Planets & Moons








Planetary Attributes

Mass 1.9885e30 kg
Mean radius 696,392 km
Volume 1.41e18 km³
Average density 1.408 g/cm³
Equatorial surface gravity 274 m/s² 28 g
Rotation period 25.05 day
Escape velocity (surface) 617.7 km/s
Planets Eight

The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.

Mercury ☿
Mass 3.3022e23 kg
Mean radius 2,439.7 km
Volume 6.083e10 km³
Aphelion 69,816,900 km
Perihelion 46,001,200 km
Orbital period 87.969 days
Equatorial surface gravity 3.7 m/s² 0.38 g
Rotation period 58.646 day
Escape velocity (surface) 4.25 km/s
Satellites None

Mercury is the innermost and smallest planet in the Solar System. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits. The perihelion of Mercury's orbit precesses around the Sun at an excess of 43 arcseconds per century; a phenomenon that was explained in the 20th century by Albert Einstein's General Theory of Relativity. Mercury is bright when viewed from Earth, ranging from −2.3 to 5.7 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun is only 28.3°. Since Mercury is normally lost in the glare of the Sun, unless there is a solar eclipse it can be viewed from Earth's Northern Hemisphere only in morning or evening twilight, while its extreme elongations occur in Declinations south of the celestial equator, such that it can be seen at favorable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky.

Venus ♀
Mass 4.8675e24 kg
Mean radius 6,052 km
Volume 9.2843e11 km³
Aphelion 108,939,000 km
Perihelion 107,477,000 km
Orbital period 224.701 days
Equatorial surface gravity 8.87 m/s² 0.904 g
Rotation period 243.025 day
Escape velocity (surface) 10.36 km/s
Satellites None

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun, and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth, or roughly the pressure found 900 m underwater on Earth. Venus is by far the hottest planet in the Solar System, with a mean surface temperature of 462°C, even though Mercury is closer to the Sun. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have had water oceans in the past, but these would have vaporized as the temperature rose due to a runaway greenhouse effect. The water has probably photodissociated, and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Venus's surface is a dry desertscape interspersed with slab-like rocks and is periodically resurfaced by volcanism.

Earth ⊕
Mass 5.97e24 kg
Mean radius 6,371 km, 6.37e6 meters
Earth GM = 3.98e14
Volume 1.083e12 km³
Aphelion 152100000 km
Perihelion 147095000 km
Orbital period 365.256363004 days
Equatorial surface gravity 9.8 m/s² 1.0 g
Rotation period 0.99726968 day
Escape velocity (surface) 11.186 km/s
Satellites: one, moon

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest of the four terrestrial planets.


Mass 7.342e23 kg
Mean radius 1737 km
Volume 2.1958e10 km³
Apogee 405400 km
Perigee 362600 km
Orbital period 27.321661 days. time taken for the moon to make one complete orbit about the earth, referenced to the stars.
Synodic period 29.530 days. time that it takes for the moon to reappear at the same point in relation to a fixed point on the earth.
Equatorial surface gravity 1.62 m/s² 0.165 g
the Orbital period is 27.321 days
Rotation period 27.321661 day
Escape velocity (surface) 2.38 km/s
Satellites None

The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). The Moon is after Jupiter's satellite Io the second-densest satellite in the Solar System among those whose densities are known.

The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia.

Mars ♂
Mass 6.4171e23 kg
Mean radius 3389 km
Volume 1.6318e11 km³
Aphelion 249200000 km
Perihelion 206700000 km
Orbital period 686.971 days
Equatorial surface gravity 3.72076 m/s² 0.3794 g
Rotation period 1.025957 day
Escape velocity (surface) 5.027 km/s
Satellites: Phobos & Deimos

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, and is often referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.

The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan.


Mass 1.0659e16 kg
Mean radius 11.2667 km
Volume 5783.61 km³
Apoapsis 9517.58 km
Periapsis 9234.42 km
Orbital period 0.31891 days
Equatorial surface gravity 0.0057 m/s² 581.4 µg
Rotation period Synchronous
Escape velocity (surface) 11.39 m/s

Phobos (systematic designation: Mars I) is the innermost and larger of the two natural satellites of Mars, the other being Deimos. Both moons were discovered in 1877 by American astronomer Asaph Hall.

Phobos is a small, irregularly shaped object with a mean radius of 11 km and is seven times as massive as the outer moon, Deimos. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite (Venus) and the personification of fear (cf. phobia).


