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Physics News Update - 06/18/97
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 326 June 18, 1997 by Phillip F. Schewe and Ben Stein
[snip]
THE EARTH HAS A COMPANION IN ADDITION TO THE
MOON. The object, asteroid 3753, is in orbit not around the Earth
but in concert with it in a horseshoe-shaped trajectory that co-rotates
with the Earth in its orbit around the sun; with respect to the sun,
the trajectory is an eccentric ellipse somewhat inclined to the
ecliptic plane. The discovery in 1906 of such an asteroid, 588
Achilles, near Jupiter, confirmed Joseph-Louis Lagrange's theory
that planet-sun systems have points (now called Lagrangian points)
where a third object of negligible mass could reside in stable
equilibrium. Many such captive asteroids have been since found
near our planetary neighbors, but only two of them, Janus and
Epimetheus (companions of Saturn) have horseshoe orbits.
Asteroid 3753, 5 km in diameter, was first spotted in 1986, but its
trajectory was not understood until now with the numerical
modeling research of astronomers at York University (Ontario) and
the University of Turku (Finland). (Paul Wiegert et al., Nature, 12
June 1997.)