Seeing In The Dark As Saturn Lights Up Iapetus

SATURN DAILY

Saturn's moon Iapetus.

Pasadena CA (JPL) Dec 09, 2004
Never-before-seen features on the Saturn-facing part of Iapetus' bright trailing hemisphere are visible for the first time, including many dark spots, and a sharper view of a dark, circular structure that was first seen at very low resolution by NASA's Voyager 1 in 1980. Iapetus diameter is 1,436 kilometers (892 miles).

The image shows mainly the night side of Iapetus; part of the far brighter sunlit side appears at the right and is overexposed due to the long integration time of 180 seconds.

Despite this long exposure time, almost no blurring due to the spacecraft's motion is apparent. This technique for imaging the night side of Iapetus will be used again during a flyby on Jan. 1, 2005, when Cassini will pass 13 times closer to the icy moon.

The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 22, 2004, at a distance of 1.6 million kilometers (994,000 miles) from Iapetus, and from a Sun-Iapetus-spacecraft, or phase, angle of 161 degrees. The view is centered on 0.4 degrees north latitude, 317 degrees west longitude on Iapetus. The image scale is 9.4 kilometers (5.8 miles) per pixel.

Cassini Brings A Waning Iapetus Into View

An ultraviolet, green and infrared view of Iapetus

These are the sharpest views of Iapetus from Cassini so far, and they represent better resolution than the best images of this moon achieved by NASA's Voyager spacecraft.

Images obtained using ultraviolet (centered at 338 nanometers), green (568 nanometers) and infrared (930 nanometers) filters were combined to produce the enhanced color views at left and center; the image at the right was obtained in visible white light. The images on the bottom row are identical to those on top, with the addition of an overlying coordinate grid.

These views show parts of the moon's anti-Saturn side - the side that faces away from the ringed planet--which will not be imaged again by Cassini until Sept., 2007. In the central view, part of the moon's eastern edge was not imaged and appears to be cut off.

With a diameter of 1,436 kilometers (892 miles), Iapetus is Saturn's third largest moon. It is famous for the dramatic contrasts in brightness on its surface - the leading hemisphere is as dark as a freshly-tarred street, and the trailing hemisphere and poles almost as bright as snow.

Many impact craters can be seen in the bright terrain and in the transition zone between bright and dark, and for the first time in parts of the dark terrain. Also visible is a line of mountains that appear as a string of bright dots in the two color images at left, and on the eastern limb in the image at right.

These mountains were originally detected in Voyager images, and might compete in height with the tallest mountains on Earth, Jupiter's moon Io and possibly even Mars. Further observations will be required to precisely determine their heights. Interestingly, the line of peaks is aligned remarkably close to the equator of Iapetus.

The large circular feature rotating into view in the southern hemisphere is probably an impact structure with a diameter of more than 400 kilometers (250 miles), and was first seen in low-resolution Cassini images just two months earlier.

These images were taken with the Cassini spacecraft narrow angle camera between Oct, 15 and 20, 2004, at distances of 1.2, 1.1 and 1.3 million kilometers (746,000, 684,000 and 808,000 miles) from Iapetus, respectively. The Sun-Iapetus-spacecraft, or phase, angle changes from 88 to 144 degrees across the three images. The image scale is approximately 7 kilometers (4.5 miles) per pixel.

SATURN DAILY

Second Space Christmas For ESA: Huygens To Begin Final Journey To Titan

Paris, France (ESA) Dec 08, 2004
At 1.25 billion km from Earth, after a 7-year journey through the Solar system, ESA's Huygens probe is about to separate from the Cassini orbiter to enter a ballistic trajectory toward Titan, the largest and most mysterious moon of Saturn, in order to dive into its atmosphere on 14 January.

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