Notes 2-2 The Planets 2/11/09 Pick up the assignments you did in the computer lab the last two days in the wire basket at the front. If you missed either day, get a blank copy on the desk.

Mercury Size – Mercury is 4880 km in diameter (38% the size of Earth). It is the 8th largest planet in the solar system. Mass – Mercury is only 5.5% the mass of the Earth. Temperature – Temperature variations on Mercury are the most extreme in the solar system ranging from -298° F to 800° F. Orbit - Mercury's orbit is highly eccentric; at perihelion it is only 46 million km from the Sun but at aphelion it is 70 million. Mercury’s year is 87.97 Earth days long. Rotation – Mercury rotates only 3 times in 2 of its years. That makes Mercury’s day 58.65 Earth days long.

Mercury Gravity – Mercury has only 38% the gravity of earth. A 150 lb person would weigh only 57 lbs on Mercury. Atmosphere – Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. Thus in contrast to the Earth whose atmosphere is stable, Mercury's atmosphere is constantly being replenished Surface – Mercury’s surface is very similar to our moon. It has many impact craters, remnants of volcanic activity and maria. Moons – Mercury has no moons.

Mercury In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky. Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by Hubble Space Telescope). A new discovery-class mission to Mercury, MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys.

Venus Size – Venus is 12104 km in diameter (95% the size of Earth). It is the 6th largest planet in the solar system. Mass – Venus is 81.5% the mass of the Earth. Temperature – The temperature on the surface of Venus is about 890° F with hot spots up to 1300° F. Orbit – The orbit of Venus is fairly circular. A year on Venus is 224.7 days long. Rotation – Venus rotates backwards! The sun rises in the West and sets in the East. This backward rotation is slow, it takes 243 days for Venus to rotate around 1 full time, but because it is also moving around the sun, the solar day is 116.8 days long.

Venus Gravity – Venus has 91% the gravity of earth. A 150 lb person would weigh 136.5 lbs on Venus. Atmosphere – Venus has dense sulfuric acid clouds covering the entire surface, acid rain and 90 times the atmospheric pressure of Earth. It is probably the most inhospitable planet for life. Surface – The surface of Venus has a similar density and chemical composition to Earth and relatively few impact craters suggesting its surface is very young. Any water that may have once existed has since boiled away leaving a very dry surface. Moons – Venus has no moons.

Venus Venus is the goddess of love and beauty. The planet is so named probably because it is the brightest of the planets known to the ancients. The first spacecraft to visit Venus was Mariner 2 in 1962. It was subsequently visited by many others (more than 20 in all so far), including Pioneer Venus and the Soviet Venera 7 the first spacecraft to land on another planet, and Venera 9 which returned the first photographs of the surface. Most recently, the orbiting US spacecraft Magellan Magellan radar map (false color) produced detailed maps of Venus' surface using radar.

Earth Size – The Earth is 12,756.3 km in diameter. It is the 5th largest planet in the solar system. Mass – The Earth has a mass of 5,972,000,000,000,000,000,000,000 kg. Temperature – The temperature on the surface of Earth ranges from about -130° F to 140° F. Orbit – The orbit of Earth is fairly circular. A year on Earth is 365.25 days long. Rotation – Earth rotates once every 24 hours and is tilted 23.5° on its axis.

Earth Gravity – The acceleration due to gravity on Earth is 9.8 m/s2, a.k.a. 1 g. Atmosphere – The Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. Surface – 71% of the Earth's surface is covered with water. Earth is the only planet on which water can exist in liquid form on the surface. The Earth is geologically active with many volcanoes and earthquakes. Moons – The Earth has 1 moon.

Earth Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. Since the inception of the space program we have sent several manned and unmanned mission into space to orbit the Earth and visit the moon.

Mars Size – Mars is 6787 km in diameter (53% the size of Earth). It is the 7th largest planet in the solar system. Mass – Mars is 10.8% the mass of the Earth. Temperature – The temperature on the surface of Mars ranges from about -117° F to 72° F. Orbit – The orbit of Mars is very elliptical. A year on Mars is about 687 days long. Rotation – One day is 24 hours and 40 minutes.

Mars Gravity – Mars has 38% the gravity of earth. A 150 lb person would weigh 57 lbs on Mars. Atmosphere – Mars has a very thin atmosphere composed mostly of the tiny amount of remaining carbon dioxide plus nitrogen, argon and traces of oxygen and water. The average pressure on the surface of Mars is less than 1% of Earth's. Dust storms occasionally envelope the entire planet. Surface – Mars is covered with dust. There is very clear evidence of erosion in many places on Mars including large floods and small river systems. At some time in the past there was clearly some sort of fluid on the surface. Moons – Mars has two tiny moons, Phobos and Deimos.

Mars Mars is the god of War. The planet probably got this name due to its red color; Mars is sometimes referred to as the Red Planet. The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on July 4, 1997. In 2004 the Mars Expedition Rovers "Spirit" and "Opportunity" landed on Mars sending back geologic data and many pictures; they are still operating after more than a year on Mars. Three Mars orbiters are also currently in operation.

Jupiter Size – Jupiter is 142,948 km in diameter (11.2 times the size of Earth). It is the largest planet in the solar system. Mass – Jupiter is more than twice as massive as all the other planets combined and more than 318 times the mass of Earth. Temperature – The average temperature on the surface of Jupiter is -186° F. Orbit – The orbit of Jupiter is fairly circular. A year on Jupiter is about 4333 days long. Rotation – One day is 9 hours 55 minutes.

