Original Caption Released with Image: Looming like a giant flying saucer in
our outer solar system, Saturn puts on a show as the planet and its magnificent
ring system nod majestically over the course of its 29-year journey around the
Sun. A series of Hubble Space Telescope images, captured from 1996 to 2000, show
Saturn's rings open up from just past edge-on to nearly fully open as it moves
from autumn towards winter in its Northern Hemisphere (for the composite view of
all images seePIA03156.
Saturn's equator is tilted relative to its orbit by 27 degrees, very similar to
the 23-degree tilt of the Earth. As Saturn moves along its orbit, first one
hemisphere, then the other is tilted towards the Sun. This cyclical change
causes seasons on Saturn, just as the changing orientation of Earth's tilt
causes seasons on our planet. The first image in this sequence, on the lower
left, was taken soon after the autumnal equinox in Saturn's Northern Hemisphere
(which is the same as the spring equinox in its Southern Hemisphere). By the
final image in the sequence, on the upper right, the tilt is nearing its
extreme, or winter solstice in the Northern Hemisphere (summer solstice in the
Southern Hemisphere).
Astronomers are studying this set of images to investigate the detailed
variations in the color and brightness of the rings. They hope to learn more
about the rings' composition, how they were formed, and how long they might
last. Saturn's rings are incredibly thin, with a thickness of only about 30 feet
(10 meters). The rings are made of dusty water ice, in the form of boulder-sized
and smaller chunks that gently collide with each other as they orbit around
Saturn. Saturn's gravitational field constantly disrupts these ice chunks,
keeping them spread out and preventing them from combining to form a moon. The
rings, as shown here, have a slight pale reddish color due to the presence of
organic material mixed with the water ice.
Saturn is about 75,000 miles (120,000 km) across, and is flattened at the poles
because of its very rapid rotation. A day is only 10 hours long on Saturn.
Strong winds account for the horizontal bands in the atmosphere of this giant
gas planet. The delicate color variations in the clouds are due to smog in the
upper atmosphere, produced when ultraviolet radiation from the Sun shines on
methane gas. Deeper in the atmosphere, the visible clouds and gases merge
gradually into hotter and denser gases, with no solid surface for visiting
spacecraft to land on.
The Cassini/Huygens spacecraft, launched from Earth in 1997, is well on its way
to the Saturn system. It will arrive in 2004 to land a probe on Titan, Saturn's
largest moon, and to orbit the planet for four years for a detailed study of the
entire Saturn system
