arXiv subjects

Paul Wiegert

Publications and source records attributed to Paul Wiegert.

39 records · Page 3Linked to original sources

arXiv1999

Earth Trojan asteroids: A study in support of observational searches

Observational searches for asteroids orbiting near Earth's triangular Lagrange points face unique obstacles. A population of such asteroids would occupy a large projected area on the sky (possibly hundreds of square degrees) and is not favorably placed with respect to the Sun. Here we examine the properties of synthetic populations of Earth ``Trojans'' in order to aid in the optimization of observational searches for them. We find that the highest on-sky projected number densities are not located at the positions of the L4 and L5 points themselves, but rather a few degrees closer to the Sun. Also, asteroids on orbits about the L4 and L5 points typically brighten as the difference between their ecliptic longitude and that of the Sun increases owing to phase effects, but their number density on the sky concurrently falls rapidly.

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arXiv1998

Long-Term Stability of Planets in Binary Systems

A simple question of celestial mechanics is investigated: in what regions of phase space near a binary system can planets persist for long times? The planets are taken to be test particles moving in the field of an eccentric binary system. A range of values of the binary eccentricity and mass ratio is studied, and both the case of planets orbiting close to one of the stars, and that of planets outside the binary orbiting the system's center of mass, are examined. From the results, empirical expressions are developed for both 1) the largest orbit around each of the stars, and 2) the smallest orbit around the binary system as a whole, in which test particles survive the length of the integration (10^4 binary periods). The empirical expressions developed, which are roughly linear in both the mass ratio mu and the binary eccentricity e, are determined for the range 0.0 <= e <= 0.7-0.8 and 0.1 <= mu <= 0.9 in both regions, and can be used to guide searches for planets in binary systems. After considering the case of a single low-mass planet in binary systems, the stability of a mutually-interacting system of planets orbiting one star of a binary system is examined, though in less detail.

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arXiv1997

The Evolution of Long-Period Comets

We study the evolution of long-period comets by numerical integration of their orbits, following comets from their origin in the Oort cloud until their final escape or destruction, in a model solar system consisting of the Sun, the four giant planets and the Galactic tide. We also examine the effects of non-gravitational forces and the gravitational forces from a hypothetical solar companion or circumsolar disk. We confirm the conclusion of Oort and other investigators that the observed distribution of long-period comet orbits does not match the expected steady-state distribution unless there is fading or some similar process that depletes the population of older comets. We investigate several simple fading laws. We can match the observed orbit distribution if the fraction of comets remaining observable after m apparitions is proportional to m to the power -0.6 +/- 0.1 (close to the fading law originally proposed by Whipple 1962); or if approximately 95% of comets live for only a few (~6) returns and the remainder last indefinitely. Our results also yield statistics such as the expected perihelion distribution, distribution of aphelion directions, frequency of encounters with the giant planets and the rate of production of Halley-type comets.

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