[sci.astro] StarDate: October 14 Trojan Asteroids

dipper@utastro.UUCP (Debbie Byrd) (10/14/86)

Jupiter and the Trojan Asteroids -- when we come back.

October 14  Trojan Asteroids

Gravity works in a variety of ways in our solar system.  It lets
planets orbit the sun, and moons orbit planets -- and more.

For example, in 1772, a French mathematician predicted that two large
bodies in orbit around each other should create two other places where
smaller bodies can get gravitationally "stuck." According to Joseph
Lagrange, smaller bodies will move through space with the two larger
ones -- never getting much closer to or farther from either of them.
These special places -- where small objects in space are
gravitationally balanced with two large objects -- are now called
Lagrangian points.

More than a century after Lagrange's prediction, an unusually dark
asteroid was sighted moving in the orbit of Jupiter -- at the
Lagrangian point in front of Jupiter.  Just as Lagrange had predicted,
the asteroid, the sun, and Jupiter all remain about 500 million miles
apart -- forming a triangle with sides of equal length.

Soon more asteroids were found around that Lagrangian point -- and near
the second Lagrangian point -- also in Jupiter's orbit -- 500 million
miles behind the giant planet.  Both groups of asteroids became known
as the Trojan Asteroids.  The largest ones moving in front of Jupiter
were named for Greek heroes of the Trojan War -- and those following
Jupiter for the defenders of Troy.  There are two exceptions, however
-- each group has one asteroid named for an enemy prisoner.

There are dozens of Trojan asteroids -- with perhaps three and a half
times as many moving in front of Jupiter as moving behind.  Why that
is, no one knows.  It's another of the many puzzles in the solar system
remaining to be solved.

Script by Bill Edrington.
(c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin