for the launches and in return get instrument space onboard the satellite and rover.

Many ESA members are struggling with tight budgets, and a number of proposed space projects have been sidelined. A plan to send a European lander to the Moon made no headway given the agency's money crunch.

During Wednesday's meeting, European Space Agency members approved a multi-year budget of $12.3 billion.