Mars

"The Red Planet"
Mars, the red planet, is the fourth planet from the sun and the most Earth-like planet in our solar system. It is about half the size of Earth and has a dry, rocky surface and a very thin atmosphere.

MARS' SURFACE

A Mollweide projection of Mars made from four pictures taken by Hubble Space Telescope in 1999. A storm is visible in the top left near the pole.

The surface of Mars is dry, rocky, and mostly covered with iron-rich dust. There are low-lying plains in the northern hemisphere, but the southern hemisphere is dotted with impact craters. The ground is frozen; this permafrost extends for several kilometers.

Olympus Mons, the largest volcano on Mars; it is perhaps the largest volcano in the Solar System. It is 17 miles (27 km) tall and over 320 miles (520 km) across. It is thought to be extinct.

The north and south poles of Mars are covered by ice caps composed of frozen carbon dioxide and water.





Scientists have long thought that there is no liquid water on the surface of Mars now, but recent photos from Mars indicate that there might be some liquid water near the surface. The surface of Mars shows much evidence of the effects of ancient waterways upon the landscape; there are ancient, dry rivers and lakes complete with huge inflow and outflow channels. These channels were probably caused by catastrophic flooding that quickly eroded the landscape.

Scientists think that most of the water on Mars is frozen in the land (as permafrost) and frozen in the polar ice caps.

G. Schiaparelli was an Italian astronomer who first mapped Mars (in 1877) and brought attention to the network of "canali" (Italian for canals or channels) on Mars. These "canals" were later found to be dry and not to be canals at all. A Martian impact crater (Crater Schiaparelli, 461 km = 277 mi in diameter) and a hemisphere of Mars have been named after Schiaparelli.

SIZE
Mars is about 4,222 miles (6790 km) in diameter. This is 53% (a little over half) of the diameter of the Earth.

PLANETARY COMPOSITION
Crust and Surface: Mars' surface is composed mostly of iron-rich basaltic rock (an igneous rock). Mars has a thin crust, similar to Earth's.

Mantle: Silicate rock, probably hotter than the Earth's mantle at corresponding depths.

Core: The core is probably iron and sulphides and may have a radius of 800-1,500 miles (1,300-2,400 km). More will be known when data from future Mars missions arrives and is analyzed.

MASS AND GRAVITY
Mars' mass is about 6.42 x 10^23 kg. This is 1/9th of the mass of the Earth. A 100-pound person on Mars would weigh 38 pounds.

LENGTH OF A DAY AND YEAR ON MARS
Each day on Mars takes 1.03 Earth days (24.6 hours). A year on Mars takes 687 Earth days; it takes this long for Mars to orbit the sun once.

MARS' ORBIT
Mars is 1.524 times farther from than the sun than the Earth is. It averages 141.6 million miles (227.9 million km) from the sun. Its orbit is very elliptical; Mars has the highest orbital eccentricity of any planet in our Solar System except Pluto.

ATMOSPHERE
Mars has a very thin atmosphere. It consists of 95% carbon dioxide (CO₂), 3% nitrogen, and 1.6% argon (there is no oxygen). The atmospheric pressure is only a fraction of that on Earth (about 1% of Earth's atmospheric pressure at sea level), and it varies greatly throughout the year. There are large stores of frozen carbon dioxide at the north and south poles. During the warm season in each hemisphere, the polar cap partly melts, releasing carbon dioxide. During the cold season in each hemisphere, the polar cap partly freezes, capturing atmospheric carbon dioxide.
The atmospheric pressure varies widely from season to season; the global atmospheric pressure on Mars is 25% different (there is less air, mostly carbon dioxide) during the (northern hemisphere) winter than during the summer. This is mostly due to Mars' highly eccentric orbit; Mars is about 20% closer to the Sun during the winter than during the summer. Because of this, the northern polar cap absorbs more carbon dioxide than the southern polar cap absorbs half a Martian year later.
Occasionally, there are clouds in Mars' atmosphere. Most of these clouds are composed of carbon dioxide ice crystals or, less frequently, of frozen water crystals.
There are a lot of fine dust particles suspended in Mars' atmosphere. These particles (which contain a lot of iron oxide) absorb blue light, so the sky appears to have little blue in it and is pink/yellow to butterscotch in color.


