Trace Gas Orbiter: Ozone And Carbon Dioxide May Cause Interference In The Search For Methane In The Martian Atmosphere
While exploring the Martian atmosphere, the Trace Gas Orbiter (TGO) spacecraft first encountered two unique signals from ozone and carbon dioxide molecules. They may be the reason why methane is so difficult to find in the red planet's atmosphere. Articles describing the work are available in the scientific journal Astronomy & Astrophysics (1, 2).
"The fact that we detected a signal from ozone and carbon dioxide molecules in the part of the spectrum where we are trying to find traces of methane was a very important discovery. Previously, we did not know about their existence, and thus these gases could generate some of the signals that our colleagues in the past considered traces of Martian methane," said Alexander Trokhimovsky, one of the authors of the work, an employee of the Institute for space research of the Russian Academy of Sciences.
The Trace Gas Orbiter (TGO), which operates as part of the Russian-European ExoMars mission, has been studying the red planet's atmosphere for three years, measuring the concentrations of various gases in it. One of the main tasks of the mission is to assess the concentration of methane in the Martian atmosphere and find possible sources of this gas.
The first results of observations showed that for the first full year of operation, TGO instruments did not record even the smallest amount of methane in the atmosphere of Mars. At the same time, the Gale crater is believed to have released methane: it was detected by the sensors of the Mars Rover Curiosity.
Trokhimovskii and his colleagues are working with the Russian spectrometer ACS that is installed on TGO. They made two unexpected discoveries that potentially explain why the spacecraft did not find methane in the Martian atmosphere, and why other scientists recorded traces of it using other spacecraft and ground-based telescopes.
The methane riddle of Mars
While working with the ACS data, scientists analyzed signals from the mid-infrared region. In areas that are presumably associated with the presence of methane in the Martian atmosphere, they encountered two sets of signals. After studying their spectrum in detail, Trokhimovsky and his colleagues discovered that the source of these signals is not methane, but two completely different substances – ozone and carbon dioxide.
The atmosphere of Mars is almost entirely made up of CO2, and ozone in its upper layers was found by the Mars Express mission at the beginning of the XXI century. At the same time, as the researchers note, scientists did not previously suspect that in the part of the spectrum of infrared radiation that was previously associated with methane, there may be signals from these two substances.
The researchers checked these results several dozen more times, and also estimated the concentration of ozone in the circumpolar regions of Mars. Previously, it was measured by the PFS instrument installed on Board the Mars Express vehicle. Traces of ozone and CO2 were not lost, and the measured ACS concentration of ozone coincided with the data of the European probe. Thanks to this, scientists have made sure that the data from TGO devices is correct.
Trokhimovskii and his colleagues cautiously suggest that, in some cases, the "discovery" of methane on Mars actually could be the traces of ozone and carbon dioxide. Low sensitivity could prevent the instruments from recognizing that the signals in the spectrum belonged to these substances and not to methane. At the same time, scientists emphasize that they do not dispute the results of other scientific groups, but offer to check all previous data together.
"Now, we are actively establishing contacts with colleagues from other missions and plan to coordinate work with them. Our discovery cannot be called a cause for doubt in past measurements. It's rather an incentive for all of us to study the atmosphere of Mars is even more detail and depth, " concluded another author of the study, a planetary scientist from the University of Oxford (UK), Kevin Olsen.