The occurrence of Jovian planets and the habitability of planetary systems
-
Edited by Robert P. Kirshner, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, and approved December 12, 2000 (received for review November 1, 2000)
Abstract
Planets of mass comparable to or larger than Jupiter's have been detected around over 50 stars, and for one such object a definitive test of its nature as a gas giant has been accomplished with data from an observed planetary transit. By virtue of their strong gravitational pull, giant planets define the dynamical and collisional environment within which terrestrial planets form. In our solar system, the position and timing of the formation of Jupiter determined the amount and source of the volatiles from which Earth's oceans and the source elements for life were derived. This paper reviews and brings together diverse observational and modeling results to infer the frequency and distribution of giant planets around solar-type stars and to assess implications for the habitability of terrestrial planets.
Footnotes
-
↵ * E-mail: jlunine{at}lpl.arizona.edu.
-
This paper was submitted directly (Track II) to the PNAS office.
-
↵ † “Solar-type” stars are considered here to be F-, G-, and K-type stars, on which the Doppler spectroscopic search for planetary companions is focused. The Sun itself is a G-type star, so designated in a well-characterized sequence based on spectral classification, so my use of the term “solar-type” is a loose one.
-
↵ ‡ There is no standardized nomenclature in this field. In this paper, the term “Jovian mass” does not denote an object of exactly one Jupiter mass, but rather one that ranges from 0.1–13 Jupiter masses. The upper mass is the minimum mass for deuterium fusion in solar-composition objects (7), a convenient and perhaps not entirely arbitrary (8) cutoff for planets. The term “giant planets” used earlier in the text is defined here to refer specifically to bodies in the mass range given above that are primarily hydrogen–helium, with a greater or lesser admixture of heavier elements. Such objects implicitly are like our own giant planets in rough composition. There is only one extrasolar planet that we can assign with confidence to be a “giant planet,” because we know its radius, hence bulk density and composition. In our own system, Uranus and Neptune barely qualify, because they are so rich in heavy elements; some planetologists call them “ice giants” to distinguish them from Jupiter and Saturn.
-
↵ § American Astronomical Society Division for Planetary Sciences Meeting 2000, Pasadena, Talk no. 31.02.
- Abbreviations:
- AU,
- astronomical unit;
- D/H,
- deuterium-to-hydrogen ratio;
- SMOW,
- Standard Mean Ocean Water
- Copyright © 2001, The National Academy of Sciences
