Io (moon)

innermost of the 4 Galilean moons of Jupiter

Io is a moon of the planet Jupiter. It is Jupiter's third biggest moon with a diameter of 3642 km, slightly bigger than Earth's moon.

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 has about 400 active volcanos. It is the most volcanically active body in the Solar System. Volcanoes erupt massive volumes of silicate lava, sulphur and sulphur dioxide. This constantly changes Io's appearance.

The picture of Jupiter's moon Io was produced by combining the best images from both the Voyager 1 and Galileo Missions. Superbly detailed Voyager 1 images cover longitudes from 240 W to 40 W and the nearby southern latitudes.

Io has highest density of any moon, the strongest surface gravity of any moon, and the lowest amount of water of any known astronomical object in the Solar System.

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. Io is a prolate spheroid, pulled out of round by tidal stress from Jupiter’s gravity.

References change

  1. EYE-oh, or as Greek: Ἰώ
  2. Thomas, P. C.; et al. (1998). "The Shape of Io from Galileo Limb Measurements". Icarus. 135 (1): 175–180. Bibcode:1998Icar..135..175T. 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. Bibcode:2004Icar..169..127R. doi:10.1016/j.icarus.2003.12.021.