Transit method in the context of "Transiting Exoplanet Survey Satellite"

The Kepler space telescope is an inactive 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 orbit. The principal investigator was William J. Borucki. After nine and a half years of operation, the telescope's reaction control system fuel was depleted, and NASA announced its retirement on October 30, 2018.

Designed to survey a portion of Earth's region of the Milky Way to discover Earth-size exoplanets in or near habitable zones and to estimate how many of the billions of stars in the Milky Way have such planets, Kepler's sole scientific instrument is a photometer that continually monitored the brightness of approximately 150,000 main sequence stars in a fixed field of view. These data were transmitted to Earth, then analyzed to detect periodic dimming caused by exoplanets that cross in front of their host star. Only planets whose orbits are seen edge-on from Earth could be detected. Kepler observed 530,506 stars, and had detected 2,778 confirmed planets as of June 16, 2023.

William J. (Bill) Borucki (born 1939) is a space scientist who worked at the NASA Ames Research Center. Upon joining NASA in 1962, Borucki joined the group conducting research on the heat shield for Apollo program spacecraft. He later turned his attention to the optical efficiency of lightning strikes in the atmospheres of planets, investigating the propensity that these lightning strikes could create molecules that would later become the precursors for life. Subsequently, Borucki's attention turned to extrasolar planets and their detection, particularly through the transit method. In light of this work, Borucki was named the principal investigator for NASA's Kepler space telescope mission, launched on March 7, 2009 and dedicated to a transit-based search for habitable planets. In 2013, Borucki was awarded the United States National Academy of Sciences's Henry Draper Medal for his work with Kepler. In 2015 he received the Shaw Prize in Astronomy.

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. "Timing variation" asks whether the transit occurs with strict periodicity or if there exists 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.

The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable stars (pulsating and eclipsing), discovery of microlensing events, dwarf novae, and studies of the structure of the Galaxy and the Magellanic Clouds. Since the project began in 1992, it has discovered a multitude of extrasolar planets, together with the first planet discovered using the transit method (OGLE-TR-56b) and gravitational microlensing. The project has been led by professor Andrzej Udalski since its inception.