Mass 1.4762e15 kg
Mean radius 6.2 km
Volume 999.78 km³
Apoapsis 23470 km
Periapsis 23455 km
Orbital period 1.263 days
Equatorial surface gravity 0.003 m/s² 306 µg
Rotation period Synchronous
Escape velocity (surface) 5.556 m/s

Deimos (systematic designation: Mars II) is the smaller and outermost of the two natural satellites of the planet Mars, the other being Phobos. Deimos has a mean radius of 6.2 km and takes 30.3 hours to orbit Mars. Deimos is 23,460 km from Mars, much further than Mars's other moon, Phobos. It is named for Deimos who in Greek mythology is the twin brother of Phobos, and personifies terror.

Deimos was discovered by Asaph Hall, III at the United States Naval Observatory in Washington, D.C. on 12 August 1877, at about 07:48 UTC. Hall also discovered Phobos on 18 August 1877, at about 09:14 GMT, after deliberately searching for Martian moons.

Jupiter ♃
Mass 1.8986e27 kg
Equatorial radius 71,492 km
Polar radius 66,854 km
Volume 1.43128e15 km³
Aphelion 816,520,800 km
Perihelion 740,573,600 km
Orbital period 4,332 days
Equatorial surface gravity 24.79 m/s² 2.528 g
Rotation period 9.925 hours
Escape velocity (surface) 59.5 km/s
Satellites 79

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Together, these four planets are sometimes referred to as the Jovian or outer planets.

It is primarily composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules. It may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rapid rotation, the planet's shape is that of an oblate spheroid (it has a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope.


Mass 1.4819e23 kg
Mean radius 2634 km
Volume 1.4819e23 km³
Apoapsis 1071600 km
Periapsis 1069200 km
Orbital period 7.154 days
Equatorial surface gravity 1.428 m/s² 0.146 g
Rotation period synchronous
Escape velocity (surface) 2.741 km/s

Ganymede (Jupiter III) is the largest and most massive moon of Jupiter and in the Solar System. The ninth largest object in the Solar System, it is the largest without a substantial atmosphere. It has a diameter of 5,268 km and is 8% larger than the planet Mercury, although only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. Outward from Jupiter, it is the seventh satellite and the third of the Galilean moons, the first group of objects discovered orbiting another planet. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.


Mass 4.800e22 kg
Mean radius 1561 km
Volume 1.593e10 km³
Apoapsis 676938 km
Periapsis 664862 km
Orbital period 3.551 days
Equatorial surface gravity 1.314 m/s² 0.134 g
Rotation period synchronous
Escape velocity (surface) 2.025 km/s

Europa (Jupiter II) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa, the Phoenician mother of King Minos of Crete and lover of Zeus.

Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a very thin atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, but craters are relatively few. In addition to Earth-bound telescope observations, Europa has been examined by a succession of space probe flybys, the first occurring in the early 1970s.


Mass 8.9319e22 kg
Mean radius 1821.6 km
Volume 2.53e10 km³
Apoapsis 423400 km
Periapsis 420000 km
Orbital period 1.7691 days
Equatorial surface gravity 1.796 m/s² 0.183 g
Rotation period synchronous
Escape velocity (surface) 2.558 km/s

Io (Jupiter I) is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus' lovers.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites—Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km above the surface. Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of Io's silicate crust. Some of these peaks are taller than Mount Everest. Unlike most satellites in the outer Solar System, which are mostly composed of water ice, Io is primarily composed of silicate rock surrounding a molten iron or iron-sulfide core. Most of Io's surface is composed of extensive plains coated with sulfur and sulfur-dioxide frost.


Mass 1.0759e23 kg
Mean radius 2410 km
Volume 5.9e10 km³
Apoapsis 1897000 km
Periapsis 1869000 km
Orbital period 16.6890 days
Equatorial surface gravity 1.235 m/s² 0.126 g
Rotation period synchronous
Escape velocity (surface) 2.440 km/s

Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. It is not in an orbital resonance like the three other Galilean satellites—Io, Europa, and Ganymede—and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward; Jupiter appears to stand nearly still in Callisto's sky. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt.

Saturn ♄
Mass 5.6834e26 kg
Mean radius 58,232 km
Volume 8.2713e14 km³
Aphelion 1,514.50e6 km
Perihelion 1,352.55e6 km
Orbital period 10,759.22 days
Equatorial surface gravity 10.44 m/s² 1.065 g
Rotation period 10h 33m
Escape velocity (surface) 35.5 km/s
Satellites 62 plus rings

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. It has only one-eighth the average density of Earth, but with its larger volume Saturn is over 95 times more massive. Saturn is named after the Roman god of agriculture; its astronomical symbol (♄) represents the god's sickle.


