Backlit views (left pair) show a giant volcanic plume as a bulge on
the crescent edge of Jupiter’s moon Io, and more fully lit views (right
pair) reveal rings where sulfur-rich plume material has fallen back to
the ground, in images captured by NASA’s Galileo spacecraft in early
August 2001.
Io is the most volcanically active world known. Galileo and NASA’s
Voyager and Cassini spacecraft have caught several of Io’s
volcanoes in action lofting plumes of gas and particles high above the
large moon’s surface. However, none of the plumes seen previously has
climbed as high as the one evidenced in three of these pictures.
During its Aug. 6, 2001, close encounter with Io, Galileo flew right
through a space where a plume from the Tvashtar volcano near Io’s north
pole had been active
when Galileo and Saturn-bound Cassini imaged Io seven months
earlier. To see if the Tvashtar plume was still active in August,
scientists used Galileo‘s camera to acquire images when the spacecraft
was nearly on the opposite side of Io from the Sun, so that Io appears
as a backlit crescent.
Tvashtar’s plume did not show up, but another one did, rising from a
previously undiscovered and still unnamed volcano about 600 kilometers
(370 miles) south of Tvashtar. The left two images are color coded to
reveal the faint outer plume. The bright inner plume rises about 150
kilometers (90 miles) high, and the top of the faint outer plume can be
detected at 500 kilometers (310 miles) above the surface, making this the
largest plume ever detected on Io. A portion of the plume with intermediate
brightness extends north of the eruption’s source vent. (The vertical lines,
bright spots and short streaks in these two images are noise.)
One of the more fully illuminated color images of Io (second image
from right) reveals a bull’s-eye ring of new dark and light materials
marking the eruption site. No obvious volcanic center had previously
been seen at this location, 41 degrees north latitude and 133 degrees
west longitude. The bright material of the new plume deposit overlies
the red-ring plume deposit encircling the Tvashtar volcano at 63 degees
north, 123 degrees west.
Tvashtar’s ring deposit was first seen in
Galileo images taken in late December 2000.
Another new full-disc color image of Io (far right) reveals yet another
new plume deposit near Io’s north pole, encircling the Dazhbog Patera
volcanic site. This red ring has a diameter of about 1,000 kilometers
(620 miles), suggesting a plume height of about 300 kilometers (190 miles).
This plume deposit was not present in January 2001, so it is evidence of
a new eruption.
Infrared imagery from Galileo or Earth-based telescopes has
detected intense hot spots at the sites of all three of these giant plumes.
Giant polar plumes represent a class of eruption seen by the Voyager
spacecraft in 1979, but not during Galileo‘s first five years of
orbiting Jupiter. Voyager was unable to measure temperatures or
other properties of these eruptions, so scientists are pleased Galileo
has survived long enough to do so. Galileo reached Jupiter in late
1995. Its original two-year orbital mission has been extended three times
to take advantage of the spacecraft’s continuing capability to return
valuable scientific information about the Jupiter system.
Image produced by: Alfred McEwen,
Planetary Image Research Lab. (PIRL)
, Lunar and Planetary Lab. (LPL),
University of Arizona
The Jet Propulsion Laboratory, a division of the California Institute of
Technology in Pasadena, manages the Galileo mission for NASA’s
Office of Space Science, Washington, D.C. Additional information about
Galileo and its discoveries is available on the Galileo mission
home page at
http://galileo.jpl.nasa.gov/.
Background information and educational context for the images can be found at
http://galileo.jpl.nasa.gov/images/io/ioimages.html.
