Astron. Astrophys. 362, 746-755 (2000)

4. Conclusions

We give explicit, analytic formulas for the solar radiation dynamical effects on the orbits of Near-Earth Asteroids: this includes the radiation pressure due to the absorbed and reflected sunlight, not neglecting the -correction. The effects of zonal albedo variations, with an odd-symmetry with respect to the equator, and of a biaxial ellipsoidal shape are considered. Both are interesting, since they produce long-term variations of the orbital elements which produce accumulation of the orbit perturbation.

For objects with observations spanning a long interval of time and with a high-eccentricity orbit, the dynamical effect of a non uniform albedo can result in a perturbation considerably larger than the other effects considered here. For instance, a conservative assumption about the north/south albedo asymmetry, too small to be detected from the photometry, results in multikilometer perturbation of the orbit of the NEA Icarus during the next close approach to the Earth. When analyzing the radar data which we presume will be taken during this future approach, one should pay a detailed attention to this effect. The perturbation due to the nonsphericity of Icarus shape are still larger then the observation uncertainty, but much smaller than the albedo effects. Our results also indicate a surprisingly large influence of the Poynting-Robertson effect.

We also remind that all perturbations studied in this paper are smaller than those due to the Yarkovsky effect, which is likely to remain the dominant radiation-related perturbation in the NEA orbits. Only for objects with very large north/south albedo asymmetry the direct radiation pressure effect (7) may exceed in magnitude the perturbation due to the Yarkovsky effect.

Since this paper only initiates the application of the radiation force dynamical effect for the NEA orbits, a number of approximations has been adopted. A further progress in removing these simplifications is desirable. For instance, generalization of the results presented in this paper for triaxial ellipsoids or objects of more complex shape may be an interesting extension of this work. Similarly, a more systematic analysis of the albedo variation effects (dropping out the assumption of the axial symmetry and isotropy of the sunlight reflection on the surface) might be another interesting extension of this work.

© European Southern Observatory (ESO) 2000

Online publication: October 24, 2000
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