Searching for signature gases in the Martian atmosphere

The 2016 ExoMars Trace Gas Orbiter is the first in a series of Mars missions to be undertaken jointly by the two space agencies, ESA and Roscosmos. A key goal of this mission is to gain a better understanding of methane and other atmospheric gases that are present in small concentrations (less than 1% of the atmosphere) but nevertheless could be evidence for possible biological or geological activity.

Schiaparelli separating from the Trace Gas Orbiter. Credit: ESA/ATG medialab

Investigations with observatories in space and on Earth have demonstrated the presence of small amounts of methane in the Martian atmosphere that has been shown to vary with location and time. Since methane is short-lived on geological time scales, its presence implies the existence of an active, current source of methane. It is not clear, yet, whether the nature of that source is biological or chemical. Organisms on Earth release methane as they digest nutrients. However, other purely geological processes, such as the oxidation of certain minerals, also release methane.

The Trace Gas Orbiter carries a scientific payload capable of addressing this scientific question, namely the detection and characterisation of trace gases in the Martian atmosphere. From its approximately 400-km-altitude science orbit, the instruments onboard the Trace Gas Orbiter will be deployed to detect a wide range of atmospheric trace gases (such as methane, water vapour, nitrogen oxides, acetylene), with an improved accuracy of three orders of magnitude compared to previous measurements.

The Trace Gas Orbiter will monitor seasonal changes in the atmosphere’s composition and temperature in order to create and refine detailed atmospheric models. Its instruments will also map the subsurface hydrogen to a depth of a metre, with improved spatial resolution compared with previous measurements. This could reveal deposits of water-ice hidden just below the surface, which, along with locations identified as sources of the trace gases, could influence the choice of landing sites of future missions.

Communicating on Mars

Deployment test of the high-gain antenna. Credit: ESA - B. Bethge

The Trace Gas Orbiter carries the Entry, Descent and landing demonstrator Module (EDM), known as Schiaparelli, on the journey from Earth towards Mars and, as it approaches the planet, deploys it for entering the Martian atmosphere on its way to land on the surface of the planet. After deployment, the Orbiter will monitor the UHF transmission from Schiaparelli from its coasting to Mars until its landing on the Red Planet. It will also facilitate the real-time transmission to Earth of the most important data measured by Schiaparelli.

Scientific investigations will take top priority until the second mission in the ExoMars programme begins, with the arrival of the ExoMars rover in 2021. At that stage the Orbiter will become a valuable Mars telecommunications asset, providing communication services to the Rover operating on the surface of Mars. The Orbiter will act as a data relay centre for sending commands to the rover and downloading data to Earth through the ESA space communications network.

The ExoMars Trace Gas Orbiter Design

The Trace Gas Orbiter spacecraft, designed by ESA, builds on the heritage accumulated from earlier ExoMars mission scenarios. The main characteristics of the Orbiter are determined by the functions that it will perform and the launch vehicle, a Proton launcher, provided by Roscosmos.