Exoplanet Detection Methods
EXOPLANETS are planets orbiting stars OTHER than our sun. As of 2026, astronomers have confirmed over 5,500 exoplanets. They're detected indirectly — most are too far and too small to see directly. Two main methods: TRANSIT METHOD and RADIAL VELOCITY (also called Doppler). Both detect tiny effects of a planet on its star.
How they work. TRANSIT METHOD: when a planet passes in front of its star (from our viewpoint), the star DIMS slightly — by a tiny percentage. By measuring the dimming amount and pattern, astronomers can determine planet size and orbit. NASA's Kepler and TESS satellites used this to find thousands. RADIAL VELOCITY: a planet pulls slightly on its star, causing the star to wobble. We can detect this through Doppler shifts in starlight (red and blue shifting). The first exoplanets around sun-like stars (1995) were found this way.
When a planet TRANSITS its star (passes in front of it), what do astronomers OBSERVE?
Other methods. DIRECT IMAGING: blocking the star's light to see the planet directly (only works for big planets far from their stars). GRAVITATIONAL MICROLENSING: a foreground star's gravity bending light from a background star — a planet can show up as a small extra bump. ASTROMETRY: measuring star motion ultra-precisely. Each method finds different planet types. Together they've revealed an astonishing diversity — hot Jupiters close to stars, super-Earths, ice giants, planets around binary stars.
Try It
Hold up a tiny pen against a bright lamp. Move it slowly across so it briefly blocks part of the bulb. The lamp dims when the pen passes. That's exactly how the transit method works — just much, much more precisely.
Detecting exoplanets has gone from impossible (1990) to routine (now). Each year reveals more — including potentially habitable ones. The hunt for "Earth 2.0" is ongoing.
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