NASA·APOD每日天文一图2022.6.29 [超高清]

泛星彗星C/2017 K2

Imaged on June 20 2022, comet C/2017 K2 (PanSTARRS) shares this wide telescopic field of view with open star cluster IC 4665 and bright star beta Ophiuchi, near a starry edge of the Milky Way. On its maiden voyage to the inner Solar System from the dim and distant Oort cloud, this comet PanSTARRS was initially spotted over five years ago, in May 2017. Then it was the most distant active inbound comet ever found, discovered when it was some 2.4 billion kilometers from the Sun. That put it between the orbital distances of Uranus and Saturn. Hubble Space Telescope observations indicated the comet had a large nucleus less than 18 kilometers in diameter. Now visible in small telescopes C/2017 K2 will make its closest approach to planet Earth on July 14 and closest approach to the Sun this December. Its extended coma and developing tail are seen here at a distance of some 290 million kilometers, a mere 16 light-minutes away.

这幅广域望远镜照片拍摄于2022年6月20日，在银河边缘的富星区域，泛星彗星C/2017 K2与疏散星团IC4665和亮星蛇夫座β离得很近。这颗泛星彗星是在五年前（2017年5月）被发现的，当时它正在进行从暗淡而遥远的奥尔特云进入内太阳系的首次航程，是在接近太阳的过程中被发现的最遥远的活跃彗星，被发现时距离太阳约24亿公里，这距离介于天王星和土星的轨道距离之间。哈勃空间望远镜的观测表明，这颗彗星有一个直径近18公里的大彗核。C/2017 K2现在已能在小型天文望远镜中观测到，7月14日，它将最接近地球；今年12月，它将最接近太阳。拍这张图时该彗星距离我们约2.9亿公里（仅16光分），可以看到它扩展的彗发和正在“发育”的彗尾。