Saturn Seen From Far and Near
May 26, 2004
As Saturn grows closer through the eyes of the Cassini
spacecraft, which is hurtling toward a rendezvous with the
ringed world on June 30 (July 1, Universal Time), both
Cassini and the Earth-orbiting Hubble Space Telescope
snapped spectacular pictures of the planet and its
magnificent rings.
Cassini is approaching Saturn at an oblique angle to the Sun
and from below the ecliptic plane. Cassini has a very
different view of Saturn than Hubble's Earth-centered view.
For the first time, astronomers can compare views of equal
sharpness of Saturn from two very different perspectives.
The view from Hubble, taken on March 22, 2004, is so sharp
that many individual Saturnian ringlets can be seen. When
Cassini returned its picture of Saturn on May 16, it was so
close to the planet that the imaging science subsystem
narrow-angle camera could not fit the whole planet in its
field-of-view. Cassini is still about 20 million kilometers
(about 12.4 million miles) away and only 36 days from
reaching Saturn.
Hubble's exquisite optics, coupled with the high resolution
of its Advanced Camera for Surveys, allow it to take
pictures of Saturn which are nearly as sharp as Cassini's,
even though Hubble is nearly a billion miles farther from
Saturn than Cassini. Cassini will ultimately far exceed the
resolution of Hubble during its close encounter with Saturn.
Cassini's sharpness began to surpass Hubble's when it came
to within 23 million kilometers (14 million miles) of Saturn
earlier this month.
Camera exposures in four filters (blue, blue-green, green
and red) were combined to form the Hubble image, to render
colors similar to what the eye would see through a telescope
focused on Saturn. The subtle pastel colors of ammonia-
methane clouds trace a variety of atmospheric dynamics.
Saturn displays its familiar banded structure, and haze and
clouds of various altitudes. Like Jupiter, all bands are
parallel to Saturn's equator. Even the magnificent rings, at
nearly their maximum tilt toward Earth, show subtle hues,
which indicate the trace chemical differences in their icy
composition.
Cassini has two cameras, a wide angle and narrow angle.
This narrow angle image was made using a combination of
three filters (red, green, blue) and was taken at a range of
24.3 million kilometers (15.1 million miles). The view is
from 13 degrees below the equator. Enceladus, one of
Saturns 31 known moons, appears near the south pole at the
bottom of the image.
The color differences between the Hubble and Cassini images
are mainly due to the different sets of filters used.
More than two decades have passed since a spacecraft last
visited Saturn -- NASA's Voyager-2 flew by Saturn in August
1981. Since 1990, Hubble has produced high-resolution Saturn
images, tracking storms and auroral activity while providing
crisp views of the rings over time and from various angles.
Cassini will begin a four-year mission in orbit around
Saturn when it arrives on June 30, 2004 (July 1, 2004
Univeral Time). Six months later it will release its
piggybacked Huygens probe for descent through Titan's thick
atmosphere.
The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc.,
for NASA, under contract with the Goddard Space Flight
Center, Greenbelt, Md. The Hubble Space Telescope is a
project of international cooperation between NASA and the
European Space Agency. The Cassini-Huygens mission is a
cooperative mission 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 mission for NASA's Office of Space
Science, Washington, D.C. The Cassini orbiter and its two
onboard cameras were designed, developed and assembled at
JPL.
Hubble images and additional information on Hubble are
available at: http://hubblesite.org/news/2004/18
Cassini images and information is available at:
http://saturn.jpl.nasa.gov.
Hubble Photo Credit: NASA, ESA and Erich Karkoschka
(University of Arizona)
Cassini Photo Credit: NASA/JPL/Space Science Institute