The document summarizes the planets in our solar system. It describes the inner planets Mercury, Venus, Earth and Mars, and their key characteristics such as solid composition and proximity to the Sun. It then discusses the outer gas giants Jupiter, Saturn, Uranus and Neptune, noting their lower densities and that they are mostly gaseous. The document provides details on features of individual planets like Jupiter's Great Red Spot and Saturn's rings.

1. THE SOLAR SYSTEM By Mrs. JoAnn Kwasnick

2. OBJECTIVES IDENTIFY THE INNER AND OUTER PLANETS. IDENTIFY IMPORTANT CHARACTERISTICS AND FEATURES OF PLANETS. COMPARE AND CONTRAST VENUS AND EARTH. COMPARE EARTH AND MARS WITH ATTENTION TO LANDSCAPE AND ATMOSPHERE.

3. PLANETS THE INNER Mercury Venus Earth Mars THE OUTER Jupiter Saturn Uranus Neptune

4. NOTE PLUTO- In spite of having a moon (Charon) has been downgraded to a minor planet. It is not considered a direct part of our solar system. The status change of Pluto was determined by the International Astronomical Union.

5. THE INNER PLANETS MERCURY,Venus, Earth, and Mars are the inner Planets. These planets are relatively close TO THE SUN. ALL ARE SOLID ROCKLIKE BODIES IN CONTRAST TO THE OUTER PLANETS, WHICH ARE MOSTLY GASEOUS.

6. MERCURY Mercury is the second smallest planet in the solar system. Usually, Mercury cannot be viewed because it is too close to the sun. When Mercury can be seen, it is close to the horizon in the early morning or late evening sky. Mercury has a very heavily cratered surface like that of the moon. The terrain is more rugged than that of our moon. Some of the cliffs on Mercury are nearly three kilometers high. Mercury’s density suggests an iron rich core, but its magnetic field is extremely weak. Its atmosphere, which is mostly sodium, is very thin. Because Mercury is a relatively dark object, it does not reflect much of the sunlight falling on it. Its temperatures range from over 450 degrees Celsius by day to about -170 degrees Celsius by night.

7. Venus and earth Venus and Earth are similar to each other in size, mass, and shape. Therefore, it called Earth’s twin. Because it is closer to the sun, Venus receives twice as much sunlight as Earth. Nearly three-fourths of this sunlight as Earth. Nearly three-fourths of this sunlight is reflected into space by the clouds in Venus’ dense atmosphere and only 2 percent reaches the surface. This small amount is trapped by the cloud cover. Temperatures near the surface can reach 400 degrees Celsius, due to the greenhouse effect. The atmosphere of Venus is 97 percent carbon dioxide. Droplets of sulfuric acid give the clouds of Venus a yellow color. Venus appears to go through phases similar to those of our moon. These phases occur due to the orbit of Venus around the sun inside the orbit of Earth. A compete cycle for these phases takes under two years. Venus has a retrograde or opposite rotation from that of most other planets. Rotation is extremely slow, 243 Earth days.

8. earth Earth is the third planet from the sun. It orbits the sun at a mean distance of 150 million km, or one AU (Astronomical unit). Earth rotates on its axis once in about 24 hours. It revolves around around the sun once in about 360 days. Our measurements of time are based on these motions. Within the solar system, Earth days and years are used to describe the motions of other planets. Earth’s atmosphere is unique among the planets in our solar system. Water vapor has been held in place by gravity. Earth’s atmosphere moderates temperature, allowing water to exist as a solid, liquid, or gas. Also, Earth’s atmosphere allows most meteors to burn up before they reach the surface. It protects life from the sun’s intense radiation. In addition, oxygen has been added to the atmosphere over time.

9. MARS Mars is the fourth planet from the sun. It is referred to as the red planet due to the iron oxide in the weathered rocks on its surface. We have known about its polar caps for a long time, but many crustal features have since been discovered by probes. These probes are Mariner 9 (1971-1972) and Viking 1 and 2 (1976) which gave to us Important information about Mars. The Martian terrain consists of ridges and valleys. Rift zones, areas of fractures or cracks in the crust, extend for over four thousand kilometers across Mars. Olympus Mons, though extinct, is the largest known volcano in the solar system. It rises 25 kilometers above the Martian surface. Martian craters are numerous. Ejected material seems to have flowed away from the crater. Mars’ atmosphere includes clouds and fog. Water vapor condenses at night and evaporates when the sun rises. Most of the atmosphere is carbon dioxide, with small amounts of nitrogen, argon, and oxygen are present. Dust storms are common on Mars. They may be local, or they may spread completely around the planet.

