Geoscience Reference
In-Depth Information
this mission. In particular, Gaia will also produce a major breakthrough in
our knowledge of the asteroids.
In what follows we will present a forcedly brief summary of the results
of a number of investigations carried out since a couple of years by our-
selves and by a number of other scientists from different European coun-
tries which have been active in the Gaia Solar System Working Group.
Interested readers may find copies of interesting presentations made during
different meetings of the Gaia SSWG at the URL address http:www.obs-
nice.fr/tanga/SSWG/ (and links within it).
According to a large body of simulations carried out these years, Gaia
astrometric data will be so accurate that asteroid orbital elements computed
using Gaia observations alone, spanning over only 5 years, will be more pre-
cise than those resulting from all ground-based observations obtained over
200 years of ground-based astrometry, including also new observations that
will be presumably obtained from the ground in the lapse of time between
now and the end of the operational lifetime of the mission, expected to be
launched in 2011. This apparently extravagant conclusion is fully justified
by the unprecedented accuracy of Gaia astrometry, which is a major prop-
erty of the overall Gaia concept. Simulations indicate that Gaia astrometric
data will allow us to derive the masses of about 100 Main Belt asteroids,
by means of measurements of tiny mutual perturbations occurring during
mutual asteroid-asteroid close approaches. This particular topic is exten-
sively discussed elsewhere,
1
and will not be further developed in the present
paper. In addition to masses, the unprecedented astrometric accuracy of
Gaia observations will also make it possible in many cases to measure the
tiny deviations of the observed motion with respect to the predictions of
newtonian dynamics, due to the first correction terms predicted by General
Relativity. In particular, for the most eccentric orbits with small semi-major
axes, like in the case of several near-Earth asteroids, the secular perihelion
precession will be measurable and compared to the relativistic predictions.
With respect to the current situation, in which relativistic effects have been
measured only in the case of the planet Mercury, Gaia will extend the
available measurements to several tens of objects. Finally, Gaia data are
expected to provide also direct determinations of a Yarkovsky-driven drift
in orbital semi-major axis,
2
another major advancement with further impli-
cations for studies of the thermal properties of asteroid surfaces and of the
dynamical evolution of asteroid families.
Another major application of Gaia will be the direct measurement of
sizes of objects having diameters down to a few tens of kilometers. Coupled
