By Soncirey Mitchell
Reader Staff
The average person on the street thinks about planets as large, spherical rocks orbiting their respective sun — but that isn’t always the case. There are also rogue planets (a.k.a. free-floating planets or isolated planetary-mass objects) that float around the universe unbound gravitationally to any one star.
The Milky Way alone is estimated to have billions or trillions of rogue planets, though the likelihood of one making its way to our neck of the woods is negligible. There are several possible origins for iPMOs, but the two leading theories are that they’re created like a star outside of a planetary system (and that, in itself, can mean many different things) or that they’re regular planets that, for one reason or another, were ejected from their original orbits. Nothing is set in stone in terms of iPMOs, as far as astronomers and physicists are concerned, but the International Astronomical Union has proposed that iPMOs that form through the collapse of a gas cloud or disk — like stars — should be classified as sub-brown dwarfs. Brown dwarfs, or failed stars, are lighter than true stars and consequently cannot sustain stable hydrogen fusion; therefore, sub-brown dwarfs would be even smaller. Flunked out stars, if you will.
Astronomers can discover iPMOs through a phenomenon called microlensing, which doesn’t show the rogue planets so much as it shows their effects on surrounding light waves. The gravitational field of the planet — or another celestial body — acts as a magnifying glass, concentrating light from distant stars when it passes in front of them and creating a spike in brightness visible to sensitive telescopes.
Microlensing reveals an object’s presence, and measuring the duration of the spike and the increase in brightness reveals its mass. Members of the Microlensing Observations in Astrophysics and the Optical Gravitational Lensing Experiment have identified 10 probable rogue planets comparable to Jupiter’s mass within the Milky Way, leading some to estimate that there are between 0.25 and two Jupiter-like iPMOs for every star in that galaxy.
It is the fate of most rogue planets to float alone through space forever, though they can interact with stars and planetary systems as they pass by. iPMOs can become weakly bound to a star and even replace exoplanets already in orbit, staying for a time before continuing on their journey. During this time, the planet may introduce new chemical elements or compounds to the system, potentially spreading the ingredients necessary to develop life.
Some rogue planets escape this lonely fate by forming a binary or triple system with one another, floating through space locked in a reciprocal embrace. Forty possible binary iPMO systems have been discovered in the Orion Nebula, adding another wrinkle to the puzzle of how iPMOs are formed. If they began like typical stars, then we need to understand why the original cloud or disk of dust and gas was dense enough to split into two, but not dense enough to form protostars. If they formed as typical planets and were ejected into interstellar space, then the question becomes: How and why did they stay together?
From a layman’s perspective, their formation as sub-brown dwarfs orbiting one another makes the most sense, but the idea of two planets leaving their system together is far more romantic. You could fully anthropomorphize them as literal star-crossed lovers fleeing an ill-fitting orbit, but even if you see them as nothing more than masses of gas and rock, it’s nice to know that they don’t have to be alone.
The vastness of space makes it an inherently lonely place, and yet humanity continues to venture out in search of other life like our own, though we may never live to see such a discovery. In that way, binary rogue planets are an inspiration, demonstrating how fitting pairs can find one another in all that void, despite the laws we ascribe to the universe. Not only that, but iPMOs potentially carry life-giving chemicals to new solar systems and, with them, our hope for companionship. Maybe one day these wandering planets will lead humanity to new peoples, cultures and friendships.
