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

Only since the 1990s has science revealed their existence.

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

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

Perhaps surprisingly, these rogue planets should be extraordinarily common.

Many young planets get ejected as solar systems form, creating “orphaned” planets.

Others formed as members of insufficiently massive, failed solar systems.

Altogether, rogue planets should outnumber the stars in our Milky Way.

Direct infrared imaging only reveals high-mass rogue planets.

But another method — gravitational microlensing — has begun to change everything.

Any planet passing between us and a star will gravitationally bend the intervening space.

This magnifies, distorts, and creates multiple images of the background star.

From physics, we can then infer the rogue planet’s properties.

In September, the first Earth-sized rogue planet was discovered this way.

Fast imaging is a necessity: the entire event lasted just 42 minutes.

NASA’s Nancy Roman Telescope, launching in the mid-2020s, will conduct a space-based microlensing survey.

By 2030, we’ll discover thousands of microlensed planets.

These otherwise invisible cosmic vagabonds cannot hide from gravity’s inescapable effects.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.