Most Planets In Our Galaxy Don’t Orbit Stars

“Two possibilities exist: Either we are alone in the Universe or we are not. Both are equally terrifying.” —Arthur C. Clarke

In A Nutshell

Our galaxy, the Milky Way, contains anywhere from 200 to 400 billion stars. Astronomers are finding that a large number of these are like our Sun, with planets in orbit around them. Most people, asked to imagine what an alien planet may be like, would see it whizzing around a parent star. For decades, that was the consensus of astronomy. Recent research, however, suggests that rogue planets flying around interstellar space, free from any stars, outnumber the number of stars in our galaxy by 100,000 to 1. Even if every star in the Milky Way had as many planets as are in our solar system, there would still be 12,500 rogue planets for every planet in an orbit.

The Whole Bushel

Scientists have been discovering extrasolar planets—that is, planets outside of our solar system, at a good rate. There are 974 that we know about so far, orbiting 744 stars. A rogue planet is defined as a body with planetary mass that doesn’t orbit a star. Only four specific candidates exist for that title that we know about, but scientists have been able to deduce that there must be many more.

Rogue planets are hard to observe because our current detection methods for extrasolar planets rely on observing the effects they have on their parent star. A planet can pass in front of it during orbit and dim it, or make it wobble with its gravitational pull, both of which we can observe with a telescope. Rogue planets, being without any source of radiation, are much harder to find. They do produce a small amount of infrared radiation, which has allowed us to detect the ones we have so far.

Scientists used to think that all rogue planets were formed during the creation of a typical solar system and ejected out into space, left to orbit the center of the galaxy like stars. This would account for billions of planets that are out there, but recent observations suggest that rogue planets could form independent of a star. Stars form in massive dust clouds, but if a small cluster of dust breaks off, it will form what scientists term a “globulette.” These globulettes are still pretty big, 50 times as wide as the distance between Neptune and the Sun, but not big enough to produce a star. Instead, the dust will condense into a planet, destined to catapult alone through the galaxy.

Could a rogue planet support life? Possibly. There may be subterranean oceans at a suitable temperature, according to astrobiologists. As on Earth, life could evolve around thermal vents, in an ecosystem that requires no sunlight. There’s also the possibility that a rogue planet could pass a lot closer to Earth than those planets around another star, so a rogue planet may be the first extrasolar visit we make as a species.

Show Me The Proof

The Extrasolar Planet Encyclopedia
How to find an extrasolar planet
Rogue planets may form on their own
Rogue Planets Could Harbor Life in Interstellar Space, Say Astrobiologists

  • inconspicuous detective

    very interesting. rouge planets i’d heard of, but not of how numerous they are nor of the possibility they could have life on them! that would be an amazing discovery.

  • Exiled Phoenix

    My god!! Nibiru;)

  • Culture Vulture

    This is giving me space dementia…

  • Jeff Alessi

    Planets without a star couldn’t harbor life because water wouldn’t be liquid, also there would be no reason for the planet to develope an ozone layer (natures radiation shield…) forget these “rogue” marbles.

    • testyardallen

      Would disagree with you there friend. If the planet’s core remain hot for billions of years and it is surrounded by water ice there is a possibility that it could harbor life. Internal heating will melt the ice into water. And you don’t need an ozone layer to filter out the radiation. Europa, the moon of Jupiter is thought to be bombarded by a huge amount of radiation emanating from Jupiter’s magnetic field. I think it is about Europa’s a million rads a day, where 400 is the 50% lethality level for a human being. However, it’s ice is believed to be a huge shield against the radiation.

      Internal heating to help melt ice into water plus a thick layer of ice protecting it’s interior from radiation = possibility of life. And that is just on Europa. I would think that, provided the planet is made up of the right composition, chances are good for it to harbor life.

      Have a nice day! 🙂

  • Kaydot Mcdiamonds

    Nice list. Let’s just hope Nibiru or any other rogue planet isn’t on a collision course with Earth.

  • Hillyard

    Very interesting. I thought that the idea of ‘rouge planets’ was strictly sci-fi.

  • Prarthana

    Any appromixate numbers ? fascinating to know about our own galaxy.
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