TEMPERATURE RANGE
Mars' surface temperature averages -81 °F (-63 °C). The temperature ranges from a high of 68° F(20° C) to a low of -220° F(-140° C). Mars is much colder than the Earth.

MARS' MOONS
Mars has 2 tiny moons, Phobos and Deimos. They were probably asteroids that were pulled into orbit around Mars.

SPACECRAFT VISITS
Mariner 4 was the first spacecraft to visit Mars (in 1965). Two Viking spacecraft landed in 1976. Mars Pathfinder landed on Mars on July 4, 1997, broadcasting photos.

THE FACE ON MARS
This photograph of the Cydonia Mense region of Mars was taken by NASA's Mars Global Surveyor in 1998. It is a coincidental alignment of rocks and other geologic formations that happens to look like a human face from this angle.

DISCOVERY OF MARS
Mars has been known since ancient times.

MARS' NAME AND SYMBOL

This is the symbol of the planet Mars.

Mars was named after the Roman god of war.

MARS STATISTICS

STATISTICS ON MARS

Distance from Sun	1.524 AU 141.6 million miles 227.9 million km
Diameter	4,222 miles 6,787 km
Mass	6.42 x 1023 About 1/9 of Earth
Number of Moons	2
1 Martian Day (Period of Rotation)	24.6 Earth hours 1.026 Earth days
1 Martian Year (Period of Revolution Around the Sun)	686.98 Earth days
Escape Velocity	5,000 m/sec
Average Temperature	-9 °F -23 °C
Temperature Range	150-310 K
Albedo (reflectivity)	0.15
Density	3,940 kg/m3
Apparent Size from Earth	4-25 arc seconds
Oblique Axis (Tile of the Axis)	25°
Orbital Inclination	1.85°
Orbital Eccentricity (Deviation from circular)	0.093
Perihelion closest to sun	1.38 AU
Aphelion farthest from sun	1.67 AU

THE MOONS OF MARS

Mars has two moon, Phobos and Deimos. They were discovered by the American astronomer Asaph Hall (1829-1907) in 1877.
They are both small moons; Phobos is 13.8 miles (22.2 km) across and Deimos is only 7.8 miles (12.6 km) across.
These moons are heavily-cratered and are composed of rock and iron. They are probably former asteroids that were captured by Mars' gravitational field. They have no atmosphere.

PHOBOS Phobos (meaning "fear") is the larger of the two tiny moons of Mars. It is only 13.8 miles (22.2 km) across and has a mass of 1.08 x 1016. It orbits Mars at a mean distance of 5,600 miles (9,000 km). Its major feature is a large crater, named Stickney (Hall's wife's maiden name), which is 6.2 miles (10 km) wide. Phobos was discovered by astronomer Asaph Hall in 1877.

DEIMOS Deimos (meaning "terror") is the smaller of the two tiny moons of Mars. Deimos is only 7.8 miles (12.6 km) across and has a mass of 1.80 x 1015. It orbits at a mean distance of 14,300 miles (23,000 km) from Mars. It was discovered by A. Hall in 1877.

Missions to Mars

Mariner 4 was the first spacecraft to visit Mars in 1965. The first spacecraft orbited on Mars in 1971. The first spacecraft landed on Mars in 1976.

Missions	Date	Accomplishment
Mariner 4	1965	Fly-by mission: photos transmitted
Mariner 6 and 7	1969	Fly-by mission: atmosphere examined
Mariner 9	1971	Orbiter: First orbiter around another planet- mapping mission
Viking 1 and 2	1976	Lander: surface photos, soil biochemistry investigated. Orbiter: global mapping from orbit.
Phobos 2	1989	Orbiter: photos of Phobos
Mars Pathfinder	1997	Lander: (the first bouncing landing) plus "Sojourner" roving vehicle which performed rock analysis,
Mars Global Surveyor	1997	Orbiter: examine surface features, atmosphere, and magnetic properties.
Mars Climate Orbiter (NASA)	1998	Orbiter: study Martian weather and climate.
Mars Polar Lander (NASA)	1999	Lander: study soil and meteorology near Mars South Pole.
Mars Surveyor 2001 Orbiter (NASA)	March, 2001	Orbiter: study Mars from orbit, test aerocapture techniques, and act as a communications relay for the upcoming lander (see next entry).
Mars Surveyor 2001 Lander (NASA)	April, 2001	Lander: To bring the remote-controlled rover "Athena" to the surface, which will continue studying the Martian surface.
Mars Surveyor 2003 Orbiter (NASA)	2003-2004	Orbiter: study Mars from orbit, and serve as communications relay for the lander (see next entry)
Mars Surveyor 2003 Lander (NASA)	2003-2004	Lander: Brought the remote-controlled rover (Spirit) to the surface, which will continue studying the Martian surface.

