Tomorrow, October 19, the European Space Agency's ExoMars lander will touch down, marking the first time the ESA has landed a spacecraft with—we hope—total success on the red planet, setting the stage for a new era of planetary exploration by the Europeans. You can follow the action live on ESA's Facebook page beginning at 8 a.m. EDT. During the six-minute descent, which should begin at 9:42 a.m. EDT, the lander will return up to 15 images of the rapidly approaching surface, and once on the ground will activate a temporary weather system that will run for approximately two days. If all goes according to plan, the photos captured during the descent will be presented the following day, October 20, during a press briefing.
Named Schiaparelli after the 19th-century Italian astronomer Giovanni Schiaparelli, who drew the first maps of Mars, the lander is a technology proof-of-concept. Launched on March 14, it was built by Thales Alenia Space, a French-Italian aerospace contractor, and is intended to demonstrate that ESA has Mars landing capability—no small achievement. Mars is notoriously inhospitable to landers, having eaten several spacecraft from Roscosmos, NASA, and most recently, ESA; its Beagle-2 lander apparently touched down in 2003 but failed to function thereafter. Data collected during the descent and landing of Schiaparelli will be applied to the next phase of the ExoMars mission, tentatively set for 2020, in which an actual, ESA-built rover will be placed on the Martian surface for an exploration mission.
ExoMars is a joint mission between ESA and Roscosmos, the Russian space agency. As originally conceived, the mission would have been a collaboration between ESA and NASA. But the U.S. agency withdrew from the project, leaving ESA in the lurch and intensifying already stormy relations between the two agencies following NASA's withdrawal from the Europa Jupiter System Mission in 2011. (ESA's part of the Jovian project has been redesigned as a standalone mission called JUICE, for JUpiter ICy moons Explorer.) When NASA walked away, Russia agreed to help ESA, providing a launch vehicle and scientific instruments for this phase of the mission, and agreeing to build the lander and instruments for the next.
On October 16, the lander separated from its mothership, a newly arrived Martian satellite called the Trace Gas Orbiter. While the lander performs its brief mission on the surface, the orbiter will circle Mars in preparation for its science mission, set to begin in 2018. (The delay is due to the aerobraking maneuvers necessary to take it to a tight, circular orbit about 250 miles above the Martian surface.) Once its mission is underway, the orbiter will search the Martian atmosphere for such gases as methane, an indicator of possible active and ongoing life. It will also image the planet's surface in an attempt to find water ice. When the ExoMars rover arrives in the 2020s, the Trace Gas Orbiter will be its data relay; the rover will send data to the orbiter, and the orbiter will send the data back to Earth.
As for the lander: During its descent, it will measure changes in temperature, density, and pressure. Once on the ground, it will perform an analysis of the electrical properties of the Martian atmosphere and perform meteorological tests—humidity, wind speed and direction, pressure, and temperature, among other things.
In addition to the ExoMars Facebook Live and Livestream feeds, the agency is also running a liveblog of ongoing mission activities and updates. This can help provide context and granular-level information on what is happening and why.