Wednesday   22 April 2015    / Hour 1, Block C: Hotel Mars, episode n. Bill Bottke, Southwest Research Institute, Planetary Science Directorate, Institute for Science of Exploration Targets, in re:   The Earth has tides and a beautiful Moon. [See: Science Journal article, "How Did the Moon Really Form?" April 8, 2015]   Once upon a time the Earth had no Moon; a Mars-size planet came by and wham! hit the Earth, creating the Moon.  We think the Moon is a natural by-product of how [everything in the Solar System] formed; the event may have been 100 million years ago? How old is the Moon?  Oldest samples have been heavily beat up and damaged by vulcanism.  In the collision, maybe 1% of the mass of the Earth is ejected and flies around; when it hits asteroid, it created craters; we think some of the meteors falling on Earth today are remnants of that.  Moon now seems to be [4.5 billion years old].  First a giant collision, with a huge disc of debris around the Earth (imagine Saturn's rings). Then it starts to consolidate, begins to form a Moon, which moves away from the Earth. Little moonlets accrete, join the big moon.   All in the first 100 million years of the Solar System.  The younger Moon craters from the Late Heavy Bombardment, 4 bil years ago: destablizing event.   Moon will now be slowly moving away from the Earth for a long time to come.  The probe Dawn around Ceres, the dwarf planet/largest asteroid in the asteroid belt. Velocities,  high heat, melt, impacts, impact-melt, craters. Ceres may be water-rich, might have an ocean subsurface.   . . .  The Moon is still magic.