For Centauri Dreams, the most exciting part of the exoplanet hunt is the refinement of our models. We know, for example, of numerous planetary systems dominated by gas giants. Now we’re trying to figure out which of these may contain smaller, rocky worlds, and that means learning more about solar system dynamics. A step in the right direction emerges from a June paper that analyzes what happens to moon-sized protoplanets as they evolve in systems with gas giants.
Based on computer simulations, the work assumes a giant planet the size of Jupiter and manipulates the position and mass of the protoplanets in these settings over time, testing four systems with known planets: 55 Cancri, HD 38529, HD 37124 and HD 74156. The most interesting result is the ready formation of terrestrial worlds around 55 Cancri, often with orbits in the habitable zone. HD 38529 also produced a rocky world, one about the size of Mars, and showed conditions favorable to an asteroid belt as well. No further planets evolved around HD 37124 and HD 74156.
“It’s exciting that our models show a habitable planet, a planet with mass, temperature and water content similar to Earth’s, could have formed in one of the first extrasolar multi-planet systems detected,” said Rory Barnes, a postdoctoral researcher at the University of Arizona who is a co-author of the study.
Exciting indeed. 55 Cancri, a G-class star in Cancer 41 light years from Earth, is already thought to be orbited by as many as four planets. Learning more about such systems will help us refine the target list for planet hunting space missions like New Worlds Imager. Remarkably, we may be no more than a decade or so away from being able to see such planets, and transit methods may snare a terrestrial world sooner still.
The paper is Raymond, Barnes and Kaib, “Predicting Planets in Known Extrasolar Planetary Systems. III. Forming Terrestrial Planets,” Astrophysical Journal 644, pp. 1223-1231, with abstract here.
Interesting as all hell. And here I thought that the exoplanet info we’d recieved so far suggested terrestrial planets were rarer than we thought (although I suspect that may very well be the case). I wonder if the discovery of an extrasolar terrestrial planet will make waves with the public at large because the discovery of water in Enceladus certainly hasn’t.
Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope
Authors: Jacob L. Bean, Barbara E. McArthur, G. Fritz Benedict, Amber Armstrong
(Submitted on 11 Sep 2007 (v1), last revised 12 Sep 2007 (this version, v2))
Abstract: We report the discovery of a third planetary mass companion to the G0 star HD 74156. High precision radial velocity measurements made with the Hobby-Eberly Telescope aided the detection of this object. The best fit triple Keplerian model to all the available velocity data yields an orbital period of 347 days and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup respectively for the previously known planets. Preliminary calculations indicate that the derived orbits are stable, although all three planets have significant orbital eccentricities (e = 0.64, 0.43, and 0.25).
With our detection, HD 74156 becomes the eighth normal star known to host three or more planets. Further study of this system’s dynamical characteristics will likely give important insight to planet formation and evolutionary processes.
Comments: 23 pages, 4 tables, 6 figures. Accepted for publication in ApJ. V2 fixed table 4 page overrun
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0709.1656v2 [astro-ph]
Submission history
From: Jacob Bean [view email]
[v1] Tue, 11 Sep 2007 19:31:13 GMT (124kb)
[v2] Wed, 12 Sep 2007 16:09:04 GMT (124kb)
http://arxiv.org/abs/0709.1656
The long-term stability of extrasolar system HD 37124. Numerical study of resonance effects
Authors: Krzysztof Gozdziewski, Slawomir Breiter, Wojciech Borczyk
(Submitted on 29 Oct 2007)
Abstract: We describe numerical tools for the stability analysis of extrasolar planetary systems. In particular, we consider the relative Poincare variables and symplectic integration of the equations of motion. We apply the tangent map to derive a numerically efficient algorithm of the fast indicator MEGNO (a measure of the maximal Lyapunov exponent) that helps to distinguish chaotic and regular configurations. The results concerning the three-planet extrasolar system HD 37124 are presented and discussed. The best fit solutions found in earlier works are studied more closely. The system involves Jovian planets with similar masses. The orbits have moderate eccentricities, nevertheless the best fit solutions are found in dynamically active region of the phase space. The long term stability of the system is determined by a net of low-order two-body and three-body mean motion resonances. In particular, the three-body resonances may induce strong chaos that leads to self-destruction of the system after Myrs of apparently stable and bounded evolution. In such a case, numerically efficient dynamical maps are useful to resolve the fine structure of the phase space and to identify the sources of unstable behavior.
Comments: 11 pages (total), 8 figures. Accepted for publication in MNRAS. The definitive version will be/is available at this http URL The astro-ph version is prepared with low resolution figures. To obtain the manuscript with full-resolution figures, please visit this http URL
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0710.5440v1 [astro-ph]
Submission history
From: Krzysztof Gozdziewski [view email]
[v1] Mon, 29 Oct 2007 16:01:55 GMT (799kb)
http://arxiv.org/abs/0710.5440