THE satellite, called the ExoMars Trace Gas Orbiter (TGO), lifted off from Baikonur in Kazakhstan at 09:31 GMT.
The probe will investigate whether the methane in the world’s atmosphere is coming from a geological source or is being produced by microbes.
If all goes well, the two space powers expect to follow up this venture with a rover, to be assembled in the UK, which will drill into the surface.
That could launch in 2018, or, as seems increasingly likely, in 2020.
It will take the carrier rocket more than 10 hours to put the satellite on the right trajectory to go to Mars.
This involves a series of engine burns by the Proton’s Breeze upper-stage to build up the velocity needed to break free of Earth’s gravity.
These will fling the TGO away from Earth with a relative velocity of 33,000km/h.
The flight sequence is sure to strain the nerves of space agency officials.
For Russia especially, the Red Planet represents a destination of wretched fortune.
It has previously launched 19 missions to the fourth planet from the Sun, and most of those have been outright failures.
Many could not get off the pad cleanly; others simply stalled above the Earth and fell back down; a few crashed and burned at Mars or sailed straight past.
Assuming everything works out this time, controllers at the European Space Agency’s operations centre in Darmstadt, Germany, can expect a signal from the TGO after it has been released on its way by the Breeze boost stage.
This should come through at 21:28 GMT. It is then a seven-month cruise to Mars.
Three days out from arrival, on 16 October, the satellite will eject a small landing module known as Schiaparelli.
Once on the surface, on 19 October, its aim is to operate a few science instruments, but engineers are primarily interested to see how the module performs during the entry, descent and touchdown.
In particular, Schiaparelli will showcase a suite of technologies – radar, computers and their algorithms – that will be needed to put a later, British-built rover safely on the planet.
This second step in the joint European-Russian ExoMars project is supposed to leave Earth in 2018, although this is now looking increasingly doubtful because of funding and scheduling issues. Many connected with ExoMars are now talking about 2020 as being a more realistic launch date.