In April 2018, the ExoMars Trace Gas Orbiter (TGO) passed over the Gale Crater where earlier rovers and spacecraft picked up strong spikes of methane. Its Nomad chemical analyzer failed to detect any signs of methane in the air 250 miles (400 kilometers) above the ground.
Designed to detect extremely low concentrations of atmospheric methane, Nomad also possessed enough sensitivity to determine whether or not the carbon in methane came from inorganic or organic sources. Researchers expected it to provide additional verification of the presence of methane.
Despite its cutting-edge sensor, the ExoMars orbiter didn't detect a whiff of the methane spikes reported by preceding NASA and ESA studies.
In addition to looking for the missing methane spikes, TGO also investigated a massive dust storm that currently covered Mars. The orbiter recorded the weather phenomena from the very beginning and studied how the dust interacted with water vapor in the thin Martian atmosphere. (Related: If Mars has methane, does it mean there’s life on the red planet?)
“The measurements we have made are very surprising,” explained Open University (OU) researcher Dr. Manish Patel. “The methane previously detected by ground-based telescopes, the ESA (European Space Agency) Mars Express spacecraft and the Nasa Curiosity rover seems to have disappeared.”
Patel oversaw the team running the Nomad instrument aboard the TGO. He and his team published their findings in the journal Nature.
The OU researcher threw the earlier studies a bone by suggesting the presence of an unknown process in the Martian atmosphere that got rid of large amounts of methane much faster than experts predicted. Of course, such a process raised new questions about Mars that also need investigation.
TGO represents the first half of the ExoMars mission. The other half consists of the Rosalind Franklin rover, which is currently being built by Airbus in Stevenage, U.K.
Slated for launch in 2020, Rosalind Franklin will touch down on Mars in 2021 if all goes well. The rover carries scientific equipment for drilling beneath the surface. It will look for evidence of Martian lifeforms in the past or present of the planet.
The Gale Crater on Mars measures 96 miles wide. Experts believe it used to host an ancient lake when liquid water flowed across the surface of the planet.
Two separate Martian missions reported finding methane near the crater within a day of each other. Since the gas had strong links to biological activity on Earth, researchers considered methane to be potential evidence of alien life.
NASA's Curiosity rover landed inside Gale Crater in 2012. It first detected the methane spikes on June 15, 2013. However, doubtful researchers raised questions about the reliability of the findings
Next, European researchers pored over the data sent the ESA's Mars Express spacecraft. They learned that the orbiter detected a methane spike a day after Curiosity made its discovery.
“Although parts per billion in general means a relatively small amount, it is quite remarkable for Mars – our measurement corresponds to an average of about 46 tonnes of methane that was present in the area of 49,000 square kilometers observed from our orbit,” explained Institute for Space Astrophysics and Planetology researcher Marco Giuranna.
Giuranna's report suggested that the methane spikes came from inside Gale Crater. But TGO's findings appeared to disprove his theory.