ExoMars Trace Gas Orbiter
This member of the ExoMars team is a vital component in the hunt for methane in the Red Planet’s atmosphere
ExoMars is a collaborative effort between the European Space Agency (ESA) and Russia’s Roscosmos. Launched in March 2016, the Trace Gas Orbiter (TGO) is part of the first instalment of an extensive exploratory mission, a venture that also includes the Rosalind Franklin rover, scheduled for touchdown on Mars in mid-2023. Accompanying the TGO was the descent module named Schiaparelli.
The TGO swung into Martian orbit on 19 October 2016 and, soon after arrival, Schiaparelli detached from the orbiter and began its journey to the surface. This module was created to demonstrate how a robotic lander could enter, descend and land on the surface of Mars. However, this demonstration was unsuccessful as conflicting information in the module’s computer led to a crash landing. While Schiaparelli was demonstrating how not to land on the surface, the TGO was preparing itself for a new level of atmospheric analysis.
Before the orbiter could begin any in-depth scientific studies it had to calibrate its equipment. It then shifted itself into an orbit around Mars that would allow it to get up close. Next the orbiter tested its instruments and provided some amazing images of the Red Planet’s surface, courtesy of the Colour and Stereo Surface Imaging System (CaSSIS). At the time the ESA’s TGO project scientist, Håkan Svedhem, said: “This first impression provides a fantastic preview of what’s to come when we start collecting data for real. Not only is the spacecraft itself clearly performing well, but I am delighted to see the teams working together so effectively.”
The images and data returned from the initial instrument calibration excited astronomers back on Earth, but they had to wait until the spacecraft had gone from a extremely elliptical orbit – which took it 98,000 kilometres (61,000 miles) from the planet’s surface – to a planet-hugging, circular orbit that had it hovering just 400 kilometres (250 miles) above the surface – a similar altitude to the International Space Station around Earth.
The technique used to alter the spacecraft’s orbit is known as ‘aerobraking’. It uses the planet’s upper atmosphere to slow the spacecraft down and reduce the size of its orbit. This took around a year, and in-depth scientific investigation only truly began in April 2018. “Then the craft was reoriented to keep its camera pointing downwards and its spectrometers towards the Sun so as to observe the Mars atmosphere, and we could finally begin the long-awaited science phase,” says Svedhem.
But what exactly is it looking for? If you’ve not gathered from the name already, the orbiter’s primary objective is to build an inventory of the gases that make up less than one per cent of the Martian atmosphere by volume. These gases include water vapour, nitrogen oxides, acetylene and – most important of all – methane.
The planet’s atmosphere is dominated by carbon dioxide, which constitutes a whopping 95 per cent of the atmosphere. This gas is deadly to us humans, but it is methane that scientists are more interested in, as it can be a calling card for biological activity. This short-lived compound is produced as a by-product of human life, but it can also be created in abiotic, chemical reactions. The issue is that so far no orbiter, rover or astronomer with a prying telescope can pin down the source of the methane, and henceforth cannot say with certainty that biological life of some sort is releasing this methane into the atmosphere.
“Just as the question of the presence of methane and where it might be coming from has caused so much debate, the issue of where it is going, and
how quickly it can disappear, is equally interesting,” says Svedhem. “We don’t have all the pieces of the puzzle or see the full picture yet, but that is why we are there with TGO, making a detailed analysis of the atmosphere with the best instruments we have to better understand how active this planet is – whether geologically or biologically.”
The other duty of TGO is to act as a communications buffer between operations on the surface of Mars and the hardworking teams based on Earth. As part of a test run the orbiter was in constant communication with Schiaparelli as it made its descent to the surface, and it will again provide a communications relay between the Earth and the Rosalind Franklin rover when it reaches the Red Planet.