...And returned safely to the Earth

40 years ago today, the Apollo astronauts splashed down in the Pacific Ocean after visiting the moon. While it is nice that they went there, it is even better that they came back. Especially since they brought rocks with them.

The scientific return from the Apollo mission is often understated. Just the other day, Mark at Cosmic Variance said "But what grabbed me was the exploration, and the adventure. Not the science.". But while it is true that the mission was not designed as a scientific experiment, the scientific return was nothing short of phenomenal.

There were a number of non-geologic accomplishments of the mission- such as the first collection and return of solar wind, and various discoveries relating to lunar ranging, etc. But the rocks alone are worth considering.

"...and all we brought back were some rocks." is a common criticism on the Apollo program. Of course, geology isn't about the rocks. Geology is about the stories rocks tell. And what a story.

Prior to the return of Apollo 11, people really had no idea what the Moon was made of, nor how it got there. Based on Terrestrial geology, people made various educated guesses about the composition and origin of the moon. And they were all wrong.

Earth is thought to have formed by the collisions of tens to hundreds of smaller bodies. In contrast, the Moon condensed from material vaporized during one of these Earth-forming collisions. It then cooled, crystallized, and aside from some sporadic magmatism, had done little else since.

Despite being co-genetic with the Earth, the Moon is completely and totally different. In fact, it is so different as to be beyond any of the theories dreamed up prior to the return of the Moon rocks. As such, it set a pattern for the characterization of other planetary bodies- first in our own solar system, and more recently, around far away stars. Time and time again, planets defy our expectations. The geysers of Triton and Enceladus. Perchlorates on Mars. The extreme eccentricity and small orbits of extrasolar planets.

The key revelation from Apollo- which has been repeated every time planetary science has stepped farther out into the galaxy- is this:
Planetary formation is stochastic. Planets are not like aluminum atoms, electrons, or whatever-it-is that the LHC is supposed to discover. There is no formula you can devise to predict the details of all the planets in the Galaxy. They are not interchangeable. You have to actually go out and observe them, in order to figure out their stories. This lesson was first learned from the Apollo samples, and it is incredible important. Because every time scientists forget it, the universe shows them up.