All_About_Space_-_Issue_94_2020

Copernican period

It is generally thought lunar volcanism
had ceased by the Copernican period.
However, evidence from Ina and 70
other similar-looking mare patches
suggest small-scale volcanism may
have continued.

fracturing. “It's a great idea,” says Wilson. “It'sa fast
and cheap mission. And that is not a criticism.”
However, while he sees the potential forgreat
science, he doubts IMPEL alone can date Ina.
“Detailed morphological studies by a landerwould
be enormously useful in establishing exactly
what happened, but only radiometric datingwill
convince me of when.” However, he still seesvalue
in SmallSats to answer this question. In fact,Wilson
suggests sending more. “Why not send fiveofthese
things to five candidate IMPs to establish themost
interesting one, then send the larger missionto
collect samples.”
In the meantime the rest of the communityis
left with orbital images. Here there have beenno
signs of any structural changes that could indicate
present-day activity. “It is still a leap to sayit[the
Moon] is still active today,” states Stopar. “However
this could be based on the limited timetablewe
have been observing.”
“If any form of observation were to capture
unambiguous images of any actual eruption,
then of course I would accept that there is
something fundamentally wrong with ourcurrent
understanding of the Moon's interior – andrelish
trying to understand what we have been doing
wrong all these years,” says Wilson.
Stopar believes the implications of sucha
discovery might go well beyond the lunar interior.
If the Moon could support recent volcanism,then
we would need to re-examine assumptionsabout
other small moons and dwarf planets. Thisincludes
whether the same mechanism for preserving
residual heat could be keeping sub-surfacewater
liquid elsewhere, maintaining more of the oceans
known to exist within Jupiter’s Europa andSaturn’s
Enceladus. “We need to go there to Ina becauseit
is a place where we can answer a really important
question with big implications, just based onthis
one small area,” Stopar concludes.

The Moon's explosive outgassing

Outburstscouldexplaintheappearanceofthelunarsurface

1.Buildingupofgas

Gasbuildsupbetweenthelunarmegaregolith

andtheupperlayerofregolith(whichhasa low

diffusivity).Thepressureisbuiltupbythegas,

liftinga coneofmaterialtothesurface.

3.Moonmatterescapestocrater

Thecloudcontinuestoexpanduntilitreaches

a pointwhereit'snotverythickwhenviewed

fromabove.Regoliththathasfallenfromthegas

cloudpilesuparoundthecrater.

2.Mixtureofgasandmaterial

Theconcoctionofregolithandgasnowcreatesa

substantialvolumeonthesurface.It'sfilledwith

shellsofregolithparticles.Thecloudofmatter

andgasexpands.

4.Allgasescapes

Allofthegasstartstoleakoutandanylunar

materialthatwastrappedwithinthecloudhas

managedtoescape.Itisdepositedontothe

groundaroundandinsidethe'impact'.

1 .0 BYA

Above:

N A S A’s L u n a r

Reconnaissance

Orbiter has

returned images

of 70 similar-

looking sites to

Ina, collectively

known as

Irregular

Mare Patches © NASA

Illustrations © Nicholas Forder

The Moon is alive