Jan
04
2012

Twin satellites reunite above the moon

A lonely space-bot searches for its brother: We all know what that's like, don't we?
A lonely space-bot searches for its brother: We all know what that's like, don't we?Courtesy NASA
Man, I had this dream last night that my brother and I had each taken a long trip, and at the end of the trips we met up and floated around the sky while singing to each other about our feelings. What a strange dream. I think it means that I’m afraid of death. That’s what my dream analysis book says anyway, just like it says for every dream.

On an unrelated note, one of NASA’s latest experiments, the “GRAIL mission,” is ticking away smoothly.

If, like me, you assumed that the GRAIL mission was a lot like Indiana Jones and the Last Crusade, I’m afraid you’re about to be sorely disappointed. “GRAIL,” in fact, stands for “Gravity Recovery And Interior Laboratory,” so you shouldn’t expect any bullwhips or crusty old knights. No, the GRAIL mission will be carried out by the two identical satellites that just reunited in orbit around the moon, after a slow trip from Earth (Apollo program vessels made it to the moon in just three days, but the GRAIL satellites sort of took a scenic route that required less energy to get to the moon, but a lot more time—between three and four months.)

The satellites arrived at the moon on different days (the 31st and the 1st), but now that they’re back in the same neighborhood they’re going to be traveling around the moon together at about 35 miles above the surface. As they move, they’ll be transmitting radio signals to each other, which will allow them to precisely calculate the distances between them. As one or the other of the satellites flies over an area of the moon with greater or lesser gravity, the distance between the satellites will change slightly.

Because tiny differences in gravity are determined by the interior composition of an object in space*, these satellites will tell us more about the inside of the moon, and how it formed. And because the moon originally came from Earth, we’ll learn more about the formation of our planet from this mission as well.

*More mass means more gravity, so the satellites will be able to detect not only visible features on the moon, like hills and craters, but underground structures as well. Moons and planets after all, aren’t totally uniform inside—they’re less like giant marshmallows than giant scoops of rocky road ice cream.

The things that happen in space … amiright? Crazy!

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