ner_tags: O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation O O O O O O O O B-CelestialObject O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O B-Mission I-Mission O O O O O O B-Telescope I-Telescope B-Telescope O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O B-Instrument I-Instrument I-Instrument B-Instrument O O O O O B-Citation I-Citation I-Citation O O B-Instrument I-Instrument I-Instrument B-Instrument O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O B-Instrument O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O B-Instrument O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObjectRegion I-CelestialObjectRegion I-CelestialObjectRegion O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: methane possesses strong and distinctive absorption signatures. An annotated list of these attempts can be found in Zahnle et al. (2011) , Knutsen et al. (2021) , and in tabulated form in Pla-Garcia et al. (2019) . Hitchcock Lovelock (1967) pointed out that the composition of the Martian atmosphere could provide clues as to the possible presence of life on the planet. Therefore, methane has long been seen as the most accessible testimony of potential signs of life ( Atreya et al. 2003 , 2007 ) or of a remnant geophysical activity on Mars. Indeed, the presence of methane has such a strong connotation of Mars being potentially an active or even a life-hosting planet, contrary to all other chemical or geophysical evidence suggesting the opposite, that it has attracted the attention of a wide community extending far beyond those interested in Martian atmospheric composition. However, the succession of failed and successful attempts to detect methane has also created a blurred picture, and a comprehensive understanding of the existence and origin of methane on Mars has remained out of reach. Several attempts that were initially presented as positive detections were later either retracted or questioned. This is the case of the Mariner 7 detection (as explained above) and the Canadian-France-Hawaii Telescope (CFHT) observations of Krasnopolsky et al. (2004) – whose spectrum quality raised the suspicion of Zahnle et al. (2011) , who also questioned the seasonal variations of methane found by Geminale et al. (2008) based on a survey carried out with the Planetary Fourier Spectrometer (PFS). Finally, the methane mapping of Fonti Marzo (2010) using the Thermal Emission Spectrometer (TES) was later retracted by the same authors in Fonti et al. (2015) . Of all the detections made between 2003 and 2010, only a few survived the scrutiny of the community. The PFS 2003 detection reported in Formisano et al. (2004) , while bearing evident shortcomings regarding its resolving power and sensitivity, has resisted criticism and remains to this date the first non-rebutted detection of methane in the Martian atmosphere. In addition, Mumma et al. (2009) published the first ground-based evidence of methane collected the same year as the PFS, the scientific implications of which were bolstered by the revelation of puzzling spatial and seasonal variations attributed to a sudden release from the Nili Fossae region. Several studies have explored the chemical ramifications ( Lefèvre Forget 2009 ) as well as the spectroscopic consistency of these detections ( Zahnle et al. 2011 ). These works converged toward the idea that our current understanding of the physics and chemistry governing the Martian atmosphere is incompatible with the observed variable behaviour of methane, which should rely on an extraordinary, yet undefined mechanism. Together with the fact that detections had long lain on the fringe of the detection capability of all instruments used at that time, the