How space works
How astronomers find exoplanets
Most exoplanets are discovered through changes in starlight or motion. Each method measures something different, and each favors certain kinds of worlds.
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Transits: a small loss of starlight
A transit occurs when a planet crosses its host star as seen from Earth. The depth of the brightness dip helps constrain the planet-to-star radius ratio. Repeated dips establish a period, while the duration and shape supply information about the crossing geometry. The star's own radius is needed to turn a relative size into a planetary radius.
A transit does not automatically establish mass. Eclipsing stars, blended background sources, and instrumental effects can imitate parts of the signal. Confirmation or statistical validation requires further checks. Only systems whose orbital planes line up suitably with our viewpoint transit, so a missing dip does not establish that a star has no planets.
Radial velocity: the star moves too
A star and its planet orbit their common center of mass. Spectra can reveal the component of the star's motion toward and away from Earth through shifting spectral lines. A repeated velocity pattern can constrain the orbit and the planet's influence on the star. Larger masses and shorter periods are generally easier to detect.
If inclination is unknown, a radial-velocity solution commonly provides a minimum mass, M sin i. A nearly face-on orbit can hide much of the motion from this method. Stellar spots, magnetic activity, and other signals must also be separated from orbital motion. Combining a transit with radial velocity can provide both radius and a much better constraint on true mass.
Images, astrometry, and microlensing
Direct imaging separates light associated with a planet from the glare of its host. Young, hot, widely separated giant planets are favorable targets. Their brightness often needs cooling models to estimate mass, so a directly imaged planet is not necessarily weighed by its light alone.
Astrometry follows the star's changing position across the sky. Microlensing looks for the brief gravitational amplification of a more distant star's light, with a planet perturbing the lensing pattern. Microlensing can probe planetary systems at great distances, but an event usually cannot simply be repeated on demand. These methods expand the range of planets accessible beyond the strongest transit and radial-velocity samples.
A discovery catalog is a filtered view
A method's strengths affect which planets appear first in its catalog. Short-period transits repeat more often during a finite survey. A large planet blocks more light. A massive close companion moves its star more strongly. Wide-orbit planets may need years of observations before their paths are secure.
For that reason, the mix of known planets is not a direct census of all planets in the galaxy. Population studies model survey completeness and detection efficiency. Space Pixel records the archive's discovery method for each profile and links the source solution. The measurement table describes the selected published record; the discovery label alone does not explain every later observation of that planet.