Transit-Timing and Duration Variations for the Discovery and Characterization of Exoplanets
Transiting exoplanets in multi-planet systems have non-Keplerian orbits which can cause the times and durations of transits to vary. The theory and observations of transit-timing variations (TTVs) and transit duration variations (TDVs) are reviewed. Since the last review, the Kepler spacecraft has detected several hundred perturbed planets. In a few cases, these data have been used to discover additional planets, similar to the historical discovery of Neptune in our own solar system. However, the more impactful aspect of TTV and TDV studies has been characterization of planetary systems in which multiple planets transit. After addressing the equations of motion and parameter scalings, the main dynamical mechanisms for TTV and TDV are described, with citations to the observational literature for real examples. We describe parameter constraints, particularly the origin of the mass/eccentricity degeneracy and how it is overcome by the high-frequency component of the signal. On the observational side, derivation of timing precision and introduction to the timing diagram are given. Science results are reviewed, with an emphasis on mass measurements of transiting sub-Neptunes and super-Earths, from which bulk compositions may be inferred.
EA acknowledges support from NASA Grants NNX13AF20G, NNX13A124G, and NNX13AF62G, from National Science Foundation (NSF) grant AST-1615315, and from NASA Astrobiology Institute’s Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C. DCF acknowledges support from NASA under Grant No. NNX14AB87G issued through the Kepler Participating Scientist Program and from the Alfred P. Sloan Foundation. We thank Sam Hadden, Jack Lissauer, Kento Masuda, Mahmoudreza Oshagh, and Jason Steffen for feedback, and we thank the Other Worlds Laboratory at UC Santa Cruz for hospitality while revising this paper.
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