microlensing

Gravitational lensing, the deflection of light by mass, was predicted by general relativity and first measured during the 1919 solar eclipse. Strong lensing produces Einstein rings and multiple images, weak lensing maps dark matter statistically, and microlensing reveals planets through brief brightenings of background stars.

There may be more rogue planets — wandering worlds without stars — than there are stars in the galaxy. If one drifted into our solar system, even a brief passage could destabilize planetary orbits and reshape Earth's climate for millennia.

Rogue planets, also called free-floating planets, are planetary-mass objects that orbit no star. Some were ejected from planetary systems and some may have collapsed from gas clouds on their own. Microlensing surveys suggest they are common, and a thick hydrogen atmosphere could in theory keep a few of them warm enough for liquid water.