ExoMars Trace Gas Orbiter

What is the ExoMars Trace Gas Orbiter?

The ExoMars Trace Gas Orbiter is the first of two missions in ESA’s ExoMars program, which asks whether life has ever existed on Mars.[1][2] It launched with Russia’s space agency, Roscosmos, as partner, on a Proton-M/Breeze-M rocket from Baikonur, Kazakhstan, on Mar 14, 2016.[3][4] The orbiterOrbiterAn orbiter circles Mars without landing, studying the planet from above — and many also relay rover data back to Earth.More in the glossary reached Mars on Oct 19, 2016, with a test lander called Schiaparelli.[2][4] The program’s second mission, the Rosalind Franklin rover, is targeting launch in 2028.[1]

A trace gas makes up less than 1% of an atmosphere.[3] TGO’s main job is to find such gases, methane above all, and help tell whether they come from geology or biology.[3][6] It is also the busiest data relay for NASA’s rovers.[18]

ESA, NASA and University of Bern figures, as of the dates shown.[2][8][3][14][9][18]

What happened to the Schiaparelli lander?

Schiaparelli crashed on Oct 19, 2016, after its computer wrongly decided it was already on the ground.[7] It was a test of European landing technology, not a long-lived science station. It was built to last only a few days on batteries.[3] It separated from TGO on Oct 16 and headed for Meridiani Planum.[3][7]

Much of the six-minute descent went to plan. About three minutes after entry, the parachute opened and the landerLanderA lander touches down on Mars and works from one spot, unlike a rover, which drives.More in the glossary began spinning faster than expected. That briefly overloaded, or “saturated,” the inertial measurement unit, the sensor that measures its rotation. The software’s sense of which way it was pointing went badly wrong. Combined with radar readings, it calculated that it was below ground level.[7]

So it released the parachute early, fired its thrusters for 3 seconds instead of 30, and acted as if it had landed. It actually fell from about 3.7 km (2.3 mi) and hit the ground at an estimated 540 km/h (336 mph).[7] NASA’s Mars Reconnaissance Orbiter later photographed the impact site, very close to the target. TGO had relayed Schiaparelli’s signals as it came down, while entering orbit itself, the first time this had been done in Mars exploration, which let engineers rebuild what happened.[7]

How did TGO reach its science orbit?

By aerobraking: dipping into the top of Mars’s atmosphere for about a year, so drag on its solar wings slowly lowered its orbit.[5][8] Its first orbit swung from about 200 km to 98,000 km (124 to 61,000 mi) above Mars and took four days. Aerobraking ran from March 2017 to early 2018, leaving TGO on a near-circular path about 400 km (250 mi) up, circling every two hours.[2][8] It was the first time ESA had used aerobraking to reach a science orbit around another world.[5] Science began at the end of April 2018.[9]

What instruments does TGO carry?

Four: two spectrometer suites that analyze the air, a color camera, and a neutron detector that looks for buried water.[6] Two are led from Europe and two from Russia.[20]

• 01NOMAD, Nadir and Occultation for MArs Discovery. Three spectrometers covering ultraviolet to near-infrared light. Its principal investigator is at the Royal Belgian Institute for Space Aeronomy.[3][6][9]
• 02ACS, the Atmospheric Chemistry Suite. Three more spectrometers, in near- to thermal-infrared light, led by Russia’s Space Research Institute (IKI).[3][6][9]
• 03CaSSIS, the Colour and Stereo Surface Imaging System. A color and 3D camera from the University of Bern, Switzerland, with pixels about 4.5 m (15 ft) across.[14] It photographs places that might release gases.[6]
• 04FREND, the Fine Resolution Epithermal Neutron Detector. Counts neutrons coming off Mars to map hydrogen, and so water, in the top meter (3 ft) of soil. Led by IKI, it includes a radiation monitor from Bulgaria.[6][12][20]

NASA supplied two Electra radios, which TGO uses to relay data from the rovers.[17]

Has TGO found methane on Mars?

No. Its first results, in April 2019, found no methane and set an upper limit of about 0.05 parts per billion, 10 to 100 times lower than earlier reported detections.[9][10] In 2004 Mars Express had reported about 10 parts per billion. NASA’s Curiosity rover has reported a background of about 0.2 to 0.7 parts per billion at Gale Crater that changes with the seasons, plus occasional spikes.[9]

Later data widened the gap. In 2021 the ACS team, using 1.4 Mars years of data, said any methane is likely below 0.02 parts per billion. NOMAD searched for local plumes at more than 2,000 places and found none. TGO also found no ethane, ethylene or phosphine.[11] Why Curiosity sees methane at the surface while TGO sees none a few kilometers up was still an open question, ESA said.[11] More on Mars’s atmosphere.

What else has TGO found?

Water just under the ground near the equator, a green glow in the sky, and water vapor lifted high by a dust storm.[12][13][9]

• 01Water in Valles Marineris. In December 2021 the FREND team reported an area about the size of the Netherlands in the canyon’s center where, if the hydrogen is in water, up to 40% of the top meter could be water, most likely ice.[12]
• 02A dust storm pumps water up. During the 2018 global dust storm, NOMAD and ACS saw water vapor rise to much higher altitudes within a few days.[9]
• 03A green glow. In 2020 NOMAD detected glowing green oxygen in Mars’s atmosphere, the first time this emission had been seen around a planet other than Earth. It had been predicted for about 40 years.[13]
• 04Another spacecraft. On Mar 2, 2019, CaSSIS photographed NASA’s InSight lander, the first time a European instrument had picked out a lander on Mars.[14]
• 05A comet and a solar storm. In October 2025 CaSSIS imaged the interstellar comet 3I/ATLAS from about 30 million km (19 million mi) away.[15] When a solar superstorm hit Mars in May 2024, a radiation monitor on TGO recorded the dose of about 200 normal days in 64 hours.[16]

How does TGO relay data from NASA’s rovers?

