Meet Earth's New Best Friend

image credit: NASA/JPL-Caltech/UCLA

Usually, when people utter the words "asteroid" and "Earth" in the same sentence, it's in a Deep Impact sort of context.  But an asteroid discovered last October by NASA's WISE (Wide-field Infrared Survey Explorer) satellite is news on account of its very different relationship with the Earth.  Far from being a nemesis coming to do the dinosaur number on us, it turns out 2010 TK7 is more like a frisky puppy, running around ahead of us as we perambulate in our orbit.  It's Earth's first Trojan asteroid.

As announced in the British magazine 2010 Nature last month, TK7 is in a stable orbit, 60 degrees ahead of us in our orbit around the Sun, describing a kidney-bean-shaped path around Earth-Sun Lagrange point L4.  That's one of the five points, relative to the Earth, where the gravity of the Sun and Earth exactly balance each other out.  However, since the Earth is constantly moving around the Sun, so do the Lagrange points, sending objects into those odd paths, called Lissajous curves.  2010 TK7 is currently 50 million miles from Earth.  Here's an animation of 2010 TK7's position over time:



Incidentally, if you read the comments on this video's page on YouTube, you can fear, as I do, that the human race is far too stupid to survive.  Last I checked, the consensus was that there's something sinister about this, because obviously NASA should have long ago discovered something 1,000 feet long that never gets within 12.5 million miles of us, which shares an orbit with us and is therefore in the daytime sky, and which spends most of its time well above or below the plane of the ecliptic where most orbiting objects lie.  And I guess the fact that they're announcing it now, rather than continuing to suppress knowledge of its existence, is just part of their Dark and Evil Plan.

The first Trojan asteroid was found near Jupiter in 1906.  Neptune and Mars are also known to have them. Two of Saturn's moons have two known Trojan objects each, at the moons' Lagrange points with the planet.

Of course, an object this important isn't going to go on being called "2010 TK7" for very long.  Phil Plait of the Bad Astronomy blog suggests as a permanent name either "Coeus" or "Crisus," the sons of Gaia, the Greek goddess of the Earth.  Having once lived in Los Angeles for ten years, the first name that springs to my mind is "Tommy Trojan."  But that ain't gonna happen, particularly because some of the astronomers who discovered it are at UCLA.  I like my metaphor from the first paragraph best, but I don't suppose the International Astronomical Union would be amenable to calling it "Rover."

Links:
space.com article
Wikipedia article
NASA photo (of which the one here is a detail)