And it comes as US President Barack Obama, writing for CNN,
pledged to send humans to Mars by the 2030s "with the ultimate ambition to one day remain there for an extended time."
"I'm excited to announce that we are working with our commercial partners to build new habitats that can sustain and transport astronauts on long-duration missions in deep space."
The ExoMars Trace Gas Orbiter
arrives next week to start its mission looking for more evidence about methane production and other atmospheric gases that could signal biological activity.
The venture is a joint project between the European Space Agency (ESA) and the Russian state corporation Roscosmos.
In 2014, NASA's Curiosity rover detected a large spike in methane
in the atmosphere, prompting debate about what was causing it.
The ESA probe aims to find out more.
"Organisms on Earth release methane as they digest nutrients. However, other purely geological processes, such as the oxidation of certain minerals, also release methane," ESA says.
Adam Stevens, a researcher at the University of Edinburgh and the UK Centre for Astrobiology
, has worked on the science associated with the ExoMars mission and in preparation for it.
He explained that although methane is present on other planets, on Earth it is a signature of life.
"What we find on Earth is that ... some 90% of Earth's methane is biological, whether that's active now or from past biology that's decomposing," he said. "That means if we look at another planet like Mars ... maybe that's a sign of biology."
Stevens stressed that methane can be produced by other means, and not just life, but told CNN that the ExoMars mission will help "rule out some possibilities ... to tease out what is going on."
For example, he said, if methane was found at the poles where it's extremely cold then the methane is not produced by something that's melting.
ESA to test lander
ESA says the probe will also try to detect deposits of water ice below the surface, and help guide the selection of a suitable landing site for future missions.
One of the aims is to test a landing craft called Schiaparelli
. The lander will separate from the orbiter and then using a parachute and thruster will descend to the surface.
ESA says the impact will be cushioned by a structure similar to a crumple zone in a car.
The landing site has been chosen because it contains a layer of iron oxide that on Earth almost always forms in an environment containing liquid water, ESA says.
Schiaparelli has been designed to operate for a few days and will measure wind speed, temperature, humidity and pressure.
This mission is part of a longer-term ESA project to explore the Red Planet. The next ExoMars launch is planned for 2020 and will include a rover that can drill into the Martian surface to analyze samples.
The Europeans will be hoping for more success than on their previous mission to the surface of Mars. A British-built probe called Beagle 2, part of ESA's Mars Express program, was lost on Christmas Day in 2003 after contact failed during the descent.
But last year, images from NASA's Mars Reconnaissance Orbiter showed that the craft had successfully landed
but failed to properly deploy its solar panels.
Mass Mars exploration
Schiaparelli and its orbiting sister craft make up a growing swarm of satellites and surface robots that are continuing to hunt for signs of life on our neighboring planet.
Two NASA rovers, Spirit and Opportunity, arrived shortly after Beagle 2. Spirit got stuck in the Martian soil in 2009 and its mission was ended in 2011 but Opportunity has traveled more than a marathon distance of 26 miles and is still operational.
NASA's Curiosity rover arrived in 2012 and is still returning stunning images of cliff faces on Mars.
An Indian Mars probe called MOM
has been orbiting the Red Planet since 2014 and ESA's Mars Express orbiter
has been returning data since its arrival in 2003.
Nasa's MAVEN orbiter
is also investigating the Martian atmosphere after it began its mission in orbit in 2014
New missions planned
As well as ESA's future ExoMars missions, NASA is planning another rover expedition
. Landing in February 2021, it too will be scouring the surface for signs of life.
NASA says the rover will have a nuclear power source that can last at least 10 years and will include a test for producing oxygen from the Martian atmosphere -- something that might be crucial for future human exploration.
Its cameras will be able to generate 3-D maps, while instruments will try to detect and analyze organic molecules in the rocks and dust.
The rover will also be equipped with ground-penetrating radar to look for unusual features such as ice or brine.
Private companies are keen to join the trips to the Red Planet.
SpaceX has tested a new rocket
it plans to use for a future mission and Mars One says it will start training astronauts
next year, aiming for a launch in 2026.