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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 by||Galileo Galilei|
|Discovery time||January 7, 1610|
|Other names||Jupiter I|
|Shortest distance from what it orbits around||420,000 km (0.002 807 AU)|
|Longest distance from what it orbits around||423,400 km (0.002 830 AU)|
|Avg. distance from the center of its orbital path||421,700 km (0.002 819 AU)|
|How egg-shaped its orbit is
|How long it takes to complete an orbit||1.769 137 786 d (152 853.504 7 s, 42 h)|
|Average speed||17.334 km/s|
|Angle above the reference plane
2.21° (to the ecliptic)|
0.05° (to Jupiter's equator)
|What it orbits||Jupiter|
|Size and Other Qualities|
|Measures||3,660.0 × 3,637.4 × 3,630.6 km|
|Average distance from its center to its surface||1,821.3 km (0.286 Earths)|
|Area of its surface||41,910,000 km2 (0.082 Earths)|
|Volume inside it||2.53×1010 km3 (0.023 Earths)|
|Mass||8.9319×1022 kg (0.015 Earths)|
|Average density||3.528 g/cm3|
|Gravity at its surface||1.796 m/s2 (0.183 g)|
|Slowest speed able to escape into space
|How long it takes to turn around one time||synchronous|
|Turning speed||271 km/h|
|How much light it reflects||0.63 ± 0.02|
|Make up||90% sulfur dioxide|
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.
In the same way that the Moon always has the same side facing Earth, Io always has the same side facing Jupiter. The movie shows two speeded-up rotations of Io (a single rotation really takes 1.77 days), and begins with a view of the Jupiter-facing hemisphere. With rotation in an easterly direction, after two seconds the volcano Prometheus (on the equator) comes into view. The massive red deposit around Pele (seconds 5-10) is the most distinctive expression of volcanic activity on Io, and just to the north-west is the horse shoe-shaped Loki Patera, the most powerful volcano on Io.
- Thomas, P. C.; et al. (1998). "The Shape of Io from Galileo Limb Measurements". Icarus 135 (1): 175–180. .
- Yeomans, Donald K. (July 13, 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics. http://ssd.jpl.nasa.gov/?sat_phys_par. Retrieved 2007-11-05.
- "Classic Satellites of the Solar System". Observatorio ARVAL. http://www.oarval.org/ClasSaten.htm. Retrieved 2007-09-28.