[18][19][20][21] The challenge to discern the source of methane in the atmosphere of Mars prompted the independent planning by ESA and NASA of one orbiter each that would carry instruments in order to determine if its formation is of biological or geological origin,[22][23] as well as its decomposition products such as formaldehyde and methanol.

[9] On the ExoMars side, ESA authorised about half a billion Euros in 2005 for a rover and mini-station; eventually this evolved into being delivered by an orbiter rather than a cruise stage.

[4][9][25] Under the FY2013 budget President Barack Obama released on 13 February 2012, NASA terminated its participation in ExoMars due to budgetary cuts in order to pay for the cost overruns of the James Webb Space Telescope.

[31] On 15 March 2012, the ESA's ruling council announced it would press ahead with its ExoMars program in partnership with the Russian space agency Roscosmos, which planned to contribute two heavy-lift Proton launch vehicles and an additional entry, descent and landing system to the 2020 rover mission.

The Trace Gas Orbiter and descent module Schiaparelli completed testing and were integrated to a Proton rocket at the Baikonur Cosmodrome in Kazakhstan in mid-January 2016.

Additional thruster firings through mid-April circularised the spacecraft's orbit to 400 km (250 mi), and full science activities began on 21 April 2018.

[49][50] The TGO separated from the ExoMars Schiaparelli demonstration lander and would have provided it with telecommunication relay for 8 Martian solar days (sols) after landing.

[57] The nature of the methane source requires measurements of a suite of trace gases in order to characterise potential biochemical and geochemical processes at work.

For landed missions, this places severe constraints on antenna size and transmission power, which in turn greatly reduce direct-to-Earth communication capability in comparison to orbital spacecraft.

[65] NASA provided an Electra telecommunications relay and navigation instrument to assure communications between probes and rovers on the surface of Mars and controllers on Earth.

[67] The first year of science operations[68] yielded a wealth of new data and scientific discoveries, including: new observations of the atmospheric composition and structure,[69][70] water-ice cloud enhancement during a global dust storm,[71] new measurements of the atmospheric thermal structure and density,[72] estimations of the timespan of the climate record of the south polar ice sheet,[73] confirmation of dry-processes being responsible for Recurring Slope Lineae in Hale crater,[74] identifying a variety of ice and non-ice related active processes occurring on the surface in colour,[75] and high-resolution maps of shallow subsurface Hydrogen, increasing the known amounts of probably near-surface buried water ice.