Methane is a simple molecule, and astronomers
have been scouring Mars for decades in order to
find it. This is because the molecule, which consists
of one carbon atom with four hydrogen coming off
it, is a by-product of microbial life. If microbial life
existed there, and astronomers at the time thought
it did, then methane would be its calling card.
ThemoreastronomershavelearntaboutMars
anditssimilaritytoEarthbillionsofyearsago,
themoretheyspeculatedthattheplanetcould
haveharbouredmicrobes,orevenstilldoes.
AnymethanedetectiononMarswouldhugely
encouragethisspeculation.
Unfortunately,astronomershitawallinmethane
detection.NASA’sCuriosityroverhasamuchmore
sophisticatedinstrumentationsuitecomparedto
itsoldersiblings,OpportunityandSpirit,butthe
methanemysteryhascontinued.InJune 2019
a‘methanespike’detectionwasmeasured,but
afterwarditsharplydecreased,meaningitwas
likelyjustapassingplumeofmethane.Though
scientistsarestillnotgivinguponthehuntfor
lifeby-products,themissingevidenceiscertainly
throwingaspannerintheworksinunderstanding
thehistoryofMars.Missing
methane
Winds
Astronomersweresurprisedby
thelackofmethanedetected
aswindshouldcirculatethe
moleculeandmakeitspresence
uniformglobally.Meteorites
Martianmeteoritesthatfell
toEarthhavebeenanalysed
andshowntohavemethane
trappedwithin.Cometimpacts
Methanecouldformfrom
theimpactcloudafterthese
dirtysnowballssmashinto
theMartiansurface.Frozenin
thecrust
Pocketsofmethane
couldstillexistin
thesubsurface
crustfrompast
microbes.Asthese
pocketsburst,it
couldexplainits
presenceonMars.Volcanoes
Martianvolcanoeshave
beenlargelyinactivein
recenttimes,suggesting
thattheyaremorethan
likelynottheanswer.
Subsurfacevents
IfMarshasa liquidlayer
beneaththecrust,then
deeperinterioractivity
couldcausehydrothermal
ventstodispersemethane.Methaneclathrate
Compoundsknownfortrapping
methaneincrystalstructuresinwater,
butonlyoccurwhentemperaturesare
lowandwatericeiscommon.Microbes
Thelong-sought-aftermicrobes
producemethaneasa productof
mixingwaterandcarbondioxide.Destruction
of methane
Oxidation
OccursinMars’loweratmosphereWater Methane FormaldehydeElectrochemicalreaction
DrivenbydustdevilsandwindHydrogen
peroxide Methane FormaldehydeMethane EthaneUltraviolet
radiationPhotochemicalreaction
Occursmainlyabove60km(37mi)The methane mystery:
does it exist or is it just hiding?
WaterCarbon
monoxide MethaneOlivine Water HydrogenHydrogen Carbon
monoxide MethaneSpaceAtmosphereSurface
UndergroundAquifer
Curiosity has long been on the
hunt for signs of life on Mars© NASA/JPL-Caltech; Illustraetion by Tobias RoetschMars