Day 10 Thursday February 20
Before the planetarium show "Cosmic Collisions" we reviewed the various
objects still lying between the planets. There use to be lots more of this
junk, but the planets and the sun have sucked it in like cosmic vacuum
- ASTEROIDS: between Mars and Jupiter, consisting of material that was
prevented from forming a planet by the gravitational influence (tidal) of
There are about 100,000 asteroids, but their total mass is quite small,
perhaps only 0.04% of the mass of the earth.
Resonances with Jupiter cause gaps in the asteroid belt and also send
some asteroids along orbits that cross the earths orbit.
Collisions between asteroids also send some of them toward the earth.
Asteroids appear on the earth as meteorites.
- COMETS: These appear to be chunks of dirty ice left over from the
days of the solar system. They have variable amounts of carbon (soot-like)
covering them, which determines their variably "activity". Those that are
totally covered with soot have SHUT OFF; sunlight can not reach the ice
and cause it to evaporate.
When they fall to the earth, many comets may produce air blasts, similar
to that of Tunguska, when the ice become suddenly vaporized.
There is a great reservoir of comets in the Oort comet cloud which extends
to perhaps 100,000 AU; one-third the distance to the nearest star, Alpha
- METEORS: Those meteors that occur in showers such as that of the
of August 12 come from comets and are dropped along the orbits as the ice
melts and rock fragments are released. These tiny fragments are vaporized
high in the atmosphere.
Sporadic meteors which are not associated with showers may be from comets
or they may be small asteroids.
- METEORITES: These largely come form the asteroid belt and by
are large enough to reach the earths surface. Twelve meteorites collect on
the Antarctic ice appear to have come from Mars, blasted off its surface
from the meteorite impact. Two of those contain evidence for life on Mars.
- INTERPLANETARY DUST: Debris from asteroid collisions and evaporated
comets collects as dust between the planets and is concentrated in the
ecliptic plane. The dust is visible in the evening or dawn at the Zodiacal
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