Solar System Overview

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Evelyn Horton
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1 Solar System Overview Planets: Four inner planets, Terrestrial planets Four outer planets, Jovian planets Asteroids: Minor planets (planetesimals) Meteroids: Chucks of rocks (smaller than asteroids) (Mercury, Venus, Earth, Mars) (Jupiter, Saturn, Uranus, Neptune, Pluto) Meteor: Light flash which occurs when a meteoroid hits Earth s atmosphere (commonly referred to as a falling star) Meteorite: Meteoroid which survives passage through Earth s atmosphere and hits ground Comets: Ice balls (nucleus, coma, head, hydrogen gas envelope, tails) Mercury Planetary Flyby (Some Highlights) Mercury s spin-orbit coupling is 3:2, i.e., for every two revolutions around the Sun, Mercury spins (or rotates) three times on its own axis. This means for every two Mercury years there are only three Mercury days. Since Mercury has virtually no atmosphere (Why not?): 1. Mercury has no protection from meteoroids 2. There is no erosion on Mercury s surface other than that due to volcanoes 3. The surface of Mercury is similar in appearance to moon Mercury has a large metal core, but its magnetic field is weak (only 1% as strong as Earth s) since Mercury rotates so slowly. Very large temperature swings -297 F to +873 F. Why? Venus Venus is called the morning and evening star, but is never overhead late at night (Why not?). It has strange rotation properties. Venus s has the slowest spin (or rotation) of all the planets; it completes one Venus day every 243 Earth days. It also rotates retrograde, i.e., opposite of its orbital direction around the Sun! Venus has many earthlike surface features such as highlands (Ishtar Terra) and lowlands. The highest point is Maxwell Montes (7 miles high). 1

Meteoroid which survives passage through Earth s atmosphere and hits ground Comets: Ice balls (nucleus, coma, head, hydrogen gas envelope, tails) Mercury Planetary Flyby (Some Highlights) Mercury s

2 Venus s atmosphere is the most dense of all the terrestrial planets. The high concentration of CO 2 causes a runaway greenhouse effect, making Venus much hotter than it would be otherwise. Earth The presence of water is unusual compared to other terrestrial planets. Water covers 70% of Earth s surface. A better name for our planet would have been WATER! Earth s moon is unusually large relative to size of planet. Where does our moon come from? Mars Mars is the red planet. It appears orange-red to the naked eye. There are many earthlike features on Mars: 1. Canyons (Valles Marineris, like a giant Grand Canyon) 2. River basins which were probably formed by water some time ago 3. Volcanic mountains (Olympus Mons a shield volcano that is 340 miles across and 15 miles high, the largest mountain in the solar system!) There is no water evident at present. Maybe some is still frozen below the surface. Where did the water go? Mars has two moons Phobos (means panic) and Deimos (means terror). They are potatoshaped. White polar caps are frozen CO 2 (carbon dioxide), not H 2 O (ice)! Why life is probably insupportable on Mars: 1. The Martian atmosphere is too thin (only 1% that of Earth s atmosphere), and is mostly carbon dioxide. 2. No ozone or magnetic field around Mars to block harmful radiation and cosmic rays. 3. As far as we know there is little (or no) water on Mars. 4. Mars is much colder than Earth. Mercury Venus Earth Atmospheres of Terrestrial Planets Almost no atmosphere. Very small amounts of hydrogen, helium, and oxygen detected by Mariner 10 flyby ( ). Hot, poisonous atmosphere (96% CO 2, 3.5% N 2, minor amounts of Ar, H 2 O, SO 2 ). The dense CO 2 atmosphere is responsible for the greenhouse effect! 1% as dense as Venus (78% N 2, 21% O 2, minor amounts of Ar, CO 2, and some others) Mars 1% as dense as Earth (95% CO 2, 3% N 2 ) 2

Earth s moon is unusually large relative to size of planet. Where does our moon come from? Mars Mars is the red planet. It appears orange-red to the naked eye.

