木星 月惑星研究会 関西支部
Jupiter Image 2000/12/13(UT)
South up South up
The Cassini-Huygens mission
The familiar banded appearance of Jupiter at low and middle latitudes gradually gives way to a more mottled appearance at high latitudes in this striking true color image taken Dec. 13, 2000, by NASA's Cassini spacecraft.
The intricate structures seen in the polar region are clouds of different chemical composition, height and thickness. Clouds are organized by winds, and the mottled appearance in the polar regions suggests more vortex-type motion and winds of less vigor at higher latitudes.
The cause of this difference is not understood. One possible contributor is that the horizontal component of the Coriolis force, which arises from the planet's rotation and is responsible for curving the trajectories of ocean currents and winds on Earth, has its greatest effect at high latitudes and vanishes at the equator. This tends to create small, intense vortices at high latitudes on Jupiter. Another possibility may lie in that fact that Jupiter overall emits nearly as much of its own heat as it absorbs from the Sun, and this internal heat flux is very likely greater at the poles. This condition could lead to enhanced convection at the poles and more vortex-type structures. Further analysis of Cassini images, including analysis of sequences taken over a span of time, should help us understand the cause of equator-to-pole differences in cloud organization and evolution.
By the time this picture was taken, Cassini had reached close enough to Jupiter to allow the spacecraft to return images with more detail than what's possible with the planetary camera on NASA's Earth-orbiting Hubble Space Telescope. The resolution here is 114 kilometers (71 miles) per pixel. This contrast-enhanced, edge-sharpened frame was composited from images take at different wavelengths with Cassini's narrow-angle camera, from a distance of 19 million kilometers (11.8 million miles). The spacecraft was in almost a direct line between the Sun and Jupiter, so the solar illumination on Jupiter is almost full phase.
Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.
NASA/JPL/University of Arizona
[NASA/JPL/Space Science Institute]