A European spacecraft orbiting Mars is to start searching for signs of life on the Red Planet.
The ExoMars Trace Gas Orbiter (TGO) is due to begin its mission within the next two weeks, after completing a critical year-long aerobraking manoeuvre.
Its primary goal is to "sniff" the Martian atmosphere and look for evidence of methane, which may be an indication of active life on or below the planet's surface.
The TGO is circling Mars every two hours while new software is installed and calibrated.
Pia Mitschdoefer, the European Space Agency (ESA) mission manager, said: "This is a major milestone for our ExoMars programme, and a fantastic achievement for Europe.
"We have reached this orbit for the first time through aerobraking and with the heaviest orbiter ever sent to the Red Planet, ready to start searching for signs of life from orbit."
The aerobraking manoeuvre meant the spacecraft skimmed through the top of the thin Martian atmosphere using drag on its solar panels to slow it down.
Gradually its highly elliptical path was transformed into a low near-circular orbit around 248 miles from the planet's surface.
TCO is designed to sample and analyse minute amounts of trace gases that make up less than 1% of the Martian atmosphere.
They are thought to include methane, hints of which have previously been found by the ESA's Mars Express spacecraft and Nasa's Curiosity rover.
Atmospheric methane is broken down by sunlight and disappears if it is not continually replenished.
Much of Earth's methane is generated by the activity of living microbes. The gas can also be released by volcanic activity or naturally occurring hydrocarbon reservoirs.
TGO is equipped to tell if any Martian methane is most likely to have a biological or geological origin.