Vesta

The asteroid Vesta is shown with size comparison to several other asteroids. This image of Vesta was taken by the Dawn spacecraft. When Dawn entered orbit around Vesta on July 15, 2011, it was the first probe to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

This image of Vesta was taken as Dawn was leaving its orbit around the asteroid. Vesta is 330 miles (530 kilometers) in diameter and the second most massive object in the asteroid belt after Ceres. Ground- and space-based telescopes have obtained images of Vesta for about two centuries, but they have not been able to see much detail on its surface.

这张照片是 Dawn 卫星在离开围绕小行星的轨道时拍摄的。维斯塔的直径为 330 英里（530 公里），是小行星带中仅次于谷神星的第二大天体。地面和空间望远镜在过去两个世纪中已经获得了维斯塔的图像，但尚未能清晰看到其表面的细节。

Minor planet (4) Vesta was first sighted through a telescope on March 29, 1807 by Heinrich Wilhelm Matthaus Olbers (1758-1840). Subsequent observations determined that the planetary body has an orbital period of 3.63 years, with a semi-major axis of around 2.36 AUs (slightly closer than Ceres's 2.77 AUs) and an eccentricity of 0.090 and an inclination of 7.14 degrees from the plane of the ecliptic. Its orbit places Vesta in the Main Asteriod Belt, but the object more closely resembles a small planet or Earth's Moon than another asteroid.

小行星(4)维斯塔于1807年3月29日首次通过望远镜被观测到，由海因里希·威廉·马atus·奥伯斯(1758-1840)发现。后续观测确定该天体的轨道周期为3.63年，半长轴约为2.36个天文单位（略小于谷神星的2.77个天文单位），偏心率为0.090，轨道倾角为7.14度，相对于黄道面。其轨道将维斯塔置于主小行星带中，但该天体更接近于一颗小行星或地球的月球，而非另一颗小行星。

Image credit: Vesta site

图片版权：Vesta site

"Unlike Ceres, which orbits just around or beyond the Solar System's ice line, Vesta's surface is not icy, like Ceres, Vesta appears to be an evolved body. In 1972, basaltic rocks (made of solidified lava) were detected on Vesta's surface, which indicated that the planetary body had melted early in its past. Vesta appears to have been large enough and hot enough to melt internally from decaying radioactive elements as well as impacts so that lighter elements floated upwards from denser material to form layers towards its surface. As a result, Vesta "differentiated" into a relatively dense metallic core (of approximately 136 miles or 220 kilometers across), lighter mantle, and crust, like the rocky inner planets, many large planetary satellite's like the Earth's Moon, and probably most, if not all, of the newly named "dwarf planets" like Ceres."solstation.com

小行星维斯塔与几个其他小行星的尺寸对比如图所示。这张维斯塔的图片是由“Dawn”探测器拍摄的。当Dawn于2011年7月15日进入绕维斯塔轨道时，这是首次有探测器进入位于火星和木星之间主小行星带中的天体轨道。“与谷神星不同，谷神星的轨道位于太阳系冰线之内或之外，而维斯塔的表面并不像谷神星那样冰冻，维斯塔似乎是一个演化体。1972年，探测到维斯塔表面有玄武岩（由固化的岩浆组成），这表明这个天体在早期历史中曾熔化。维斯塔似乎足够大且足够热，能够因放射性元素衰变和撞击而内部熔化，使得较轻的元素从较密的物质中浮起，形成向表面延伸的层。因此，维斯塔“分化”成一个相对致密的金属核心（直径约136英里或220公里），较轻的地幔和地壳，类似于 rocky 内行星，许多大卫星，如地球的月球，以及可能大多数，如果不是全部，新命名的“矮行星”，如谷神星。