The amount of lava gushing from individual volcanoes on
Jupiter’s moon Io dwarfs earthly comparisons, and the pace at
which lava is repainting Io’s surface suggests a novel technique
for determining the relative ages of surface regions there.

The latest research about Io, much of it based on data from
NASA’s Galileo spacecraft, was reported Wednesday at the Lunar
and Planetary Science conference in Houston, Texas.

Knowing the relative ages of surface features on a planet or
moon is crucial for understanding the processes shaping that
world. The favorite age gauge of planetary scientists is counting
impact craters. The more impacts still showing, the older the
surface. However, volcanoes are resurfacing Io so fast, not a
single impact crater has been found there.

“It appears that the same process that destroys the
traditional way of dating surfaces is going to provide a new way
to date surfaces,” said Dr. Dennis Matson, a research scientist
at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “On Io,

surface temperature can give us an indication of surface age.”

Calculations of Io’s total heat flow suggest that virtually
everywhere on Io, even the oldest surfaces were produced by fresh
lava so recently that they are still cooling off, Matson said.
With some allowances for differences in composition and thickness
of the flows, colder surface areas should be older surface areas.

“If we get this technique worked out, we look forward to
combining it with other types of information to read the history
of Io’s surface,” he said. “We hope to be able to tell whether
lava flows that are far apart on the surface happened at
approximately the same time.”

Some of the first calculations were reported Wednesday for
how fast lava is being produced by individual volcanic features
on Io. One thermally steady volcano that produces broad flow
fields named Amirani and Maui churns out about 100 cubic meters
(about 3,500 cubic feet) of lava every second, said Dr. Ashley
Davies, a JPL volcanologist. That’s about 200 times as productive
as the Kilauea volcano in Hawaii. It’s fast enough to overflow
two Olympic size swimming pools every minute or three Houston
Astrodomes every day.

Ionian volcanoes Monan, Tupan, Prometheus, Culann and Zamama
each produce one-third to one-half as much lava as Amirani-Maui
does, Davies calculates.

Estimates of the volume rate of an eruption are important
for understanding what is happening under the surface and at the
surface of each volcano. “Flow rate is tied to the source of the
magma and the conduits the magma follows to the surface,” Davies
said. “It strongly influences how the lava landscape forms and
how heat is lost from the lava as time passes.”

The volume-rate estimates also help crosscheck estimates of
the thickness of flows where Galileo’s repeat flybys have
provided information about how rapidly the flows increase in
area. Davies used infrared spectral measurements from Galileo
plus modeling of cooling rates to calculate surface coverage
rates and eruption volumes. The calculations suggest typical
lava-flow thicknesses on Io of one to two meters (three to six
feet), he said.

Additional information about Galileo’s observations of Io
and other jovian moons since the spacecraft began orbiting
Jupiter in 1995 is available online at . JPL, a division of the
California Institute of Technology in Pasadena, manages the
Galileo mission for NASA’s Office of Space Science, Washington,