3 Jupiter Jupiter is the largest planet (mass is 318 times that of Earth). It s a big gas ball (90% hydrogen, 10% helium). Some wonder if Jupiter is the Sun s sister (or brother). It may be a failed twin star of the Sun. It is the planet with the Great Red Spot. The Great Red Spot is bigger than Earth itself and is a gigantic hurricane which has lasted 100 s of years! There are also alternating bands of light and dark going from north to south due to atmospheric circulation (storms) and contain winds which move up to 300 mph. Jupiter has the strongest magnetic field of all the planets. Why is Jupiter s magnetic field so much stronger than the terrestrial planets? Jupiter has rings, but they are not as developed as those around Saturn. There are at least 62 moons (or satellites) that orbit Jupiter. The four Galilean satellites are Io, Europa, Ganymede, Callisto. Why is Io famous? The answer to this is that Io is the only place we have observed a volcano as it was happening other than on Earth. Saturn This is the planet with the highly developed ring structure. The rings are made of bits and pieces of ice and rocks circling the planet. Like Jupiter, Saturn is a big gas ball (94% hydrogen, 6% helium). Does it rain helium on Saturn? Some scientists think so. Saturn has at least 35 moons (or satellites). Titan is one of the 17 Saturn moons and is one of the largest or moons in the solar system. Titan is unique in that it is the only moon to have its own atmosphere. Uranus Uranus is a really strange rotator. Its spin axis aligned almost to the ecliptic! Thus, Uranus tends to roll along the ecliptic as it orbits the Sun. Uranus s magnetic field (it s a pretty strong one) is not line up at all with its spin axis as with other planets. Furthermore, the center of the magnetic field does not correspond to the center of the magnetic field does not correspond to the center of the planet! Uranus has nine rings (rings discovered in 1977 by star occultation) and 27 satellites. 3

There are also alternating bands of light and dark going from north to south due to atmospheric circulation (storms) and contain winds which move up to 300 mph.

4 Neptune Neptune was the first planet to be discovered after its existence was predicted. Neptune was discovered in Its existence was predicted beforehand by noticing small irregularities in Uranus s orbit. Neptune takes a long time to orbit the Sun, once every 165 years. Neptune has not yet made one complete orbit since its discovery! There are winds of up to 700 miles per hour along equator of Neptune. Why are there such strong winds if there is little heat to drive them? The answer is related to the fact that the inside of the planet rotates faster than the outside. Neptune has the Great Dark Spot and the scooter, both are atmospheric storms and are like smaller versions of the Great Red Spot on Jupiter. Pluto (dethroned as planet!) Pluto s orbit is unusual in two ways. The orbit has a large inclination to the ecliptic. The orbit is also highly eccentric, and even crosses Neptune s orbit at times. Is it possible that Pluto and Neptune will collide sometime in the future? We still have relatively little information about Pluto. It is 10,000 times too dim to be seen by the unaided eye from Earth. Most information about Pluto is from remote, Earth-based sensing apparatus. No spacecraft from Earth has been near Pluto yet. We do know Pluto is chilly since the temperatures there are -210 C! Even gasses are frozen solid at this temperature. Pluto s moon, Charon, was discovered in 1978 when a little bump on telescope pictures of Pluto was seen. 4

Neptune has not yet made one complete orbit since its discovery! There are winds of up to 700 miles per hour along equator of Neptune.

5 General Differences Between the Inner and Outer Planets # INNER small size small mass high overall density surface is terrestrial, i.e., Earth-like (rocky surface) relatively large and dense metal cores (Mars is exception) weak or no magnetic fields OUTER large size (except for Pluto) large mass low overall density surface is Jovian, i.e., Jupiter-like ( surface is gas) relatively small rocky cores strong, intense magnetic fields thin, tenuous atmospheres: CO 2, O 2, N 2 thick, heavy atmospheres: H 2, He, CH 4 warm main elements: O, Si, Fe, Mg, Ni, Al very few (0-2) satellites cold (-200 to -400 F) main elements: H, He many satellites (>13), except for Pluto # Pluto not included among outer planets 5

THE SOLAR SYSTEM - EXERCISES 1

THE SOLAR SYSTEM - EXERCISES 1 THE SUN AND THE SOLAR SYSTEM Name the planets in their order from the sun. 1 2 3 4 5 6 7 8 The asteroid belt is between and Which planet has the most moons? About how many?