Halley's comet is a case in point. By comparing ancient records against observations made when Halley's comet made its 35th recorded fly-by in 1986, we can see that the comet has not changed much in 2600 years. It still has about the same mass as before, an important bit of information to scientists researching the history of the solar system.
比如由古代彗星資料比對，研究人員發現，直到一九八六年第三十五次哈雷彗星現身，二千六百年循環往復，哈雷彗星沒有太大變化，顯然質量並未損耗，這是從彗星研究太陽系演化的重要訊息。