The landing module of a European-Russian spacecraft detached from its satellite on Sunday and began its descent on Mars.
The 600-kilogram landing module, named Schiaparelli, is expected to reach the surface of the desert planet on Wednesday, the European Space Agency (ESA) said on its website.
Meanwhile the satellite - called the Trace Gas Orbiter - will remain in orbit to analyse the Red Planet's atmosphere for traces of methane and other gases that could be evidence of life.
The mission is the first of two unmanned missions for the project dubbed ExoMars, a joint effort between ESA and Russian space agency Roscosmos.
The craft took off from Kazakhstan in March.
Schiaparelli will test capabilities for safely landing the second unmanned mission on the planet.
The second mission, scheduled to blast off in 2018, plans to bring a rover robot to study the planet's soil.
