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Asteroid 2012 TC4 is a small ($\sim$10 m) near-Earth object that was observedduring its Earth close approaches in 2012 and 2017. Earlier analyses of lightcurves revealed its excited rotation state. We collected all availablephotometric data from the two apparitions to reconstruct its rotation state andconvex shape model. We show that light curves from 2012 and 2017 cannot befitted with a single set of model parameters -- the rotation and precessionperiods are significantly different for these two data sets and they must havechanged between or during the two apparitions. Nevertheless, we could fit alllight curves with a dynamically self-consistent model assuming that the spinstates of 2012 TC4 in 2012 and 2017 were different. To interpret our results,we developed a numerical model of its spin evolution in which we included twopotentially relevant perturbations: (i) gravitational torque due to the Sun andEarth, and (ii) radiation torque known as theYarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. Despite our modelsimplicity, we found that the role of gravitational torques is negligible.Instead, we argue that the observed change of its spin state may be plausiblyexplained as a result of the YORP torque. To strengthen this interpretation weverify that (i) the internal energy dissipation due to material inelasticity,and (ii) an impact with a sufficiently large interplanetary particle are bothhighly unlikely causes its observed spin state change. If true, this is thefirst case when the YORP effect has been detected for a tumbling body.

Spin Change of Asteroid 2012 TC4 probably by Radiation Torques