Transit-timing variation is a method for detecting exoplanets by observing variations in the timing of a

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

. 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. "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 Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

. The transiting planet

Kepler-19b Kepler-19b is a planet orbiting around the star Kepler-19. The planet has an orbital period of 9.3 days, with an estimated radius of roughly 2.2 times that of the Earth Earth is the third planet from the Sun and the only astronomical ...

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 Kepler-19c is an extra-solar planet orbiting the star Kepler-19 approximately 717 light years from Earth. Discovery The planet was discovered as a result of examinations of data from the previously discovered exoplanet, Kepler-19b. Timing va ...

, which has a period that is a near-rational multiple of the period of the transiting planet. In 2010, researchers proposed a second planet orbiting

WASP-3 WASP-3 is a magnitude 10 yellow-white dwarf star located about 800 light-years away in the Lyra constellation. It appears to be variable; it "passed from a less active (log R'_hk=-4.95) to a more active (log R'_hk=-4.8) state between 20 ...

based on transit-timing variation, but this proposal was debunked in 2012. Transit-timing variation was first convincingly detected for planets

Kepler-9b __NOTOC__ Kepler-9b is one of the first planets discovered outside the solar system (exoplanets) by NASA's Kepler Mission. It revolves around the star Kepler-9 within the constellation Lyra. Kepler-9b is the largest of three planets detected in ...

and

Kepler-9c Kepler-9c is one of the first seven extrasolar planets, exoplanets, discovered by NASA's Kepler Mission, and one of at least two planets orbiting the star Kepler-9. Kepler-9c and Kepler-9b were the first exoplanets confirmed to be transiting thei ...

and gained popularity by 2012 for confirming exoplanet discoveries. 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) and numerical (TTVFast and Mercury) 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.

References

External links

TTV papers
{{Exoplanet Exoplanetology Articles containing video clips Stellar occultation