NASA's Hubble Space Telescope (HST) has acquired a stunning image of Jupiter, the largest planet, and its largest moon, Ganymede. The picture shows Ganymede (5,250 km across) just before disappearing beyond its colorful giant parent planet.

This color image was composed from three images taken on 9 April 2007, with HST’s Wide Field Planetary Camera 2 in red, green, and blue filters. The colors of this Jovian family portrait are close to natural colors.

Ganymede orbits Jupiter every seven days, at an average distance of approximately 1 million km. As Ganymede's orbit is oriented nearly edge-on to Earth, it frequently can be observed passing in front of and disappearing behind Jupiter, and then reappear later.

Ganymede is the largest moon in our Solar System; it is even larger than the planet Mercury (4880 km across), the smallest planet. Earth’s Moon is 3,476 km across. Ganymede is composed of rock and ice. Jupiter is so big that only part of its Southern Hemisphere is visible in this image.

Hubble's view is so crisp that astronomers can distinguish features on Ganymede's surface, particularly the white impact crater, Tros, and its system of rays, bright streaks of debris flung from the crater. Tros and its ray system are roughly the width of Arizona.

The image also shows Jupiter's Great Red Spot (GRS), the large reddish oval at upper left. It is a gigantic storm, twice as wide as Earth. The GRS has been swirling for more than 300 years. Hubble's exquisite view also reveals the details of the clouds in the Jovian atmosphere as well as various other storms and vortices.

Such images are interesting for studying Jupiter's upper atmosphere. As Ganymede passes behind Jupiter, it reflects sunlight, which then passes through Jupiter's atmosphere. Imprinted on that light is information about the Jupiter's turbulent atmosphere, which yields valuable information about the properties of the planet’s high-altitude haze.

Further Reading

The Websites of the Hubble Space Telescope
http://hubblesite.org/
www.spacetelescope.org/

Aymen Mohamed Ibrahem
Senior Astronomy Specialist