探索宇宙！每天一幅不同的影像或照片，并由专业天文学家简明的解说，带你遨游迷人的宇宙。

土星前方的土卫六
影像提供: NASA, JPL-Caltech, Space Science Institute



说明: 类似地球的月亮，土星最大的卫星土卫六也是受到潮汐锁定，而在进行同步自转。这张由卡西尼号航天器在2012年5月拍摄的照片拼接而成的组合影像，呈现了土卫六永远背对这颗环系气态巨行星那面的景观。土卫六是太阳系的天体中唯一拥有厚重大气的卫星，也是太阳系除了地球之外，现知表面有经常性液体湖泊，以及类似地球有降液体雨及蒸发循环的天体。在这张呈现5,000公里直径的土卫六，悬在土星环系和云顶上方的影像里，它高层的雾霾云清楚可辨。其中，土卫六中心附近的暗色沙丘区名为”香格里拉“。卡西尼号携带的惠更斯号探测器，在进行离地球最远距的航天器着陆之后，长眠在中左下方的区域里。

Titan: Moon over Saturn
Image Credit: NASA, JPL-Caltech, Space Science Institute

Explanation: Like Earth’s moon, Saturn’s largest moon Titan is locked in synchronous rotation with its planet. This mosaic of images recorded by the Cassini spacecraft in May of 2012 shows its anti-Saturn side, the side always facing away from the ringed gas giant. The only moon in the solar system with a dense atmosphere, Titan is the only solar system world besides Earth known to have standing bodies of liquid on its surface and an earthlike cycle of liquid rain and evaporation. Its high altitude layer of atmospheric haze is evident in the Cassini view of the 5,000 kilometer diameter moon over Saturn’s rings and cloud tops. Near center is the dark dune-filled region known as Shangri-La. The Cassini-delivered Huygens probe rests below and left of center, after the most distant landing for a spacecraft from Earth.