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Structure of the Edgeworth-Kuiper Belt (EKB) dust disk and implications for extrasolar planet(s) in 8 Eridani

J.-C. Lioua, H. A. Zookb, J. S. Greaves0, W. S. Holland0, H. Boehnhardtd and J. M. Hahne aLockheed Martin Space Operations, Houston, TX, USA.

bNASA Johnson Space Center, Houston, TX, USA.

°Joint Astronomy Center, Hilo, HI, USA.

dEuropean Southern Observatory, Chile.

eLunar and Planetary Institute, Houston, TX, USA.

Numerical simulations of the orbital evolution of dust particles from Edgeworth-Kuiper Belt (EKB) objects show that the three giant planets, Neptune, Jupiter, and Saturn impose distinct and dramatic signatures on the overall distribution of EKB dust particles. The features are very similar to those observed in the dust disk around the nearby star e Eridani. Numerical simulations of dust particles in the e Eridani system show that planetary perturbations may be responsible for the observed features.

1. INTRODUCTION

Over the past 10 years infrared surveys have discovered many stellar systems with dust rings or disks around the central stars. Small dust particles (micrometer to millimeter sized), once created from their large parent objects, spiral slowly toward the central star via Poynting-Robertson (PR) and stellar wind drag [1], On their way toward the star, dust particles would interact with planets if planets exist in the system. The three major planetary perturbations on dust particles are resonance trapping, gravitational ejection, and secular perturbation. These perturbations may cause large-scale features on a dust disk. A good example is our Solar System's zodiacal cloud. Resonance trapping with the Earth triggers the formation of an enhanced dust ring around the Earth's orbit [2, 3] while secular perturbation causes the plane of symmetry of the cloud to be different from the invariable plane [4]. Similar features should exist in the EKB dust disk in the outer Solar System and, in fact, have been observed in several circumstellar dust disks. By analyzing the long-term evolution of dust particles under interactions with the planets in our Solar System, we may be able to decode some of the structures in other circumstellar dust disks and use the information to identify the existence of extrasolar planets.

2. STRUCTURE OF THE EKB DUST DISK

Since the discovery of the first EKB object in 1992, more than 280 trans-Neptunian objects have been discovered as at the end of July 2000. The dust production rate in the EKB region should be at least comparable to that in the main asteroid belt. Numerical simulations of dust particles between 1 and 100 |im from the EKB region show that giant planets induce large-

scale structures on the EKB dust disk [5, 6]. Trapping into exterior mean motion resonances (MMRs) with Neptune dominates the orbital evolution of dust particles 5 p,m and greater from the EKB region. The main resonances are the 2:1 and 3:2 exterior MMRs. Trapping into MMRs with Uranus is rare because gravitational perturbations from Neptune usually make the resonance trap highly unstable. Once particles escape MMRs with Neptune, they continue to spiral toward the Sun. About 80% of the particles are eventually ejected from the Solar System by Jupiter and Saturn. The signatures of giant planets imprinted on the EKB dust disk, due to these effects, include: (1) the deviation of radial spatial density distribution from that determined by PR drag alone; (2) an enhanced ring-like structure along the orbit of Neptune; (3) a brightness variation along the ring with an opening (a dark spot) located where Neptune is and with two bright arcs about 70° apart on either side of Neptune; (4) a seasonal variation of features in the ring that moves along with Neptune's orbital motion; and (5) a relative lack of particles inside about 10 AU.

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