NASA/JPL/University of Arizona

In this movie, the inner-most satellite of Jupiter, Io, is in the eclipse shadow of Jupiter (Jupiter is blocking the Sun for Io). This allowed NASA's spacecraft Cassini to image the active moon in darkness. These images were taken over a two-hour period and nearly capture the entire eclipse which took place on January 1, 2001. The spacecraft was over 10 million kilometers (6.3 million miles) away, yielding a resolution of 61 kilometers (40 miles) per pixel on these images.

Glows on Io

While Io is enshrouded in darkness, several glows are revealed to us. The bright points of light are hot lava from the active volcanoes on Io. The brightest of these is the volcano Pele which appears to be erupting constantly. To the right and slightly above Pele is a pair of bright spots from the volcano Pillan, the source of a major eruption in 1997. A second source of glow on Io is the faint, diffuse emission of atmospheric aurorae. Similar to the aurora borealis (northern lights) on Earth, the aurorae on Io result from collisions of charged particles (from the electrical currents that flow between Jupiter and Io) with gases in Io's tenuous atmosphere. The aurorae are seen here as a faint glow around Io's equator.

Ellen Cohen

NASA/JPL/University of Arizona

This brief animation shows the motion of the clouds in the Jovian atmosphere. Most notable is the dark, oval-shaped Great Red Spot. The animation was compiled from blue filter images taken using the narrow-angle camera on NASA's Cassini spacecraft during seven rotations of Jupiter between October 1 and October 5, 2000. The images reveal an area on Jupiter centered on the equator that extends about 50° north and south and covers 100° east-west (about a quarter of Jupiter's circumference).

Video: 428 kB, Animated GIF

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The dynamics of the Jovian atmosphere

Jupiter's atmosphere is driven by strong zonal winds, analogous to the jet stream on Earth. However, unlike Earth, the atmosphere is made up of an array of belts and zones which rotate in an east-west direction. The light zones are regions of upwelling air, forming ammonia cirrus clouds. The dark belts are regions where the cooler the circulation moves downward. Because there are no ammonia clouds, we can see deeper into the atmosphere in these regions. The speed of the main equatorial jet is about 300 km/hr and these speeds have not changed for hundreds of years.

The Great Red Spot

Jupiter's Great Red Spot is a storm that has been present for centuries, first observed by Galileo 400 years ago. The storm lies in the southern hemisphere and is about 30,000 kilometers by 14,000 kilometers, much larger than the planet Earth! It is an anticyclonic storm and has a high-pressure center (unlike storms on Earth that have low-pressure centers). Its winds rotate counterclockwise and have a period of about 6 days. Scientists do not know what drives the storm or if the storm will ever dissipate. One theory suggests the Great Red Spot is continually fueled by the smaller storms that merge with the giant storm.

Ellen Cohen

NASA/JPL-CalTech

This animation shows the terrain of Mars as the planet rotates. The data were taken using the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor. The instrument transmits infrared laser pulses to the Martian surface and measures the time of flight to compute the range of the spacecraft to the surface. These measurements are then used to construct a precise topographic map of Mars.

The Martian Terrain

The information from MOLA gives scientists some of the most detailed information about the surface of Mars. The first pictures of the surface from space came in 1965 from the Mariner 4 spacecraft. In the 1970s, the Viking spacecraft landed on the surface and returned detailed information about the soil composition. Mars is divided into two main types of terrain: ancient cratered areas and younger, volcanic regions. Ancient cratered terrain is found mainly in the southern hemisphere. The volcanic plains are mainly in the northern hemisphere and lie several kilometers below the southern uplands. Mars has the largest volcano in the Solar System, Olympus Mons, which is 25 kilometers above the surrounding plains and 500 kilometers in diameter. Mars also has runoff channels, where the runoff of ancient rainstorms once flowed.

The Great Red Spot

Jupiter's Great Red Spot is a storm that has been present for centuries, first observed by Galileo 400 years ago. The storm lies in the southern hemisphere and is about 30,000 kilometers by 14,000 kilometers, much larger than the planet Earth! It is an anticyclonic storm and has a high-pressure center (unlike storms on Earth that have low-pressure centers). Its winds rotate counterclockwise and have a period of about 6 days. Scientists do not know what drives the storm or if the storm will ever dissipate. One theory suggests the Great Red Spot is continually fueled by the smaller storms that merge with the giant storm.

Ellen Cohen