Observations of solar system objects with GAIA

Abstract

This paper discusses the observability by gaia of solar system objects belonging to the group of near-earth objects, an important issue in the scientific program whose relevance for gaia has been questioned. A simulation based on the most up-to-date distribution of the orbital parameters has been conducted over five years to determine the probability that an object will be in the field of view of the instrument with an apparent brightness larger than the limiting magnitude. It is found (for an albedo of 0.1) that most objects with a diameter larger than 2 km will be observed at least five times by gaia and much more often for larger bodies. The detection survey will be 50% complete for objects of diameter 1 km, while smaller objects (D < 0:5 km) will usually escape detection. Very interestingly, it is shown that most observations will take place at small angular distance from the Sun, a zone where the ground-based surveys are the most biased, allowing to extend the existing surveys of atens and to probe into the virtually unknown population of objects orbiting inside the Earth's orbit. The distribution of the along-scan velocity averages near 40 mas/s (145 arcsec/h), permitting excellent detection during a transit over the focal plane of gaia. gaia scientists therefore will be in a good position to alert a ground-based follow-up program.