The Long Range Reconnaissance Imager (LORRI) on New Horizons captured
another dramatic picture of Jupiter's moon Io and its volcanic plumes, 19
hours after the spacecraft's closest approach to Jupiter on Feb. 28, 2007.
LORRI took this 75 millisecond exposure at 0035 Universal Time on March 1,
2007, when Io was 2.3 million kilometers (1.4 million miles) from the
spacecraft.
Io's dayside is deliberately overexposed to bring out faint details in the
plumes and on the moon's night side. The continuing eruption of the
volcano Tvashtar, at the 1 o'clock position, produces an enormous plume
roughly 330 kilometers (200 miles) high, which is illuminated both by
sunlight and "Jupiter light."
The shadow of Io, cast by the Sun, slices across the plume. The plume is
quite asymmetrical and has a complicated wispy texture, for reasons that
are still mysterious. At the heart of the eruption incandescent lava, seen
here as a brilliant point of light, is reminding scientists of the fire
fountains spotted by the Galileo Jupiter orbiter at Tvashtar in 1999.
The sunlit plume faintly illuminates the surface underneath. "New Horizons
and Io continue to astonish us with these unprecedented views of the solar
system's most geologically active body" says John Spencer, deputy leader
of the New Horizons Jupiter Encounter Science Team and an Io expert from
Southwest Research Institute.
Because this image shows the side of Io that faces away from Jupiter, the
large planet does not illuminate the moon's night side except for an
extremely thin crescent outlining the edge of the disk at lower right.
Another plume, likely from the volcano Masubi, is illuminated by Jupiter
just above this lower right edge. A third and much fainter plume, barely
visible at the 2 o'clock position, could be the first plume seen from the
volcano Zal Patera.
As in other New Horizons images of Io, mountains catch the setting Sun
just beyond the terminator (the line dividing day and night). The most
prominent, seen as a bright vertical line, is the edge of a plateau about
4.5 kilometers (15,000 feet) high, similar in altitude to the Colorado
Rockies. Io itself has a diameter of 3,630 kilometers (about 2,250 miles).
The image is centered at Io coordinates 4 degrees S, 165 degrees W. It has
been processed to reduce contrast, in order to show details over the full
1000-to-1 brightness range of the original data.