Is there, or has there ever been, life on Mars? European and Russian scientists are hoping to find out, with the first test probe set to land on Mars on Wednesday.
Tension at the European Space Agency's (ESA) mission control in Darmstadt, Germany is rising as the European-Russian ExoMars probe makes its final descent to the Red Planet.
ESA dispatched the experimental paddling pool-sized probe in March to explore the planet's atmosphere and search for signs of life. Seven months and 496 million kilometers (308 million miles) later, the Schiaparelli demonstrator module along with the Trace Gas Orbiter (TGO), a joint project of the European Space Agency and Russia's Roscosmos, are set to reach their target destination - the Meridiani Planum in the Martian highlands - on Wednesday.
"Everything has to function to millisecond precision," ExoMars project scientist Jorge Vago said ahead of the planned landing. "And our options for intervening are precisely zero."
Data transmitted from the Red Planet takes around 10 minutes to reach Earth. This signal delay means a computer will control the landing maneuver for the 600 kilogram (1,322 pounds) high-tech machine. Should anything go wrong, the craft will be a pile of scrap metal embedded into the surface of Earth's nearest neighbor before scientists are aware of its fate.
There were nervous moments for ground controllers on Sunday when the Trace Gas Orbiter, designed to enter Mars' orbit to analyze its atmosphere for signs of life, stopped sending status updates for over an hour before coming back online.
The panic was short-lived. In the early hours of Monday, the TGO successfully completed a planned maneuver allowing it to change course and avoid crashing into the Martian surface, ESA said.
If all goes to plan in the final hours before landing, Schiaparelli will reach the atmosphere at an altitude of 121 kilometers, moving a brisk 21,000 kilometers per hour (13,000 miles per hour).
The whole trip will take no longer than six minutes.
As it approaches the Martian surface, a discardable "aeroshell" will protect the lander against the heat generated by atmospheric drag, while a supersonic parachute and nine thrusters will brake it.
Cushioning its final impact will be a crushable structure attached to the lander's underside.
The ExoMars mission will be the first time this entry and landing combination will be used. The data gleaned from the maneuver will be crucial to planning the safe landing for much bigger and more expensive rovers in future.
Schiaparelli will send data on temperature, humidity, density profile and electrical properties.
Without solar panels, the lander is completely battery-driven.
Once landed on the Red Planet's surface, the TGO, with its state-of-the-art trace gas sensors, as well as an atomic particle detector that will have the ability to identify buried water-ice deposits, will set off to study Mars' other surface features, including those containing gas sources such as volcanoes.
This should keep the TGO busy until early 2018.
Of particular interest, ESA said, is methane, which could point to active geological or biological processes on the planet.
During its time on the surface of the Red Planet, TGO's travel partner, Schiaparelli, will conduct an array of environmental studies, including measuring electric fields that, in combination with measurements of atmospheric dust concentration, will provide new insight into the role of electric forces and dust lifting, a possible trigger for dust storms, ESA reported.
ExoMars blasted off from the Baikonur spaceport in Kazakhstan on March 14. DW was at ESA mission control for the launch - take a listen to our broadcast below.
Europe has contributed 1.3 billion euros ($1.4 billion) to the mission, while America's NASA, which was due to contribute $1.4 billion, pulled out due to budget cuts in 2012, causing Europe to turn to Russia to work on the shared project with Roscosmos. The joint mission with Roscosmos is Europe's first attempt at reaching Earth's closest neighbor after a failed bid 13 years ago to place the first non-US rover on the Red Planet.