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The Question
(Submitted August 10, 1998)
I noticed that the orbits between Mars and Jupiter (where the asteroid belt
is) looks as though there ought to be a planet there instead of the asteroid
belt. Has it ever been considered that the asteroid belt was maybe a destroyed
planet?
The Answer
Thank you for your question! The fact that the asteroid belt has such a
well-defined, high concentration of asteroids suggests two things. One,
that they are fragments of a planet that broke-up long ago, or two, that
they are rocks that never managed to accumulate into a genuine planet.
Currently, scientists tend to favor the latter explanation. According to
Eric Chaisson and Steve McMillan, the authors of the text book "Astronomy
Today", 1993 edition, "There is far too little mass in the belt to
constitute a planet, and the marked chemical differences between individual
asteroids strongly suggest that the asteroids could not all have
originated in a single planet. Instead, astronomers believe that the
strong gravitational field of Jupiter continuously disturbs the motions of
these chunks of primitive matter, nudging and pulling at them, thereby
prohibiting them from aggregating into a planet. The existence and
composition of the asteroid belt joins the general properties of the
planets and their moons on our list of features that any theory of solar
system formation must explain."
Here is a good web page about the asteroids:
http://www.seds.org/nineplanets/nineplanets/asteroids.html
Hope this helps!
Maggie Masetti & Koji Mukai
for Ask an Astrophysicist
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