information that is available. These include the exact shape of the asteroid, its orientation, and its albedo. Calculations are further complicated by the effects of shadowing and thermal "reillumination", whether caused by local craters or a possible overall concave shape. The Yarkovsky effect also competes with radiation pressure, whose net effect may cause similar small long-term forces for bodies with albedo variations or non-spherical shapes. As an example, even for the simple case of the pure seasonal Yarkovsky effect on a spherical body in a circular orbit with 90° obliquity, semi-major axis changes could differ by as much as a factor of two between the case of a uniform albedo and the case of a strong north–south albedo asymmetry. Depending on the object's orbit and spin axis, the Yarkovsky change of the semi-major axis may be reversed simply by changing from a spherical to a non-spherical shape. Despite these difficulties, utilizing the Yarkovsky effect is one scenario under investigation to alter the course of potentially Earth-impacting near-Earth asteroids. Possible asteroid deflection strategies include "painting" the surface of the asteroid or focusing solar radiation onto the asteroid to alter the intensity of the Yarkovsky effect and so alter the orbit of the asteroid away from a collision with Earth. The OSIRIS-REx mission, launched in September 2016, studies the Yarkovsky effect on asteroid Bennu. In 2020, astronomers confirmed Yarkovsky acceleration of the asteroid 99942 Apophis. The findings are relevant to asteroid impact avoidance as 99942 Apophis was thought to have a very small chance of Earth impact in 2068, and the Yarkovsky effect was a significant source of prediction uncertainty. In 2021, a multidisciplinary professional-amateur collaboration combined Gaia satellite and ground-based radar measurements with amateur stellar occultation observations to further refine 99942 Apophis's orbit and measure the Yarkovsky acceleration with high precision, to within 0.5%. With these, astronomers were able to eliminate the possibility of a collision with the Earth for at least the next 100 years. See also Asteroid Poynting–Robertson effect Radiation pressure YORP effect References External links Asteroid Nudged by Sunlight: Most Precise Measurement of Yarkovsky Effect – (ScienceDaily 2012-05-24) Orbital perturbations Rotation Asteroids Radiation effects