Methods of detecting exoplanets
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the exoplanets reported as of January 2024 have been observed directly, with even fewer being resolved from their host star.
Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. As of 2016, several different indirect methods have yielded success.
Other possible methods[edit]
Flare and variability echo detection[edit]
Non-periodic variability events, such as flares, can produce extremely faint echoes in the light curve if they reflect off an exoplanet or other scattering medium in the star system.[118][119][120][121] More recently, motivated by advances in instrumentation and signal processing technologies, echoes from exoplanets are predicted to be recoverable from high-cadence photometric and spectroscopic measurements of active star systems, such as M dwarfs.[122][123][124] These echoes are theoretically observable in all orbital inclinations.
Transit imaging[edit]
An optical/infrared interferometer array doesn't collect as much light as a single telescope of equivalent size, but has the resolution of a single telescope the size of the array. For bright stars, this resolving power could be used to image a star's surface during a transit event and see the shadow of the planet transiting. This could provide a direct measurement of the planet's angular radius and, via parallax, its actual radius. This is more accurate than radius estimates based on transit photometry, which are dependent on stellar radius estimates which depend on models of star characteristics. Imaging also provides more accurate determination of the inclination than photometry does.[125]
Auroral radio emissions[edit]
Auroral radio emissions from giant planets with plasma sources, such as Jupiter's volcanic moon Io, could be detected with radio telescopes such as LOFAR.[127][128] If confirmed, the Earth-sized planet candidate Gliese 1151b - whose aurora was suspected to be the source of radio emission from Gliese 1151 system - would be the first exoplanet to be discovered via this method.[129]
Optical interferometry[edit]
In March 2019, ESO astronomers, employing the GRAVITY instrument on their Very Large Telescope Interferometer (VLTI), announced the first direct detection of an exoplanet, HR 8799 e, using optical interferometry.[130]
Detection of dust trapping around Lagrangian points[edit]
Identification of dust clumps along a protoplanetary disk demonstrate trace accumulation around Lagrangian points. From the detection of this dust, it can be inferred that a planet exists such that it has created those accumulations.[132]
Space telescopes[edit]
Most confirmed extrasolar planets have been found using space-based telescopes (as of 01/2015).[140] Many of the detection methods can work more effectively with space-based telescopes that avoid atmospheric haze and turbulence. COROT (2007-2012) and Kepler were space missions dedicated to searching for extrasolar planets using transits. COROT discovered about 30 new exoplanets.
Kepler (2009-2013) and K2 (2013- ) have discovered over 2000 verified exoplanets.[141] Hubble Space Telescope and MOST have also found or confirmed a few planets. The infrared Spitzer Space Telescope has been used to detect transits of extrasolar planets, as well as occultations of the planets by their host star and phase curves.[18][19][142]
The Gaia mission, launched in December 2013,[143] will use astrometry to determine the true masses of 1000 nearby exoplanets.[144][145]
TESS, launched in 2018, CHEOPS launched in 2019 and PLATO in 2026 will use the transit method.