All the planets orbit the Sun in the same direction B All the planets move in orbits that lie in nearly the same plane. The planets nearest the Sun contain only small amounts of substances that condense at low temperatures. All the planets and the Sun, to the extent that we know, are the same age. All of the above. As the young Sun heated up, the water boiled, creating hollow pockets in the rock. There are about known comets and more are discovered each year.
Every comet has a nucleus of ice, gas, and dust between 1 and 10 kilometers 0. The ice is made of varying amounts of water, carbon dioxide, ammonia, and methane.
The dust may contain hydrogen, oxygen, carbon, nitrogen, silica, and some metals. The nucleus may also have traces of hydrocarbons. Astronomy Picture of the Day.
As comets approach our Sun [within about million kilometers million miles ], they heat up and the ice begins to sublimate, transforming from a solid into a gas. As comets move close to the Sun, they develop tails of dust and ionized gas.
Comets have two main tails, a dust tail and a plasma tail. The dust tail appears whitish-yellow because it is made up of tiny particles — about the size of particles of smoke — that reflect sunlight. Dust tails are typically between 1 and 10 million kilometers about , to 6 million miles long.
The plasma tail is often blue because it contains carbon monoxide ions. Solar ultraviolet light breaks down the gas molecules, causing them to glow. Plasma tails can stretch tens of millions of kilometers into space.
Rarely, they are as long as million kilometers almost million miles. A third tail of sodium has been observed on Comet Hale-Bopp.
Comet Hale Bopp, taken by Joe Orman, showing the long, straight, blue plasma tail and the broader, shorter, whitish dust tail. Orman motorola. Comets are surrounded by a broad, thin sparse hydrogen cloud that can extend for millions of kilometers. This envelope cannot be seen from Earth because its light is absorbed by our atmosphere, but it has been detected by spacecraft.
Comets travel around our Sun in highly elliptical oval-shaped orbits. The time it takes to make a complete orbit is called a comet's period. Comets are divided into short-period comets and long-period comets. Short period comets — such as Comet Halley — orbit our Sun in less than years. Their orbital paths are close to the same plane of orbit as Earth and the other planets, and they orbit our Sun in the same direction as the planets.
Based on these orbital characteristics, short-period comets are believed to originate in the Kuiper belt , a disk-shaped region extending beyond Neptune.
The Kuiper belt contains small, icy planetary bodies, only a few of which have been imaged. Occasionally the orbit of a Kuiper belt object will be disturbed by the interactions of the giant planets in such a way that it will have a close encounter with Neptune and either be flung out of the solar system or pushed into an orbit within our solar system.
Their orbital path is random in terms of direction and plane of orbit. Based on calculations from their observed paths, long-period comets are believed to originate in the Oort cloud, a round region that may extend 30 trillion kilometers approximately 20 trillion miles beyond our Sun.
Oort cloud objects have never been imaged. Meteor showers occur when Earth passes through the trail of dust and gas left by a comet along its elliptical orbit.
The particles enter Earth's atmosphere and most burn up in a lively light show — a meteor shower. Some meteor showers, such as the Perseids in August and the Geminids in December, occur annually when Earth's orbit takes it through the debris path left along the comet's orbit. Comet Halley's trails are responsible for the Orionids meteor shower. For upcoming meteor showers and viewing suggestions, explore StarDate's listing of the year's meteor showers.
LPI Education. Ice Worlds! As the atmopshere got even hotter, the surface rocks that contained carbonates heated up and put more carbon dioxide into the atmosphere, another greenhouse gas.
The exosphere is the top of the atmosphere the outer atmosphere where molecules can move around with little chance of hitting other molecules. If they are moving fast enough, they can escape the atmosphere and go off into space. It starts at about to 1, kilometers above the surface and extends out into space. For comparison, the International Space Station orbits at kilometers above the surface of the Earth. There are two primary factors: size and distance from the Sun. Also, if you are closer to the Sun, the atmosphere is hotter and the molecules are moving faster and so can reach escape velocity.
This is why Mercury has no atmosphere, but much smaller and colder Pluto can still retain a thin atmosphere. There are other factors, too. Some moons have a thin atmosphere because they have some internal heat and thus volcanoes and geysers that can replenish their very thin atmospheres. Then there is Venus, where it got so hot what is called a runaway greenhouse that some of the rocks have boiled away.
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