Jupiter

Jupiter is the fifth and largest planet in our solar system. This gas giant has a thick atmosphere, 39 known moons, and a dark, barely-visible ring. Its most prominent features are bands across its latitudes and a great red spot (which is a storm).

Jupiter is composed mostly of gas. This enormous planet radiates twice as much heat as it absorbs from the Sun. It also has an extremely strong magnetic field. It is slightly flattened at its poles and it bulges out a bit at the equator.

SIZE
Jupiter's diameter is 88,700 miles (142,800 km). This is a little more than 11 times the diameter of the Earth. Jupiter is so big that all the other planets in our Solar System could fit inside Jupiter (if it were hollow).




MASS AND GRAVITY
Jupiter's mass is about 1.9 x 10²⁷ kg. Although this is 318 times the mass of the Earth, the gravity on Jupiter is only 254% of the gravity on Earth. This is because Jupiter is such a large planet (and the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of its radius squared).

A 100-pound person would weigh 254 pounds on Jupiter.

LENGTH OF A DAY AND YEAR ON JUPITER
It takes Jupiter 9.8 Earth hours to revolve around its axis (this is a Jovian day). It takes 11.86 Earth years for Jupiter to orbit the sun once (this is a Jovian year).

Jupiter is made up of gases and liquids, so as it rotates, its parts do not rotate at exactly the same velocity. It rotates very rapidly, and this spinning action gives Jupiter a large equatorial bulge; it looks like a slightly-flattened sphere (it is oblate)

JUPITER'S ORBIT
Jupiter is 5.2 times farther from than the Sun than the Earth. On average, it is 480,000,000 miles (778,330,000 km) from the sun.

At aphelion (the place in its orbit where Jupiter is farthest from the Sun), Jupiter is 815,700,000 km from the Sun. At perihelion (the place in its orbit where Jupiter is closest to the Sun), Jupiter is 749,900,000 km from the Sun. Jupiter has no seasons. Seasons are caused by a tilted axis, and Jupiter's axis is only tilted 3 degrees (not enough to cause seasons).

JUPITER'S MOONS
Jupiter has four large moons and dozens of smaller ones (there are 39 moons known so far). More moons are being found all the time.

Galileo first discovered the four largest moons of Jupiter, Io (which is volcanically active), Europa, Ganymede (the largest of Jupiter's moons, pictured at the left), and Callisto in 1610; these moons are known as the Galilean moons. Ganymede is the largest moon in the Solar System.



RINGS
Jupiter has faint, dark rings composed of tiny rock fragments and dust. These rings were discovered by NASA's Voyager 1 in 1980. The rings were investigated further when Voyager 2 flew by Jupiter. The rings have an albedo of 0.05; they do not reflect very much of the sunlight that they receive.



TEMPERATURE RANGE
The cloud-tops average 120 K = -153°C = -244°F.

DISCOVERY OF JUPITER
Jupiter has been well-known since ancient times. It is the third-brightest object in the night sky (after the moon and Venus).

COMET SL9 HITS JUPITER

An SL-9 impact site on Jupiter, July 6, 1994. Photo by Hubble Space Telescope.

Shoemaker-Levy 9 (SL-9) was a short-period comet that was discovered by Eugene and Carolyn Shoemaker and David H. Levy. As the comet passed close by Jupiter, Jupiter's gravitational forces broke the comet apart . Fragments of the comet collided with Jupiter for six days during July, 1994, causing huge fireballs in Jupiter's atmosphere that were visible from Earth.

