Transit-timing variation

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Animation showing difference between planet transit timing of 1-planet and 2-planet systems. Credit: NASA/Kepler Mission.

Transit-timing variation is a method for detecting exoplanets by observing variations in the timing of a transit. This provides an extremely sensitive method capable of detecting additional planets in the system with masses potentially as small as that of Earth. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change. Detecting this effect by measuring the change is known as Transit Timing Variations.[1][2][3][4][5][6] "Timing variation" asks whether the transit occurs with strict periodicity or if there's a variation.

The first significant detection of a non-transiting planet using transit-timing variations was carried out with NASA's Kepler telescope. The transiting planet Kepler-19b shows transit-timing variation with an amplitude of 5 minutes and a period of about 300 days, indicating the presence of a second planet, Kepler-19c, which has a period that is a near-rational multiple of the period of the transiting planet.[7][8]

In 2010, researchers proposed a second planet orbiting WASP-3 based on transit-timing variation,[9][10] but this proposal was debunked in 2012.[11]

Transit-timing variation was used to discover Kepler-9d and gained popularity by 2012 for confirming exoplanet discoveries.[12]

TTV can also be used to indirectly measure the mass of the exoplanets in compact, multiple-planet systems and/or system whose planets are in resonant chains. By performing a series of analytical (TTVFaster[13]) and numerical (TTVFast[14] and Mercury[15]) n-body integrations of a system of six gravitationally interacting, co-planar planets, the initial mass estimates for the six inner planets of TRAPPIST-1, along with their orbital eccentricities, were determined.[16]


  1. ^ The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower
  2. ^ Transit Timing Observations from Kepler: VII. Confirmation of 27 planets in 13 multiplanet systems via Transit Timing Variations and orbital stability
  4. ^ Miralda-Escude (2001). "Orbital perturbations on transiting planets: A possible method to measure stellar quadrupoles and to detect Earth-mass planets". The Astrophysical Journal. 564 (2): 1019–1023. arXiv:astro-ph/0104034Freely accessible. Bibcode:2002ApJ...564.1019M. doi:10.1086/324279. 
  5. ^ Holman; Murray (2004). "The Use of Transit Timing to Detect Extrasolar Planets with Masses as Small as Earth". Science. 307 (1291): 1288–91. arXiv:astro-ph/0412028Freely accessible. doi:10.1126/science.1107822. PMID 15731449. 
  6. ^ Agol; Sari; Steffen; Clarkson (2004). "On detecting terrestrial planets with timing of giant planet transits". Monthly Notices of the Royal Astronomical Society. 359 (2): 567–579. arXiv:astro-ph/0412032Freely accessible. Bibcode:2005MNRAS.359..567A. doi:10.1111/j.1365-2966.2005.08922.x. 
  7. ^ "Invisible World Discovered". NASA Kepler News. 8 September 2011. 
  8. ^ Ballard, S.; Fabrycky, D.; Fressin, F.; Charbonneau, D.; Desert, J.-M.; Torres, G.; Marcy, G.; Burke, C. J.; Isaacson, H.; Henze, C.; Steffen, J. H.; Ciardi, D. R.; Howell, S. B.; Cochran, W. D.; Endl, M.; Bryson, S. T.; Rowe, J. F.; Holman, M. J.; Lissauer, J. J.; Jenkins, J. M.; Still, M.; Ford, E. B.; Christiansen, J. L.; Middour, C. K.; Haas, M. R.; Li, J.; Hall, J. R.; McCauliff, S.; Batalha, N. M.; Koch, D. G.; Borucki, W. J. (2011), "The Kepler-19 System: A Transiting 2.2 R $_⊕$ Planet and a Second Planet Detected via Transit Timing Variations", ApJ, 743: 200, arXiv:1109.1561Freely accessible, Bibcode:2011ApJ...743..200B 
  9. ^ Planet found tugging on transits, Astronomy Now, 9 July 2010
  10. ^ Maciejewski, G.; Dimitrov, D.; Neuh\auser, R.; Niedzielski, A.; Raetz, S.; Ginski, C.; Adam, C.; Marka, C.; Moualla, M.; Mugrauer, M. (2010), "Transit timing variation in exoplanet WASP-3b", MNRAS, 407: 2625, arXiv:1006.1348Freely accessible, Bibcode:2010MNRAS.407.2625M 
  11. ^ M Montalto; et al. (Nov 2, 2012). "A new analysis of the WASP-3 system: no evidence for an additional companion". MNRAS. 427: 2757–2771. arXiv:1211.0218Freely accessible. Bibcode:2012MNRAS.427.2757M. doi:10.1111/j.1365-2966.2012.21926.x. 
  12. ^ The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower
  13. ^ Agol, E.; Deck, K. (2016), "Transit Timing to First Order in Eccentricity", ApJ, 818: 177, arXiv:1509.01623Freely accessible, Bibcode:2016ApJ...818..177A 
  14. ^ Deck, K. M.; Agol, E.; Holman, M. J.; Nesvorn\'y, D. (2014), "TTVFast: An Efficient and Accurate Code for Transit Timing Inversion Problems", ApJ, 787: 132, arXiv:1403.1895Freely accessible, Bibcode:2014ApJ...787..132D 
  15. ^ Chambers, J. E. (1999), "A hybrid symplectic integrator that permits close encounters between massive bodies", MNRAS, 304: 793, Bibcode:1999MNRAS.304..793C 
  16. ^ Gillon, M.; Triaud, A. H. M. J.; Demory, B.-O.; Jehin, E.; Agol, E.; Deck, K. M.; Lederer, S. M.; de, Wit J.; Burdanov, A.; Ingalls, J. G.; Bolmont, E.; Leconte, J.; Raymond, S. N.; Selsis, F.; Turbet, M.; Barkaoui, K.; Burgasser, A.; Burleigh, M. R.; Carey, S. J.; Chaushev, A.; Copperwheat, C. M.; Delrez, L.; Fernandes, C. S.; Holdsworth, D. L.; Kotze, E. J.; Van, Grootel V.; Almleaky, Y.; Benkhaldoun, Z.; Magain, P.; Queloz, D. (2017), "Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1", \nat, 542: 456, Bibcode:2017Natur.542..456G 

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