Moon Still Has Hot Core

Japanese scientists have determined that a soft, hot core remains in the center of the moon, contrary to expectations.

A question resulting from a new model of the lunar interior made by scientists at the National Astronomical Observatory of Japan is, “how can the bottom of the lunar mantle maintain its softer state for a long time?”  The researchers used measurements from their Selene orbiter to infer a hot core that should not be there.

Another investigator, Prof. Junichi Haruyama of Institute of Space and Aeronautical Science, Japan Aerospace Exploration Agency, mentioned the significance of this research, saying, “A smaller celestial body like the Moon cools faster than a larger one like the Earth does. In fact, we had thought that volcanic activities on the Moon had already come to a halt. Therefore, the Moon had been believed to be cool and hard, even in its deeper parts. However, this research tells us that the Moon has not yet cooled and hardened, but is still warm. It even implies that we have to reconsider the question as follows: How have the Earth and the Moon influenced each other since their births? That means this research not only shows us the actual state of the deep interior of the Moon, but also gives us a clue for learning about the history of the system including both the Earth and the Moon.”

Another article on tidal heating and lunar history was published by the University of California, Santa Cruz, but the press release doesn’t mention whether the heat should have lasted for billions of years.  Presumably, tidal heating can preserve some of the primordial heat from the moon’s formation for a time, but heat is lost more rapidly from a small body than a large one.  The problem is explained in the opening paragraph of the paper in Nature:

The theory of equilibrium figures of rotating fluid bodies is a classic problem in geophysics, and it has been helpful in understanding the shapes of the Sun and planets. However, the origin of the Moon’s shape has remained an open problem in the past century, and the body’s deviations from any simple tidal–rotational (spherical harmonic degree-2) figure are large. This difficulty is surprising given the Moon’s presumably simple early thermal history: born hot and quickly cooled, one might expect the Moon to be described by a simple figure of equilibrium.

The authors found a way to model the “surprising” observations (see Sid Perkins’ summary on Science Magazine).  It remains true, nevertheless, that what they found was not what they expected.

Lunar lightning:  Another surprising finding was announced by the University of New Hampshire: there may be lightning in the soil of the moon.  Because the lunar surface is dry, there is no way to dissipate the buildup of electrostatic charges from the solar wind except by sparking.  The discharges in the top levels of soil would have the effect of breaking up rock particles and creating lunar regolith, or soil.

The study, published recently in the Journal of Geophysical Research-Planets, proposes that high-energy particles from uncommon, large solar storms penetrate the moon’s frigid, polar regions and electrically charge the soil. The charging may create sparking, or electrostatic breakdown, and this “breakdown weathering” process has possibly changed the very nature of the moon’s polar soil, suggesting that permanently shadowed regions, which hold clues to our solar system’s past, may be more active than previously thought.

Assuming similar processes occur on other bodies, this finding “could change our understanding of the evolution of planetary surfaces in the solar system,” the article says.

Life on the moon:  New Scientist published a hypothesis that rocks launched from earth could carry certain microbes to the moon, where they might survive as fossils.  Meanwhile, the Russians are wondering how sea plankton found its way onto the exterior of the Space Station: did the station get contaminated by human transport, or did the organisms get launched upwards naturally somehow?  See breaking news on Space.com.

These are the kinds of findings the simplistic animations on TV shows don’t talk about, but you need to know.  They have the effect of complicating simple stories of how the solar system came to be over millions and billions of years.  It takes a lot of parameter tweaking to keep the old-and-gradual scenario going.  It’s strange how when processes imply that bodies cannot be as old as claimed, the scientists either go silent or change the subject.