SPACECRAFT VISITS
Jupiter was first visited by NASA's Pioneer 10, which flew by Jupiter in 1973. Later fly-by visits included: Pioneer 11, Voyager 1, Voyager 2, Ulysses, and Galileo.

JUPITER'S NAME AND SYMBOL

This is the symbol of the planet Jupiter.

Jupiter was named after the Roman primary god, Jupiter. 





ATMOSPHERE AND PLANETARY COMPOSITION
Atmosphere: Jupiter is a gaseous planet; it does not have a solid surface like the Earth does (but probably has a solid, rocky core 10 to 15 times the mass of the Earth). When we look at Jupiter, we are seeing icy clouds of gases moving at high speeds in the atmosphere. Jupiter's atmosphere is composed of about 90% hydrogen and 10 % helium. There are only minute traces (0.07%) of methane (CH₃), water, ammonia, and rock dust.

Mantle: Pressurized hydrogen in the mantle may generate electric currents which generate Jupiter's powerful magnetic field. The outer mantle is liquid hydrogen; the inner mantle is liquid metallic hydrogen. The layers of extraordinarily-compressed hydrogen are in a state so extreme that it has never been produced on Earth. The pressure is so great that the hydrogen molecules inside Jupiter conduct heat and electricity very well, in a metal-like fashion (they do not do this under Earth-like condition). Inside Jupiter, electrons from hydrogen molecules move freely from molecule to molecule (like the electrons of a metal); this is what allows the electrical and heat conductivity. Core: At the center of the planet is a molten rock core which is many times bigger and more massive than the entire Earth. It is 20,000 °C, about three times hotter than the Earth's core.
Internal Heat: Jupiter is a heat source; it radiates 1.6 times a much energy as it receives from the Sun. This energy is produced by Jupiter's shrinking due to gravity, and this produces heat. Also, it is still cooling down, losing its initial energy (the energy it received as the Solar System formed).
Does Jupiter produce energy by nuclear fusion -- NO. Jupiter, the biggest of the gas giants, is too small to produce a core temperature that is hot enough to undergo fusion (you need about 3 million degrees to start the fusion of hydrogen). You'd need a body that was many times the mass of Jupiter to get nuclear fusion (the theoretical limit is about 8 percent of the mass of the Sun).

Magnetic Field: Jupiter has a very strong magnetic field. The magnetic field is probably generated as the planet spins its deep metallic-hydrogen layer with electrical currents .

Jupiter's magnetic field (Jupiter's magnetosphere) extends for millions of miles into space. The tail of this magnetic field (which is extended by the solar wind), extends into the orbit of Saturn! A tremendous amount of charged particles are trapped within this magnetosphere, especially in the inner parts of this field. This makes Jupiter the most deadly radiation environment of any of the planets.

THE GREAT RED SPOT
Jupiter's Great Red Spot is a huge, long-lasting storm in the atmosphere of the Southern Hemisphere of Jupiter. It is an anti-cyclonic (high pressure) storm, much like a gargantuan hurricane. Its color is actually pink to orange.

This whirlwind varies in size and color from year to year. It is about 17,000 miles (28,000 km) long and 9,000 miles (14,000 km) wide; it is the biggest storm in this solar system. It is so big that the three Earths would fit in it with room to spare.

Jupiter's Great Red Spot was discovered in 1664 by Robert Hooke. Part of the reason it lasts so long in comparison with Earth storms (other than the huge difference in scale and the existence of an internal heat source on Jupiter) is that this storm never goes over land; on Earth, hurricanes loses most of their energy and die when they stray over land.

The smaller white spots are also giant storms. The colors we see are the result of chemical reactions occurring in the atmosphere.
BELTS AND ZONES

Jupiter's gaseous surface is very windy, with wind speeds exceeding 400 mph (620 kph) in wide bands of latitude. Winds in adjacent bands blow in opposite directions. The light colored bands we see are called zones; the dark ones are called belts.

The differences in colors are caused by slight differences in chemical composition and temperature, but the reasons are mostly unknown. The color of a region depends on its altitude (height).

