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Oh, Io! Hubble views volatile moon

Io (left) casts a shadow as it passes over the surface of Jupiter

   3-D VRML


April 20, 1999
Web posted at: 2:44 p.m. EDT (1844 GMT)

(CNN) -- The Space Telescope Institute released stunning images Thursday of Jupiter's moon Io sweeping across the face of the giant planet, along with a closeup of the satellite spewing volcanic "snow."

The pictures of the planetary duo were released to commemorate the ninth anniversary of the Hubble telescope's launch on April 24, 1990. All of these images were taken with the Wide Field and Planetary Camera 2.

Three overlapping snapshots show in crisp detail Io passing above Jupiter's turbulent clouds over a 1.8-hour time span. Io is roughly the size of Earth's moon.

In two of the images, Io appears to be skimming Jupiter's cloud tops, but it's actually 310,000 miles (500,000 km) away. Io races around Jupiter in 1.8 days, whereas the moon circles Earth every 28 days.

The conspicuous black spot on Jupiter is Io's shadow and is about the size of the moon itself (2,262 miles, or 3,640 km across).

The colors do not correspond closely to what the human eye would see because ultraviolet light is invisible.

In the close-up ultraviolet picture of Io, the mound rising from Io's surface is actually an eruption from Pillan, a volcano that had previously been dormant.

"Other observations have inferred sulfur dioxide 'snow' in Io's plumes, but this image offers direct observational evidence for sulfur dioxide 'snow' in an Io plume," said John R. Spencer of Lowell Observatory in Flagstaff, Arizona.

Scientists will get a closer look at Io later this year during a pair of close flybys to be performed by NASA's Galileo spacecraft, which has been orbiting Jupiter and its moons for nearly 3 1/2 years.

The first Galileo flyby is scheduled for October 10 at an altitude of 379 miles (610 km), and the other will take place November 25, when the spacecraft passes only 186 miles (300 km) above Io's fiery surface.

If the spacecraft survives this daring journey into the intense Jovian radiation environment near Io, it will send back images with dramatically higher resolution than any obtained before, according to mission scientists.

Hubble views aging stars inside brilliant cluster
April 2, 1999
Hubble images reveal dynamic seasons on Uranus
March 30, 1999
'Closer to God'
January 26, 1999

Space Telescope Science Institute
   • The Next Generation Space Telescope: Space Telescope Science Institute
Galileo Project Information
Galileo (JPL)
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