The European Space Agency’s probe Schiaparelli was supposed to land on Mars on October 19.
A radio transmission that should have allowed scientists to follow the probe to the surface was not received.
Controllers hope that satellites in orbit at Mars will have detected it and will shortly be able to confirm that the probe got down safely.
Landing on Mars is always a daunting prospect.
It is a high-speed approach that has to be got just right or the spacecraft runs the risk of crashing into the ground.
Schiaparelli had a heatshield, a parachute and rocket thrusters to try to get itself to the surface intact.
The ESA will not be rushed to judgement on whether this mission has been a success or a failure.
It will wait on the reports of the satellites. Both European and American orbiters were tasked with tracking the event.
If Schiaparelli is later confirmed as down and safe, it will spend the next few days making measurements of the Martian environment and current weather conditions – at least until its batteries run out.