Mercury	Mercury is the second smallest planet in our solar system. Only the planet Pluto is smaller. Mercury is about the same size as our Moon. It is the closest planet to the sun. Mercury travels around the Sun faster than any other planet. Mercury can only be seen from Earth just before sunrise or just after sunset, but not in the middle of the night. That is because Mercury always appears near the Sun when viewed from Earth. Mercury has a very thin atmosphere. Humans would not be able to live there. The surface of Mercury has holes in it where objects such as meteorites and asteroids crashed into it.
Venus	Venus and Earth are almost the same size. Venus is the closest planet to Earth, but it does not have oceans or human life like Earth. The temperature rises to 484 degrees Celsius on the side facing the Sun. Venus has very thick, rapidly spinning clouds which cover its surface. These clouds hold heat in. That is why Venus gets so hot. These clouds also reflect sunlight. That is why Venus appears so bright to us here on Earth. There are constant thunderstorms in these clouds. The surface of Venus has many craters which were made by meteorites and asteroids crashing into the planet. Venus also has volcanoes. This planet is unusual because it rotates in a direction opposite that of all of the other planets. Venus spins very slowly as it orbits the Sun.
Earth	Earth is the third closest planet to the Sun. It has an atmosphere made up of many different gases, but mainly it is nitrogen and oxygen. The atmosphere gives us air to breathe. We live on the planet Earth. The Earth orbits around the Sun. It takes one year to go around the Sun one complete time. The Earth also rotates, or spins, on its axis. It takes one day to spin around one complete time. The Earth's axis is not straight up and down, but tilted a little bit. This tilt is responsible for us having seasons. Otherwise, the temperature would be pretty much the same all year long.
Mars	The temperature on Mars can be very, very cold. On its warmest day, Mars can still be a very cold place. At the top and bottom of the planet are poles just like on Earth. During the Martian winter, ice caps can be seen at the poles.  Space probes have landed on Mars.They performed experiments on the Martian dirt and atmosphere. The dirt was found to contain clay which was rich in iron. The iron is what gives Mars its red color. Mars has many craters which were formed by meteorites or asteroids hitting it. Mars also has some of the tallest volcanoes and some of the deepest valleys in our solar system. Mars has two moons, Phobos and Deimos which have unusual shapes. Scientists think these potato-shaped moons were once asteroids captured by Mars' gravitational pull .
Jupiter	Jupiter is a large gas planet whose clouds change colors daily. This planet is made mostly of hydrogen and helium gases. Jupiter gives off two times more heat than it gets from the Sun. It shines very brightly in the night sky for nine months of the year when it is closest to Earth. Huge areas of swirling gases can be  found in Jupiter's atmosphere. The largest swirling  area of gas is called the Great Red Spot. Scientists  believe this is a large hurricane-like storm which has lasted for hundreds of years. Large bolts of lightning  have also been seen in Jupiter's atmosphere. Pictures   taken by space probes have shown thin rings around   Jupiter. Jupiter has sixteen known moons (and may   have more than 28!). One of Jupiter's moons, Io, has  active volcanoes on it. Areas on Io that are near the volcanoes are very, very hot.
Saturn	Saturn is a very large gas planet which spins very rapidly on its axis. It spins so fast that it flattens ou the top and the bottom of the planet. The fast spin also causes Saturn to bulge at its equator. Saturn's atmosphere has winds which can blow at over 1800 kilometers per hour! The white spots on Saturn are believed to be powerful storms. Saturn is surrounded  by over 1000 rings made of ice and dust. Some of the rings are very thin and some are very thick. The size of the particles in the rings range from pebble-size to house-size. Scientists believe that the  particles came from the destruction of moons circling  the planet. As comets and meteorites smashed the  moons, Saturn's gravitational pull shaped the particles into rings. Saturn has a least 18 known moons. Some of these moons orbit the planet within the rings, creating gaps in the rings.
Uranus	Uranus tilts over so far on its axis that it rotates on its side. Because of this, its poles are sometimes pointed almost directly at the Sun. Uranus' atmosphere is made up of hydrogen, helium, and methane. The temperature in the upper atmosphere is very cold. The cold methane gas is what gives Uranus its blue-green color. The rapid rotation of Uranus causes winds up to 600 kilometers per hour to blow in its atmosphere. Uranus has eleven known rings which contain  dark, boulder-sized particles. Uranus has at least 20 known moons. Some of these moons are less than 100 kilometers wide and black as coal. One more moon may have been found by astronomers. Other scientists are trying to confirm the discovery.
Neptune	Neptune and Uranus are very much alike. They are both large gas planets that look like big blue-green balls in the sky. Neptune has winds in its atmosphere which blow at over 2000 kilometers per hour! This planet has large, dark circles on its surface which astronomers believe to be storms. Neptune has two thick and two  thin rings which surround it. Neptune also  has eight moons. Four of these moons orbit the planet within the rings. One of Neptune's moons, Triton, orbits the planet in a direction opposite that of the seven other moons. Due to Pluto's unusual elliptical shaped orbit, Neptune is actually the farthest planet from the Sun for a 20 year period out of every 248 Earth years.
Pluto	Pluto is usually the farthest known planet from the Sun. It has a very unusual orbit. Once every 248 Earth years, Pluto swings inside the orbit of Neptune. It stays there for twenty years. During those twenty years, Pluto is closer to the Sun than Neptune. While it is closer to the Sun, Pluto has an atmosphere. The methane and nitrogen frozen at the poles thaw out, rise, and temporarily form an atmosphere. As it moves toward its farthest point from the Sun, Pluto's atmosphere freezes and falls back on the surface of the planet. Pluto has only one known moon. Pluto's moon, Charon, is half the size of Pluto. Some astronomers call Pluto and Charon a double planet because they are so close in size. Other astronomers do not think Pluto is a real planet at all. They think it may be a moon which escaped from Neptune's gravitational pull .

Last updated: June 3, 2003