Normally, we don’t think of the north and south pole of a
planet as something subject to change. New research, however, suggests
that the poles of the moon were once displaced by massive amounts of
volcanic activity — and that we can chart this event by examining the
distribution of hydrogen on the Moon’s surface.
Before the Apollo landings, scientists didn’t think the moon
harbored water at all. Absent any kind of atmosphere, there was thought
to be no way for liquid ice to have remained present, and the trace
amounts of water found in the rock samples returned by the astronauts
were dismissed as contamination. Little by little, scientific surveys
and probes returned enough data to confirm that the moon almost
certainly did have ice deposits. Such deposits could only survive if
they were kept in permanent shadow, but such shadows exist at the north
and south poles of the moon.
Data from Indian probes and NASA’s continued efforts
eventually confirmed the existence of both permanently darkened craters
and substantial amounts of hydroxide. Later missions have nailed down
where those deposits actually are across the surface, which became
something of a problem — because they aren’t where you’d expect them to
be.
Data from Nature. Click to enlarge
The diagram above is from the Nature study
and illustrates how the deposits “wander” across the poles rather than
being concentrated in a single area. The current theory is that massive
volcanic eruptions in the Procellarum region of the moon actually tilted
its axis by altering the density of its structure and the distribution
of its mass.
Yesterday, we wrote about the continuing analysis of ancient scrolls buried by the Vesuvius eruption
of AD 79. Imagine that, instead of burying Pompeii and Herculaneum in a
few dozen meters of volcanic fallout, Vesuvius had blown a load of
magma capable of burying Europe and parts of Africa under 5-30
kilometers of molten rock.
The Procellarum (shown above) is an area of 1.5 million
square miles across the lunar surface and was likely formed by either an
impact on the far side of the moon or by irregular heating and cooling
within the moon’s core. Either way, the volcanic activity would’ve been
extreme, and the moon’s axis appears to have wandered as a result. This
would explain some of the irregular distribution of hydrogen across the
polar ice, and implies that much of the water currently existing on the
moon’s surface was delivered early in the solar system’s formation, as
opposed to being deposited by later activity.
One theory is that the massive eruptions on the lunar
surface could have been driven by the impact of a second moon that once
graced the skies of Earth. Granted, said moon was in the sky not long
after the ground of Earth would have been transformed into
molten lava, making practical observation rather difficult. If the moon
was created by the impact of a nearly Mars-sized body, nicknamed Theia,
than a second moon might have coalesced near one of the Lagrange points.
This orbit wasn’t fully stable, however, and the second moon pancaked
on to the dark side of its larger sibling. This would explain certain
features on the far side of the moon, as well as accounting for the
massive magma ocean of the Procellarum.
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