A recent study suggests between 100 and 10,000 rogue planets exist for every star in the Milky Way. This would mean around one quadrillion rogue planets are traveling through our galaxy.

The universe is a wonderful yet mysterious place. The more we explore it, the more we are left perplexed by it. Today, we know that our solar system is not the only star system in the galaxy home to planets. But a few decades ago, this was not the case. Many astronomers theorized that other stars should have planets orbiting them. However, they didn’t have evidence to support their theory at the time. As of writing, NASA has confirmed the existence of 5,235 exoplanets. 9,169 are still waiting for confirmation. And while this may sound like much, it is nothing compared to the estimated 200,000 billion planets believed to exist in the Milky Way Galaxy alone. These worlds are believed to orbit a star or a system of stars. But there are other worlds as well.

What are rogue planets?

Rogue planets are worlds that travel through the galaxy and do not orbit a star. These mysterious and strange worlds did not form in interstellar space. They, once, too, were orbiting their host star. But they were kicked out of their cosmic family for whatever gravitational reason. For example, the planets in our solar system have stable orbits around our star for the foreseeable future. But gravitational perturbations from other worlds, or a passing star, could destabilize the orbit of a planet and swing it out of the system.

How do we find a rogue planet?

We can discover a rogue planet through a technique astronomers call gravitational microlensing. A rogue world can be spotted traveling through space when it gravitationally focuses light from a star in the background as it makes its way in front of it. This study, for example, has proposed hundreds of rogue planet candidates, but astronomers believe these could number in the billions in the Milky Way Galaxy alone. Interestingly, a recent study suggests between 100 and 10,000 rogue planets exist for every star in the Milky Way. This would mean around one quadrillion rogue planets are traveling through our galaxy.

Can life thrive on a rogue planet?

The short answer is yes, life could theoretically thrive on free-floating rogue planets. If Earth, for example, were to be kicked out of the solar system, our entire surface would freeze, including the oceans. (Imagine a planet Earth where life did not come into existence.) Astronomers believe that liquid water would still remain in existence beneath the kilometer-thick ice layer. As explained by Professor Avi Loeb, the subsurface water would be warmed by the radioactivity of isotopes in our planet’s rocky core. Thermal wents could exist on the ocean floor and provide a much-needed environment for single-cell organisms to survive. However, complex life is unlikely to form without an oxygen-rich atmosphere above the ocean and some landmass. However, the only way complex lifeforms could exist on such worlds is that they pre-existed on the planet before the world was kicked out into interstellar space.

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