One of the Solar System’s famous ocean worlds is an
exciting prospect for further exploration
uropa is one of the four Galilean moons
that orbit the Solar System’s largest
planet, Jupiter. Although Europa is the
smallest of its satellite siblings – Io,
CallistoandGanymede, carrying on in that order
fromsmallest to largest – it is certainly the one with
the most potential for exciting scientific discovery.
Underneath its icy, scarred surface could lie a salty
ocean, just like the oceans that make up 71 per cent
of the Earth’s surface.
The Galilean moons were discovered in 1610
by Italian astronomer Galileo Galilei, and through
the ages astronomers have been fixating their
telescopes on the speck of light that orbits Jupiter
once every three-and-a-half days. Europa is also
tidally locked to Jupiter, meaning that the same
faceofthemoonispointingattheJoviangiantat
alltimes,muchliketheMoonandEarth.Anothersimilarity is the two moons' sizes: Europa has an
equatorial diameter of 3,100 kilometres (1,940 miles),
which is 90 per cent of the Moon’s diameter. If you
were to replace the Moon with Europa in our sky,
to the naked eye they would both seem about the
same size. However, Europa would be much brighter
on account of its surface ice reflecting 5.5-times
more sunlight than the Moon.
The process behind the creation of Jupiter’s
largest moons is still hotly debated, but astronomers
largely agree that they formed from leftover debris
from the formation of Jupiter roughly 4.5 billion
years ago. Fast-forward to today and Europa is a
water-ice ball with fractures criss-crossing all over
the surface. The number of craters currently found
all over its cracked terrain indicate that the moon is
noolderthan 90 millionyearsold,suggesting there
islikelytobesomeformofsurfacereplenishment
thatalsobringssaltsandsulphurcompounds to
theouterlayer.Surroundingtheicyworldis a thin
atmosphere,composedofmolecularoxygen.
Thecoreismostlikelymadeofiron,surrounded
bya tough,rockymantle.Inbetweenthatand the
icycrustisa suspectedbodyofliquid.Some may
wonderhowsucha smallworld,sofaraway from
theheatoftheSun,canmaintainanocean of salty
watersimilartoEarth's.Theansweristhat it's likely
duetothegrandgravitationaleffectsofJupiter,
pullingandpushingtheinsidesofEuropa,causing it
toheatupand,inturn,transformingiceinto water.
Thisprocessisknownas‘tidalheating’,and it can
beobservedhappeningwithgrandereffect on
fellowmoonIo– itsinteriorisheatedupto such an
extentthatvolcanoeshavepoppedup.
Thistidalheatingiswhatmaintainstheocean
andprovidestheenergytoreplenishthesurface
viatheoutburstofplumesora formoficy plate
tectonics.Eversinceastronomersbecameaware of
thevitalisinginteriorofEuropa,theyhavepieced
togetherthatithasthefundamentalbuilding blocks
forlifetoexist:liquidwater,chemicalcompounds
forconsumptionandanenergysource.For this
reasonespecially,planetaryscientistsareexcited to
returntotheGalileanmoon.Thereisa high chance
thatlifecouldexistinthispartoftheSolar System,
evenifit’sjustintheformofsimplemicrobes.Europa
E
Thisshowsalmost-purewater
ice,showninwhite,brokenupby
contaminatedwaterice,showninred“Underneath
its icy, scarred
surface could lie a
salty ocean”
H2O layer