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Jupiter has many Trojan asteroids located at Lagrangian points L4 and L5 and Hilda asteroids dispersed between points L3, L4, and L5.

Does the Earth have similar satellites? If so, how many?

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up vote 7 down vote accepted

Yes, but just barely (i.e. only one so far), and only for the L4 point. And this was only recently discovered. Dr. Phil Plait (an Astronomer) covers this at his Discover Magazine blog in his usual easy to read style.

NASA’s Wide-field Infrared Survey Explorer (WISE) has found the very first asteroid that (more or less) shares an orbit with Earth! Called 2010 TK7, this asteroid is about 300 meters (roughly 1000 feet) across, and is the first in an up-to-now theoretical class of objects called Earth Trojans.

The University of Western Ontario astronomer Paul Weigert has a page describing this.

Additionally, you can get a pre-print of their paper (PDF).

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2010_TK7's Wikipedia page –  Peter Mortensen Sep 10 '11 at 0:34
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