Andrea Boattini

Atens: Importance among Near-Earth Asteroids and search strategies

Abstract The class of Near-Earth Asteroids known as Atens are very important search targets for two reasons: first, recent studies have shown that they have the highest intrinsic frequency of close encounters with the Earth, and second, they are probably undersampled in the known NEA population, as searches have always concentrated toward the opposition region. In order to remove this bias, we outline a few search strategies to increase their discovery rate with the available equipment, before an all-sky survey up to magnitude 22 is implemented (the Spaceguard Survey). Searches should concentrate on two regions located between 50° and 120° of elongation from the Sun. The Campo Imperatore Near-Earth Object Survey (CINEOS) will be the first specific search program to implement such a strategy.

Spaceguard-1: a space-based observatory for NEO physical characterization and discovery

We investigate a broad system design for a space-based observatory operating at mid-infrared and visible wavelengths to perform physical characterization and discovery of near-Earth objects (NEOs) in the inner solar system. Our goals require measurements that are much more efficiently done from space. The mission objectives are to obtain accurate diameters, albedos and multiband reflectance properties for the known NEOs, and to conduct a search for objects spending most or all their orbital period inside Earths orbit. The purpose is to observe a large fraction of the existing population during a mission operational lifetime of two years. A rather modest sized telescope (70 cm primary mirror and Ritchey-Chretien optical configuration) is found to be adequate to meet the objectives.

Low solar elongation searches for NEO: a deep sky test and its implications for survey strategies

A survey for NEO aiming at 90% completeness for a given size range cannot ignore that a significant fraction of the population is observable essentially only at low solar elongation, in the so called “sweet spots” There are several penalties for such low elongation: poorer observing conditions imply a lower limiting magnitude, shorter available time in each night and a more difficult orbit determination. Our aim is to show that these difficulties can be overcome. We have tested the observation procedures and the mathematical methods of orbit determination on two sweet spot test runs. One was performed at ESO La Silla in Jan–Feb 2005, the other at Mauna Kea in Sept–Dec 2005. The results of the tests are presented in this paper; the observed area was not large enough (especially at Mauna Kea) to discover a significant number of new NEO, the purpose was rather to identify the problems. These tests have allowed us to identify all the key elements to be accounted for in the strategy for a successful sweet spot NEO survey. When very short arc observations from different nights have to be identified, a specific difficulty occurs at the sweet spots: the same set of observations from three nights can be fitted to two incompatible orbits, in most cases including one NEO and one MBA. This can lead to two different failures (false positive, false negative) in deciding whether a NEO has been discovered. The classical theory of preliminary orbits shows that three observations at an elongation less than 116.5° can be compatible with two different orbits. From this theory we have derived an algorithm to find the alternate solution, if it exists, when only one is available. In this way we have generated a set of examples of possible discoveries with two well determined but incompatible solutions. Most of the MBA-NEO alternatives have been solved by finding a known MBA which could be identified; in two cases the MBA solution has been confirmed by a later observation.