- Original Caption Released with Image:
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The New Horizons Multicolor Visible Imaging Camera (MVIC) took this image
of Jupiter's volcanic moon Io at 04:30 Universal Time on February 28,
2007, about one hour before New Horizons' closest approach to Jupiter,
from a range of 2.7 million kilometers (1.7 million miles). Part of the
Ralph imaging instrument, MVIC is designed for the very faint solar
illumination at Pluto, and is too sensitive to image the brightly lit
daysides of Jupiter's moons. Io's dayside is therefore completely
overexposed in this image, and appears white and featureless. However, the
Jupiter-lit nightside of Io and the giant plume from the Tvashtar
volcano are well exposed, and the versions of the image shown here have
been processed to bring out each of these features.
The scale of the original image is 53 kilometers (33 miles) per pixel; Io
itself has a diameter of 3,630 kilometers (2,250 miles).
The nightside of Io (left panel) is illuminated brightly enough by Jupiter
to reveal many details in full color to MVIC's sensitive vision. The
nightside color has been corrected to account for the greenish hue of
Jupiter's light as seen by MVIC -- see the April 2 Featured Image of Io
and Europa (PIA09256) -- so the colors approximate what the human eye
would see in daylight illumination. The image shows Io's reddish-brown
polar areas and the yellow and white colors of its equatorial regions,
mostly due to various forms of sulfur.
Several dark volcanic centers are also visible -- the most prominent,
appearing as an elongated spot just above and to the right of the disk's
center, is called Fjorgynn. Near the disk center, just over the night side
of the terminator (the line separating day and night), is a row of three
or four pale yellow patches, which likely are volcanic plumes catching the
setting sun. These features have caught the attention of New Horizons
scientists because no major plumes have been seen previously in this
region of Io, and it is rare for Io's plumes to cluster so closely
together.
The right panel shows the bluish color of the plume from Tvashtar, rising
above the overexposed edge of Io's disk at the 11 o'clock position. The
plume is blue because it contains fine dust that preferentially scatters
blue light, in the same way that smoke appears blue. The red line on the
edge of the disk, below the plume, is an artifact caused by the
overexposure of Io's surface.
The image is centered at Io coordinates 26 degrees west, 6 degrees south,
and is produced using MVIC's blue, red and near-infrared filters. In the
original image, the overexposure of Io's dayside hemisphere caused
extensive electronic "blooming" of the image toward the left and bottom
edges of the frame, and this has been removed from the versions shown
here.
- Image Credit:
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NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
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