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To the right is a picture of our solar system, and the bodies in it. Started by the sun, the planets are arranged in the following order in orbit: Sun, Mercury, Venus, Earth,Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto... and at the bottom right there is a shot of a comet, meteorite, and asteroid.
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To the right there is a picture of the Sun. This ball of gas is the closest star to the earth, as you may know. It is made of about 75% hydrogen, and 25% helium; about 0.1% of the Sun is made of metal. These change slowly over time as the Sun coverts hydrogen to helium in its core. The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. Conditions at the core are extremely hott! The temperature there is about 15.6 million Kelvin,( I dont know what that means but its a measure of temperature) and the pressure is 250 billion atmospheres. The Sun's energy output is produced by nuclear fusion reactions. The surface of the Sun, called the photosphere, is a temperature of about 5,800 K.(Kelvin) Sunspots are cool regions, only 3,800 K, they look dark only by comparison with the surrounding regions. Sunspots can be large, as much as 50,000 km in diameter, they are caused by complicated and not very well understood interactions with the Sun's magnetic feild. A small region above the photosphere is called the chromosphere, above that is called the corona. The corona is only wisible during eclipses. The Suns magnetic feilds is so extremely strong, it's known as the magnetosphere, this extends well beyond Pluto! In addition to heat and light, the Sun also emits a low density stream of charged particles (mostly electrons and protons) known as the solar wind, which propagates throughout the solar system in about 450 km/sec! There are 9 planets, and a number of small objects orbiting the Sun. The Sun is a major part of our solar system and with out it we wouldn't survive!
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To the right is a picture of Mercury. Mercury is the closest planet to the Sun. It has been visited only once by a spacecraft, Mariner 10, it flew by 3 times in 1973 and 1974. Only 45% of the surface was mapped by MARINER 10. Mercury's orbit is highly eccentric. 19th century astronemers made very careful observations of Mercury's orbital parameters but could not exactly explain it! Temperature's on Mercury vary extremley, from 90 to 700 K. The temperature on Venus is slightly higher but very stable. In many ways Mercury is similar to the moon: its surface is heavily cratured and very old; it has no plate tectonics. On the other hand it is much denser than the moon, and denser than earth. It has a very thin mantle and crust, its interior is dominated by a large iron core whose radius is 1800 to 1900 km. The outer shell of Mercury is 500 to 600 km thick. Some of its core is probably molten. It has a very thin atmosphere, made up of atoms blasted off itsd surface by the solar wind. Because it is not hot, thses atoms quickly escape out into space. Amazingly evidence, from radar observations show that on the north pole of Mercury, there is evidence of water and ice in the protected shadows of some craters. We do not know muc about Mercury, but we sure hope someday we will know a lot more!
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