At a Glance: Exoplanet Detection

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Astronomers have found nearly all exoplanets by examining the light of the planets' host stars. A sensitive telescope can detect a planet by looking for minuscule, periodic dips in starlight.  

Produced by the Space Telescope Science Institute’s Office of Public Outreach.
All images, illustrations, and videos courtesy of NASA except:
·       Illustration of planets orbiting a red dwarf courtesy of ESO
·       Illustration montage of exoplanets courtesy of C. Pulliam & D. Aguilar (CfA)
·       Taurus constellation drawing from Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius, courtesy of the United States Naval Observatory
·       Image of solar spectrum courtesy of N.A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF
·       Animation of planets orbiting star HD 10180 courtesy of ESO/L. Calçada
·       Animation of transiting planet and light curve courtesy of G. Bacon and B. Preston (STScI)
·       Animation of transiting planet with spectrum courtesy of G. Bacon, B. Preston, and J. Godfrey (STScI)
·       Ariane 5 rocket launch image ©2008 ESA – CNES – Arianespace/Photo by Optique Video CSG
·       James Webb Space Telescope animation courtesy of G. Bacon (STScI)
·       Protoplanetary disk animation courtesy of ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO)/M. Kornmesser (ESO)/Nick Risinger ( Sky Survey 2
·       Animation of disk and planet around Beta Pictoris courtesy of ESO/L. Calçada
·       James Webb Space Telescope illustration courtesy of G. Bacon (STScI)/Northrop Grumman
·       Animation of HD 189733 b’s atmosphere courtesy of ESA/Hubble (M. Kornmesser & L. L. Christensen)
·       Animation of planet transiting a star courtesy of ESO/L. Calçada
·       Absorption spectrum diagram courtesy of A. Feild (STScI)
·       Illustration of exoplanet OGLE-TR-L9 b courtesy of ESO/H. Zodet
·       Water, carbon dioxide, and methane molecule animations courtesy of G. Bacon (STScI)
·       Emission spectrum of a planet courtesy of J. Godfrey (STScI)
·       Animation of exoplanet GJ 1214 b courtesy of ESO/L. Calçada
Written by Vanessa Thomas
Designed by John Godfrey
Music courtesy of Association Production Music

Galaxies in space above the Earth's curvature.
A sunrise above a planet's curvature against a backdrop of stars in space.
Text, Astronomers have discovered thousands of planets outside our solar system.
Most of these exoplanets, however, have never been seen.
Astronomers have found nearly all of them by examining the light of the planets' host stars as the light from those stars dims or shifts.
A planet passes in front of a star. A brightness scale below dips from 100% to 99% as the planet traverses in front of the star, then returns to 100% as the planet passes behind the star. This repeats.
Text, DIMMING, As they orbit, some planets pass in front of their stars from our point of view. When they do, they block a tiny bit of their star's light. A sensitive telescope can detect a planet by looking for minuscule, periodic dips in starlight.
By measuring the time that elapses between the dips, astronomers can figure out how long it takes the planet to orbit.
And from the amount of starlight blocked out, they can estimate the planet's size.
A planet orbits a star. A color spectrum bar is displayed above the star. As the planet orbits the star, the output colors on the spectrum bar shift back and forth from left to right. This repeats.
Text, SHIFTING. Although planets are puny compared to most stars, they do exert a small gravitational tug on the stars they orbit. Astronomers can detect this slight swaying motion by studying the star's spectrum. If the lines in a star's spectrum shift back and forth in a regular pattern, an orbiting planet could be pulling the star toward and away from us.
The period of the swaying lines reveals how quickly the planet orbits its star.
How much the lines sway depends on how massive the planet is.