The European Space Agency's Schiaparelli lander stopped sending back data during its descent towards Mars.
Mission staff told media on Thursday morning (NZ time) it's "not a good sign" the signal stopped. The silver lining is that the Trace Gas Orbiter (TGO) - the spacecraft which carried the lander to the red planet - is safely in orbit, and working fine.
Diagnostic data is being downloaded and engineers will work "all night" to find out what happened to Schiaparelli.
"Cross your fingers," said ESA director Jan Woerner, who says the mission will still be considered a success even if the lander is lost because the TGO can still carry out its work.
This was Europe's first attempt to land a craft on Mars since the Beagle 2's "heroic failure" more than a decade ago.
The disc-shaped 577kg Schiaparelli lander is meant to be testing technologies for a rover due to follow in 2020.
During the six-minute descent to the surface, it used a parachute and thrusters to slow from a speed of nearly 21,000 km/h.
The lander is named for Giovanni Schiaparelli, the Italian astronomer who in 1877 began mapping the topography of Mars, extending study of what are now known as the planet's canals, a mistranslation of the Italian word canali, or channels.
"Mars has already inspired people for centuries," ESA's Woerner told Reuters TV.
Schiaparelli is part of the European-Russian ExoMars program, which will search for signs of past and present life on Mars and represents only the second European attempt to land a craft on the red planet.
Britain's Beagle 2 was ejected from the Mars Express spacecraft in 2003 but never made contact after failing to deploy its solar panels upon landing. At the time it was dubbed "a heroic failure".
The primary goal of ExoMars is to find out whether life has ever existed on Mars. The spacecraft on which the Schiaparelli lander travelled to Mars, Trace Gas Orbiter (TGO), carries an atmospheric probe to study trace gases such as methane around the planet.
Scientists believe that methane, a chemical that on Earth is strongly tied to life, could stem from micro-organisms that either became extinct millions of years ago and left gas frozen below the planet's surface, or that some methane-producing organisms still survive.
The second part of the ExoMars mission, delayed to 2020 from 2018, will deliver a European rover to the surface of Mars. It will be the first with the ability to both move across the planet's surface and drill into the ground to collect and analyse samples.
The ExoMars 2016 mission is led by the European Space Agency (ESA), with Russia's Roscosmos supplying the launcher and two of the four scientific instruments on the trace gas orbiter.
Reuters / Newshub.