Geoscience Reference
In-Depth Information
with the above-mentioned mass derivations, Gaia will produce a data-set
of about 100 average densities of asteroids belonging to most taxonomic
classes. This will be certainly a major milestone in the history of aster-
oid research. Major Gaia contributions will not come, however, uniquely
from astrometric and high-resolution data. Very important applications will
come also from disk-integrated spectrophotometric observations. An obvi-
ous application of the multi-band data collected by Gaia will be asteroid
taxonomy. Another major application will be the derivation of spin proper-
ties and overall shapes for thousands of asteroids as a nice exploitation of
Gaia disk-integrated photometric data. The present paper is mainly devoted
to summarize the results of preliminary analyzes of these topics.
2. The Measurement of Sizes
The determination of asteroid sizes with Gaia will be obtained by means of a
careful analysis of their generated signals in the Gaia focal plane. We give in
what follows a general summary of the basic ideas and the algorithms that
have been developed to attack the problem of asteroid size measurements,
and we discuss the general results of a large body of numerical simulations.
An assessment of the capability of Gaia in determining asteroid sizes
is based on a detailed simulation of the signals that will be produced by
these objects. In particular, for the purposes of size determinations, we deal
with the Gaia astrometric focal plane. We remind here that every object
will be observed many times (typically several tens, according to current
simulations) in different sky locations, during the operational lifetime of
the mission. Asteroidal sources detected by Gaia will have two major prop-
erties: first, they will be (at least those above the resolution limit of the
optics) extended sources; second, they will have an apparent and measur-
able motion across the Gaia focal plane during each single detection. We
note that the measurement of this motion will be of primary importance
for the purposes of asteroid orbit reconstruction, but this is not the topic
of the present discussion.
The measurement of asteroids' apparent angular sizes will be possible,
in principle, down to a limit that must be determined. The fact of dealing
with moving objects, in this respect, is very important because this will
influence the actual signals recorded by the Gaia detectors.
A detailed model of the expected asteroid signals is an obvious pre-
requisite to carry out any analysis of the predicted performances of Gaia
in measuring asteroid sizes, and also to derive an estimate of the shift
