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Missions to Mars: ExoMars Trace Gas Orbiter (TGO)

Mission Concept

The ExoMars Trace Gas Orbiter mission is a joint endeavour by the European Space Agency (ESA) and its Russian equivalent, RosCosmos. It will demonstrate key technologies for future flight and in-situ exploration missions and will make important scientific discoveries, fundamental to the exploration of Mars. It will also act as a data communications relay for other future Mars missions.


ExoMars Mission


The ExoMars programme consists of two missions.

  • The first is the ExoMars Trace Gas Orbiter mission described here, of which Belgium and IASB-BIRA have a heavy involvement. It is a mission under ESA lead, consisting of an orbiter and a lander demonstrator (EDL), which was launched in 2016 by a Proton rocket from Kazahkstan.
  • The second mission is an ESA rover containing Russian scientific instruments, which will be launched in 2020 by another Proton rocket.



Mission Origins: The 2016 Mars Orbiter Bus Joint Instrument Definition Team

In November 2009, the scientific goals and a strawman mission were described in detail in the Report of the Joint Investigation Definition Team (JIDT). Frank Daerden of the Belgian Institute for Space Aeronomy was a member of this team. The JIDT report discussed a potential set of instruments to address the mission science goals and was used in the formulation of a Joint Announcement of Opportunity for instruments on a 2016 orbiter.

JIDT (2009). Final Report from the 2016 Mars Orbiter Bus Joint Instrument Definition Team, November 2009. (.pdf)


ExoMars Trace Gas Orbiter (TGO)

The spacecraft is designed, built and integrated by ESA and includes an Orbiter which will carry the scientific trace gas payload instrumentation and an Entry, Descent and Landing (EDL) Demonstration Module.

ExoMars logo

The spacecraft was launched in March 2016 by a Proton launch vehicle. Arrival at Mars is foreseen in October 2016. The release of the EDL Demonstration Module is planned a few days before the critical Mars Orbit Insertion manoeuvre by the orbiter, after which point the orbiter will be captured by the gravity of Mars.

The orbiter will first follow an elliptical orbit around Mars, which takes 4 sols (a sol is a Martian day). This orbit is maintained during 8 sols.

Then the orbiter moves to a 1 sol orbit and further to a circular orbit with an altitude in the range of 350 to 420 km.

ExoMars trace Gas Orbiter

The science operations phase begins in mid-2017 and will last for one Martian year. After the science operations phase the orbiter will serve as a communications and data relay channel for the ExoMars 2018 mission, a rover, launched two years after the Trace Gas Orbiter.

The EDL Demonstrator will be used as a test for future larger landers. It is expected to survive for only a short time on the surface of Mars (about 8 sols).



This plot shows the orbital tracks over 4 Martian days. TGO will be in its 400km orbit for a whole Martian year (2 Earth years). During this time it will collect a lot of data.


During the day and the night the nadir instruments will be pointed at the planets surface. NOMAD will be observing the total column of atmosphere between the satellite and the surface.

It will even be able to measure light emitted from, or reflected off the surface if the atmosphere is not too dusty. During dust storms (see Mars, the planet, NOMAD will study the composition and density of the dust particles.

At the day-night terminators (moments where the satellite sees a sunrise or sunset from its orbital vantage point), the entire satellite rotates to point instruments such as NOMAD towards the sun. They measure the light from the sun as it passes through the Martian atmosphere. Which wavelengths of light are absorbed tells us about the composition of the atmosphere.


Science Objectives

Recent observations of the planet Mars, both from satellites in orbit around Mars as well as from Earth, have indicated the presence of methane. Current photochemical models cannot explain the presence of methane and its variations in space and time. These observations raise questions about the origin of methane, the possible presence and variation of other trace gases, the processes taking place on and below the surface and in the atmosphere of Mars, etc.

These questions lead to the following scientific goals:

    1. Detect a broad suite of atmospheric trace gases and key isotopes
    2. Characterise the spatial and temporal variability of methane and other key species
    3. Localise sources and derive the evolution of methane and other key species and their possible interactions
    4. Image surface features possibly related to trace gas sources and sinks



Instruments on TGO 2016

  • NOMAD: A high resolution solar occultation and nadir spectrometer
    A suite of three spectrometers designed to detect traces of the components of the Martian atmosphere and to map where they are on the surface
    Contact: Ann C. Vandaele, Royal Belgian Institute for Space Aeronomy, Brussels, Belgium.
  • ACS: Atmospheric Chemistry Suite
    Three spectrometers for mapping gases, dusts and clouds
  • FREND: Fine Resolution Epithermal Neutron Detector
    An instrument for measuring the hydrogen content of the surface and subsurface
  • CaSSIS: Camera and Stereo Surface Imaging System
    A camera for taking high-resolution images of the Martian surface


Read more on: ESA ExoMars Trace Gas Orbiter and Schiaparelli Mission (2016)



Operation Phases

March 2016: Launch
October 2016: EDL Demonstrator – orbiter separation
October 2016: Orbiter in elliptical orbit around Mars
Between May and August 2017: Start Orbiter science phase
January 2021: Arrival of 2020 rover mission and rover landing
Between April and July 2021: Start data relay for rover
December 2024: End of mission


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