The ESA's Trace Gas Orbiter satellite immortalizes InSight from Mars' orbit | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS


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  The ESA's Trace Gas Orbiter satellite immortalizes InSight from Mars' orbit

On March 2, 2019, the Trace Gas Orbiter Probe (TGO) of the European Space Agency's ExoMars program was able to photograph the InSight probe on the surface of the red planet. This is the first time that a European satellite has achieved this technical feat, which requires not only a high-performance camera, but also special shooting conditions, given the relatively small size of the devices to be resolved.


The ESA's Trace Gas Orbiter Probe (TGO) supports the InSight mission for telecommunications and meteorite impact mapping, which are potential seismic sources for the SEIS seismometer. (© ESA/David Ducros)

Launched on March 14, 2016, the Trace Gas Orbiter entered Martian orbit on October 16 of the same year, almost thirteen years after the European Space Agency's first Martian probe, the Mars Express satellite. After a year of air-braking to reach its final mapping orbit, TGO began its scientific observation campaign at the end of April 2018. While its main objective is to study in a very detailed way the gaseous species that make up the Martian atmosphere, the orbiter can also play other roles, including that of radio relay.


Trace Gas Orbiter actually carries two Electra radio transponders, provided by NASA, which allows it to communicate with exploration devices on the surface, including the InSight probe. With the US Space Agency's Mars Reconnaissance Orbiter (MRO) and Mars Odyssey (MO) satellites, TGO regularly relays the data provided by this geophysical station to Earth since its landing on Elysium Planitia on November 26, including during critical operations.


Until now, the geometry of the InSight landing site overflights had not allowed the TGO CaSSIS camera to be pointed at the lander and the equipment it abandoned behind it during its perilous descent towards the Martian equator. On March 2, when the HP3 heat flux sensor began its attempts to sink below the surface, TGO passed directly over InSight, a configuration that made it possible to take a snapshot of the landing site.


InSight probe landing site image obtained by the CaSSIS camera of the Trace Gas Orbiter probe. (© ESA/CaSSIS team)

While the image obtained by TGO is certainly less accurate than the images acquired by the HiRISE spy camera of Mars Reconnaissance Orbiter (MRO) in December 2018 and February 2019, it nevertheless shows several details, such as the blast zone located around the landing gear (where the dust was blown by the back flares), the heat shield, as well as the rear shield (the parachute cover is not clearly identifiable, however). The plate covers an area of 2.25 km2, and the resolution varies from 5 to 6 meters per pixel (compared to HiRISE resolution which is 25 cm/pixel). The image has not been reoriented to place the north at the top.


In addition to its role in telecommunications, TGO will continue to support InSight by photographing at regular intervals the areas around the landing site to identify any new meteorite impacts. To determine the internal structure of Mars, the SEIS seismometer can rely on two seismic sources: earthquakes caused by sudden ruptures of rock materials in the crust and mantle of Mars, but also shock waves related to the impact of extraterrestrial cars on the surface. The ability to locate an impact very precisely (and therefore the epicentre of the associated earthquake) will indeed greatly assist in the interpretation of the data recorded by SEIS.