All_About_Space_-_Issue_94_2020

What’s been happening at Europa?

Table salt found sprinkled on the surface

Europa has had visitors in the past, notably NASA’s Voyager and Galileo spacecraft.

On their flybys of the moon, analyses showed that the icy crust consisted of water ice

and a substance originally thought to be magnesium sulphate. After recently revisiting

the surface using the W. M. Keck Observatory based  in Hawaii and the Hubble Space

Telescope, astronomers now know that it wasn’t magnesium sulphate and was actually

sodium chloride – more commonly known as table salt.

As Voyager and Galileo had only an infrared spectrometer to work with, they couldn’t

see what was hiding in the visible light spectrum. Keck and Hubble were able to unveil

the hidden secret. “We thought that we might be seeing sodium chlorides, but they

are essentially featureless in an infrared spectrum,” says Mike Brown, the Richard and

BarbaraRosenbergprofessorofplanetary astronomy at Caltech in Pasadena, California.

ItwassomelaboratorytestsbyKevin

HandatNASA'sJetPropulsionLaboratory,

alsoinPasadena,thatrevealedthatirradiating

oceansaltsunderEuropa-likeconditions

exhibitdistinctfeaturesandayellowish

colour–tablesaltexhibitsthiscolouronthe

surfaceofEuropa,confirmingitspresence.

SetbacksforEuropa’snextexplorer

NASAhasitssightssetonsendingtwoveryambitiousmissionstoEuropa,oneofwhichisdue

tolaunchin2023.UnfortunatelytheEuropaClippermission,anorbiterthatwillspendabout

threeyearsatthemoon,andtheproceedingEuropaLandermissionseemtohavecomeunder

scrutinyafteranine-monthinvestigationconcludedthatthereareseriousissuesthatneedtobe

addressedinordertosatisfybothNASAandtheUnitedStatesCongress.

"Ourauditfoundthatdespiterobustearlystagefunding,NASA'saggressivedevelopment

schedule,astringentconflict-of-interestprocessduringinstrumentselection,aninsufficient

evaluationofcostandscheduleestimatesandtechnicalworkforceshortageshaveincreased

instrumentintegrationchallengesanddevelopmentrisksfortheClippermission,"JohnSchultz,a

managementanalystattheOfficeofInspectorGeneral,saidinastatement.

Afterfindingtheseconflictsofinterestandissuesinthebudget,theinvestigationteamhave

concludedthattenchangesshouldbemadeinordertogettheprojectbackontrack,including

alteringtheoverallstaffingregime,reschedulingmilestonesandmakingsurethatanyestimates

TheEuropaClippermissionisestimated bemadeinaccordancewithotherprojects.

tocostatleast£2.2billion($2.8billion)

TaraRegioisasectionofEuropathatflaunts

theyellowishsignatureoftablesalt

Strugglingtofindtheplumes

Europaisamoonthatsharesmanysimilaritieswith

Saturn’smoonEnceladus–

bothareicyworldsthatexhibitsignsofasubsurface

oceanthatcouldharbour

potentiallife.Onemajordifferencethoughisthat

Enceladushasbeenstudied

muchmorethoroughly,courtesyofNASA’sCassini

mission.Inthisclose-

upanalysisCassinidetectedplumesofmaterial

emergingfromthesurface

ofEnceladus,alongwithadistincttemperature

spikeinthedatatomatch.

However,thisdoesn’tappeartobethesamefor

Europa.

"WesearchedthroughtheavailableGalileo

thermaldataatthelocations

proposedasthesitesofpotentialplumes.Reanalysis

oftemperaturedata

fromtheGalileomissiondoesnotshowanything

specialinthelocationswhere

plumeshavepossiblybeenobserved.There

arenohotspotsignaturesateither

ofthesites,"saysJulieRathbun,aseniorscientist

atthePlanetaryScience

Institute."ThisissurprisingbecausetheEnceladus

plumeshaveaclearthermal

signatureattheirsiteoforigin,sothissuggests

thateithertheEuropaplumes

areverydifferent,ortheplumesareonlyoccasional,

thattheydon'texistorthat

theirthermalsignatureistoosmalltohavebeendetected

bycurrentdata."

A build-up of heat under the crust can cause

plumes to emerge, spraying out salty water

“We searched through the available Galileo thermal data

at the locations proposed as the sites of potential plumes”

© NASA/JPL

© NASA/ESA

© NASA

Moon profile Europa