Janus is the sixth of Saturn's known satellites:
orbit: 151,472 km from Saturn
diameter: 178 km (196 x 192 x 150)
mass: 2.01e18 kg
Janus was the god of gates and doorways, depicted with two faces looking in opposite directions; also the root of the English word "January".
Discovered by the French astronomer Audouin Dollfus in 1966.
Dollfus is credited with the discovery of Janus but it's not really certain whether the object he saw was Janus or Epimetheus and his observations led to a spurious orbit. (Walker discovered it independently but his telegram arrived a few hours after Dollfus'.) Larson and Fountain determined in 1978 that there are in fact two moons at about 151000 km from Saturn. This was confirmed in 1980 by Voyager 1.
Janus and Epimetheus are "co-orbital". The orbital radii of Janus and Epimetheus differ by only 50 km, less than the diameter of either. Their orbital velocities are thus very nearly equal and the lower, faster one slowly overtakes the other. As they approach each other they exchange a bit of momentum the end result of which is to boost the lower one into a higher orbit and to drop the higher one to a lower orbit. They thus exchange places. The exchange takes place about once every four years. The orbital data given here is as of the time of the Voyager encounters.
Janus is extensively cratered with several craters larger than 30 km but few linear features. Its surface appears to be older than Prometheus' but younger than Pandora's.
Janus 是土星已知衛(wèi)星中距其第六近的一顆：
公轉(zhuǎn)軌道：距土星 151,472 千米
衛(wèi)星直徑：178 千米（196×192×50）
質(zhì)量：2.01e18 千克
杰納斯是門與門口的神，他被描繪成在相反方向擁有兩張臉。它也是英語(yǔ)單詞“January（一月）”的詞根。
它是在1966年被法國(guó)天文學(xué)家Audouin Dollfus發(fā)現(xiàn)的。
Dollfus被公認(rèn)為發(fā)現(xiàn)了土衛(wèi)十，但這不能肯定。他看到的物體是土衛(wèi)十還是土衛(wèi)十一不能確定，而且他的觀察進(jìn)入了一個(gè)錯(cuò)誤的軌道。（步行者號(hào)獨(dú)立發(fā)現(xiàn)了它，但是它的電報(bào)比Dollfus的晚到幾個(gè)小時(shí)）Larson和Fountain在1978年認(rèn)定事實(shí)上在土星上空大約151000千米處有兩顆衛(wèi)星。這在1980年被旅行者1號(hào)證實(shí)了。
土衛(wèi)十和土衛(wèi)十一是“雙星”，兩者公轉(zhuǎn)軌道相關(guān)僅50千米，連它們?nèi)魏我粋€(gè)的半徑都不到。它們的軌道運(yùn)行速度近似相等。低的、快的那一顆會(huì)慢慢地趕上另一顆，當(dāng)他們相互靠近時(shí)，他們交換一些動(dòng)量。這樣最后導(dǎo)致低的一顆升到一個(gè)高的軌道，而高的一顆降低到低的軌道上。他們就這樣交換位置。
這種轉(zhuǎn)變每四年發(fā)生一次，這里所給出的軌道數(shù)據(jù)是當(dāng)年旅行者號(hào)測(cè)得的。
土衛(wèi)十被廣泛地認(rèn)為擁有大于30千米的環(huán)形山（隕石坑），但少有直線相貌。它的表面看上去比土衛(wèi)十六的古老，但比土衛(wèi)十七的年輕。
orbit: 151,472 km from Saturn
diameter: 178 km (196 x 192 x 150)
mass: 2.01e18 kg
Janus was the god of gates and doorways, depicted with two faces looking in opposite directions; also the root of the English word "January".
Discovered by the French astronomer Audouin Dollfus in 1966.
Dollfus is credited with the discovery of Janus but it's not really certain whether the object he saw was Janus or Epimetheus and his observations led to a spurious orbit. (Walker discovered it independently but his telegram arrived a few hours after Dollfus'.) Larson and Fountain determined in 1978 that there are in fact two moons at about 151000 km from Saturn. This was confirmed in 1980 by Voyager 1.
Janus and Epimetheus are "co-orbital". The orbital radii of Janus and Epimetheus differ by only 50 km, less than the diameter of either. Their orbital velocities are thus very nearly equal and the lower, faster one slowly overtakes the other. As they approach each other they exchange a bit of momentum the end result of which is to boost the lower one into a higher orbit and to drop the higher one to a lower orbit. They thus exchange places. The exchange takes place about once every four years. The orbital data given here is as of the time of the Voyager encounters.
Janus is extensively cratered with several craters larger than 30 km but few linear features. Its surface appears to be older than Prometheus' but younger than Pandora's.
Janus 是土星已知衛(wèi)星中距其第六近的一顆：
公轉(zhuǎn)軌道：距土星 151,472 千米
衛(wèi)星直徑：178 千米（196×192×50）
質(zhì)量：2.01e18 千克
杰納斯是門與門口的神，他被描繪成在相反方向擁有兩張臉。它也是英語(yǔ)單詞“January（一月）”的詞根。
它是在1966年被法國(guó)天文學(xué)家Audouin Dollfus發(fā)現(xiàn)的。
Dollfus被公認(rèn)為發(fā)現(xiàn)了土衛(wèi)十，但這不能肯定。他看到的物體是土衛(wèi)十還是土衛(wèi)十一不能確定，而且他的觀察進(jìn)入了一個(gè)錯(cuò)誤的軌道。（步行者號(hào)獨(dú)立發(fā)現(xiàn)了它，但是它的電報(bào)比Dollfus的晚到幾個(gè)小時(shí)）Larson和Fountain在1978年認(rèn)定事實(shí)上在土星上空大約151000千米處有兩顆衛(wèi)星。這在1980年被旅行者1號(hào)證實(shí)了。
土衛(wèi)十和土衛(wèi)十一是“雙星”，兩者公轉(zhuǎn)軌道相關(guān)僅50千米，連它們?nèi)魏我粋€(gè)的半徑都不到。它們的軌道運(yùn)行速度近似相等。低的、快的那一顆會(huì)慢慢地趕上另一顆，當(dāng)他們相互靠近時(shí)，他們交換一些動(dòng)量。這樣最后導(dǎo)致低的一顆升到一個(gè)高的軌道，而高的一顆降低到低的軌道上。他們就這樣交換位置。
這種轉(zhuǎn)變每四年發(fā)生一次，這里所給出的軌道數(shù)據(jù)是當(dāng)年旅行者號(hào)測(cè)得的。
土衛(wèi)十被廣泛地認(rèn)為擁有大于30千米的環(huán)形山（隕石坑），但少有直線相貌。它的表面看上去比土衛(wèi)十六的古老，但比土衛(wèi)十七的年輕。