The ESA/Roscosmos Trace Gas Orbiter (TGO) is mere weeks away from commencing its atmospheric search for evidence of recent geological activity, and possibly life on everyone's favorite Red Planet. The TGO forms one part of the ExoMars program – a joint European and Russian endeavour with the overarching goal of improving humankind's understanding of the Martian environment, and demonstrating new technologies that will benefit future missions.

The TGO made its highly anticipated rendezvous with the Red Planet back in October 2016, after enduring a seven-month journey through interplanetary space.

The probe's handlers were able to guide the robotic explorer from our Blue Marble to its neighboring red cousin, and deploy the ill-fated Schiaparelli descent and landing demonstrator.

Upon completing its capture burn, the TGO found itself traversing a highly eccentric path around the Red Planet. At the closest point in its orbit, known as the periapsis, the probe passed just 200 km (124 miles) from the Martian surface, while at its farthest, the apoapsis, it was roughly 98,000 km (60,894 miles) distant.

In order to make the most of the TGO's advanced suite of scientific instruments, the spacecraft needed to transition to a much lower, near-circular orbit.

This orbital shift was achieved through an ambitious set of maneuvers that saw the spacecraft skim through the uppermost layers of the Martian atmosphere. During these passes, the TGO's solar panels were fully extended, which, with a combined wingspan of 17.5 m (57 ft), essentially acted as a parachute, maximizing the drag between the speeding spacecraft and atmospheric particles.

Each pass only made a difference in velocity of at most 17 mm per second, which doesn't sound like much, but repeated over the course of 950 orbits in 11 months resulted in a deceleration of roughly 3,600 km/h. The team were able to successfully execute the risky deceleration campaign, manipulating the TGO into a 400 km (249 mile)-high, circular orbit perfect for taking detailed measurements of the tenuous Martian atmosphere, and its barren surface.

"We have reached this orbit for the first time through aerobraking and with the heaviest orbiter ever sent to the Red Planet, ready to start searching for signs of life from orbit," said Håkan Svedhem, project scientist for the TGO in a recent ESA press release. "We will start our science mission in just a couple of weeks and are extremely excited about what the first measurements will reveal."

All that remains for the science team prior to beginning observations is to calibrate the probe's equipment, and install new software. Once operational, the TGO will use a mix of advanced spectroscopic instruments, a high-resolution camera capable of imaging the surface with a resolution of 5 m (16 ft) per pixel, and a neutron detector to scan the atmosphere and surface of the dusty world.

The orbiter's first task will be to take an inventory of the trace gasses that make up roughly one percent of the Martian atmosphere, with a focus on hydrocarbons and sulphur species that could be taken as evidence of geologic or biologic activity.

The detection of methane is of particular interest to the TGO science team, as on Earth a large quantity of the gas is produced by living organisms, and through the release of gasses from hydrocarbon gas reservoirs. On Mars, the creation of methane could follow similar paths, with the gas either being produced as part of a geologic process, or even being created by subsurface microbial life. In both scenarios, the methane would eventually be released through cracks permeating the Martian surface.

Methane can only persist in the Martian atmosphere for about 400 years before being broken down by ultraviolet light from the Sun, and altered through interactions with other myriad elements of Mars' gaseous envelope. Therefore, any detection of the gas would be a great indicator of recent, or even ongoing activity.

The TGO's instruments are capable of detecting and analyzing extremely low concentrations of trace gasses with an accuracy up to 1,000 times greater than any previous ground or orbital mission. The probe will also be able to discover the specific origin of important trace gasses like methane, which have more than one possible method of formation.

Upon detection, the probe will map the location and altitude of the trace gasses, noting how they react to the shifting Martian seasons. Possible sources of the trace gasses can then be followed up on using the probe's high-res camera.

The spacecraft will also search for evidence of subsurface reservoirs of water ice. The discovery of such a deposit could help inform the location of future crewed and robotic missions hoping to follow up on a geological find, or eventually use the water for something practical, like making rocket fuel.

Furthermore, readings taken by the TGO regarding the quantity of aerosols, water vapor, ozone, and temperature of the Martian atmosphere will allow scientists to create an updated model of circulation processes occurring in the atmosphere of the Red Planet.

The population of robots on and around Mars is set to jump in the next couple of years with the arrival of a raft of new and exciting science missions, including NASA's Mars 2020 rover, the InSight lander, and the ground-based partner of the TGO – the ExoMars rover.

Alongside working to achieve its own scientific goals, the TGO will act as a communications relay between robots exploring the Martian surface, and Earth.

Source: ESA

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