Detection Methods
Explore the various techniques astronomers use to discover exoplanets, from transit photometry and radial velocity measurements to direct imaging and gravitational microlensing.
Topics Covered:
Transit Photometry
This is the most widely used method. When a planet passes in front of its host star (as seen from Earth), it blocks a tiny fraction of the star's light. This creates a small, regular dip in brightness called a transit.
By carefully measuring these dips, astronomers can determine the planet's size, orbital period, and even hints about its atmosphere. NASA's Kepler and TESS missions primarily use this method.
Radial Velocity (Doppler Spectroscopy)
As a planet orbits its star, the star itself also wobbles slightly due to gravitational pull. This wobble causes the star's light spectrum to shift — towards blue when it moves toward us, and towards red when it moves away. This effect is called the Doppler shift.
By studying these shifts, scientists can estimate the planet's mass and orbital characteristics. This method confirmed some of the very first exoplanets.
Direct Imaging
Normally, stars are millions of times brighter than their planets, making planets invisible. But with advanced telescopes and special instruments that block starlight, astronomers can sometimes directly capture images of exoplanets.
This method works best for large planets far from their stars, and it allows scientists to study the atmospheres, colors, and even weather patterns of those worlds.
Gravitational Microlensing
When a planet and its host star pass in front of a distant background star, their gravity bends and magnifies the background star's light — like a natural cosmic magnifying glass. If a planet is present, it creates a small but detectable extra signal in the magnification pattern.
This method can find planets that are too far away or too small for other techniques, even those thousands of light-years from Earth.
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