Asteroids and the asteroid belt:
The asteroid belt is a bunch of large rocks, perhaps hundreds of thousands of them, that
are orbiting the Sun somewhere between the orbits of Jupiter and Saturn.
1)How and Why were asteroids first discovered? In the late 1700’s two astronomers
noticed that there is a regularity to the distances from the Sun to the planets, but they
noticed a gap between Jupiter and Mars. Many astronomers began to look for one in that
area—what they found was a whole lot of very small objects we now call asteroids.
2)Why didn’t the asteroids coalesce to form a single planet? Jupiter’s gravity kept the
asteroids from coalescing into one planet.
3)What do asteroids look like? The largest 3 or 4 asteroids have enough gravity to pull
themselves into a round shape, the rest are irregularly shaped. Many of them have large
craters, all of them have small craters. Their colors are similar to the grays and blacks we
see on the Moon.
4) How might an asteroid have caused the extinction of the dinosaurs? There is
considerable that a large asteroid collided with the Earth about 65 million years ago and
the debris thrown up caused the extinction of the dinosaurs.
5)What are the differences among meteors, meteoroids, and meteorites? Meteoroids are
asteroids (space rocks) which are smaller than about 1000 feet in size. Meteors are
meteoroids that have entered the Earth’s atmosphere. Meteorites are meteors that have
hit the surface of the Earth (most meteors burn up long before they make it to the
surface).
7)Why do comets have tails? Comets have 2 tails. The ion tails are caused by the solar
wind pushing charged particles away from the comet (the ion tail is straight), and the dust
tail (which is curved) is caused by radiation (light) pressure on the (uncharged) dust
particles around the comet.
8)Where do comets come from? Comets come from the Kuiper belt, which is in the
plane of the solar system beyond Neptune, and they also come from the Oort cloud which
is all around the solar system (not just in the plane of the solar system) and extends out
much farther than the Kuiper belt.
9)About how many orbits do comets last before they are “burned out?” Comets typically
last 100-200 orbits before all their ice has melted and they are a scattered pile of rocks
and dust.
10)What is the connection between comets and meteor showers? Comets only last about
100 to 200 orbits. After that their remains (rocks and dust) continue to move around their
orbit, but the rocks and dust continue along the orbital path, and after a long time
becomes distributed along the pathway. When the Earth passes thru the orbital path of a
“dead comet” we get a meteor shower as the particles burn up in our atmosphere.
13) Are all of the asteroids orbiting between Jupiter and Mars? No, some of them have
highly elliptic orbits that get outside this range..
14) Why are there gaps in the asteroid belt? They are caused by Jupiter’s gravity.
15) How are the gaps similar to the gaps in Saturn’s rings? The gaps are caused by
Jupiter’s gravity. The gaps in Saturn’s rings are caused by the gravity of its moons.
17) What is the evidence that an asteroid could have cause the extinction of the
dinosaurs? We find a thin global layer of iridium that dates to 65 million years ago.
Iridium is common in asteroids, but not very common on Earth. Also, there is an impact
site near the Yucatan peninsula in Mexico which dates to that time.
18) What are the parts of a comet? Dust tail, Ion tail, nucleus, coma (you should know
what each of these is.)
19) Why is the phrase “dirty snowball” appropriate in describing a comet? Because
comets are rock and ice.
20) How many tails does a typical comet have? Two, the dust tail and the ion tail.
21) What is the Kuiper belt? The Kuiper belt is a region of space in the solar system
beyond the orbit of Neptune (from about 30-500AU) where there are a large number of
comets (objects made of ice and rock). Objects in the Kuiper belt orbit the Sun in the
plane of the solar system (or nearly so).