http://www.c3.lanl.gov/~cjhamil/SolarSystem/io.html (Einblicke ins Internet, 10/1995)Jupiter I
Io [EYE-oh] can be classified as one of the most unusual moons in our solar system. Active volcanism on Io was the greatest unexpected discovery at Jupiter. It was the first time active volcanoes had been seen on another body in the solar system. The Voyagers observed the eruption of nine volcanoes on Io altogether. There is also evidence that other eruptions occurred between Voyager encounters. Plumes from the volcanoes extend to more than 300 kilometers (190 miles) above the surface with material being ejected at speeds up to a kilometer per second.
Io's volcanoes are apparently due to heating of the satellite by tidal pumping. Io is perturbed in its orbit by Europa and Ganymede, two other large satellites nearby, then pulled back again into its regular orbit by Jupiter. This tug-of-war results in tidal bulging as great as 100 meters (330 feet) on Io's surface.
The temperature on Io's surface is about -143° C (-230° F); however, a large hot spot associated with a volcanic feature measured about 17° C (60° F). Scientists believe the hot spot may be a lava lake, although the temperature indicates the surface is not molten. This feature is reminiscent of lava lakes on Earth.
Io is composed primarily of rocky material with very little iron. Io is located within an intense radiation belt of electrons and ions trapped in Jupiter's magnetic field. As the magnetosphere rotates with Jupiter, it sweeps past Io and strips away about 1,000 kilograms (1 ton) of material per second. The material forms a torus, a doughnut shaped cloud of ions that glow in the ultraviolet. The torus's heavy ions migrate outward, and their pressure inflates the jovian magnetosphere to more than twice its expected size. Some of the more energetic sulfur and oxygen ions fall along the magnetic field into the planet's atmosphere, resulting in auroras.
Io acts as an electrical generator as it moves through Jupiter's magnetic field, developing 400,000 volts across its diameter and generating an electric current of 3 million amperes that flows along the magnetic field to the planet's ionosphere.
Discovered by ................ Simon Marius & Galileo Galilei Date of discovery ...................................... 1610 Mass (kg) .......................................... 8.94e+22 Mass (Earth = 1) ................................. 1.4960e-02 Equatorial radius (km) ................................ 1,815 Equatorial radius (Earth = 1) .................... 2.8457e-01 Mean density (gm/cm^3) ................................. 3.55 Mean distance from Jupiter (km) ..................... 421,600 Rotational period (days) ........................... 1.769138 Orbital period (days) .............................. 1.769138 Mean orbital velocity (km/sec) ........................ 17.34 Orbital eccentricity .................................. 0.004 Orbital inclination ................................... 0.040° Escape velocity (km/sec) ............................... 2.56 Visual geometric albedo ................................ 0.61 Mean surface temperature ............................. -143°C Magnitude (Vo) ......................................... 5.02
Animations of Io
Io
(GIF, 192K)
Voyager 1
took this picture of Io on March 4, 1979. The brown, orange
areas are probably covered by sulphur of a mixture containing sulphur.
The light areas may be sulphur dioxide snow and the pock-marks are
mostly volcanic calderas
up to 200 km across. Mountainous regions
exist near both poles, with some features rising 8 km or more above
their surroundings.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
Hubble Resolves Volcanoes on Io
(GIF, 192K;
caption)
This image of Jupter and its satellite Io were taken on March 5, 1994.
Io is too small for ground-based telescopes to see the surface details.
Several of the volcanoes periodically are active because Io is heated
by tides raised by Jupiter's powerful gravity. The volcano Pele
appears as a dark spot surrounded by an irregular orange oval in the
lower part of the image. The orange material has been ejected from
the volcano and spread over a huge area. Though the volcano was first
discovered by Voyager, the distinctive orange color of the volcanic
deposits is a new discovery in these HST images. (Voyager missed it
because its cameras were not sensitive to the near-infrared
wavelengths where the color is apparent).
(Credit: John Spencer, Lowell Observatory; NASA)
Volcanic Plumes
(GIF, 27K)
Voyager 2
took this picture of Io on the evening of July 9, 1979,
from a range of 1.2 million kilometers. On the limb of Io are
two blue volcanic eruption plumes about 100 kilometers high.
These two plumes were first seen by voyager 1 in March 1979 and
are designated Plume 5 (upper) and Plume 6 (lower). They have
apparently been erupting for a period of at least four months and
probably longer. A total of six plumes have been seen by voyager
2, all of which were first seen by Voyager 1. The largest plume
viewed by Voyager 1, Plume 1, is no longer erupting. Plume 4 was
not viewed on the edge of Io's disc by Voyager 2 and therefore it
is not known whether or not it is still erupting.
(Courtesy NASA/JPL).
Loki Volcano
(GIF, 21K)
Voyager 1 took this picture of the Loki volcano on March 4, 1979. The
volcanic eruption can be seen on the limb of Io.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
Loki Patera
(GIF, 341K)
This is a close up view of the surface of Io in the northern hemisphere.
The central feature has been named Loki Patera. The large dark
area may be a lake of liquid sulfur with a raft of solid sulfur
inside.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
Haemus Mons
(GIF, 220K)
Haemus Mons is a mountain located near the south pole and in this image
near the terminator
of Io. Its base measures about 200 by 100 km.
Several mountain peaks are found on Io some measuring as high as 10 km
tall.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
Volcano Pele
(GIF, 358K)
The heart shaped feature in the center of this image was caused by
volcanic ejecta
thrown out of the eruptive Pele.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
Ra Patera
(GIF, 412K)
Ra Patera is a large shield volcano with multi colored flows. This image
shows at least a dozen dark flows originating from the central dark vent.
Some of these flows are 300 km in length.
(Credit: Calvin J. Hamilton, Los Alamos National Laboratory)
