[酷图] 卡西尼号最新图片——土卫九表面超清晰特写(2004年06月13日)

Phoebe's Surprise
06.13.04  

Phoebe delivers on its promise to reveal new wonders to Cassini by showing probable evidence of an ice-rich body overlain with a thin layer of dark material. The sharply-defined crater at above center exhibits two or more layers of alternating bright and dark material. Imaging scientists on the Cassini mission have hypothesized that the layering might occur during the crater formation, when ejecta thrown out from the crater buries the pre-existing surface that was itself covered by a relatively thin, dark deposit over an icy mantle. The lower thin dark layer on the crater wall appears to define the base of the ejecta blanket. The ejecta blanket itself appears to be mantled by a more recent dark surface lag.

This image was obtained on June, 11 2004 at a phase, or Sun-Phoebe-spacecraft, angle of 79 degrees, and from a distance of 13,377 kilometers (8,314 miles). The image scale is approximately 80 meters (263 feet) per pixel. No enhancement was performed on this image.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens 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. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Image Credit: NASA/JPL/Space Science Institute

2004年06月14日 09:17



　　中新网6月14日电 美国宇航局官员12日说，美国和欧洲合作制造的卡西尼号
(Cassini)太空探测器,11日已经近距离飞过了土星最外层的卫星土卫九(Phoebe)，准备对
土星进行四年的探测。

　　新加坡联合早报报道，宇航局喷气推进实验室官员说，以钚为燃料的卡西尼携带了12
种科学探测仪器，它以2068公里的近距离飞过了黑暗的土卫九。

　　造价33亿美元(约56.6亿新元)的卡西尼号上的仪器对土卫九进行探测后，调整天线到
地球方向，卡西尼发出的数据在星期日早上到达宇航局的外太空网络。

　　官员还说，卡西尼号状态很好，工作正常。

　　探测项目科学家沃森说：“虽然这是第一次近距离的土星探测，却也是唯一探测土卫
九的机会，谜一般的土卫九令科学家极感兴趣，这次关键飞行可以让人们对它了解得多一
些。”

　　从星期六发布的黑白照片上，看起来颇有几分似人头骨的土卫九上遍布着陨石坑，有
一半还覆盖在阴影里。土星的这颗卫星于1898年首次由美国天文学家皮克林发现，它直径
约220公里，约9小时16分钟自转一周，平均每18个月绕土星公转一圈。土卫九距离土星最
远，达到1300万公里，而且它围绕土星运行的方向与其他卫星刚好相反。另外，土卫九表
面很暗，吸收的太阳光照仅有约6%被反射出来。

　　通过卡西尼号传回的数据，科学家可以了解土卫九的质量和成分。小组另一研究人员
约翰逊说：“从照片看，土卫九表面伤痕累累，到处都是其他太空物体过去撞击留下的深
陨石坑。”

　　与土卫九擦肩而过之后，卡西尼号下周三将调整飞行轨道，预计在6月30日进入绕土
星轨道，成为土星的第一颗人造卫星。

The Face of Phoebe

Phoebe's true nature is revealed in startling clarity in this mosaic of two images taken during Cassini's flyby on June 11, 2004. The image shows evidence for the emerging view that Phoebe may be an ice-rich body coated with a thin layer of dark material. Small bright craters in the image are probably fairly young features. This phenomenon has been observed on other icy satellites, such as Ganymede at Jupiter. When impactors slammed into the surface of Phoebe, the collisions excavated fresh, bright material -- probably ice -- underlying the surface layer. Further evidence for this can be seen on some crater walls where the darker material appears to have slid downwards, exposing more light-colored material. Some areas of the image that are particularly bright – especially near lower right – are over-exposed.

An accurate determination of Phoebe's density – a forthcoming result from the flyby – will help Cassini mission scientists understand how much of the little moon is comprised of ices.

This spectacular view was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 84 degrees, and from a distance of approximately 32,500 kilometers (20,200 miles). The image scale is approximately 190 meters (624 feet) per pixel. No enhancement was performed on this image.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 13, 2004 (PIA 06064)

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土卫九上的环形山。
Crater Close-up on Phoebe

This eye-popping high-resolution image of Phoebe's pitted surface taken very near closest approach shows a 13-kilometer (8-mile) diameter crater with a debris-covered floor. Part of another crater of similar size is visible at left, as is part of a larger crater at top and many scattered smaller craters. The radial streaks in the crater are due to downslope movements of loose fragments from impact ejecta. Also seen are boulders ranging from about 50 to 300 meters (160 to 990 feet) in diameter. The building-sized rocks may have been excavated by large impacts, perhaps from some other region of Phoebe rather than the craters seen here. There is no visible evidence for layering of ice and regolith or a hardened crust in this region, as on other parts of this moon.

Some of the relatively bright spots are from small impacts that excavated bright material from beneath the dark surface. Images like this provide information about impact and regolith processes on Phoebe.

This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78 degrees, and from a distance of 11,918 kilometers (7,407 miles). The image scale is approximately 18.5 meters (60.5 feet) per pixel. The illumination is from the right. No enhancement was performed on this image.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 13, 2004 (PIA 06068)

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Dark Desolation

On June 11, 2004, at its closest approach to Phoebe, Cassini obtained this extremely high resolution view of a dark, desolate landscape. Regions of different reflectivity are clearly visible on what appears to be a gently rolling surface. Notable are several bright-rayed impact craters, lots of small craters with bright-colored floors and light-colored streaks across the landscape. Note also the several sharply defined craters – probably fairly young features – near the upper left corner.

