自從1992年第一次發現有所謂的海王星外星體(TNO)以來，陸續已有將近千顆的這類星體被歸納在我們的太陽系之中，這些物體甚至有接近或大過冥王星的尺寸。一般來說，TNO指的是我們太陽系之中那些在海王星軌道之外的物體，這類物體的大小分布和數目多寡，將有助於讓我們了解整個太陽系的形成。但是由於這類的物體不但距離地球很遠，而且一般來說他們的尺寸都不大，因此若要直接觀測的話有實際上的困難，只能直接觀測一些大概直徑幾十公里以上但數目又不會很多的物體。然而我們可以藉由掩星的方式來估計出一些尺度比較小的但是數量很多的物體，一般來說我們可以藉由光學波段的掩星方法來尋找一些大小差不多在幾百公尺到幾公里的物體，而且也有一些成果。但那些更小也許更多的物體呢?所以，我們在這裡介紹了我們利用X-ray波段的掩星方法，藉由利用RXTE衛星觀測天蠍座X-1的數據，在毫秒尺度找到了一些可能的X-ray掩星事件，而這方法將可讓我們了解一些大小在100公尺左右或更小的物體的分布情形，而這也是我們第一次在X-ray波段所發現掩星事件，而這方法的持續研究將能讓我們對於太陽系的形成會有更多的幫助，因次在此提出來和大家分享。

Since the first discovery of the Trans-Neptunian objects (TNOs) in 1992, nearly one thousand new members have been added to our solar system, among which several are of size comparable to or even larger than Pluto. TNOs are objects in the outskirt of our solar system beyond the orbit of Neptune. Their population properties such as the size distribution and the total number are valuable information for understanding the formation of the solar system. Because TNOs are distant and small, direct detection is only possible for larger ones with diameter above several tens of kilometers. For smaller ones, which are expected to be more abundant in number, occultation of background stars by TNOs as a way to study their properties has been proposed but without any definite detection so far. We report the possible discovery of such occultation events at
millisecond time scales in the X-ray light curve of Scorpius X-1. The estimated sizes of these occulting TNOs are about or less than 100 m. This is the first time that TNOs of such a small size are detected. Our discovery of the X-ray occultation demonstrates a new method to study smaller TNOs.

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