The most
powerful eruption ever detected
on any planet
in our Solar
System has been seen
on Io, one of
Jupiter's moons. Io,
one of the four large
Jovian satellites, is
highly volcanic with
high-temperature eruptions
similar to
those on Earth.
The outburst was
detected using an
advanced optical system on
the Keck II telescope
in Hawaii. The
eruption took place in
February 2001, though image
analysis has only
recently been
completed. "It
is clear that
this eruption is
the most energetic ever seen,
both on Io and
on Earth," says Frank
Marchis of the University
of California, US.
Adaptive optics employs a
technique to remove
the distorting effects
of atmospheric
turbulence - the same
effect that makes
the stars twinkle - by flexing telescope
mirrors fast enough to
stabilise and
focus the bouncing image.
The 2001 Io
eruption was very
close to Surt, the
site of a large
eruption in 1979
that took place between
the Voyager 1 and
Voyager 2 spacecraft flybys. "We
were lucky to detect
the beginning of an
outburst eruption," says
Imke de Pater, also of
the University of
California.
The Keck telescope
captured images
of Io on
two days in February 2001.
On the first day,
Io was mostly quiet,
with visible surface
features such as dark calderas
and relatively
bright areas rich in
sulphur dioxide
frost. Two days later, however,
what seemed a small hot spot on
the surface had
become a large,
bright eruption.
"We observed
the same side of the
satellite and were
amazed to see a very bright eruption
that had suddenly
appeared," says Marchis.
"The Surt eruption
appears to
cover an area
larger than the
city of Los
Angeles and even larger
than the entire
city of London,"
Marchis says. "The total
amount of energy
being released by the
eruption is amazingly
high, with the thermal
output from this one eruption
almost matching the total
amount of energy
emitted by all of
the rest of
Io's other volcanoes
included."
"This eruption
is truly massive,"
says Ashley Davies,
a scientist
at the US space
agency's (Nasa) Jet
Propulsion Laboratory.
The volcano
on Io is
far more powerful than
any eruption recorded by
scientists on
Earth, with an estimated
eruptive power
output of about 78,000
gigawatts. By comparison,
the power produced
by the last significant
eruption of Mount
Etna in Italy
in 1992 was
just 12 gigawatts.
Terrestrial geological records indicate
that there may have been some comparably
large eruptions many
millions of years
ago in Siberia and
in India, which
may have contributed to
the demise of the dinosaurs.
The observations
will also help reveal
more about the nature
of Io, says
Lionel Wilson at the
Planetary Science
Research Group at
Lancaster University,
UK. "These
results may be the
first to allow us to make a good estimate
of the volume eruption
rate of lava
on Io in
a large volume eruption with
a high eruption rate. Building up
statistics on the
range of eruption
conditions that can occur on
Io will allow us
to deduce much
more about the structure of
the crust and
mantle than we
understand at the moment.
The observed energy
indicates the presence
of a vigorous,
high-temperature
volcanic eruption.
The kind of eruption
to produce
this thermal signature
has incandescent
fire fountains of
molten lava which
are kilometres high,
propelled at
great speed out of the ground by
expanding gases,
accompanied by extensive
lava flows on the surface."
The results
are published
in the November
issue of the planetary
sciences journal Icarus. |
