Io (moon)

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True-color image taken by the Galileo orbiter
Galileo spacecraft true-color image of Io. The dark spot just left of the center is the erupting volcano Prometheus. The whitish plains on either side of it are coated with volcanically deposited sulfur dioxide frost, whereas the yellower regions contain a higher proportion of sulfur.
Discovered byGalileo Galilei
Discovery date8 January 1610
Jupiter I
Orbital characteristics
Periapsis420000 km (0.002807 AU)
Apoapsis423400 km (0.002830 AU)
Mean orbit radius
421700 km (0.002819 AU)
1.769137786 d (152853.5047 s, 42.45930686 h)
17.334 km/s
Inclination0.05° (to Jupiter's equator)
2.213° (to the ecliptic)
Satellite ofJupiter
Physical characteristics
Dimensions3,660.0 × 3,637.4 × 3,630.6 km[2]
Mean radius
1821.6±0.5 km (0.286 Earths)[3]
41910000 km2 (0.082 Earths)
Volume2.53×1010 km3 (0.023 Earths)
Mass(8.931938±0.000018)×1022 kg (0.015 Earths)[3]
Mean density
3.528±0.006 g/cm3[3]
1.796 m/s2 (0.183 g)
0.3755±0.0045[4] (estimate)
2.558 km/s
Equatorial rotation velocity
271 km/h
Surface temp. min mean max
Surface 90 K 110 K 130 K[6]
5.02 (opposition)[5]
Surface pressure
5 to 40 nbar
Composition by volume90% sulfur dioxide

Io is a moon of the planet Jupiter. It is Jupiter's third biggest moon with a diameter of 3642 km, being slightly bigger than Earth's moon. Io has about 400 active volcanos.

Io is the most volcanically active body in the Solar System. Volcanoes erupt massive volumes of silicate lava, sulphur and sulphur dioxide, constantly changing Io's appearance. This new basemap of Jupiter's moon Io was produced by combining the best images from both the Voyager 1 and Galileo Missions. Although the subjovian hemisphere of Io was poorly seen by Galileo, superbly detailed Voyager 1 images cover longitudes from 240 W to 40 W and the nearby southern latitudes.

Due to the same tidal locking that makes the Moon have the same side always facing Earth, Io always has the same side facing Jupiter. Unlike most celestial bodies, Io is a prolate spheroid, pulled out of round by tidal stress from Jupiter’s gravity.

References[change | change source]

  1. EYE-oh, or as Greek: Ἰώ
  2. Thomas, P. C. (1998). "The Shape of Io from Galileo Limb Measurements". Icarus 135 (1): 175–180. doi:10.1006/icar.1998.5987. 
  3. 3.0 3.1 3.2 3.3 Yeomans, Donald K. (13 July 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics.
  4. Showman, Adam P.; Malhotra, Renu (October 1999). "The Galilean Satellites". Science 286 (5437): 77–84. doi:10.1126/science.286.5437.77. PMID 10506564. 
  5. "Classic Satellites of the Solar System". Observatorio ARVAL. Archived from the original on 25 August 2011. Retrieved 28 September 2007.
  6. Rathbun, J. A.; Spencer, J.R.; Tamppari, L.K.; Martin, T.Z.; Barnard, L.; Travis, L.D. (2004). "Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument". Icarus 169 (1): 127–139. doi:10.1016/j.icarus.2003.12.021.