Asteroids in the Inner Solar System II – Observable Properties

This paper presents synthetic observations of long-lived, coorbiting asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed by taking the limiting semimajor axes, differential longitudes and inclinations for long-lived stability provided by simulations. The intervals are randomly populated with values to create initial conditions. These orbits are re-simulated to check that they are stable and then re-sampled every 2.5 years for 1 million years. The Mercurian sample contains only horseshoe orbits, the Martian sample only tadpoles. For both Venus and the Earth, the greatest concentration of objects on the sky occurs close to the classical Lagrange points at heliocentric ecliptic longitudes of 60 and 300. The distributions are broad especially if horseshoes are present in the sample. The full-width half maximum (FWHM) in heliocentric longitude for Venus is 325 and for the Earth is 328. The mean and most common velocity of these coorbiting satellites coincides with the mean motion of the parent planet, but again the spread is wide with a FWHM for Venus of 27.8 hr and for the Earth of 21.0 hr. For Mars, the greatest concentration on the sky occurs at heliocentric ecliptic latitudes of ±12. The peak of the velocity distribution occurs at 65 hr, significantly less than the Martian mean motion, while its FWHM is 32.3 hr. The case of Mercury is the hardest of all, as the greatest concentrations occur at heliocentric longitudes of 16.0 and 348.5 and so are different from the classical values. The fluctuating eccentricity of Mercury means that these objects can have velocities exceeding 1000 hr, although the most common velocity is 459 hr, which is much less than the Mercurian mean motion. A variety of search strategies are discussed, including wide-field CCD imaging, space satellites such as The Global Astrometry Interferometer for Astrophysics (GAIA), ground-based surveys like The Sloan Digital Sky Survey (SDSS), as well as infrared cameras and space-borne coronagraphs.