10. MARS CONTINUED Mars has two moons. Both are irregular in shape. Phobos is about 25 kilometers in diameter. Deimos is about 13 kilometers in diameter. The surfaces of both moons are heavily cratered much like Earth’s moon. Phobos revolves around Mars about three times during a Martian day. Thus, when viewed from Mars, Phobos rises in the west and sets in the east. Phobos is the only solar system moon to do so. Phobos is in an orbit which Is spiraling inward towards Mars. It is expected to impact Mars in about 50 million years.

11. THE OUTER PLANETS

12. THE OUTER PLANETS The first four planets from the sun are rocky Objects whose mean density is about 4.7 g/cm 3 . Between 5 and 30 Au s lies the realm of the giant Gaseous planets. These outer planets are much More massive than the terrestrial planets. The mean densities of the Jovian (outer) Planets are much lower.

13. JUPITER Jupiter is the largest planet in the solar system and the fifth planet from the sun. Jupiter and its 16 moons resemble a miniature solar system. Four of these moons are very large. Io, the moon closest to Jupiter, is mostly solid rock. Io has its own very thin atmosphere of sulfur and sodium as well as a number of erupting volcanoes. Europa is mostly rock with a thick coating of ice. Ganymede , the largest of all the solar system moons, is half rock, and half ice. Callisto’s composition is similar to Ganymede’s. Some of Jupiter’s other moons may captured space objects. Scientists believe that Jupiter is mostly liquid and gaseous hydrogen with some helium, ammonia, methane, and water vapor. The composition of the planets core is unknown. White to reddish-brown cloud bands alternate around Jupiter. Light bands are due to rising columns of gas. Dark bands are descending gas. These alternating bands are generated by heat from Jupiter’s core. The Great Red Spot on Jupiter is its most Spectacular feature. Also, lighting has been observed within Jupiter’s clouds.

14. saturn Saturn is another gaseous planet like Jupiter. It is the sixth planet from the sun and also is known as the ringed planet. It is 95 times more massive than Earth. Although it is the second largest planet. Saturn has lowest density. Due to this low density Saturn would float on water. Much data has been gathered about Saturn by the voyager probes. Over one thousand rings have been discovered. Saturn also has 18 or more moons. The largest of Saturn’s moons is Titan, which has a dense atmosphere. Saturn’s atmosphere is about 60 percent hydrogen with more methane and less ammonia than Jupiter’s atmosphere. Saturn has an internal heat source. It radiates almost three times more energy into space than it receives from the sun. Like Jupiter, Saturn appears to rotate faster at its equator than at the poles.

15. uranus Uranus is a large gaseous planet with at least ten dark rings, with ten arc-shaped rings, and 15 moons. Uranus is the seventh planet from the sun and was not discovered until 1781. Its rotational axis is inclined to its orbit by 98 degrees, so its rotation is retrograde. Uranus’ moons have retrograde revolution. Uranus is thought to be made up of hydrogen and methane gas. It is methane that give the planet its blue-green color. Uranus has few storm systems and no cloud bands.

16. neptune Neptune is also a gaseous planet similar in size and composition to Uranus. Discovered in 1846. It is the eighth planet from the sun most of the time. However, Pluto’s orbit crosses inside Neptune’s during a part of its voyage around the sun. Neptune’s atmosphere is similar to that of Uranus. The methane content gives Neptune its distinctive blue-green color just as it does for Uranus. Neptune appears to be surrounded by at least three partial ring arcs less than 20 kilometers wide. Neptune has eight moons. The largest is Triton , which is larger than Pluto. Neptune’s magnetic field is tilted about 55 degrees from its rotational axis and offset from the center by half of Neptune’s radius.

17. Note to students Interested students in astronomy can find a wealth of additional information by contacting astronomy clubs in their local areas.