Howdo we
know thatthe
Moonis alive?
Thereareincreasing
signsofongoinglifeFinding Ina
In 1971 as part of
Apollo 15, Alfred
Worden took a picture
of a strange, blotchy
feature. Later named
Ina, the exposure
represented a uniquely
dynamic landscape.Like liquid drops
of mercury
Against a lunar
landscape of almost
continuous flat vistas
covered in a layer of
broken-up rock and dusty
regolith, Ina’s smooth, steep-
sided mounds stand out.Pristine Ina
Ina's unusually well-
preserved deposits
and lack of superposed
impact craters led to
suggestions it must be
no older than 100 million
years old – very recent
compared to the lunar surface.IMP speculation
In 2014 a team
from Arizona State
University, analysing
data from NASA’s
LRO, found 70 similar-
looking sites to Ina, which
are collectively known as
Irregular Mare Patches.Patchy Aristarchus
One IMP is located on
top of the ejecta of the
Aristarchus crater. This
fresh crater is itself
only 200 million years
old, providing further
evidence this new class of
lunar features are young.IMP concentration
Grouping of IMP sites
in one region might
provide additional
support for young
volcanism by reducing
the amount of internal
heat the Moon needs to
have retained to power them.Ina is different. It comprises steep, 20-metre
(65-foot), smooth-sided mounds surrounded by
lower relief, rougher deposits. Like drops of “dirty
mercury” on the lunar surface was how astronomer
Ewen Whitaker described the mounds, which are
typically less than a few hundred meters across.
However, with 45-degree slopes, they represent
some of the steepest deposits on the Moon. It would
be quite a sight. “It will look even more dramatic
than even a fresh impact crater,” says Stopar. “The
rough materials around it will look a bit like a rough
sea around the smooth island mounds.”
The unusually well-preserved deposits and lack
of superposed impact craters led to suggestions
Ina was formed by volcanic eruptions during
the last 100 million years – possibly gaseous
basaltic lava f lows surrounded by ashy pyroclastic
deposits. “Metre-scale topography cannot survive
for long, geologically speaking, due to the constant
sandblasting of micro-meteoroid and macro-
meteoroid bombardment,” says Mark Robinson, a
lunar researcher at NASA.
“It certainly looks much younger than anything
else on the surface bar the youngest impact craters,”
observes Stopar. But this was a significant claim
at the time, and has been a cause of much debate
ever since. “It would totally destroy our current
understanding of the thermal history of the
Moon,” says Lionel Wilson, planetary scientist at
Lancaster University and sceptic of the young
volcanism hypothesis.
Wilson isn’t alone in his hesitance, especially
after higher resolution imaging by the Lunar
Reconnaissance Orbiter (LRO). In 2012 NASA’s
Brent Garry argued the lack of crisp fractures, often
associated with young volcanic deposits due to the
surface cooling quicker than the interior, implies
either they eroded over billions of years, or never
formed, and therefore Ina was not volcanic. For
modellers of the Moon’s evolution it is a tempting
conclusion. Dismissing the young volcanism
hypothesis certainly makes for a better fit with
everything we know about our celestial companion.
However, no matter how logical it was to ignore,
the suggestion that in Ina we are looking at
evidence of a planetary body that is still alive, or at
least was very recently, won't go away.
“It is really hard to explain how you can have
young volcanism based on everything we know
about the Moon. However, others say we can't
possibly preserve these features for 3 billion
years, so it has to be young,” says Stopar. And
if Ina was proving hard to explain, the Lunar
Reconnaissance Orbiter found 70 similar-looking
sites, collectively known as Irregular Mare Patches,
or IMPs. And for some IMPs, the evidence for youth
might be stronger still.
“There is one IMP located on the ejecta of the
Aristarchus crater. This is a young crater that we
think is roughly 200 million years old,” says Stopar.
So we have near-pristine Ina, IMPs seemingly
superimposed on crater material only a few
hundred million years old, plus a collection of 70
other features for ongoing monitoring. Surely we
can allow ourselves to imagine lava spewing out
somewhere on the lunar surface today? “It's not
much of a stretch,” agrees Robinson.
With such a tantalising prospect at stake – not
to mention our entire theoretical basis for the
structure and evolution of the Moon – a resolution
between observation and simulation was required.
Theories to account for the ill-fitting Ina and its
IMP friends have fallen into two categories: thoseThe Moon is alive