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).