This five-frame sequence of New Horizons images captures the giant plume
from Io's Tvashtar volcano. Snapped by the probe's Long Range
Reconnaissance Imager (LORRI) as the spacecraft flew past Jupiter earlier
this year, this first-ever "movie" of an Io plume clearly shows motion in
the cloud of volcanic debris, which extends 330 kilometers (200 miles)
above the moon's surface. Only the upper part of the plume is visible from
this vantage point -- the plume's source is 130 kilometers (80 miles) below
the edge of Io's disk, on the far side of the moon.
The appearance and motion of the plume is remarkably similar to an
ornamental fountain on Earth, replicated on a gigantic scale. The knots
and filaments that allow us to track the plume's motion are still
mysterious, but this movie is likely to help scientists understand their
origin, as well as provide unique information on the plume dynamics.
Io's hyperactive nature is emphasized by the fact that two other volcanic
plumes are also visible off the edge of Io's disk: Masubi at the 7 o'clock
position, and a very faint plume, possibly from the volcano Zal, at the 10
o'clock position. Jupiter illuminates the night side of Io, and the most
prominent feature visible on the disk is the dark horseshoe shape of the
volcano Loki, likely an enormous lava lake. Boosaule Mons, which at 18
kilometers (11 miles) is the highest mountain on Io and one of the highest
mountains in the solar system, pokes above the edge of the disk on the
right side.
The five images were obtained over an 8-minute span, with two minutes
between frames, from 23:50 to 23:58 Universal Time on March 1, 2007. Io
was 3.8 million kilometers (2.4 million miles) from New Horizons; the
image is centered at Io coordinates 0 degrees north, 342 degrees west.
The pictures were part of a sequence designed to look at Jupiter's rings,
but planners included Io in the sequence because the moon was passing
behind Jupiter's rings at the time.
