Volcanoes on the Moon
TheMoon has been volcanically active for most of its history
Pre-Nectarian period
Lunar crust formed via mineral
crystallisation of a global magma
ocean, forming the lunar highlands.
With liquid surface volcanism not
possible, hot vapour release did
createanatmosphere,however.
Early Imbrian epoch
The mantle lying below the lunar
basins melted due to frequent
giant meteorite impacts that
came with the late heavy
bombardment and thinned
theoverlyingcrust.Late Imbrian epoch
The thinned crust led to peak rates
of effusive wide-ranging basalt
eruptions, creating the famous
mare, the dark, smooth lowlands of
the Moon. There is also evidence of
occasionalpyroclasticeruptions.Eratosthenian period
The massive basaltic volcanism of
the Imbrian period tapered off and
ceased. During this era late-stage
volcanism filled low-lying regions
in and around Mare Imbrium and
OceanusProcellarum.3.9 billion years ago (BYA) 3 .0 BYA 2. 5 BYA 2 .0 BYA 1. 5 BYAAbove:
Planetary
scientistJulie
Stoparhas
proposeda
‘fastandcheap’
SmallSatlander
missiontovisit
Inaandlookfor
signsofrecent
volcanismTheconstant
recyclingof
rockthrough
platetectonics
andvolcanism
acrossEarth’s
historymakesit
a poorrecordof
planetaryand
SolarSystem
history©Getty©NASA
have had such a tough job reaching the surface.
This was one conclusion of earlier work, again
involving Stopar, which challenged the locked-up
surface hypothesis. “There are lots of young tectonic
features on the Moon that suggest the crust is still
moving around,” she explains.
While Robinson sees Ina and the other IMPs as
compelling evidence for lunar volcanism in the last
few 100 million years, Stopar sees problems with
both hypotheses, and Wilson is maintaining his
scepticism. “The discussion can get quite heated,”
he says.One way out of the impasse would be to visit an
IMP, with Ina preferred due to its size and history
of being studied. While the Lunar Reconnaissance
Orbiter is providing the best-ever images of the
surface, the evidence of collapse features or recent
volcanism on the sub-metre scale is unlikely to be
resolved. “We actually have to be there. It requires
us looking into the soil on the landform. I don't
think we can get that from orbit,” argues Stopar.
But who is ‘we’? In the same year US Vice
President Mike Pence called on NASA to return
American astronauts to the Moon by 2024, is Stopar
suggesting setting up camp around the base of Ina
and mounting its smooth slopes? Not exactly.
Putting a geologist on the Moon has benefits.
There are many interesting sites where complex
scientific questions could be chipped away.
These include the south pole, where elevated
concentrations of rare lunar water could explain
our own blue planet. This is one reason the US has
targeted it for a lunar base.
The Ina mystery is different. It represents a
relatively straightforward puzzle where we think we
know what we are looking for. The key indicators
include the small fractures that Garry couldn’t see
from orbit, lava f low textures and collapse pits,
as well as the general size, shape, porosity and
mineralogical content of surface grains, which
should all be indicative if derived from broken-up
foamy lavas. In fact, so well defined is the question
that Stopar and colleagues have offered to answer
it for just $100 million, a knock-down price in
planetary exploration.
For that money you get the Irregular Mare Patch
Exploration Lander, or IMPEL, a SmallSat mission
proposed this April in the journal Planetary and
Space Science. The lander would carry a mast
camera for high-resolution colour imaging of the
landing site, and a microscopic imager for close-up
analysis of the surface regolith and any signs ofThe Moon is alive