Volume 541, May 2012
|Number of page(s)||25|
|Section||Planets and planetary systems|
|Published online||19 April 2012|
Debris disks as signposts of terrestrial planet formation⋆
II. Dependence of exoplanet architectures on giant planet and disk properties
Université de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2
rue de l’Observatoire, BP
2 CNRS, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, 33271 Floirac Cedex, France
3 JILA, University of Colorado & NIST, Boulder CO 80309, USA
4 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder CO 80309, USA
5 Department of Astrophysics, Center for Astrobiology, Ctra. de Ajalvir, km 4, Torrejón de Ardoz, 28850 Madrid, Spain
6 Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544, USA
7 Institute of Astronomy, Cambridge University, Madingley Road, Cambridge, UK
8 University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 1A1, Canada
9 Department of Physics, Weber State University, Ogden, UT, USA
10 NASA Goddard Space Flight Center, Code 693, Greenbelt, MD 20771, USA
11 Department of Astronomy, Boston University, 725 Commonwealth Ave, Boston, MA 02215, USA
12 Visiting Investigator, Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
Accepted: 16 February 2012
We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple marginally unstable gas giants. We previously showed that in such systems, the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and cold dust, i.e., debris disks, which is particularly pronounced at λ ~ 70 μm. Here we present new simulations that show that this connection is qualitatively robust to a range of parameters: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk when the giant planets become unstable. We discuss how variations in these parameters affect the evolution. We find that systems with equal-mass giant planets undergo the most violent instabilities, and that these destroy both terrestrial planets and the outer planetesimal disks that produce debris disks. In contrast, systems with low-mass giant planets efficiently produce both terrestrial planets and debris disks. A large fraction of systems with low-mass (M ≲ 30 M⊕) outermost giant planets have final planetary separations that, scaled to the planets’ masses, are as large or larger than the Saturn-Uranus and Uranus-Neptune separations in the solar system. We find that the gaps between these planets are not only dynamically stable to test particles, but are frequently populated by planetesimals. The possibility of planetesimal belts between outer giant planets should be taken into account when interpreting debris disk SEDs. In addition, the presence of ~ Earth-mass “seeds” in outer planetesimal disks causes the disks to radially spread to colder temperatures, and leads to a slow depletion of the outer planetesimal disk from the inside out. We argue that this may explain the very low frequency of >1 Gyr-old solar-type stars with observed 24 μm excesses. Our simulations do not sample the full range of plausible initial conditions for planetary systems. However, among the configurations explored, the best candidates for hosting terrestrial planets at ~1 AU are stars older than 0.1–1 Gyr with bright debris disks at 70 μm but with no currently-known giant planets. These systems combine evidence for the presence of ample rocky building blocks, with giant planet properties that are least likely to undergo destructive dynamical evolution. Thus, we predict two correlations that should be detected by upcoming surveys: an anti-correlation between debris disks and eccentric giant planets and a positive correlation between debris disks and terrestrial planets.
Key words: planets and satellites: formation / planets and satellites: dynamical evolution and stability / infrared: stars / circumstellarmatter / methods: numerical / astrobiology
Three movies associated to Figs. 1, 3, and 7 are available in electronic form at http://www.aanda.org
© ESO, 2012
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