A scientific staff led by researchers from the Laboratory for Planetary and Atmospheric Physics (LPAP) on the College of Liège (BE) has simply noticed, for the primary time, lights within the evening sky over Mars utilizing the UVIS-NOMAD instrument on board the Hint Gasoline Orbiter (TGO) satellite tv for pc of the European Area Company (ESA). This instrument is a part of the NOMAD spectrometer suite developed on the Royal Institute for Area Aeronomy in Uccle, and examined and calibrated on the Liège Area Centre. It was inserted into round Martian orbit at an altitude of 400 km in 2008.
Initially designed to map the ozone layer surrounding the planet within the ultraviolet, UVIS-NOMAD covers a spectral vary extending from the close to ultraviolet to purple. For this objective, the instrument is often oriented in the direction of the centre of the planet and observes daylight mirrored by the planetary floor and ambiance.
“Primarily based on a proposal from our laboratory, the instrument was oriented in the direction of the limb of the planet with a view to observe its ambiance from the sting,” explains Jean-Claude Gérard, planetologist at ULiège. Again in 2020, we have been already capable of detect the presence of a inexperienced emission between 40 and 150 km in altitude, current through the Martian day. This was as a result of dissociation of the CO2 molecule, the principle constituent of the ambiance, by ultraviolet photo voltaic radiation”.
A protracted journey for oxygen atoms
The TGO satellite tv for pc, when observing the ambiance at evening, has simply detected a brand new emission between 40 and 70 km altitude.
“This emission is as a result of recombination of oxygen atoms created in the summertime ambiance and carried by the winds in the direction of the excessive winter latitudes,” explains Lauriane Soret, a researcher at LPAP. There, the atoms recombine on contact with CO2to reform an O2 molecule in an excited state that relaxes and emits mild within the seen vary”.
This mild emission is concentrated within the polar areas to the north and south, the place the oxygen atoms converge within the downward department of the large trajectory from the other hemisphere. The depth of the emission is excessive, within the seen vary. This course of appears to be reversed each half Martian yr*, and the luminosity then modifications hemisphere. An identical emission was analysed on Venus by the identical staff utilizing photos from the Venus Specific satellite tv for pc. On Venus, the atoms journey from the sunlit facet to the darkish facet the place they emit the identical glow as on Mars.
ULiège researchers on the forefront
LPAP researchers performed a key position in these observations. After highlighting the presence of a layer of inexperienced mild surrounding the planet on the day facet, they recognized the night-time emission.
“The research will probably be continued through the TGO mission and can present us with beneficial details about the dynamics of the Martian higher ambiance and its variations over the course of the Martian yr,” continues Lauriane Soret. “Now we have seen that one other ultraviolet emission as a result of nitric oxide (NO) molecule can be noticed by UVIS in the identical areas. Evaluating the 2 emissions will allow us to refine the prognosis and establish the processes concerned”.
The NO molecule additionally emits mild when oxygen and nitrogen atoms recombine. As with the radiation from the O2 molecule, the atoms are fashioned in daylight, transported by the winds to the opposite hemisphere and recombine through the downward movement within the polar areas.
“These new observations are surprising and fascinating for future journeys to the Pink Planet,” enthuses Jean-Claude Gérard. The depth of the evening glow within the polar areas is such that easy and comparatively cheap devices in Martian orbit may map and monitor atmospheric flows. A future ESA mission may carry a digicam for world imaging. As well as, the emission is sufficiently intense to be observable through the polar evening by future astronauts in orbit or from the Martian floor.”
Benoit Hubert, researcher at LPAP, concludes: “Distant sensing of those emissions is a superb software for probing the composition and dynamics of Mars’ higher ambiance between 40 and 80 km. This area is inaccessible to direct strategies of measuring composition utilizing satellites.”
(* A Martian yr lasts 687 Earth days.)