Annotated Version
On February 24, 2007, the LEISA (pronounced "Leesa") infrared spectral
imager in the New Horizons Ralph instrument observed giant Jupiter in 250
narrow spectral channels. At the time the spacecraft was 6 million
kilometers (nearly 4 million miles) from Jupiter; at that range, the LEISA
imager can resolve structures about 400 kilometers (250 miles) across.
LEISA observes in 250 infrared wavelengths, which range from 1.25
micrometers (µm) to 2.50 µm. The three images shown above from that
dataset are at wavelengths of 1.27 µm (left), 1.53 µm (center) and 1.88 µm
(right).
The bright areas in the image frames are caused by solar radiation
reflected from clouds and hazes in Jupiter's atmosphere. Dark areas
correspond to atmospheric regions where solar radiation is absorbed before
it can be reflected. The dark circular feature in the upper left of all
three images is the shadow of Jupiter's innermost large moon, Io.
Light at 1.53 µm (center frame) comes from relatively high in the
atmosphere. The other two channels probe deeper atmospheric levels.
Features that are bright in all three pictures come from high-altitude
clouds. Features that are bright in the 1.27 and 1.88 µm channels, but
darker in the 1.53-µm channel come from lower clouds. For example, there
is an isolated circular feature (the "Little Red Spot") in the lower left
of the 1.53-µm image. In the 1.27 and 1.88 µm data, this circular feature
is surrounded by other structures. The implication is that the "Little Red
Spot" is caused by a system that extends far up into the atmosphere, while
other structures are lower.
At closest approach to Jupiter on February 28, at a distance of about 2.5
million kilometers (1.4 million miles), LEISA's resolution was about three
times better than it was on February 24. LEISA images made at that
far-better resolution are still stored in the spacecraft's data recorder,
awaiting downlink from New Horizons.
