There’s a scene in Contact where Dr. Arroway (Jodie Foster) is overwhelmed by the beauty of outer space and says that they should have sent a poet to describe it, not an atronomer. But there is also something to be said for sending a geologist. Two recent articles in The New York Times and Science describe how a geologist, Harrison Schmitt, collected a very special rock from the moon during the Apollo 17 mission that may settle the question of whether the moon ever had a molten core like the Earth’s and produced its own magnetic field.
Troctolite 76535 is a 4.2 billion year-old piece of olivine and plagioclase that shows evidence of two magnetic fields, one from when it originally formed, and one in another direction from when it slowly cooled after being heated and dislodged by a meteorite. The fact that it cooled slowly after impact is important. Meteor impacts create a temporary magnetic field, and so moon rocks that cool quickly after impact are imprinted with these temporary fields, but the second magnetic field in “Trocto” (as the rock is affectionately called) could only have arisen from a stable core-generated magnetic field.
So NASA is looking pretty clever for sending a geologist who managed to pick out a rock that is nearly as old as the Earth and Moon are. It’s hard enough to find rocks that old on Earth—imagine doing it in a space suit in only three days! Well done, Dr. Schmitt.