Astronomy’s Nice model from earlier this century speculates that Jupiter migrated in the early solar system, moving closer to the Sun than its present position then retreating farther away. Similarly, this article hypothesizes that Mercury formed beyond the orbit of Mars because its high potassium/thorium ratio indicates that it formed farther from the Sun, and migrated inwards. The Moon’s potassium level is approximately ten times lower than that of Venus or Earth. Therefore, it would have been closer to the Sun than Mercury is today and much of its potassium would have evaporated into space. A couple of theories regarding lunar origins can be divided into Darwinian fission and Theian fission. * * “Fission” refers to Darwinian fission...