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Trojans
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Title: Trojan capture by terrestrial planets
Author: Richard Schwarz, Rudolf Dvorak

The paper is devoted to investigate the capture of asteroids by Venus, Earth and Mars into the 1:1 mean motion resonance especially into Trojan orbits. Current theoretical studies predict that Trojan asteroids are a frequent by-product of the planet formation. This is not only the case for the outer giant planets, but also for the terrestrial planets in the inner Solar System. By using numerical integrations, we investigated the capture efficiency and the stability of the captured objects. We found out that the capture efficiency is larger for the planets in the inner Solar System compared to the outer ones, but most of the captured Trojan asteroids are not long term stable. This temporary captures caused by chaotic behaviour of the objects were investigated without any dissipative forces. They show an interesting dynamical behaviour of mixing like jumping from one Lagrange point to the other one.

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RE: Planetary Trojans
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As Jupiter sinks low in the west these evenings, its influence is holding together a swarm of asteroids located far away from it, very high in the southwestern part of the sky. Jupiter also shapes a second, similar asteroid swarm on its opposite side, very far below the horizon toward the northwest.
These asteroids are locked in a special relationship with the planet due to an odd combination of its gravity and the sun's. The swarms share Jupiter's orbit but precede it and follow it by about a sixth of a circle. Each swarm, Jupiter, and the sun form an equilateral triangle.

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Centaurs
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Cosmic Trojans may sneak comets towards Earth

Many comets swing into the inner solar system every 200 to 300 years. The origin of such so-called "short-period comets" is unknown but the immediate source is thought to be the Centaurs. These are a collection of an estimated million icy objects more than 1 kilometre across on elliptical orbits that come closest to the sun between the orbits of Jupiter and Neptune.
Only about 250 of these Centaurs have been imaged by telescopes. All are on unstable orbits, and have a big chance of receiving a gravitational boost when their orbit brings them near Jupiter or one of the other giant planets. Such perturbation could redirect them into the inner solar system - and possibly towards Earth. As a wayward Centaur approaches the sun, its heat begins to evaporate the icy contents, resulting in a cometary tail.

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Posts: 128733
Date:
Planetary Trojans
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Title: Planetary Trojans - the main source of short period comets?
Authors: Jonathan Horner, Patryk Sofia Lykawka

We present a short review of the impact regime experienced by the terrestrial planets within our own Solar system, describing the three populations of potentially hazardous objects which move on orbits that take them through the inner Solar system. Of these populations, the origins of two (the Near-Earth Asteroids and the Long-Period Comets) are well understood, with members originating in the Asteroid belt and Oort cloud, respectively. By contrast, the source of the third population, the Short-Period Comets, is still under debate. The proximate source of these objects is the Centaurs, a population of dynamically unstable objects that pass perihelion between the orbits of Jupiter and Neptune. However, a variety of different origins have been suggested for the Centaur population. Here, we present evidence that at least a significant fraction of the Centaur population can be sourced from the planetary Trojan clouds, stable reservoirs of objects moving in 1:1 mean-motion resonance with the giant planets (primarily Jupiter and Neptune). Focusing on simulations of the Neptunian Trojan population, we show that an ongoing flux of objects should be leaving that region to move on orbits within the Centaur population. With conservative estimates of the flux from the Neptunian Trojan clouds, we show that their contribution to that population could be of order ~3%, while more realistic estimates suggest that the Neptune Trojans could even be the main source of fresh Centaurs. We suggest that further observational work is needed to constrain the contribution made by the Neptune Trojans to the ongoing flux of material to the inner Solar system, and believe that future studies of the habitability of exoplanetary systems should take care not to neglect the contribution of resonant objects (such as planetary Trojans) to the impact flux that could be experienced by potentially habitable worlds.

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