Washington University in St. Louis
Researchers at Washington University in St. Louis studying chemical data
from the Hubble Space Telescope have determined the eruption conditions of
Jupiter's volcanically active satellite, Io, and concluded that the moon has
a differentiated mantle similar to that of Earth. Differentiation is the
process where various rock types are produced from a common magma.
The researchers, Mikhail Zolotov, Ph. D., senior research scientist in earth
and planetary sciences, and Bruce Fegley, Jr., Ph.D., professor of earth and
planetary sciences, were able to take the Hubble measurements and infer the
temperature of the magma and plume pressure of Pele, one of Io's most active
volcanoes.
This is the first time that scientists have used chemical data obtained from
a telescope to study present-day interior processes of a solar system body.
Surprisingly, the magma temperature inferred from the Hubble chemical data
corresponds to the temperatures deduced from infrared measurements taken by
the Galileo spacecraft orbiting Jupiter. The study shows that Earth orbit
observations can compete successfully with expensive planetary missions.
Zolotov and Fegley published their results in the Sept. 1, 2000 issue of
"Geophysical Research Letters." Their study was funded by NASA.
Io, one of the four major satellites of Jupiter, is approximately the same
size as our moon, but has tremendous volcanic activity occurring on its
surface.
From Earth's orbit, the Hubble Space Telescope took pictures and spectra of
the massive eruptions of Pele, one of the most active volcanoes of Io, with
plumes reaching over 1,300 feet high. Through the analysis of these spectra,
collaborators Melissa McGrath, Ph.D., of the Hubble Space Telescope
Institute, and John Spencer, Ph.D., of the Lowell Observatory, detected
gaseous sulfur species and sulfur oxides inside the plumes.
Zolotov and Fegley then used the relative abundances of those gases to
calculate the temperature and pressure inside the vent of Pele.
"The composition of the plume reflects the conditions in the vent through
relatively simple calculations," explains Zolotov. "By observing the
composition of the plume of quenched volcanic gas in the volcanic
atmosphere, we can determine the temperature, pressure and concentrations of
undetected species in the vent."
In addition, Zolotov and Fegley evaluated the oxidation state of the magma
and exsolved gases. They found that the abundances of sulfur oxides and
sulfur vapors suggest a lack of iron metal from Io's mantle.
"If there is no free iron metal in the mantle, intense oxidation and
differentiation in the internal structure of Io could have occurred in the
first half billion years, or billion years, early in the history of Io,"
says Zolotov.
For this differentiation process to occur, an oxidizing agent must be
present to remove all of the iron metal from the mantle. Water acted as an
oxidizing agent when the Earth differentiated its iron billions of years
ago.
"Io's mantle is about as oxidized as the Earth's mantle," says Zolotov. "And
water, which is gone now, also could have caused the high oxidation state of
Io."
When this reaction occurs, water reacts with iron, hydrogen is released and
the iron then becomes oxidized.
"In this process, the iron metal is removed from Io's mantle and the
interior of the moon becomes oxidized," says Zolotov. "Another satellite of
Jupiter, water-rich Europa, may have differentiated in similar fashion to
Io."
September 2000