Robert Paul Butler (born April 1960) is an astronomer and staff scientist at the Carnegie Institution for Science in Washington, D.C., who searches for extrasolar planets.

He was fascinated by early astronomers and cosmologists like Galileo and Giordano Bruno, who dared to speculate about multiple worlds at a time when such ideas were considered heresy.

[3] While Butler was still working on his master's degree, he and Marcy developed a spectrographic apparatus capable of detecting the tiny gravitational effects of a planet on its host star.

By viewing the starlight they measured through a glass absorption cell containing molecular iodine, they obtained a reference set of spectral lines with sufficient precision to identify the changing light waves caused by a stellar wobble.

[7] In 1995, Marcy and Butler used their Doppler velocity measurement equipment to confirm the discovery by Michel Mayor and Didier Queloz, of the first true exoplanet to be unequivocally identified orbiting a main sequence star, 51 Pegasi b.

[13] In 2001, Butler and Marcy were awarded the Henry Draper Medal from the National Academy of Sciences[14] "for their pioneering investigations of planets orbiting other stars via high-precision radial velocities.