Mass 1.345e23 kg
Mean radius 2574 km
Volume 7.16e10 km³
Apoapsis 1257060 km
Periapsis 1186680 km
Orbital period 15.945 days
Equatorial surface gravity 1.352 m/s² 0.14 g
Rotation period Synchronous
Escape velocity (surface) 2.639 km/s

Titan is the largest moon of Saturn. It is the only moon known to have a dense atmosphere, and the only object in space, other than Earth, where clear evidence of stable bodies of surface liquid have been found.

Titan is the sixth gravitationally rounded moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the smallest planet, Mercury, but only 40% as massive.

Uranus ♅
Mass 8.6810e25 kg
Mean radius 25,362 km
Volume 6.833e13 km³
Aphelion 3008 Gm
Perihelion 2742 Gm
Orbital period 30,688.5 days
Equatorial surface gravity 8.69 m/s² 0.886 g
Rotation period 0.71833 d day
Escape velocity (surface) 21.3 km/s
Satellites 27

Uranus (from the Latin name "Ūranus" for the Greek god Οὐρανός) is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus' atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K, and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.

Neptune ♆
Mass 1.02413e26 kg
Mean radius 24,622 km
Volume 6.254e13 km³
Aphelion 4.54 billion km
Perihelion 4.46 billion km
Orbital period 60,182 days
Equatorial surface gravity 11.15 m/s² 1.14 g
Rotation period 0.6713 day
Escape velocity (surface) 23.5 km/s
Satellites 14

Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of 4.5 billion km. It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune's trident.

Mass 1.303e22 kg
Mean radius 1,188.3 km
Volume 7.057e9 km³
Aphelion 7.37593 billion km
Perihelion 4.43682 billion km
Orbital period 90,560 days
Equatorial surface gravity 0.620 m/s² 0.063 g
Rotation period 6.387230 day
Escape velocity (surface) 1.212 km/s
Satellites 5

Pluto (minor planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered and is the largest known plutoid (or ice dwarf).

Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt. In 2005, Eris, a dwarf planet in the scattered disc which is 27% more massive than Pluto, was discovered. This led the International Astronomical Union (IAU) to define the term "planet" formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet.

Mass 1.66e22 kg
Mean radius 1163 km
Volume 6.59e9 km³
Aphelion 14.602 billion km
Perihelion 5.723 billion km
Orbital period 203,830 days
Equatorial surface gravity 0.82 m/s² 0.083 g
Rotation period 25.9 day
Escape velocity (surface) 1.38 km/s
Satellites 1

Eris (minor-planet designation 136199 Eris) is the most massive and second-largest (by volume) dwarf planet (and plutoid) in the known Solar System. Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its discovery was verified later that year. In September 2006 it was named after Eris, the Greek goddess of strife and discord. Eris is the ninth most massive object directly orbiting the Sun, and the 16th most massive overall, because seven moons are more massive than all known dwarf planets. It is also the largest which has not yet been visited by a spacecraft. Eris was measured to be 2,326 kilometers in diameter. Eris's mass is about 0.27% of the Earth mass, about 27% more than dwarf planet Pluto, although Pluto is slightly larger by volume.

Planetary Attributes

    Name   Equatorial  Mass   Semi-     Orbital  Inclination  Orbital  Rotation  Con-    Axial  Rings  Atmosphere
            diameter          major     period    to Sun's    eccen-    period   firmed   tilt
            (note 1) (note 1) axis(AU)  (years)  equator (°)  tricity   (days)   moons    (°)

    Sun     109.3     333000                                             25.05
1.  Mercury   0.382    0.06    0.39      0.24       3.38       0.206     58.64     0      0.04    no    minimal
2.  Venus     0.949    0.82    0.72      0.62       3.86       0.007   −243.02     0    177.36    no    CO₂, N₂
3.  Earth     1.00     1.00    1.00      1.00       7.25       0.017      1.00     1     23.44    no    N₂, O₂, Ar
4.  Mars      0.532    0.11    1.52      1.88       5.65       0.093      1.03     2     25.19    no    CO₂, N₂, Ar
5.  Jupiter  11.209   317.8    5.20     11.86       6.09       0.048      0.41    79      3.13   yes    H₂, He
6.  Saturn    9.449    95.2    9.54     29.46       5.51       0.054      0.43    62     26.73   yes    H₂, He
7.  Uranus    4.007    14.6   19.22     84.01       6.48       0.047     −0.72    27     97.77   yes    H₂, He, CH₄
8.  Neptune   3.883    17.2   30.06    164.8        6.43       0.009      0.67    14     28.32   yes    H₂, He, CH₄
    Pluto     0.187   0.0022  39.48    248.0       11.88       0.249      6.39     5    122.53    no    N₂, CH₄, CO
    Eris      0.182   0.0027  67.78    558.0       44.04       0.441      1.08     1     44       no    CH₄

Note 1: Earth = 1


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