Frequently Asked Questions
The most-asked questions about exoplanets found by radial velocity.
What is radial velocity as an exoplanet detection method?
Radial velocity (RV) measures the tiny back-and-forth wobble a star undergoes as an orbiting planet tugs on it, causing periodic shifts in the star's spectral lines via the Doppler effect. By tracking those shifts over months or years, astronomers infer the planet's mass, orbital period, and distance from the host star.
Who are the pioneering figures most associated with RV exoplanet discoveries?
Michel Mayor and Didier Queloz of the Geneva Observatory are widely credited with the first confirmed detection of a planet around a sun-like star in 1995. In the United States, Geoffrey Marcy and R. Paul Butler built the long-running Keck and Lick RV surveys that catalogued hundreds of additional worlds.
What was the landmark first discovery made with this technique?
51 Pegasi b, announced in October 1995, was the first exoplanet confirmed orbiting a main-sequence star. It is a hot Jupiter completing an orbit in just over four days, a result that stunned the community because no planet of that type had been expected so close to its star.
Which spectrographs and telescopes are most important to the RV program?
CORALIE at La Silla and HARPS at Paranal (both ESO) have been workhorses in the southern sky, while the HIRES spectrograph on Keck and later the Lick Coudé fed the northern surveys. Newer instruments such as ESPRESSO on the VLT and HARPS-N on the Telescopio Nazionale Galileo push precision toward the few-cm/s level.
How many exoplanets have been found primarily through radial velocity?
Radial velocity accounts for roughly a third of all confirmed exoplanets, with over 1,100 detections logged in the NASA Exoplanet Archive as of recent updates. It remains the single largest detection category, slightly ahead of the transit method.
What are the main limitations of the radial velocity method?
RV is most sensitive to massive planets on short orbits, so it has a strong bias toward hot Jupiters and misses many small, distant, or low-mass worlds. Stellar activity—spots, flares, and granulation—can mimic or mask the tiny Doppler signals produced by Earth-mass planets.
How does radial velocity differ from the transit method?
Transits detect the brief dip in a star's brightness as a planet crosses its face, giving a direct measure of the planet's radius, whereas RV measures the star's velocity wobble and yields a minimum mass. Combining both techniques lets astronomers estimate a planet's density and bulk composition.
What is a 'minimum mass' (M sin i) and why does RV report it?
Because the orbital inclination angle is unknown from Doppler data alone, RV yields only M sin i, the true mass multiplied by the sine of the inclination. For nearly edge-on orbits the value is close to the real mass, but for face-on systems the true mass can be substantially larger.
Where should a newcomer start to learn about RV exoplanets?
The NASA Exoplanet Archive lets you filter the full catalog by detection method and sort by discovery year, which is a hands-on way to see the field's growth. Pairing that with the original 1995 Mayor & Queloz paper and a few review articles on Doppler precision gives both the historical context and the modern technical picture.
What are some of the most celebrated RV discoveries beyond 51 Pegasi b?
HD 80606 b, a planet whose highly eccentric orbit swings it from a scorching to a frigid distance around its star, is a favorite example of RV's reach. The multi-planet system around HD 40307, characterized with HARPS, demonstrated how the method can resolve several low-mass worlds in a single system.