The most massive and hottest types O3 and O2 are extremely rare, were only defined in 1971 and 2002 respectively, and only a handful are known in total.
質量最大且溫度最高的O2和O3都極為罕見，遲至1971年和2002年才加以定義，各自己知的總數量大約都只有近百顆。