By Jonathan Amos Science correspondent, BBC News
Europe has formally invited Russia to participate in space missions to Mars in 2016 and 2018.
A "yes" from the Russian space agency (Roscosmos) may be the only way of saving the missions which are at risk of cancellation due to lack of funds.
The 2016 mission involves a satellite to study the Martian atmosphere, while a big robot rover to investigate the surface is scheduled for 2018.
Both are being planned with the US, which is also struggling financially.
If Russia can be persuaded to provide a rocket to launch the 2016 satellite, it should make both atmospheric and surface ventures financially feasible.