LORRI took this mosaic 9½ hours -- or not quite one Jupiter rotation
period -- after snapping its previous images of the Little Red Spot on Feb
26, 2007 (see PIA09294), at a longer range of 3.5 million kilometers
(2.2 million miles) and at a lower resolution of 17 kilometers (10.5
miles) per pixel. The new mosaic was obtained with the Little Red Spot
closer to the center of the visible disk of Jupiter, so there is less
foreshortening and better illumination.
The Little Red Spot is an Earth-sized storm on Jupiter that changed its
color from white to red in 2005. Swimming to the east, its clouds rotate
counterclockwise (or in the anticyclonic direction), meaning that it is a
high-pressure region. In that sense, the Little Red Spot is the opposite
of a hurricane on Earth, which is a low-pressure region - and it is of
course much larger than any hurricane on Earth.
Scientists don't know exactly how or why the storm turned red -- though
they speculate that the change could stem from a surge of exotic compounds
from deep within Jupiter, caused by an intensification of the storm
system. In particular, sulfur-bearing cloud droplets might have been
propelled about 50 kilometers into the upper level of ammonia clouds,
where brighter sunlight bathing the cloud tops released the red-hued
sulfur embedded in the droplets - causing the storm to turn red. A similar
mechanism has been proposed for the Little Red Spot's "big brother," the
Great Red Spot, a massive energetic storm system that has existed for
centuries.
The smaller, brighter oval to the south of the Little Red Spot is another
storm moving more rapidly to the east, as can be seen by comparing the
previous mosaic to the newer one. Any feature that moved by as much as 100
pixels between the earlier mosaic and the new one -- as many features have
done -- has shifted at an average relative speed faster than 95 miles per
hour, indicating hurricane force winds. The awesome violence of the storms
in Jupiter's atmosphere contrasts with the serene isolation of New
Horizons' LORRI, snapping pictures from millions of miles away.
"The new images are further proof that LORRI is one of the best imagers
ever flown on a planetary mission," says Dr. Andy Cheng, the LORRI
principal investigator from the Applied Physics Laboratory, "and more
delights are yet to come."