NASA says the Phoenix lander on the surface of Mars has gone silent.
Engineers at the space agency last received a signal from the lander on 2 November.
Launched in August 2007, the spacecraft landed on Mars in late May to search for water and assess conditions for the possibility of sustaining life.
Phoenix has recorded snowfall, scraped up bits of ice and found that Martian dust chemically resembled seawater on Earth. More than 25,000 pictures have been sent from the planet.
By late October, the probe had surpassed its expected operational lifetime by two months.