A Specific Nongravitational Effect and Asteroid Spin Parameters

Abstract—Additional arguments for the existence of a specific nongravitational effect (NGE) in the asteroid belt, which was discovered more than 10 years ago, are presented. Under the influence of this NGE, the semimajor axes of orbits of low-albedo asteroids increase gradually relative to the semimajor axes of orbits of asteroids with higher albedos. This is confirmed by the albedo–semimajor axis distributions for separate asteroid families. The variation of semimajor axes of orbits for main-belt asteroids induced by the NGE (da) is as large as 10^–6 AU in 10 years. The physical mechanism of the NGE is similar to the cometary one. Therefore, the sign of the da values should depend on the direction of the asteroids’s axial rotation, and absolute values |da| should depend on spin period P. Such a relationship between da and P is also typical of the Yarkovsky effect, but it is 3–4 orders of magnitude weaker than the NGE. The number of asteroids with precisely determined spin directions is very small at the present moment. Therefore, the data on asteroids' spin periods were used to verify the NGE’s existence. More than 12 000 main-belt asteroids with known spin periods were selected from the MPC database. The evolution of orbits of these asteroids within the interval from 2005 to 2016 was calculated numerically, and the corresponding da values were determined. The |da|(P) dependences were plotted and analyzed. The agreement between these dependences and theoretical ones is better than 2σ. The significance of the |da|(P) dependence for asteroids with more accurate spin periods is higher, although such bodies constitute less than half of the total sample. Arguably, the obtained result is another confirmation of the NGE’s existence.