1. EUROPA: is the second closest moon to Jupiter. –It is completely covered with frozen water Some scientists believe that beneath the frozen water there might exist liquid water – the evidence that supports this is the cracks on the surface that resemble the cracked ice fields off the coast of Antarctica. –If liquid water does exist on Europa, it might be one of the most likely places in the solar system, beside the Earth, to support life in some form. The second gaseous planet in the solar system is Saturn, and is located 9.6 AU from the Sun, or 886.2 million miles. –It is composed mainly of hydrogen and helium gas, with clouds made of ammonia and methane. –The most striking attribute about Saturn is its unique rings.

2. The planet is orbited by seven main ring systems, which are composed of billions of ice particles – if we could enter these systems, it would appear as if we were in a great blizzard. –These particles range in size from tiny grains of sand to giant boulders. Saturn is also orbited by at least 22 moons. –The largest moon, Titan, is the only moon in the solar system that contains a substantial atmosphere – the atmosphere is composed mainly of nitrogen gas. –It is larger than the planets Mercury and Pluto. Uranus is the seventh planet, located 19.2 AU, or 1.783 billions miles, from the Sun. –It is also a gaseous planet that is about four times larger than Earth. –It takes 84 years to orbit the Sun and more than 17 hours to make on full rotation.

3. Uranus is unique among the planets in that its axis of rotation is tilted 90 degrees – it appears to be spinning on its side as compared with the rotation of the other planets. –It is composed mostly of ammonia and methane (which gives it the blue-green color), with an atmosphere of hydrogen and helium. Uranus is also surrounded by a ring system and at least 18 moons. Neptune is the eighth planet in the solar system, located 30.1 AU, or 2.794 billion miles from the Sun. –It is also a gaseous planet composed of hydrogen, helium, and methane – the methane gives Neptune its blue color. –Neptune orbits the Sun in approximately 168 years and makes one complete rotation on its axis every 19 hours.

4. Neptune has a small ring system and eight moons. –One of Neptune’s moons, Triton, is the coldest object in space so far recorded – it has a surface temperature of - 390 o F. Astronomers believe that this moon will eventually collide with Neptune in about 10 million to 100 million years. Dwarf Planets Pluto has been regarded as the solar system’s ninth and final planet – however in 2006, it was downgraded to a dwarf planet. Definition: a non-luminous object that orbits around a star, has sufficient gravity to form a spherical shape, and whose orbit has not cleared its path of other celestial objects –For more than 100 years, astronomers have loosely defined a planet as a large body that orbits around a central star – now the IAU (International Astronomical Union) has redefined was constitutes a planet.

5. The new criteria that now defines a planet is a non-luminous object that orbits around a star, has sufficient gravity to form a spherical shape, and whose orbit has cleared its path of other celestial objects. As a result, Pluto is no longer considered a planet because its orbit crosses that of the planet Neptune. Currently, three objects in the solar system are now considered dwarf planets: Ceres, Pluto, and Eris. –CERES: is located closest to the Sun, and was once regarded as the largest asteroid lying in the asteroid belt between the orbits of Mars and Jupiter. It is approximately 580 miles in diameter and located 2.9 AU, or approximately 277 million miles from the Sun. –PLUTO: is the second dwarf planet, and is located in the outer fringes of the solar system at 39.4 AU, or 3.666 billion miles from the Sun. It is very small, with a diameter of only 1,430 miles.

6. It is a gaseous dwarf planet composed of frozen methane, nitrogen, and carbon monoxide. It takes Pluto more than 247 years to orbit the Sun, and it completes one rotation on its axis in six days. Pluto has one moon, Charon, which is half its size – the cold moon is believed to be composed mostly of frozen water. –ERIS: is the third dwarf planet and when first discovered was temporarily named 2003 UB-313. It is larger than Pluto and falls under the category of being a Trans-Neptunian Object. –Definition: objects that orbit the Sun at a greater distance than the orbit of the planet Neptune It orbits the Sun approximately 97 AU, or roughly 9 billion miles from the Sun. It has its own moon called Dysnomia. It has an extremely eccentric orbit and takes about 560 years to complete one revolution around the Sun.

7. Small Solar System Bodies The term used to describe some types of interplanetary material  a small solar system body Definition: a category of celestial objects orbiting the Sun that are not classified as planets, dwarf planets, or moons; this includes objects known as asteroids, meteors, comets, and some trans-Neptunian objects Asteroids An area called the asteroid belt is filled with a debris field of rocky asteroids that also orbit the Sun between a distance of 2.2 and 3.3 AU from the center of the solar system. Definition: a region in the solar system located between the orbits of Mars and Jupiter where there are a high number of asteroids Definition: an object orbiting the Sun that is smaller than a planet and has no atmosphere

8. Not all asteroids lie within the asteroid belt – some are located inside the orbit of the Earth around the Sun (these are called Aten asteroids). Some asteroids are classified by their ability to cross the Earth’s orbit (these are known as Apollo asteroids). –These are a concern to astronomers because they have the potential to strike the Earth’s surface. –Astronomers estimate that an asteroid strikes the Earth once every 2,000 years.

9. Meteoroids Smaller chunks of rock that are located in the solar system are called meteoroids, meteors, and meteorites. Definition: small chunks of rock, no larger than a few feet in diameter, that travel through space Definition: a small chunk of rock, no larger than a few feet in diameter, that is traveling through space and enters the Earth’s atmosphere; commonly known as a shooting star Definition: a meteor that does not burn up in the atmosphere, and strikes the Earth’s surface –Meteorites are grouped into three categories based on their composition: Stony meteorites are composed of silicate rock material. Iron meteorites are composed of an iron-nickel alloy and are very dense.

10. Stony-iron meteorites are composed of a mixture of silicate rock and iron. During certain times of the year, many meteors enter the Earth’s atmosphere at once in an event called a meteor shower. Definition: an event that describes a group of meteors entering and burning up in the Earth’s atmosphere Comets Once referred to as dirty snowballs, comets are unique in their appearance. Definition: a mixture of frozen compounds and rock that orbits the Sun and which has a distinct tail composed of vaporized gas and dust that always points away from the Sun –A comet consists of three parts: nucleus, coma, and tail

11. –A comet’s nucleus: the frozen compounds and rock that form the core of a comet –A comet’s coma: the dust and gas surrounding the nucleus that was once held within the nucleus –A comet’s tail: the vaporized gas and dust that trail away from the nucleus of a comet Most comets come from a region at the edge of the solar system called the Oort cloud. Definition: a hypothetical area that is located approximately 100,000 astronomical units from the orbit of the planet Pluto, where comets are believed to originate –There are two main types of comets, which are classified based on their period of revolution around the Sun. Long-period comets take an extremely long time to orbit the Sun, such as 30 million years. Short-period comets orbit the Sun in periods less than 200 periods.