Measurements performed by NASA's Pioneer spacecraft in 1973 determined that the dark belts are warmer than the light zones. This probably means that the dark (warmer) belts are at lower altitudes than the light (colder) zones. 





JUPITER'S RINGS
Jupiter has faint, dark, narrow rings composed of tiny rock fragments and dust. They do not contain ice, like Saturn's rings. Jupiter's rings are continuously losing material and being resupplied with new dust from micrometeors hitting Jupiter's four inner moons (Metis, Adrastea, Amalthea, and Thebe).

Jupiter's rings were discovered by NASA's Voyager 1 in 1980. The rings were investigated further when Voyager 2 flew by Jupiter.

The rings have an albedo of 0.05; they do not reflect very much of the sunlight that they receive.


This photo of Jupiter's ring was taken by NASA's Galileo spacecraft in 1996.
Jupiter's ring is in three sections: the Main ring, a Halo that orbits closer to Jupiter, and a very wide Gossamer ring that extends far from Jupiter.

   •The Halo ring is a faint, wide ring that has the shape of a doughnut. It is about 22,800 wide and is about 20,000 km thick. This ring starts at 100,000 km from the center of Jupiter; the outer edge of the Halo merges into the Main ring.

   •The Main ring is 6,400 km wide an less than 30 km thick. This very thin ring has a mass of about 10 ¹³ kg. The ring is about 7,000 km wide; it starts at 122,800 km from the center of Jupiter and has an abrupt outer edge 129,130 km from the center of Jupiter. Two small moons, Adrastea and Metis, orbit within the Main ring; they may be the source of the dust in this ring.

   •The Gossamer ring is a very faint and very wide ring. It consists of two rings, one embedded within the other. It is composed of very tiny particles, the microscopic debris from the moons, Amalthea and Thebe. The Gossamer ring starts at 129,000 km from the center of Jupiter and extends beyond the orbit of the moon Amalthea.
 
JUPITER'S MOONS
Jupiter has four large moons and dozens of smaller ones (there are about 60 known moons so far). Galileo first discovered the four largest moons of Jupiter, Io, Europa, Ganymede, and Callisto in 1610, using a 20-power telescope; these moons are known as the Galilean moons.

The moons of Jupiter are (in order by their distance from Jupiter): Metis, Adrastea, Amalthea, Thebe, Io, Europa, Ganymede (the biggest), Callisto (the second biggest), Leda (the smallest), Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae, Sinope, and many newly-discovered moons that haven't been named yet.

METIS Metis is the closest moon to Jupiter. Metis is 25 miles (40 km) in diameter and orbits 79,500 miles (128,000 km) from Jupiter, within its main ring. Metis and the next moon, Adrastea, are probably the source of the dust in this ring. Metis has a mass of 9 x 1016kg. It orbits Jupiter in 0.294780 (Earth) days; this is faster than Jupiter rotates on its axis. Metis was discovered by Stephen Synnott (Voyager 2) in 1980.

ADRASTEA Adrastea is the second-closest moon to Jupiter. Adrastea is 12 miles (20 km) in diameter and orbits 80,000 miles (129,000 km) from Jupiter, within its main ring. Adrastea and the first moon, Metis, are probably the source of the dust in this ring. Adrastea has a mass of 1.91 x 1016kg. It orbits Jupiter in 0.29826 (Earth) days; this is faster than Jupiter rotates on its axis. Adrastea was discovered by D. Jewitt and E. Danielson (Voyager 2) in 1979.

AMALTHEA Amalthea is the third-closest moon to Jupiter and the reddest object in our solar system . Amalthea is 145 x 91 x 83 miles (232 x146 x134 km) in diameter and orbits 112,700 miles (181,300 km) from Jupiter, within the faint Gossamer ring. Amalthea and Thebe likely provide the dust for the Gossamer ring. Amalthea has a mass of 7.2 x 1021kg. It orbits Jupiter in 0.49817905 (Earth) days and is in synchronous rotation (always keeping the same side facing Jupiter). Amalthea gives off more heat than it receives from the Sun. Amalthea was discovered by Edward Emerson Barnard in 1892.

