next up previous contents
Next: About this document ... Up: The Scientific Cases for Previous: Near Earth Objects


Minor Planets

Prepared by G. Cremonese


In the last few years a new interesting subject stimulated a growth of concern on the Solar Systen physics and it regards the Kuiper Belt Objects (KBO), from the name of the first astronomer that raised the hypothesis of the existence of a belt populated by minor bodies beyond the Neptune orbit, almost 50 years ago. This so called "Kuiper Belt" is a likely product of the pre-planetary accretional phases of the Solar System, and may contain the most primitive material accessible to direct investigation. It would represent a great deal to study the Solar System origin and evolution. Several efforts have been spent in surveys to increase the number of known objects, but the large heliocentric distance and the likely low albedo make them difficult because of the low luminosity. Up to now about 60 KBOs, intermediate in size between comets and planets, are now known to exist in stable orbits around the Sun, after 6 years from the first discovery. The physical studies of the known objects and some dynamical models suggested a population estimate, based on limited sampling of the ecliptic, of more than 70000 bodies with diameters > 100 km in the 30 to 50 AU distance range, with a combined mass of order 0.1 Earth masses. Moreover some dynamical differences have been found in the sample of known objects yielding different populations and evolution. For instance 35% of the KBOs reside in the 3:2 resonance with the orbit of Neptune, the so-called "Plutinos" from Pluto that is no longer considered a planet but a KBO. The statistic available on these minor bodies is very poor and it is extremely important to increase the number of known objects to better understand the nature of the distinct dynamical classes discovered up to now that will help us to define better some steps of the evolution of the Solar System and the formation of the planets. Furthermore physical study of some bodies beloging to Centaurus (objects orbiting in the vicinity of the gas giant planets), KBO and Plutinos classes poited out to a marked difference not only due to dynamical reasons as it has been emphasized in some recent papers (Tegler and Romanishin, Nature, 1998). For instance the Centaurus appeared to have a colour (B-V, V-R) slightly redder than the Sun, while some KBOs are the reddest objects known in the Solar System, poiting at two distinct populations. At the moment it is not yet possible to understand in which way this new physical classification can be correlated with the dynamical difference because of the poor statistics. The surface density of the KBOs is estimated around 5.8 per square degree at a red magnitude of 24.8 and for the Centaurus 0.5 per square degree at 24.2. The most recent survey has been performed on a field of 51.5 sq.deg., with single images of 0.094 sq.deg., to red limiting magnitude 22.5 (50% detection threshold). If we would use a wide field camera at the first focus on LBT we would need half number of images to cover the same field, but with a red limiting magnitude of 25 providing a number of discovered objects at least 20 times higher. Furthermore it would be possible to get a much larger statistic even for smaller objects yielding a better definition of the different dynamical classes and at the same time it will allow to get information on their physical characteristics from the colours.



next up previous contents
Next: About this document ... Up: The Scientific Cases for Previous: Near Earth Objects
Guido Buscema
1999-01-29