Curiosity and Perseverance send their science data up to orbiters passing overhead, and TGO carries more of it to Earth than any other.[18] Its first relay tests with NASA’s rovers came in November 2016, weeks after it arrived.[8] From February to May 2026 it relayed an average of 2,228.1 megabits a day, up from 1,562.7 through 2025. NASA’s MAVEN orbiter fell silent in December 2025, and the other orbiters picked up its share.[18]

Average data each orbiter transmitted, in megabits (Mb), from NASA’s Mars Relay Network page. MAVEN, which averaged 897.5 Mb a day through 2025, is no longer working.[18]

What changed when Europe cut ties with Russia?

TGO kept working, but the joint rover mission was cancelled.[19][20] On Mar 17, 2022, after Russia invaded Ukraine, ESA’s Council suspended cooperation with Roscosmos on the ExoMars rover mission, then due to launch that year. In July 2022 the Council ended that cooperation.[19][20]

ESA said in 2023 that TGO’s science mission was not part of the cancellation. Data from all four instruments, including the Russian-led ACS and FREND, go into ESA’s public archive, and Russian ground stations still receive TGO data under an agreement between the agencies.[20] NASA’s relay page notes that TGO is the only orbiter that uses them.[18]

How long will TGO keep working?

ESA plans to keep it working for years: it is meant to be the main relay for the Rosalind Franklin rover, which ESA is targeting to launch in 2028 and land in 2030.[1][20] In 2023 ESA said TGO had enough fuel for three more decades.[20] Its software now lets it steer by its star trackers and switch its gyroscopes on only when needed. Its operations manager said this extends their life “from a few years to decades.”[21] It is still busy. In October 2025 it photographed a comet, and in 2026 ESA said it and Mars Express were probing the atmosphere with radio signals passed between them twice a week.[15][16]

Mission timeline

1. Mar 14, 2016Launches from Baikonur on a Proton-M/Breeze-M rocket.[4]
2. Oct 16, 2016Releases the Schiaparelli lander.[3][7]
3. Oct 19, 2016Enters orbit around Mars. Schiaparelli crashes.[2][7]
4. November 2016First relay tests with NASA’s rovers.[8]
5. March 2017Begins about a year of aerobraking.[2][8]
6. April 2018Main science mission begins.[9]
7. Apr 10, 2019First results: no methane found.[9][10]
8. Jun 15, 2020ESA reports the green oxygen glow.[13]
9. Dec 15, 2021ESA reports water near the surface in Valles Marineris.[12]
10. Mar 17, 2022ESA suspends rover cooperation with Roscosmos. TGO carries on.[19][20]
11. October 2025Photographs the interstellar comet 3I/ATLAS.[15]

Sources

1. ESA — ExoMarsPrimary · checked Oct 6, 2026
2. ESA — ExoMars FactsheetPrimary · checked Oct 6, 2026
3. ESA — ExoMars 2016 FAQsPrimary · checked Oct 6, 2026
4. ESA — How ExoMars 2016 got to MarsPrimary · checked Oct 6, 2026
5. ESA — TGO’s orbit around MarsPrimary · checked Oct 6, 2026
6. ESA — Trace Gas Orbiter instrumentsPrimary · checked Oct 6, 2026
7. ESA — Schiaparelli landing investigation completedPrimary · checked Oct 6, 2026
8. ESA — ExoMars poised to start science missionPrimary · checked Oct 6, 2026
9. ESA — First results from the ExoMars Trace Gas OrbiterPrimary · checked Oct 6, 2026
10. Nature — No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations (Korablev et al., 2019)Primary · checked Oct 6, 2026
11. ESA — ExoMars orbiter continues hunt for key signs of life on MarsPrimary · checked Oct 6, 2026
12. ESA — ExoMars discovers hidden water in Mars’ Grand CanyonPrimary · checked Oct 6, 2026
13. ESA — ExoMars spots unique green glow at the Red PlanetPrimary · checked Oct 6, 2026
14. University of Bern — Bernese Mars camera CaSSIS returns spectacular imagesPrimary · checked Oct 6, 2026
15. ESA — ESA’s ExoMars and Mars Express observe Comet 3I/ATLASPrimary · checked Oct 6, 2026
16. ESA — ESA’s Mars orbiters watch solar superstorm hit the Red PlanetPrimary · checked Oct 6, 2026
17. NASA Science — ExoMars ProgramPrimary · checked Oct 6, 2026
18. NASA Science — Mars Relay NetworkPrimary · checked Oct 6, 2026
19. ESA — N° 9–2022: ExoMars suspendedPrimary · checked Oct 6, 2026
20. ESA — FAQ: The ‘rebirth’ of ESA’s ExoMars Rosalind Franklin missionPrimary · checked Oct 6, 2026
21. ESA Operations (ESOC) — Software update offers ExoMars Trace Gas Orbiter a second windPrimary · checked Oct 6, 2026