The HD 40307 planetary system: Super-Earths or mini-Neptunes?

Rory Barnes, Brian Jackson, Sean N. Raymond, Andrew A. West, Richard J. Greenberg

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Three planets with minimum masses less than 10 M orbit the star HD 40307, suggesting these planets may be rocky. However, with only radial velocity data, it is impossible to determine if these planets are rocky or gaseous. Here we exploit various dynamical features of the system in order to assess the physical properties of the planets. Observations allow for circular orbits, but a numerical integration shows that the eccentricities must be at least 10-4. Also, planets b and c are so close to the star that tidal effects are significant. If planet b has tidal parameters similar to the terrestrial planets in the solar system and a remnant eccentricity larger than 10-3, then, going back in time, the system would have been unstable within the lifetime of the star (which we estimate to be 6.1 ± 1.6 Gyr). Moreover, if the eccentricities are that large and the inner planet is rocky, then its tidal heating may be an order of magnitude greater than extremely volcanic Io, on a per unit surface area basis. If planet b is not terrestrial, e.g., Neptune-like, these physical constraints would not apply. This analysis suggests the planets are not terrestrial-like, and are more like our giant planets. In either case, we find that the planets probably formed at larger radii and migrated early-on (via disk interactions) into their current orbits. This study demonstrates how the orbital and dynamical properties of exoplanet systems may be used to constrain the planets' physical properties.

Original languageEnglish (US)
Pages (from-to)1006-1011
Number of pages6
JournalAstrophysical Journal
Volume695
Issue number2
DOIs
StatePublished - Apr 20 2009

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Neptune (planet)
planetary systems
Neptune
planets
planet
eccentricity
stars
physical properties
physical property
orbits
Io
terrestrial planets
circular orbits
extrasolar planets
numerical integration
solar system
radial velocity
volcanology

Keywords

  • methods: N-body simulations - planetary systems
  • stars: individual (HD 40307)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The HD 40307 planetary system : Super-Earths or mini-Neptunes? / Barnes, Rory; Jackson, Brian; Raymond, Sean N.; West, Andrew A.; Greenberg, Richard J.

In: Astrophysical Journal, Vol. 695, No. 2, 20.04.2009, p. 1006-1011.

Research output: Contribution to journalArticle

Barnes, Rory ; Jackson, Brian ; Raymond, Sean N. ; West, Andrew A. ; Greenberg, Richard J. / The HD 40307 planetary system : Super-Earths or mini-Neptunes?. In: Astrophysical Journal. 2009 ; Vol. 695, No. 2. pp. 1006-1011.
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