A new method to determine the grain size of planetary regolith

► In this work, we presented a new method to determine the grain size of regolith particles by using remote measurements only. ► Therefore, measurements of the thermal inertia performed for the regolith of various objects in the Solar System were utilized. ► The grain size was derived from a comparison of the heat conductivity derived from the thermal inertia measurements with a heat conductivity model. ► We determined the grain size of planetary regolith for a large number of asteroids, the Moon, the martian moons and Mercury. ► We found an anti-correlation between the regolith grain size and the diameter of the planetary body.