We propose to use the rotation period to constrain the average density of an object with  gravitationally confined surface. The average density is inverse proportional to the square of the rotation period, while independent of the size of the object. The lower limit of the average density can be written as $\rho_0=10.9 {\ \rm g\ cm^{-3}}\left(\frac{{\ \rm hours}}{P}\right)^2$.
An asteroid with rotating period shorter than 0.7 h should consist of some unknown matter, or it is a whole rock or a bulk of ice with no rubble piles on the surface. 

https://chinaxiv.org/abs/202307.00106

Qian, Lei,Pan, Zhichen,Zhu, Boqin.(2023).Constraints on the Average Density of Gravitationally Confined Objects with the Spin Period.中国科学院科技论文预发布平台.doi:10.12074/202307.00106V1