Abstract
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.