Mercury
rethinkourtheoriesabouttheformationof
theplanet.”
Theproblemwiththisnewdiscoverywasthat
itdidn’tfitinwithexistingideasaboutMercury’s
origin,whichhadbeendevelopedovertheyears
toexplainitsunusualinternalstructure.Like
Earth,theplanetismadeupofa rockycrust
andmantlesurroundinganiron-richcore– but
inMercury’scasethecoreishuge,makingup
almost 85 percentofitsvolume.Fora longtime
itwasassumedthatMercurymusthavestarted
outlookingverysimilartoEarthinsizeand
composition. Then, billions of years ago, it had
its outer layers knocked off in a collision with a
huge asteroid.
The problem with that theory is it doesn’t explain
why there’s so much sulphur and potassium on
Mercury’s surface today. It now seems likely that
Mercury formed much as it is now, and that its
large core was a consequence of the different
physical conditions in the inner parts of the early
Solar System compared with further out where
the other planets formed. That’s supported by the
discovery of exoplanets orbiting close to other Sun-like stars, which also appear to have large metallic
cores like Mercury.
Despite its numerous discoveries, MESSENGER
left plenty of unanswered questions – but
fortunately there’s another mission, BepiColombo,
on its way to Mercury right now. Made up of two
separate spacecraft, the ESA’s Mercury Planetary
Orbiter and the Japan Aerospace Exploration
Agency’s Mercury Magnetospheric Orbiter, it’s due
to arrive in 2025. With 16 scientific instruments,
researchers are hoping BepiColombo will make just
as many discoveries as MESSENGER did.“The discovery of relatively large concentrations of elements like sulphur
and potassium on Mercury’s surface was a huge surprise” Brian cox
A newtype
offeature
Theserounded
depressionsinRaditladi
Basinareexamples
of‘hollows’– features
uniquetoMercurywhich
mayhavebeenformed
whenvolatilematerials
evaporatedintospace
longago.Mercuryon
steroids?
That’showNASA
describedexoplanet
K2-229b,whichresembles
Mercuryinbeingiron-rich
andorbitingclosetoa
Sun-likestar,butit’s
four-timesbiggerand,
at2,000°C(3,632°F),
muchhotter.Theshrinking
planet
AsMercury’sinterior
hascooleddown,the
planethasshrunk,creating
tectonicfaultlinessuch
astheonepicturedhere,
CarnegieRupes.x3 Images © NASA