The Moon

We have numerically explored the obliquity variations of a hypothetical moonless Earth using a range of initial conditions and extending our calculations for up to 4 billion years. We find that while obliquity varies significantly more than that of the actual Earth over 100,000 year timescales, the obliquity remains within a constrained range, typically 20-25 degrees in extent, for timescales of hundreds of millions of years. Retrograde planets' obliqities are more stable than that of the real Earth. So having a large moon may not be needed for a planet to be habitable.

The prevailing theory for the formation of the Moon is a giant collision between proto-Earth and a Mars-sized protoplanet, with the Moon being mainly made from the impactor's material. It is now known that the composition of the Moon is too similar to Earth's mantle to be derived from the impactor, seriously questioning the giant impact theory. However, this is a problem only if we assume that little or no angular momentum was lost from the system since its formation.

The Lunar Crater Observation and Remote Sensing Satellite (LCROSS) mission will impact into the lunar polar region on October 9th. The panelists, consisting of the mission Principle Investigator and two Science Co-Investigators, will discuss the first results obtained from the cameras and spectrometers aboard the shepherding spacecraft, as well as pictures of the impact taken around the world and in space by the Hubble Space Telescope. Will the LCROSS mission detect water in the lunar regolith? Did the mission work as planned? The panel will let us know. 

The Earth and Moon were formed by the unequal collision of two planets some 30-100 million years after the Sun was born. The smaller planet is remembered now mostly by its ghost, but the Earth has grown and prospered. Dr. Zahnle will address the hidden history of the Earth from after the Moon-forming impact until the emergence of a rock record ca 3.8 Ga.

The lunar environment, serene and unchanging to the naked eye, seethes with plasma and electromagnetic activity. Plasma, photons, micrometeorites and energetic particles constantly bombard the lunar surface, producing a tenuous exosphere and a dynamic wake region, and charging the surface to electrostatic potentials reaching kilovolts, producing surface electric fields large enough to affect lunar ions and dust. Meanwhile, plasma interacts directly with crustal magnetic fields, producing perhaps the smallest magnetospheres in the solar system. Dr.