The first launch took place on March 14, 2016 in Kazakhstan using a Russian-built launch vehicle. Both the Trace Gas Orbiter (TGO) and the Entry, Descent, and Landing Demonstrator Module (EDM) arrived in the Martian system in October 2016.
On October 16, 2016, the two components separated as planned, with the TGO performing a maneuver shortly after to remain in orbit. The primary mission of the TGO, as the name suggests, was to refine our measurements of the scarcer components of the Martian atmosphere, including methane and water vapor. From an orbit about 250 miles above the surface of the red planet, the orbiter was positioned to obtain information orders of magnitude more accurate than any previous results. Methane in particular is generated by specific geological and organic processes. While the Trace Gas Orbiter could not identify the cause of gaseous emissions by itself, it did have the capability to pinpoint the sources geographically, aiding in the selection of the ExoMars rover landing site. The orbiter itself was constructed by the ESA while the Russian agency contributed several of its instruments.
Meanwhile the EDM lander (also called Schiaparelli after the Italian astronomer Giovanni Schiaparelli) was built to demonstrate crucial techniques for landing on the Martian surface shortly after the first spacecraft arrives at Mars. Weighing over 1300 pounds, the lander required a controlled landing to reach the Martian surface safely, just like the Curiosity rover.
The probe used a heat shield and parachutes to slow its descent and a liquid propulsion braking system to control its final touchdown on Mars. However, an error in the autonomous landing system led to the parachutes being deployed too early, when the lander was still several kilometers above the surface. As a result, the lander was torn to pieces, and did not function after impact. These components, along with the lander itself, were captured in an image on October 25 by NASA's Mars Reconnaissance Orbiter. While Schiaparelli was unable to survive landing, it still provided valuable data to guide future missions.
The orbiter's mission proved more successful. After spending several months in its initial highly elliptical orbit and calibrating its science equipment, a long period of aerobraking began in March 2017. This process involved using the friction of the Martian atmosphere at the spacecraft's closest approaches to take momentum away from the spacecraft and gradually lower the furthest point on the orbit from tens of thousands of miles away from the planet to just 250 miles. Due to the tenuousness of the Martian atmosphere, this was a very slow and delicate process, and was not completed until February 2018. The probe began its science mission in April.
The above image is one of the first taken by the ExoMars Trace Gas Orbiter. It shows Korolev crater, a location in Mars's north polar region. The bright material on the crater's rim is ice.
In November 2018, the Oxia Planum region on Mars was selected as the landing site for the ExoMars 2020 rover. The landing site was chosen to lie at low altitude to maximize the amount of Martian atmosphere available for slowing the rover's descent via parachute. It is a geologically rich region lying near the equator where liquid water likely existed billions of years ago. Oxia Planum was also chosen for its flat and easily navigable terrain. Below is a black and white image of the region.
Meanwhile, after a year of gathering data, the first results from the TGO were released in April 2019. Shortly after beginning its science mission, the orbiter had observed a major dust storm on the planet's surface and measured its effect on the distribution of water vapor and "semi-heavy water vapor" (in which one of the two hydrogen atoms in H2O is the deuterium isotope with one neutron and one proton) in the atmosphere.
The image above (click to enlarge) shows that dust storms increase the atmospheric content of both types of water vapor at many altitudes. These concentrations were measured using solar occultation, in which the orbiter analyzed sunlight shining through the Martian atmosphere. The way that sunlight is scattered/absorbed reveals what gases are present. Other initial results included a surprising lack of methane in the atmosphere that disagreed with some previous measurements and a higher resolution mapping of where water-rich minerals are present on the Martian surface.
The second launch will occur sometime in 2020 (it was moved back from its original 2018 launch in 2017), carrying the European-built ExoMars rover and a surface platform on which it will land, contributed by Roscosmos. The spacecraft will arrive at Mars in early 2020 at a landing site chosen with help from the 2016 mission's data. The same technology demonstrated in the first landing will allow the second module to perform a soft touchdown on the surface of Mars. After landing, the surface platform will deploy ramps, off of which the rover will exit to begin its exploration of the surface.
The rover's mission will last at least six months. Its primary mission will be to search for organic substances on the Martian surface. Since the harsh conditions of the surface may have obliterated traces of chemicals, the ExoMars rover will have the ability to bore holes as deep as two meters to obtain better preserved samples. After collecting samples, the rover will transfer them to its onboard laboratory for chemical analysis. With its careful site selection and dedicated exobiology instruments, the ExoMars mission has perhaps the best opportunity yet of discovering definitive biosignatures on Mars. It also would accomplish the technological objective of honing the ability to make soft, precision landings on the red planet. Finally, the mission paves the way for the holy grail of Martian exploration: returning a sample from the red planet back to Earth.
Sources: http://exploration.esa.int/mars/, http://exploration.esa.int/mars/47852-entry-descent-and-landing-demonstrator-module/, http://exploration.esa.int/mars/58557-schiaparelli-crash-site-in-colour/, http://exploration.esa.int/mars/58888-exomars-science-checkout-completed-and-aerobraking-begins/, http://exploration.esa.int/mars/59184-schiaparelli-landing-investigation-completed/, http://exploration.esa.int/mars/60235-exomars-images-korolev-crater/, http://exploration.esa.int/mars/60914-oxia-planum-favoured-for-exomars-surface-mission/, http://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/ExoMars/First_results_from_the_ExoMars_Trace_Gas_Orbiter
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