Remote Characterization of NEOs
Binzel, Richard
MIT (USA) / Paris Observatory

Upon discovery, an NEO is known only by its orbit and apparent magnitude. Information on its physical characteristics (size, spin, composition) requires follow-up observations. Groundbased remote characterization of NEOs is to date, the most extensive method by which we have physical information on the NEO population as a whole. Spectral measurements, for example, allow an NEO to be recognized as belonging to specific taxonomic classes -- where assignment to a class can be thought as a very first step in remote characterization. For example, knowing the taxonomic class of an NEO can be useful for the first refined estimate of its size. This is because, within most classes, there are available direct measurements that have been made for the albedo (reflectivity) of objects in that class. A reliable albedo estimate, is of course, required for transforming the measured magnitude of an NEO into a reliable estimate of its size. Similarly, categorization of an NEO into a specific class can also provide the first estimates of its composition. Composition may be estimated by identifying a correlation between the spectral characteristics of the NEO (or the class to which it is assigned) and laboratory measurements of meteorites. For several classes, confident links to specific meteorite types can be made. These allow an inference of the detailed properties of the NEO such as likely mineralogy, grain density, bulk density, etc. From these, a first refined estimate of the mass and kinetic energy can be made in the case of a hazardous object. Apophis will be presented as an example where remote characterization has provided a first estimate of its size and composition, which currently form the basis for our physical understanding of this object. In the context of Apophis, an overall review will be made for the current status of remote characterization of the NEO population, with discussion on the prospects for ongoing characterization work.