MAGIC
TORCH
COMET MISSIONS2 of Kent.Thisis becausetheyformedcloserto the
Sun,meaningthatthewarmerenvironmentwould
affectthenumberandtypeoforganicmolecules
ontheirsurfaces.
It’snotonlychemistrythatcouldbedifferent,as
thelong-periodcometscouldalsorevealwhether
theplanetsformedviolentlyorgently.“Oneofthe
topfiveresultsfromRosettawastheshapeofthe
comet,”saysLowry.Comet67Pwasa dumbbell-
shapedobjectthatanalysisshowedwastheresult
ofa fusionbetweentwoindependentlyformed
comets.It wasa bigresultbecauseit showedthat
fullyformed cometsweremergingin a gentle
way;theircollisionspeedmusthavebeenaround
walkingpace. Yet,it wast houghtt hat planet
formationtookplacemuchmoreviolently.If the
patternrepeatsina long-periodcomet,it could
wellmeanthatourideasofplanetformationasa
wholeneedtoberevised.
Thesearch forthemission’starget beginsin
2022,whena boldnewtelescopeprojectstartsits
operations.TheLargeSynopticSurveyTelescope
(LSST)iscurrentlyunderconstructioninChile.
Withitseight-metre-widemirror, LSSTwillbe
abletoscanthewholeskyeveryfew nights.It
isexpectedtodiscoverhundredsandthousands
morecometsandasteroidsintheSolarSystem
thanarecurrentlyknowntoexist.It couldeven
finda targetbeforeCometInterceptor’sscheduled
launchin2028.
“Wedon’tactuallyexpecttheretobethatbiga
choiceof target.Withintheperiodthatthemission
hastooperate,probablythereis onlygoingtobea
handfulthatwecangoto,”saysSnodgrass.
Outofthathandful,thereis alsothepossibility
thattheywillfindsomethingtrulyrare:a comet
fromanothersolarsystementirely.Astronomers
haveidentifiedtwosuchinterstellarobjects,starting
with‘Oumuamuain 2017 andBorisovin2018.Both
of these objects followed trajectories that indicateFEATUREthattheyarenotboundtotheSun’sgravity,and
mustsimplybepassingthroughtheSolarSystem,
beingdeflectedbytheSun’sgravityenroute.
Alt houghit wouldbealmost impossibleto
saywhichstartheyformedaround,lookingat
a cometcloseupwouldbea fascinatingwayto
tellif formationprocessesaroundotherstarsare
similarto thosethattookplaceinourSolarSystem.
“Toactuallyseesomethingthat’scomefrom
anothersystemandseehow differentit looks,
orhowsimilarit lookswouldbeinteresting,”
says Snodgrass,“Ifthereisonewecanreach,
I thinkit wouldbea fairlyeasydecisionfrom
thescienceteamtosay,‘let’sgoforthat’.It would
besuchanopportunity that you couldn’t really
turn it down.”UNLOCKINGTHESECRETTOLIFEONEARTH
NomatterwhichtargetCometInterceptorgoesto,
astronomersarealreadyplanningwhatto doafter
that.Andforthem,thedrivingquestionis what
rolecometsplayedintheoriginoflifeonEarth,
andthatcomesdowntodoinganinventoryofits
surfacechemistry.Inparticular,astronomerslook
forcarbon-bearingmolecules,oftenreferredtoas
‘organicmolecules’becausetheyhavebecome
essentialforlifeonEarth.“Thecompositionof
theorganicmaterialisreally important,”says
GianricoFilacchione,a cometscientistfromthe
InstituteforSpaceAstrophysicsandPlanetology
(INAF-IAPS)inRome,Italy.“Thereis a universe
of organiccompoundsthatneedtobeidentified.”
Andtheonlywaytodo thatdefinitivelyisto
bringa samplebacktoEarthandanalyseit with
thefullforceofcurrentlaboratoryequipment.
Tothatend,Filacchioneandcolleagueshave
proposedtheAMBITIONmissionto ESAaspartof
thespaceagency’s 2050 long-termplan.If selected
for development,AMBITIONwouldland ona
comet,scoopupa sampleoftheicymaterialand
returnit toEarthina cryogeniccapsule.“Taking
a pieceofa cometbacktoEarthis theholygrail
fora cometarymission,”saysFilacchione.
Fornow,however,it isCometInterceptorthat
is inthelimelight.“Thisis anopportunityfor
ustogoandseea cometthat’scomingintothe
SolarSystemfortheveryfirsttime.Thesurface
willstillbelookingasit hasbeenoverbillions
ofyears,”saysSnodgrass.Buttoseeit requires
rewritingthewayspacemissionsaredesignedand
planned.Whilethatwillbringitsownheadaches,
Snodgrasssayshefindsit moreexcitingthanit
is daunting.Although,hethenaddswitha touch
ofhumour,“that’sbecauseI’mnotan engineer
and I don’t have to make it work.’’byD RS T UA R T
CLARK
(@D r Stu Cl ark)
Stuartis anastronomy
writer.Hislatestbookis
TheUnknownUniverse
(£14.99, WW Norton).“TAKING A PIECE OF A
COMET BACK TO EARTH IS
THE HOLY GRAIL FOR A
COMETRY MISSION”