exoplanettransits

Exoplanet transits, also known as transit photometry, are detected when a planet passes between its host star and the observer, causing a measurable dip in the star's brightness. This alignment requires an edge-on or nearly edge-on orbital geometry. The resulting light curve shows a distinct, periodic drop in flux corresponding to the planet's passage across the stellar disc.

From the transit signal, several properties can be inferred. The transit depth approximates the planet’s radius relative to the star (planet-to-star radius ratio). The duration and shape of the transit constrain the orbital inclination and impact parameter, while the interval between transits yields the orbital period. Repeated transits provide accurate ephemerides, and transit timing variations can reveal additional planets. When combined with radial-velocity measurements, mass and density can be derived. In transit spectroscopy, the wavelength dependence of the transit depth is used to probe atmospheric constituents and clouds.

Limitations and biases include the geometric requirement for favorable alignment, which makes transits detectable only for a small subset of systems. The method favors short-period and large planets around bright stars, and is susceptible to false positives such as eclipsing binaries or stellar activity. Accurate interpretation requires careful modeling of limb darkening and instrumental effects, and follow-up observations are often necessary to confirm planet candidates.

Impact and outlook: Exoplanet transits have greatly expanded the known population of planets, enabling statistical studies of planetary systems. They support atmospheric characterization with space- and ground-based facilities, including space telescopes and planned missions. Ongoing surveys like Kepler, K2, and TESS continue to discover new worlds, while future instruments aim to improve precision, detect smaller planets, and search for atmospheres around nearby stars.