When a mass passes through the line-of-sight to a distant light source, it bends, magnifies, and distorts the light. This type of event, known as gravitational microlensing, affords us an opportunity to detect massive objects like planets without stars: objects that emit no detectable light of their own. (JAN SKOWRON / ASTRONOMICAL OBSERVATORY, UNIVERSITY OF WARSAW)

First ‘Earth Without A Sun’ Discovered: Thousands More To Be Revealed Soon

The first Earth-sized planet without a parent star has just been discovered.

For countless millennia, planets beyond our Solar System were mere speculation.

Today, we know of over 4,000 confirmed exoplanets, with more than 2,500 of those found in the Kepler data. These planets range in size from larger than Jupiter to smaller than Earth. However, these methods that are so useful for detecting planets around stars, like the transit or stellar wobble methods, cannot detect rogue planets. (NASA/AMES RESEARCH CENTER/JESSIE DOTSON AND WENDY STENZEL; MISSING EARTH-LIKE WORLDS BY E. SIEGEL)

Only since the 1990s has science revealed their existence.

The radial velocity (or stellar wobble) method for finding exoplanets relies on measuring the motion of the parent star, as caused by the gravitational influence of its orbiting planets. Since the planet and star both orbit their mutual center-of-mass, the star won’t remain stationary, but will “wobble” in its orbit, with periodic redshifts and blueshifts revealing the mass and period of the orbiting exoplanet. (ESO)

Today, more than 4,000 exoplanets are known, revealed from their effects on the stars they orbit.

When planets pass in front of their parent star, they block a portion of the star’s light: a transit event. By measuring the magnitude and periodicity of transits, we can infer the orbital parameters and physical sizes of exoplanets. When transit timing varies and is followed (or preceded) by a smaller-magnitude transit, it may indicate an exomoon as well, such as in the system Kepler-1625. (NASA’S GODDARD SPACE FLIGHT CENTER/SVS/KATRINA JACKSON)

But plenty of planets should have no parent stars at all.