小行星的自旋週期極限在探測小行星內部結構時扮演了關鍵角色。直徑大於一公里的小行星，它們的自轉週期不會小於2.2小時，這被稱為「自旋屏障（spin barrier）」，其存在被解釋為小行星是重力束縛的瓦礫堆結構，因此有此自旋週期極限，否則過大的離心力將使小行星崩解。因為不同類型的小行星有不同的體積密度，它們的自旋週期可能不同。我們利用PTF的小行星週期數據庫（Chang et al. 2015, Waszczak et al. 2015）和NEOWISE任務的反照率資料庫（Masiero et al. 2011），來探討X型小行星的自旋屏障，從這個角度來研究小行星的內部結構，其中我們特別關注組成物質為鐵、鎳的M型小行星。我們找到三個各屬於不同化學成份和光譜類型的、自轉速率快的小行星，包括：P型小行星(10305) Grignard、M型小行星(34946) 2286 T-1、E型小行星(10359) 1993 TU36，並假設它們的轉動週期都接近離心力不穩定性條件，以此計算出小行星的體積密度和孔隙度，藉由分析小行星的孔隙度，我們發現E型小行星1993 TU36的內部結構可能發生過重大斷裂事件，P型小行星10305 Grignard和M型小行星 2286 T-1可能為瓦礫堆結構。 ;The spin-rate limit of asteroids plays a key role in probing the interior structure of asteroids. The 2.2-hour spin-barrier has been interpreted as a result of the “rubble-pile” structure of asteroids (i.e., gravitationally bounded aggregations). Because asteroids of different types should have different bulk densities, their spin-rate limits could be different. We use the asteroid rotation periods of the PTF project (Chang et al. 2015, Waszczak et al. 2015) and the NEOWISE albedos (Masiero et al.2011; Mainzer et al. 2011) to study the spin-rate limits of X-type asteroids. In this way, we can study their bulk densities, which in turn probes asteroid interior structure. We are particularly interested in the M-type asteroid, which is mainly made of nickel-iron. We found three fast rotating asteroids classified to different chemical compositions and spectrum types: P-type asteroid, (10305) Grignard；M-type asteroid, (34946) 2286 T-1；E-type asteroid, (10359) 1993 TU36. If their gravitational force and centrifugal force were in balance, we found that E-type asteroid, (10359) 1993 TU36, was probably heavily fractured; P-type asteroid, (10305) Grignard and M-type asteroid, (34946) 2286 T-1, were probably rubble-pile structure.
