Rogue Planets - What are they Really?

“As a kid, I would count backwards from ten and imagine at one, there would be an explosion—perhaps caused by a rogue planet crashing into Earth or some other major catastrophe.” -Lang Leav

The mysteries of the night sky have always piqued human interest and curiosity. Right from our caveman origins-the Stonehenge being an excellent relic of our ancestor’s stargazing habits- to the modern space race between U.S and erstwhile USSR, astronomy has been one constant facet in our human civilization. With the advent of modern technology and the space race of the 50s we have peaked further and further in search of the mysteries of this very night sky. Well past our galaxy we have been peering everyday into unexplored territory of the ever expanding universe (Thanks to Edwin Hubble, we know this for a fact).

The Milky Way is home to a mind-boggling number of stars and planets.Some are organised in sets, case in point being our Solar System, but not every planet orbits a star.

There are planets which wander the galaxy alone, untethered, without discernible days or nights. They exist in perpetual darkness. A NASA collection of travel posters for extraterrestrial destinations , one of these cold worlds was advertised with the motto: “Visit the planet with no star, where the nightlife never ends.”

Astronomers call these worlds free-floating, or rogue, planets. They are mysterious objects, and a small group of researchers around the world is dedicated to studying them. Przemek Mroz and his team announced the finding of the the smallest known rogue planet recently. The object is between the masses of Earth and Mars,which might seem insignificant in the context of the vast horizons of astronomy, but according to scientists’ best theories about the rise of planetary systems throughout the universe, rogue worlds should exist.

The term rogue planet, might be a misnomer,suggesting that these objects(planets) desert their stars on purpose, striking out on their own to carve a new path through the Milky Way. In reality, rogue planets usually get kicked out of their planet system, banished to a solitary existence in the abyss that is the center of the galaxy.

The beginnings of a planetary system, including our own, are thought to be quite messy. As planets swirl into shape out of the cosmic fog surrounding a newborn star, they jostle each other around. The gravitational game of pool can shove planets toward the sides of a system, and even eject them altogether. Nearby stars can scramble planets too. Some solitary planets might form otherwise, without the assistance of a parent star. These worlds emerge from collapsed clouds of gas and dust,similar to stars, but they lack enough mass to spark the nuclear reactions that make stars shine. These objects, known as “failed stars” — continue to amaze astronomers — resemble planets from afar. Rogue planets are extremely difficult to detect.So astronomers rely on a cosmic quirk of gravity. Imagine a line of sight from Earth’s telescopes to a distant star. When an object crosses that line, its presence can bend and magnify the star’s light, making the star appear more luminous than usual to us. The duration of the brightening signals the nature of the object responsible—a brightening that lasts several days indicates a star, a day means a Jupiter-mass object, and hours suggest something equaling the mass of Earth. The rogue planet recently discovered by Mroz’s team signaled its existence for just a few hours.

The most arduous task is ascertaining if , in fact, a planet is actually ‘rogue’.The stars whose light they bend can’t be their parent stars because they are too far away. And even if a parent star were closer by, it would not be possible to see through the luminous star’s glare. Astronomers must wait years,upto a decade , for the luminous star to move before they can check for a parent star. If no such star appears, the planet is probably going solo. The process is so painstakingly long that scientists haven’t yet reached this milestone for any of the dozen rogue-planet candidates, including the latest, tiniest addition.

Mroz and other astronomers studying rogue planets don’t know how many of these worlds might be coasting through the Milky Way, nor do they know much about the ones they’ve found so far. They can discern the mass of an object through their observation and compare it with worlds in our own solar system. But those analogies cannot fill in the details of rogue planets’ unknown surfaces, or the atmospheres that separate them from space.

One thing’s for sure: Without any star to warm them, rogue planets must be frozen—if not to their core, certainly at their outermost layer. They might not be so alone, either; planets could take their moons with them when they’re hurled out of their cosmic homes.

The orbits of our planets will someday become disturbed anyway. About 5 billion years from now, our Sun will start to die. The star will lose mass until it can no longer hold onto its outermost planets. Neptune and Uranus—and Pluto too—will probably become rogue planets. They will drift away, taking their icy atmospheres with them. Unbothered by the cold of interstellar space, the planets will remain mostly unchanged, relics of a solar system that once huddled close around a warm sun.

Earth will meet a different fate. Dying stars lose mass because they eject gas and dust in all directions, leaving exposed their spent cores. Our planet is expected to become enveloped in this hot mist and vaporized.

For the time being Earth is safe, on a cozy orbit from which we can look out at other, lonelier worlds. Astronomers are eager for the launch of a new telescope scheduled for the mid-2020s.

Souryatanu Saha Written by:

Beetles and eggs and blues and pour a little everything else