Billions of Rogue Alien Planets Lurk Undetected in our Galaxy

Astronomers estimate there are around 16.5 billion Rogue Planets out there.


There are rogue worlds, and then there are those typical exoplanets. Many planets in the cosmos exist in star systems like ours, where several planets orbit their host star. Astronomers have found quite a few of them. In fact, to date, astronomers have confirmed the existence of more than  5,0oo exoplanets in hundreds of planetary systems across the cosmos. Astronomers usually rely on two main methods to find exoplanets in the cosmos. The first one is the radial velocity method, where scientists try and spot the exoplanet’s gravitational pull on its star.

The second method, and probably the most famous one, is the transit method, where astronomers look for changes in the star’s brightness caused by a planet that passes in front of it. However, there are also rogue worlds in the universe. These strange planets do not orbit any known star and behave like galactic drifters. Instead, they travel freely where the universe takes them.


Billions of Rogue Alien Planets

But rogue alien worlds discovered to date are only a few. Astronomers have found around 20 rogue planets or rogue candidate planets. Compared to the 3,917 exoplanets, that’s a huge difference. Shouldn’t there be more rogue planets in the cosmos? That’s the same question astronomers at the University of Leiden in The Netherlands asked before they ran mathematical simulations to find out. They performed a computer simulation of the Orion Trapezium, a tight open cluster of stars in the heart of the Orion Nebula in Orion’s constellation.

NGC 1999: South of Orion Credit & Copyright: Robert Gendler
NGC 1999: South of Orion. Credit & Copyright: Robert Gendler

Researchers gave 500 stars a different number of planets; some were given 4, some 5, and 6 planets each, totaling 2,522 planets. Their masses ranged from three times that of our planet to 130 times the Jupiter mass. Their simulations revealed that 357 of these planets (16.5 percent) eventually became unbound from their host stars within 11 million years, ending up drifting across the cosmos. Some of these stars, although unbound, remained within the clusters. Other star systems captured some planets, but most exoplanets, 282, escaped the star cluster completely and became cosmic wanderers.

Of the 2,522 planets, computer simulations revealed that 75 worlds collided with their host stars. In addition, 35 exoplanets collided with another planet. Let’s take the 16.5 of the exoplanets found to be rouge worlds and extrapolate them across the Milky Way. Astronomers say that there are then around 16.5 billion rogue planets out there, with a total of more than 100 billion planets. The new research has been accepted for publication in Astronomy & Astrophysics and is available on the preprint server arXiv.


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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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