Trans-neptunian objects |
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Authors: | Rita Schulz |
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Institution: | (1) ESA Space Science Department, Postbus 299, 2200 AG Noordwijk, The Netherlands , NL |
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Abstract: | Summary. The trans-neptunian objects (TNOs) constitute a new class of solar system object that was discovered only recently to exist
beyond the orbit of Neptune. About 400 trans-neptunian objects have been detected over the past nine years and more than ten
new objects are being discovered every month. All of the TNOs known to date fit into three dynamical classes: the classical, the resonant and the scattered objects. The total mass of the TNOs currently orbiting the Sun is estimated from the observed luminosity distribution to
be of the order of 10–20% of the Earth's mass. However, theoretical investigations of the formation and evolution of the trans-neptunian
belt into its currently observed shape suggest that it was much more massive in the past. The physical characterisation of
TNOs starts to reveal some of the basic properties of these objects, such as size, shape and rotation and provides a first
glance into the diversity of their surfaces. TNOs cover a very diverse range of colours, possibly reflecting different surface
compositions. First evidence for the presence of water ice was found in a spectrum of one TNO while others do not show the
characteristic absorption bands. The TNOs are now regarded as the likely source of some short-period comets. Owing to giant-planet
and collisional perturbations, some TNOs may evolve into Centaurs, i.e. objects orbiting the Sun in the region between Jupiter
and Neptune, which are further perturbed to become Jupiter-family short-period comets. Together with smaller debris generated
by collisional shattering, the TNOs might represent a belt that has evolved from a more massive circumstellar disc into its
present structure.
Received 15 May 2001 / Published online 5 October 2001 |
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Keywords: | , trans-neptunian objects –, outer solar system –, Kuiper belt |
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