NASA’s Hubble and Cassini View Saturn From Far And Near

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.

Click on image to enlarge

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 Saturn’s 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