Spin State And Shape Inversion Of Fast Rotating Asteroids

An asteroid with rotational period less than 2 hours is a fast rotating asteroid.Fast rotators occupy a higher percentage among asteroids with diameter less than 0.1km.About 20%asteroids have rotating periods less than 1 hour,and the percentage reaches to 23%for those with periods less than 2 hours,according to near-earth-asteroid observations by October 2020.The proportion of fast rotators is higher in near earth asteroids than in the main belt ones.Fast rotators are small and faint,a long exposure time is needed in observation,which means that the time-integral effect should be considered.As for now,not any brightness model or inverse method was developed considering integral effect,which is considered in this dissertation.Kaasalainen’s model and inverse method are improved.Firstly,Kaasalinen’s model and lightcurve inversion method are introduced.The scattering law,spin state,shape,observing geometry,and their effects on brightness are stated.The brightness calculation method is provided with given physical conditions.An inverse method correlated to aboved model is introduced,which can be used to obtain the spin state and shape model of an asteroid.Secondly,different scattering laws,and scattering parameters are set in lightcurve simulation to see how they affect lightcurves.An improved brightness model of fast rotating asteroids is developed considering time-integral effect.Discrete form of integral is given and used in simulation for observed lightcurves of fast rotating asteroids.Different factors of multiscattering-effect are set in simulation to see how it affects observed lightcurves.Thirdly,based on the brightness model of fast rotators,a method focusing on shape inversion of fast rotators is developed.After the parameter of discrete method is determined,observed lightcurves of fast rotating asteroids are simulated and used for inversion.Shape distribution is used to confirm the advancement.Different scattering parameters,data error,time span,and exposure time are set in simulation to see how they influence on inverse results.Finally,the method is used for real lightcurves to confirm the validity.Lightcurves of asteroid(16)Psyche,(22)Kalliope,and(1036)Ganymed are averaged every 2-5 data points,from which the results are inversed by fast rotating model.The inversed model are compared to the models inversed by Kaasalainen’s model from original lightcurves.