Well, the results are in. In the end, the Moon is not composed of green
cheese.
A comprehensive analysis has shown that the Moon's interior is actually a
solid ball with an iron-like solidity. This, according to academics, will
help put to rest a protracted argument regarding whether the Moon's interior
is solid or molten and result in a better knowledge of the history of the
Moon and, therefore, the Solar System.
Our findings, according to a group led by astronomer
Arthur Briaud
at the French National Center for Scientific Research in France, "question
the evolution of the Moon magnetic field due to its demonstration of the
existence of the inner core and support a global mantle overturn scenario
that brings significant insights on the timeline of the lunar bombardment in
the first billion years of the Solar System."
Seismic data is the most useful tool for probing the internal structure of
Solar System objects. Scientists may produce a precise map of the inside of
a planet or moon by studying the path taken by quake-generated acoustic
waves as they pass through and reflect off the planet or moon's internal
material.
The Apollo expedition did record seismic data from the moon, but its
resolution is insufficient to assess the status of the inner core. Although
there is a fluid outer core, its contents are still up for discussion. With the Apollo data, models
with both a solid inner core and a core made completely of fluid do equally
well.
Briaud and his colleagues compiled a profile of numerous lunar properties
to solve the mystery once and for all by gathering information from space
missions and
lunar laser range
studies. These include its density, the change in its distance from Earth,
and the extent of its gravitational interaction with Earth.
They then carried out modeling with several core kinds to see which closely
matched the empirical data.
They discovered a number of intriguing things. First of all, active
overturn deep inside the lunar mantle is described in the models that most
nearly matched what we know about the Moon. Accordingly, the Moon's interior
is composed of less dense stuff rising higher and denser material falling
toward the center. It has long been suggested that this activity is the
cause of the elements
found in the Moon's volcanic zones. The team's research adds another piece
of evidence to the "for" column.
They also discovered that the lunar core, which has a solid inner core and
an outside fluid layer, is strikingly similar to that of the Earth. The
inner core's radius is around 258 kilometers (160 miles), whereas the outer
core's is approximately 362 kilometers (225 miles). That represents around
15% of the Moon's overall radius.
The study discovered that the inner core has a
density of around
7,822 kilograms per cubic meter as well. That comes extremely near to iron's
density.
Curiously, a team led by NASA Marshall planetary scientist Renee Weber
discovered a similar conclusion in 2011 when studying the lunar core using
then-state-of-the-art seismological methods on Apollo data.
They discovered proof
of a dense inner core with a radius of around 8,000 kilometers and a mass of
about 240 kilometers that was solid.
Their findings, according to Briaud and his team, are validation of those
earlier discoveries and present a rather compelling argument in favor of an
Earth-like lunar core. And this has some fascinating ramifications for the
development of the Moon.
We know that the Moon had a strong magnetic field not long after it
originated, which started to degrade approximately 3.2 billion years ago.
The composition of the lunar core has a significant bearing on how and why
the magnetic field vanished since such a magnetic field is produced by
motion and convection in the core.
Perhaps we won't have to wait long for seismic confirmation of these
results, given that mankind hopes to visit the Moon again in a relatively
short period of time.
The research has been published in
Nature.
