Io (moon)

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Io highest resolution true color.jpg
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. The yellower regions contain a higher proportion of sulfur
Discovered byGalileo Galilei
Discovery dateJanuary 7, 1610
Other namesJupiter I
Shortest distance from what it orbits420,000 km (0.002 807 AU)
Longest distance from what it orbits423,400 km (0.002 830 AU)
Avgdistance from the center of its orbital path421,700 km (0.002 819 AU)
How long it takes to complete an orbit1.769 137 786 d (152 853.504 7 s, 42 h)
Average speed17.334 km/s
Angle above the reference plane
2.21° (to the ecliptic)
0.05° (to Jupiter's equator)
What it orbitsJupiter
Size and other qualities
Measurements3,660.0 × 3,637.4 × 3,630.6 km[1]
Average radius1,821.3 km (0.286 Earths)[1]
Surface area41,910,000 km2 (0.082 Earths)
Volume2.53×1010 km3 (0.023 Earths)
Mass8.9319×1022 kg (0.015 Earths)
Average density3.528 g/cm3
Surface gravity1.796 m/s2 (0.183 g)
Escape velocity2.558 km/s
Rotation periodsynchronous
Turning speed271 km/h
How much light it reflects0.63 ± 0.02[2]
Surface temp. Min. Avg. Max.
Surface 130 K 200 K
Seeming brightness
("apparent magnitude")
5.02 (opposition)[3]
Make-up90% 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. 1.0 1.1 Thomas, P. C.; et al. (1998). "The Shape of Io from Galileo Limb Measurements". Icarus 135 (1): 175–180. doi:10.1006/icar.1998.5987. 
  2. Yeomans, Donald K. (July 13, 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics. Retrieved 2007-11-05.
  3. "Classic Satellites of the Solar System". Observatorio ARVAL. Retrieved 2007-09-28.