THEBE Thebe is the fourth-closest moon to Jupiter. Thebe is 68 x 56 miles (110 x 90 km) in diameter and orbits 138,000 miles (222,000 km) from Jupiter. Amalthea and Thebe likely provide the dust for the Gossamer ring. Thebe has a mass of 8 x 1017kg. It orbits Jupiter in 0.6745 day (Earth) days and is in synchronous rotation (always keeping the same side facing Jupiter). Thebe was discovered by Stephen Synnott (Voyager 1) in 1980.

THE GALILEAN MOONS

Two sulfurous eruptions on Io. Pillan Patera, a volcanic caldera at the left, spews sulfur 86 miles above the surface. IO Io is a large, rocky, volcanically active moon of Jupiter. Its volcanoes spew out molten sulfur, making Io a very colorful moon. It is the innermost of Jupiter's four large moons and the third largest. It has a diameter of 1,942 miles (3,636 km), very close in size to our moon. Io's mean distance from Jupiter is 220,000 miles (422,000 km). It has a mass of 8.93x1022 kg. It takes Io 1.77 days to orbit Jupiter. There is a doughnut-shaped plasma cloud around Jupiter near Io's orbit (known as the "Io plasma torus") This torus is caused by Jupiter's strong magnetic field, which strips ions from Io as it rotates; Io acts like an electrical generator. Io was discovered by Galileo and Marius (independently) in 1610. Ole Romer (1644-1710) was a Danish astronomer who, in 1675-1676, was the first person to demonstrate that the speed of light is finite. Romer did this by observing eclipses of Jupiter's moon Io as Jupiter's distance from Earth varied through the year. He noticed that the observed period of Io's orbit differed by about 20 minutes; he concluded that this difference was due to the extra distance that the light had to travel to Earth. His calculations put the speed of light at about 225,000 kilometers per second (it is really a bit faster, at 299,792 kilometers per second).

EUROPA Europa is a large, dense, icy moon of Jupiter. Europa is the smoothest object in our Solar System. Its surface is covered with long, crisscrossing trackways (but few craters) on water ice. Frozen sulfuric acid has been found on its surface. Europa's diameter is less than 2,000 miles (3,138 km), smaller than the Earth's moon. It takes Europa 3.55 days to orbit Jupiter (in a synchronous orbit). Its mean distance from Jupiter is about 420,000 miles (670,900 km). Its mass is 4.80x1022 kg. It was discovered by Galileo and S. Marius (independently) in 1610.

GANYMEDE Ganymede is the largest moon of Jupiter, a large, icy, outer moon that is scarred with impact craters and many parallel faults. It has a diameter of about 3,400 miles (5,268 km) and orbits Jupiter at a mean distance of 664,000 miles (1,070,000 km). It has a magnetic field and probably has a molten iron core. It takes Ganymede 171.75 hours (7.15 Earth days) to orbit Jupiter. Its mass is 1.48x1023 kg. It was discovered by Galileo and S. Marius (independently) in 1610. Ganymede is the largest moon in the solar system; it is also larger than the planets Mercury and Pluto.

CALLISTO Callisto is a large, icy, dark-colored, low-density outer moon of Jupiter that is scarred with impact craters and ejecta. It has a diameter of about 3,000 miles (4800 km), the second-largest moon of Jupiter; it is roughly the size of Mercury. Callisto has the largest-known impact crater in the Solar System, Valhalla, which has a bright patch 600 km across and rings that go out to almost 3000 km. Callisto orbits Jupiter at a mean distance of 1,170,000 miles (1,883,000 km). Its mass is 1.08x1023 kg. It takes Callisto 400.8 hours = 16.7 days to orbit Jupiter (in a synchronous orbit). Callisto was discovered by Galileo and S. Marius (independently) in 1610.

LEDA Leda is Jupiter's ninth and smallest moon. Leda is 9.9 miles (16 km km) in diameter and orbits at an average of 6,900,000 miles (11,094,000 km) from Jupiter. Leda has a mass of 5.68 x 1015kg. It orbits Jupiter in 238.72 (Earth) days. Very little is known about Leda. Leda was discovered by Charles Kowal in 1974.

