Asteroid Belt Shepherding
Today at school my teacher asked us why does not the
asteroid belt come crashing into the inner planets. Then she said
that Jupiter's gravitational pull keeps it from moving into the
inner planets. But I asked her why they do not crash into the inner
planets when the asteroids are away from Jupiter and I was wondering
if you knew?
Although Jupiter may exert some force on the objects in the asteroid belt,
these asteroids maintain their orbits much in the same way that the planets
do, their outward acceleration is opposed exactly by their inward
acceleration - or put in another way, the asteroids and planets experience
a centripetal force as the Sun's gravitational force pulls on it. The Sun's
gravitational force pulls the bodies toward it, so that the result is that
the bodies move in an orbit around the Sun.
Greg (Roberto Gregorius)
The main reason is that the asteroids,crowded as they are, leave a huge amount
of empty space among them, so collisions with the planets are rare. But they do
happen from time to time. The Earth was struck 50,000 years ago in northern
Arizona, for example.
David H. Levy
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Update: June 2012