[新闻] 卡西尼号最新照片(2004年03月12日发布)

Clumps in the F 光环

Clumps seemingly embedded within 土星's narrow, outermost F 光环 can be seen i
n these two 卡西尼 narrow angle 照相机 images taken on 2004年02月23日 from a d
istance of 62.9 million 千米 (39 million 英里). The images were taken nearly t
wo hours apart using the 照相机's broadband green filter, centered at 568 纳米
. 图片 scale is 377 千米 (234 英里) per 像素.

The core of the F 光环 is about 50 千米 (31 英里) wide, and from 卡西尼's curr
ent distance, is not fully resolvable. Contrast has been greatly enhanced, and
the images have been magnified, to aid visibility of the F 光环 and the clump
features.

The images show clumps as they revolve about the 行星. Like all particles in 土
星's 光环 system, these features orbit the 行星 in the same direction in which
the 行星 rotates. This direction is 逆时针 as seen from 卡西尼's southern van
tage point below the 光环 plane. Two clumps in particular, one of them extende
d, can be seen in the upper part of the F 光环 in the 图片 on the left, and in
the lower part of the 光环 in the 图片 on the right. Other knot-like irregula
rities in the 光环's brightness can also be seen in the right hand 图片.

Clumps such as these were first seen when the two 旅行者 飞船 flew past 土星 i
n 1980 and 1981. It is not certain what causes these features, though several
theories have been proposed, including meteoroid bombardment and inter-particl
e collisions in the F 光环.

The 旅行者 data suggest that while the clumps change very little and can be tr
acked as they orbit for 30 days or more, no identified clump survived from the
旅行者 1 flyby to the 旅行者 2 flyby nine months later. Thus, 科学家 have onl
y a rough idea of the lifetime of clumps in 土星's rings - a mystery that 卡西
尼 may help to answer.

The small dot at center right in the second 图片 is one of 土星's small moons,
土卫十 (181 千米, 112 英里 across). 土卫十 was discovered by ground-based 天文
学家 in 1966, and was first resolved by the 旅行者 1 飞船 in 1980. The moon sh
ares almost the same orbit with another small satellite, Epimetheus. 土卫十 an
d Epimetheus, both thought to consist mostly of porous ices, play a role in ma
intaining the outer edge of 土星's A 光环.

The 卡西尼—惠更斯 mission is a cooperative project of 美国国家航空航天局, the
欧洲航天局 and the 意大利航天局. 喷气推进实验室, a division of 加州理工学院 i
n 帕萨迪那, manages the 卡西尼—惠更斯 mission for 美国国家航空航天局's Office
of Space Science, Washington, D.C. The imaging team is based at the Space Sci
ence Institute, Boulder, 科罗拉多.

For information about the 卡西尼—惠更斯 mission, http://saturn.jpl.nasa.gov a
nd the 卡西尼 imaging team home page, http://ciclops.org.

Credit: 美国国家航空航天局/喷气推进实验室/Space Science Institute
发布: 2004年03月12日 (PIA 05382)
图片/Caption Information

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