HIMALIA Himalia is Jupiter's tenth moon. Himalia is 110 miles (170 km) in diameter and orbits 7,000,000 miles (11,480,000 km) from Jupiter. Himalia has a mass of 9.5 x 1018kg. It orbits Jupiter in 250.5662 (Earth) days. Very little is known about Himalia. Himalia was discovered by C. Perrine in 1904.

LYSITHEA Lysithea is Jupiter's eleventh moon. Lysithea is 15 miles (24 km) in diameter and orbits 7,200,000 miles (11,720,000 km) from Jupiter. Lysithea has a mass of 8 x 1016kg. It orbits Jupiter in 259.22 (Earth) days. Very little is known about Lysithea. Lysithea was discovered by S. Nicholson in 1938.

ELARA Elara is Jupiter's twelfth moon. Elara is 50 miles (80 km) in diameter and orbits 7,250,000 miles (11,737,000 km) from Jupiter. Elara has a mass of 8 x 1017kg. It orbits Jupiter in 259.6528 (Earth) days. Very little is known about Elara. Elara was discovered by C. Perrine in 1905.

ANANKE Ananke is Jupiter's thirteenth moon. Ananke is 12.5 miles (20 km) in diameter and orbits 13,100,000 miles (21,200,000 km) from Jupiter. Ananke has a mass of 4 x 1016kg. It orbits Jupiter in 631 (Earth) days and is in a retrograde orbit (orbiting opposite to the direction of Jupiter). Very little is known about Ananke. Ananke was discovered by S. Nicholson in 1951.

CARME Carme is Jupiter's fourteenth moon. Carme is 18.5 miles (30 km) in diameter and orbits 13,800,000 miles (22,600,000 km) from Jupiter. Carme has a mass of 9 x 1016kg. It orbits Jupiter in 692 (Earth) days and is in a retrograde orbit (orbiting opposite to the direction of Jupiter). Very little is known about Carme. Carme was discovered by S. Nicholson in 1938.

PASIPHAE Pasiphae is Jupiter's fifteenth moon. Pasiphae is 22 miles (36 km) in diameter and orbits 14,600,000 miles (23,500,000 km) from Jupiter. Pasiphae has a mass of 2 x 1023kg. It orbits Jupiter in 735 (Earth) days and is in a retrograde orbit (orbiting opposite to the direction of Jupiter). Very little is known about Pasiphae. Pasiphae was discovered by P. Melotte in 1908.

SINOPE Sinope is Jupiter's sixteenth moon. Sinope is 17.5 miles (28 km) in diameter and orbits 14,700,000 miles (23,700,000 km) from Jupiter. Sinope has a mass of 8 x 1016kg. It orbits Jupiter in 758 (Earth) days and is in a retrograde orbit (orbiting opposite to the direction of Jupiter). Very little is known about Sinope. Sinope was discovered by S. Nicholson in 1914.

S/1999 J 1 (a provisional name) The seventeenth and outermost moon; S/1999 J 1 is the smallest-known moon orbiting a major planet. This moon is 3 miles (5 km) in diameter and has an irregular orbit roughly 15 million miles (24 million km) from Jupiter. It orbits Jupiter in 774 (Earth) days and is in a retrograde orbit (orbiting opposite to the direction of Jupiter). It was discovered by Robert S. McMillan et al (at the Spacewatch program at the University of Arizona ) in 2000.

Statistics on Jupiter

FACTS-FROM-UNIVERSE

Statistics on Jupiter

Distance from Sun	5.203 AU 480,000,000 miles 778,330,000 km
Diameter	88,700 miles 142,800 km
Mass	1.9 x 1027 kg About 318 times the mass of the Earth
Number of Moons	16
1 Jovian Day (Period of Rotation)	9.8 Earth hours 0.40 Earth days
1 Jovian Year (Period of Revolution Around the Sun)	11.86 Earth years
Escape Velocity	59,500 m/sec
Mean Surface Temperature	-244 °F -153 °C 120 K
Albedo (reflectivity)	0.44
Density	1,314 kg per m3
Oblique Axis (Tilt of the Axis)	3.08°
Orbital Inclination	1.3°
Orbital Eccentricity (Deviation from circular)	0.048
Perihelion (Closest to sun)	740,900,000 km
Aphelion (Farthest from sun)	815,700,000 km