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 organized in star systems just like ours where a number of planets orbit their host star.

Astronomers have found quite a few of them.

In fact, to date, astronomers have confirmed the existence of 3,917 exoplanets in planetary systems across the cosmos.

Andrew-Art / Pixabay

To find exoplanets in the cosmos, astronomers usually rely on two main methods. 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 brightness of the star, 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. They travel freely where the universe takes them.

But rogue alien worlds discovered to date are only a few. In fact, around 20 rogue planets or candidate rogue planets have been discovered by astronomers. Compared to the 3,917 exoplanets that’s a huge difference.

Shouldn’t there be more rogue planets in the cosmos?

That’s the exact same question astronomers at the University of Leiden in The Netherlands asked, before they ran mathematical simulations in order 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 the constellation of Orion.

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

They gave 500 stars a different number of planets, some were given 4, some 5, some were given 6 planets each, totaling 2,522 planets. Their masses ranged between three times that of our planet to as much as 130 times the mass of Jupiter.

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. Some planets were captured by other stars systems, but the majority of the exoplanets, 282 escaped the star cluster completely, and ended up as cosmic wanderers.

Of the 2,522 planets, computer simulations revealed that 75 worlds collided with their host stars. 35 exoplanets collided with another planet.

If we take the 16.5 of the exoplanets found to be rouge worlds and extrapolate them across the Milky Way, astornoemrs 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 the journal Astronomy & Astrophysics and is available on the preprint server arXiv.

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