Europe makes orbit and loses Schiaparelli
One second of saturated gyro data convinced a lander it was already underground. It cut its parachute at 3.7 km and hit Mars at 540 km/h.
Two European spacecraft arrived at Mars on 19 October 2016. The Trace Gas Orbiter burned its main engine for 139 minutes and slid into orbit. Schiaparelli, the 577-kilogram demonstrator lander it had carried out from Earth, hit the ground at 540 kilometres per hour.
The descent had been going well. Schiaparelli entered the atmosphere at 21,000 km/h, deployed its parachute at 12 kilometres and 1,730 km/h, and dropped its heat shield at 7.8 kilometres. Then, as the parachute inflated, the module swung harder than anyone had modelled, and its inertial measurement unit — the gyro package that tracks rotation — saturated for roughly one second. One second of impossible rotation data corrupted the computer's estimate of which way up it was. Fed together with the radar altimeter readings that followed, that bad attitude produced a negative altitude: the navigation software concluded Schiaparelli was below ground level. Everything after that followed rigorously from a false premise. It jettisoned its parachute and back shell, fired its braking thrusters for 3 seconds instead of 30, switched on its surface systems, and fell freely from 3.7 kilometres. NASA's Mars Reconnaissance Orbiter photographed the fresh crater the next day. ESA's inquiry, published on 24 May 2017, listed four root causes and softened none of them: the parachute dynamics had been inadequately modelled, the software had no handling for a saturated IMU, the failure-detection logic never flagged an altitude that could not physically exist, and the oversight of subcontractors and hardware acceptance had been too loose.
The orbiter, which was the expensive half, worked. After a year of aerobraking to circularise its orbit, TGO began science operations in April 2018 carrying two spectrometer suites, ACS and NOMAD, built to measure trace gases down to parts per trillion — far below anything previously flown at Mars, and aimed above all at methane.
Methane is why anyone cares. It survives only a few hundred years in the martian atmosphere before ultraviolet light breaks it up, so whatever is there now was made recently, by geology or by biology. Curiosity's tunable laser spectrometer in Gale Crater had reported a background near 0.41 parts per billion with a seasonal swing, plus spikes: about 7 ppb in 2013, 21 ppb in June 2019. TGO looked from April to August 2018 across both hemispheres and found nothing whatsoever, with an upper limit of 0.05 parts per billion and a best sensitivity of 0.012.
Both results are careful, and they contradict each other. Perhaps Gale leaks small amounts of methane at night that are destroyed near the surface before they mix upward. Perhaps something aboard the rover is the source. Perhaps there is a fast destruction mechanism nobody has identified. Years on, it is unresolved, and it remains one of the better fights in Mars science.
ExoMars was designed as two missions. The second, the drilling rover Rosalind Franklin, lost its Russian launcher and landing platform when ESA severed ties with Roscosmos in 2022. ESA now targets 2028.