Volume 591, July 2016
|Number of page(s)||16|
|Section||Planets and planetary systems|
|Published online||16 June 2016|
Predictable patterns in planetary transit timing variations and transit duration variations due to exomoons
1 Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2 Luiter Straße 21b, 47506 Neukirchen-Vluyn, Germany
3 Center for Science and Technology, Schenectady County Community College, Schenectady, NY 12305, USA
4 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
5 USRA NASA Postdoctoral Program Fellow, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
6 Astronomy Department, University of Washington, Seattle, WA 98195, USA
7 NASA Astrobiology Institute’s Virtual Planetary Laboratory, Seattle, WA 98195, USA
Received: 22 March 2016
Accepted: 12 April 2016
We present new ways to identify single and multiple moons around extrasolar planets using planetary transit timing variations (TTVs) and transit duration variations (TDVs). For planets with one moon, measurements from successive transits exhibit a hitherto undescribed pattern in the TTV-TDV diagram, originating from the stroboscopic sampling of the planet’s orbit around the planet–moon barycenter. This pattern is fully determined and analytically predictable after three consecutive transits. The more measurements become available, the more the TTV-TDV diagram approaches an ellipse. For planets with multiple moons in orbital mean motion resonance (MMR), like the Galilean moon system, the pattern is much more complex and addressed numerically in this report. Exomoons in MMR can also form closed, predictable TTV-TDV figures, as long as the drift of the moons’ pericenters is sufficiently slow. We find that MMR exomoons produce loops in the TTV-TDV diagram and that the number of these loops is equal to the order of the MMR, or the largest integer in the MMR ratio. We use a Bayesian model and Monte Carlo simulations to test the discoverability of exomoons using TTV-TDV diagrams with current and near-future technology. In a blind test, two of us (BP, DA) successfully retrieved a large moon from simulated TTV-TDV by co-authors MH and RH, which resembled data from a known Kepler planet candidate. Single exomoons with a 10% moon-to-planet mass ratio, like to Pluto-Charon binary, can be detectable in the archival data of the Kepler primary mission. Multi-exomoon systems, however, require either larger telescopes or brighter target stars. Complementary detection methods invoking a moon’s own photometric transit or its orbital sampling effect can be used for validation or falsification. A combination of TESS, CHEOPS, and PLATO data would offer a compelling opportunity for an exomoon discovery around a bright star.
Key words: eclipses / methods: numerical / planets and satellites: detection / planets and satellites: terrestrial planets / planets and satellites: dynamical evolution and stability / techniques: photometric
© ESO, 2016
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