Jupiter Gravity – Jupiter has 2.54 times the gravity of earth. A 150 lb person would weigh 381 lbs on Jupiter. Atmosphere – Jupiter and the other gas planets have high velocity winds (up to 400 mph) which are confined in wide bands of latitude. The winds blow in opposite directions in adjacent bands. Surface – Jupiter is a gas planet. It consists of mostly gas with increasing pressure as you move inward. Moons – Jupiter has at least 63 moons and small faint rings (like Saturn).

Jupiter Jupiter (known as Zeus to the Greeks) was the King of the Gods, the ruler of Olympus and the patron of the Roman state. Jupiter was first visited by Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and Ulysses. The spacecraft Galileo orbited Jupiter for eight years. It is still regularly observed by the Hubble Space Telescope.

Saturn Size – Saturn is 120,536 km in diameter (9.45 times the size of Earth). It is the 2nd largest planet in the solar system. Mass – Saturn is more than 95 times the mass of Earth. Temperature – The average temperature on the surface of Saturn is -202° F. Orbit – The orbit of Saturn is fairly circular. A year on Saturn is about 10,756 days long. Rotation – One day is 378 Earth days.

Saturn Gravity – Saturn has 1.08 times the gravity of earth. A 150 lb person would weigh 162 lbs on Saturn. Atmosphere – Saturn, like Jupiter is a gas planet. Its atmosphere is very similar to Jupiters with winds up to 500 mph. Surface – Saturn has a very similar structure to Jupiter with a solid core, liquid interior and gaseous exterior. Saturn however, is the least dense planet in our solar system with a density less than that of water. If it could be placed in water, Saturn would float! Moons – Saturn has a large number of moons. The precise figure will never be certain as the orbiting chunks of ice in Saturn's rings are all technically moons. Seven of the moons are large. Saturn's most noteworthy moon is Titan, the only moon in the solar system to have a dense atmosphere.

Saturn In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word "Saturday" Saturn was first visited by NASA's Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini arrived on July 1, 2004 and will orbit Saturn for at least four years.

Uranus Size – Uranus is 51,118 km in diameter (4 times the size of Earth). It is the 3rd largest planet in the solar system. Mass – Uranus is more than 14.5 times the mass of Earth. Temperature – The average temperature on the surface of Uranus is -337° F. Orbit – The orbit of Uranus is fairly circular. A year on Uranus is about 30,707 days long. Rotation – One day is almost 370 Earth days. Uranus has an odd tilt of almost 90° in its axis. It spins sideways.

Uranus Gravity – Uranus has .91 times the gravity of earth. A 150 lb person would weigh 136.5 lbs on Uranus. Atmosphere – Uranus' atmosphere is about 83% hydrogen, 15% helium and 2% methane. Surface – Uranus is composed primarily of rock and various ices, with only about 15% hydrogen and a little helium Moons – Uranus has 27 moons.

Uranus Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus. (There is something odd going on in that family!) Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.

Neptune Size – Neptune is 49532 km in diameter (3.9 times the size of Earth). It is the 4th largest planet in the solar system. Mass – Neptune is more than 17 times the mass of Earth. Temperature – The average temperature on the surface of Neptune is -364° F. Orbit – The orbit of Neptune is fairly circular. A year on Neptune is about 60,223 days long. Rotation – One day is almost 367.5 Earth days.

Neptune Gravity – Neptune has 1.19 times the gravity of earth. A 150 lb person would weigh 178.5 lbs on Neptune. Atmosphere – Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere. Like a typical gas planet, Neptune has rapid winds confined to bands of latitude and large storms or vortices. Neptune's winds are the fastest in the solar system, reaching 2000 km/hour. Surface – Neptune's composition is probably similar to Uranus': various "ices" and rock with about 15% hydrogen and a little helium. Moons – Neptune has 13 moons.

Neptune In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea. Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. Much of we know about Neptune comes from this single encounter. But fortunately, recent ground-based and Hubble Space Telescope observations have added a great deal, too.

Pluto Size – Pluto is 2274 km in diameter (17.8% the size of Earth). It was once considered to be the smallest planet in our solar system but was demoted to “minor planet” designation in 2006. Mass – Pluto is less than 1% the mass of Earth. Temperature – Pluto is the coldest planet in our solar system. The average temperature on the surface of Pluto is -380° F. Orbit – Pluto’s orbit is elliptical, so much so that every so often Pluto crosses the orbit of Neptune and is actually closer to the sun than Neptune for 20 years. Pluto’s year is 90,613 days long. Rotation – One day is almost 366.7 Earth days.

Pluto Gravity – Pluto has .06 times the gravity of earth. A 150 lb person would weigh only 9 lbs on Pluto. Atmosphere – Little is known about Pluto's atmosphere, but it probably consists primarily of nitrogen with some carbon monoxide and methane. Surface – Pluto's composition is unknown, but its density (about 2 gm/cm3) indicates that it is probably a mixture of 70% rock and 30% water ice Moons – Pluto has 3 moons. Two of those moons were just discovered in 2005 and are yet to be given formal names.

Pluto In Roman mythology, Pluto (Greek: Hades) is the god of the underworld. The planet received this name (after many other suggestions) perhaps because it's so far from the Sun that it is in perpetual darkness Pluto is the only planet that has not been visited by a spacecraft. Even the Hubble Space Telescope can resolve only the largest features on its surface (left and above). A spacecraft called New Horizons was launched in January 2006. If all goes well it should reach Pluto in 2015.