Ch. 6: Smaller Bodies in the Solar System FIGURE 9-1 (Discovering the Universe) Different Classifications of Solar System Objects Some of the definitions of the different types of objects in the solar system overlap. For example, the largest asteroids are also being classified as dwarf planets; various trans-neptunian objects (TNOs) are asteroids or comets; some comets are satellites of Jupiter; some Kuiper belt objects (KBOs) are satellites of other KBOs. Furthermore, TNOs exist in two groups: Kuiper belt objects and Oort comet cloud bodies. Some moons are as large as dwarf planets. Indeed, some moons are as large as small planets!
Most of the ~264,000 supposed asteroids also called minor planets - are in orbits between Mars and Jupiter in the asteroid belt, but some thousands come close to Earth. The larger ones are round, because of gravity, but the smaller ones have rough shapes. Made of silicate rock as well as metals, such as iron and nickel. Some contain carbon-bearing rock Some have their own moons. Perhaps an asteroid hit Earth 65 millions years ago, and wiped out the dinosaurs. See Table 7-1 for sizes of largest asteroids
(BIG 4 ARE: Ceres, 934 km; Pallas, 526 km; Vesta, 510 km; Hygiea, 408 km) The above figure shows some of the asteroids located between Mars and Jupiter. The x- axis is the distance from the Sun in units of AU. The numbers beside the object name is the order in which they were discovered. The largest (#1) and first found is called Ceres. It is 950 km in diameter. New asteroids are found by robotic telescopes. Experts expect that it will find ~100,000 objects of various size.
Understanding the Threat That Near-Earth Objects Pose Asteroids close to Earth are called Near Earth Objects (NEOs); 624 are Potentially Hazardous Movies in 1998: Armageddon and Deep Impact. The asteroid that wiped out the dinosaurs was 10 miles in diameter.
When push comes to shove: Nudging an asteroid If we bomb and asteroid, many smaller asteroids would be produced, and potentially more dangerous. Nudging is better. But still do not know how much of a nudge is acceptable. Forewarned is forearmed: Surveying NEOs to protect Earth System to protect Earth: Measure and track all asteroids with a size of more than one mile Track orbits and compute future movements and determine possibility of striking Earth Study and learn as much as possible about them After understanding a threat, engineers can plan a defense. Searching for Small Points of Light Occultation of a star
Meteors: Wishing on a Shooting Star Meteoroid: small object in space, usually a fragment from an asteroid or comet, orbiting the Sun. Sometimes rocks blasted off Mars or Earth s Moon. Cometary meteoroids: fluffy little dust particles shed by comets. Asteroidal meteoroids: from microscopic to boulders = chips from asteroids (socalled minor planets): Meteor: a flash of light produced when a small object (a meteoroid) enter the Earth s atmosphere from space, sometimes called a shooting star or falling star. Meteorite: solid object from space that has fallen to the surface of Earth: stony, iron, stony-iron meteorites Micrometeorites are so very small that they do not create enough friction to ignite, do drift slowly to the ground. These exist in your hair and over your body, but too small to see without a microscope. Sporadic meteor : when you see a shooting star at night, you are probably
Meteor shower : many from same direction. Fireball : sometime an oooooooooooooooooo!!
A bolide is a fireball that explodes or produces a loud noise. See more meteors after midnight than before because, from midnight to noon, you are on the forward side of Earth, where our planet s plunge through space sweeps up meteoroids. After this time the opposite situation occurs. At certain times of the year can see meteor showers, when Earth passes through a great ring of meteorites that runs all the way around the comet that sheds them. The direction from which they come is the radiant. Most famous is Perseides. Do NOT have to face this direction. Best way to observe is on a lounge chair or blanket and pillow, looking half way up from the horizon to the zenith.
Comets: The Lowdown on Dirty Ice Balls Comets: great blobs of ice and dust that slowly track across the sky, looking like fuzzy balls trailing gassy veils. Usually long orbits, and coming from the Oort cloud, very far away. Comets usually have a head and a tail; the head later named the nucleus. It is a mixture if ice and frozen gases, such as carbon monoxide and carbon dioxide, and solid particles dust or dirt Origin: born from around Jupiter and out to the Oort cloud (10,000 AU; 1 AU = 93million miles). Kuiper belt. Passing stars sometimes disturb this region, and send comets in new directions. A comet far from the Sun only has a nucleus (no head or tail). May be from 2 to dozens of miles in diameter. The head and tail appear when getting close to the Sun, which heats and melts it!! The hazy shining cloud around the head is called the coma (Latin for hair). The coma is also reflected light from billions of particles from the Sun.
Also, satellites moving W to E and too slow for a meteor and to fast for a comet. A meteor lasts for seconds; a comet is visible for days, weeks, and even months. Meteors flash across the sky as they fall overhead, within 100 miles or so from the observer. Comets crawl across the sky at distances of millions of miles. Meteors are common; comets that can be seen easily with the naked eye come less than once a year, on average