This high-resolution image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 30.7 degrees, and from a distance of approximately 2,365 kilometers (1,470 miles). The image scale is approximately 14 meters (46 feet) per pixel. The image was high-pass filtered to bring out small scale features and then enhanced in contrast.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 14, 2004 (PIA 06069)

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Peering at Phoebe

Shown here is a mosaic of seven of the sharpest, highest resolution images taken of Phoebe during Cassini's close flyby of the moon. The image scales range from 27 to 13 meters (90 to 43 feet) per pixel. Smaller and smaller craters can be resolved as resolution increases from left to right. The number of blocks (or bumps on the surface) also increases to the right. The sun is coming from the right, so the bright-dark pattern is reversed between blocks and small craters. Grooves or chains of pits are seen on the left portion of the mosaic, which may mark fractures or faults induced by large impact events. Many of the small craters have bright rays, similar to recent craters on the Moon. There are also bright streaks on steep slopes, perhaps where loose regolith slid downhill during the seismic shaking of impact events. There are also places where especially dark materials are present, perhaps rich in carbon compounds.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 14, 2004 (PIA 06072)

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土卫九的南部地区。
A View to the South

A mosaic of two images of Saturn's moon Phoebe taken shortly after Cassini's flyby on June 11, 2004 gives a close-up view of a region near its South pole. The view, taken about 13,000 kilometers (8,000 miles) from Phoebe, is about 120 km (74 miles) across and shows a region battered by craters. Brighter material, likely to be ice, is exposed by small craters and streams down the slopes of large craters. The skyline is a combination of Phoebe's roundish shape and the formation of impact craters. Walls of some of the larger craters are more than 4 kilometers (2.5 miles) high. The image scale is 80 meters (264 feet) per pixel.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 14, 2004 (PIA 06074)

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Skyline View

Images like this one, showing bright wispy streaks thought to be ice revealed by subsidence of crater walls, are leading to the view that Phoebe is an icy-rich body overlain with a thin layer of dark material. Obvious downslope motion of material occurring along the walls of the major craters in this image is the cause for the bright streaks, which are over-exposed here. Significant slumping has occurred along the crater wall at top left.

The slumping of material might have occurred by a small projectile punching into the steep slope of the wall of a pre-existing larger crater. Another possibility is that the material collapsed when triggered by another impact elsewhere on Phoebe. Note that the bright, exposed areas of ice are not very uniform along the wall. Small craters are exposing bright material on the hummocky floor of the larger crater.

Elsewhere on this image, there are local areas of outcropping along the larger crater wall where denser, more resistant material is located. Whether these outcrops are large blocks being exhumed by landslides or actual ‘bedrock' is not currently understood.

The crater on the left, with most of the bright streamers, is about 45 kilometers (28 miles) in diameter, front to back as viewed. The larger depression in which the crater sits is on the order of 100 kilometers (62 miles) across. The slopes from the rim down to the hummocky floor are approximately 20 kilometers (12 miles) long; many of the bright streamers on the crater wall are on the order of 10 kilometers (6 miles) long. A future project for Cassini image scientists will be to work out the chronology of slumping events in this scene.

This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78 degrees, and from a distance of 11,918 kilometers (7407 miles). The image scale is approximately 70 meters (230 feet) per pixel. No enhancement was performed on this image.

The Cassini-Huygens mission is a cooperative project 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 Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute
Released: Jun 14, 2004 (PIA 06075)

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以上是美国宇航局6月15日公布的土星外围最大卫星——土卫九的照片。土星探测飞船“卡西尼”号11日近距离掠过土卫九，并成功拍摄到迄今最好的土卫九照片。清晰的图像显示，土卫九与彗星有点相像，表面有冰，并覆盖着灰土。

　　土星探测飞船“卡西尼”号11日近距离掠过土星外围最大的卫星——土卫九，美国宇航局公布了飞船拍到的迄今最好的土卫九照片。据美国《科学》杂志网站14日报道，美国宇航局喷气推进实验室的科学家说：“我们获得了这个不寻常天体的一些漂亮照片。”据认为它们比“旅行者2”号1981年拍到的土卫九照片好1000倍。清晰的图像显示，土卫九与彗星有点相像，表面有冰，并覆盖着灰土。在以前拍到的照片上，土卫九颜色很暗，但新照片中有许多较为明亮的斑块，它们存在于陨石坑陡峭的岩壁上，以及一些形成未久的小陨石坑中。科学家认为，这些明亮斑块是较为干净的水冰。


总的来说，土卫九似乎与彗星一样由冰、岩石和黑色有机物构成，是45亿年前太阳系形成时留下的剩余物质。有科学家猜测，土卫九形成于太阳系外缘，“游荡”到土星附近，被这颗巨大的气体行星捕获，成为它的卫星。自那以后，土卫九可能度过了一段颇为艰难的日子，屡受陨石撞击，搞得现在“伤痕累累”。目前土星的一些外围小卫星，可能是土卫九遭受猛烈撞击后裂解下来的碎片。土卫九是一个形状不规则的天体，总体说来像一个表面有很多小坑的土豆，直径约220公里。与土星的其它卫星相比，它的轨道、公转方向等特征都比较特殊，因而显得有些神秘。


“卡西尼”号飞船于11日以2.09万公里的时速在距土卫九表面约2000公里的地方掠过。这是人造飞行器迄今与这颗神秘卫星最近的“亲密接触”，距离不足上次“旅行者2”号飞船掠过土卫九时距离的千分之一。

 
　　来源： 新华网  2004-06-17 11:22