Huge Estimate Of Rogue Planets Made | Out Of This World Weekly

When we usually think of planets, an image of planets circling around their parent star pops to mind. These planets are usually imagined to orbit their host star until that star becomes unstable and vaporizes the planets in a huge explosion. Now, researchers at KIPAC have proposed that this view of planets is by far less common than previously thought. Using gravitational microlensing to make their estimate, they concluded that there may be 100,000 rogue planets for every star in the Milky Way. These rogue planets may have once had a star but now wander freely through space, no longer orbiting any star. This new estimate is huge in comparison to the amount of planets thought to be orbiting stars, which was last thought to be 1.6 planets per star.

Can these rogue planets survive when they are so far out in space that they no longer receive any significant light or heat from nearby stars? It’s quite possible that these planets could have trapped heat from the formation. This heat could be coming from a radioactive source in their interior, tectonic activity, or heat trapped in greenhouse type atmospheres. With the wide range of temperatures and conditions that bacteria can live in, it’s quite possible that these rogue planets could even support life. If there are more than 50,000 rogue planets for every planet orbiting a star this significantly improves those chances for life, especially since the estimate for planets in the Milky Way stands at 160 Billion.

Indeed, with this high an amount of rogue planets we may have to reconsider if planetary formation always occurs around a star. It may very well be possible that planets can form in interstellar dust clouds while not orbiting a star. It is also possible that more planets are ejected from their star due to gravitational effects that previously thought. While this estimation brings about many new ideas about the composition of the galaxy, confirming this number may be extremely difficult. Rogue planets are relatively small, don’t emit light or much heat, and may be relatively stationary or moving at very fast speeds. It is only through using gravitational microlensing that we have been able to detect these rogue planets. To study this phenomena we will need a whole new class of telescopes or to much refine our gravitational lensing techniques. Understanding these rogue planets could possibly give us insights into our galaxy that we have not yet considered.


  1. How did you calculate 160 Billion planets in the Milky Way?
    I'm curious because it is pretty commonly stated as fact that there are around 400 Billion STARS in the Milky Way. Even if you took the previous apparently conservative approximation of 1.6 planets per star, that would give you 640 Billion planets, and if you these "new findings" your article talks about, that number jumps to 20 Quadrillion planets.
    Please clear up this discrepancy. Thanks

    1. If you want to use maximum estimates, you will get larger numbers. However, using conservative estimates allows me to be confidant in saying there Are 160 Billion planets instead of saying there May Be as much as 640 Billion planets.

      While you can find estimates of stars in the Milky Way that range from 100 Billion to 400 Billion or more, I decided to base my estimate on the more conservative figure. This figure is also used in the Nature international journal of science article which can be found at:

      The 160 Billion planet article was made a month Before the rogue planet information was available. If you account for the rogue planets, the number of planets in the Milky Way may indeed be in the Quadrillions.

      When we consider the amount of rogue planets, the number of planets in the universe jumps to the 1 to 100 Octillion range (100,000,000,000,000,000,000,000,000,000).

      Planetary estimates are undergoing a dramatic shift as we have begun to find so many of them within the last 5 years. As new information is gathered estimates may be revised.