Apparently, planets don't always orbit stars

Because sometimes nature just likes to mess with you, here's CFBDSIR2149. It's an object in space — a relatively nearby object in space, as evidenced by the fact that this is an actual picture of it — and scientists are pretty sure that it's a planet. If they're right, then CFBDSIR2149 is also a "rogue planet", so called because it doesn't actually orbit a star. Seriously. It's just hanging out in space, doing its own thing.

Also, it's not the first time a rogue planet has been identified.

In fact, these things are probably not even particularly rare. A 2011 study published in the journal Nature estimated that rogue planets might even outnumber normal stars by 2-to-1 in the Milky Way Galaxy.

It's worth noting that rogue planets do not seem to be Earth-like. For instance, CFBDSIR2149 is roughly the size of Jupiter and, with an estimated surface temperature of 850 degrees Fahrenheit, it is not exactly a pleasant place for people. As for rogue planets come from: That's a mystery. One of the things that makes CFBDSIR2149 special, according to Phil Plait, is that it's actually close enough to us that we can collect some good data on the thing.

Read Phil Plait's description of CFBDSIR2149 at the Bad Astronomy Blog

Read the research paper announcing the discovery of CFBDSIR2149

Read about rogue planets in a Science News story from last year

Image: CFHT/P. Delorme


  1. What qualifies an object as a planet if it does not orbit a star or stellar remnant? Is it just a planet because it is big and round-ish?

      1. The definition of a planet is a celestial body orbiting a star and being big enough to be rounded by its own gravity.

        If that’s the definition then these aren’t planets, by definition.

        I’d be more inclined to call them asteroids, but then asteroids by definition are relatively small.

        I think we’re making a story out of a limited vocabulary for objects in space.  The title should actually be ‘Big rocks in space have no name yet’.

        I nominate ‘Big boy’ as the accepted terminology for these new space rocks.

          1. Apparently that’s just another name for a ‘minor planet’, defined as:

            “A minor planet is an astronomical object in direct orbit around the Sun”.


            [Edit: Removed madness.]

      2. Brown dwarfs are larger. In theory they form more like stars, and become large enough to fuse deuterium though not regular hydrogen. In practice that’s hard to tell, so they use about 13 Jupiter masses as a cut-off (when you can even measure that).

        Right now there’s no agreed definition for planet. Contrary to what Nathan said, the IAU takes them as objects around our sun which have cleared their orbit; it doesn’t regulate exoplanets. Their definition is easy to extrapolate to other solar systems, but not free objects like this.

        However, right now there’s a nice range of sizes that matches up with gaseous planets, and another that matches up with terrestrial planets plus a few moons. So “rogue planet” can fairly be taken to mean objects in that range – presumably former planets that got lost? – until we know more about them.

        1. Also, most brown dwarfs are between 20-80 Jupiter masses (there’s only a few confirmed objects with a mass between 13-20 Jupiter masses), so this would be way below the limit if it’s 4-7 Jupiter masses.

      3. It’s not an asteroid because it’s too big.  Calling Jupiter an asteroid would be silly.  It’s also not a Brown Dwarf because it’s too small.  A Brown Dwarf radiates infrared light caused by intense gravitational pressure, but the mass is too low to sustain fusion.  For anything from about the size of Ceres to about 13 Jupiters, the only word that’s handy is planet.

    1.  “If they’re right, then CFBDSIR2149 is also a “rogue planet”, so called because it doesn’t actually orbit a star.”

  2. i’m surprised that it shows up (in that photo) as a bright object – like a star – rather than only being discovered via occultation.   maybe it’s an extra shiny planet?  (“well maybe if you read the whole —‘n article…” yeah)

    1. The South will rise again, rocketing straight up from the surface of the Earth in excess of 25000 mph. But we want you to understand: It’s about heritage, not height.

  3. This is really cool. They should rename CFBDSIR2149 Planet Mongo. And all other bodies similar to this could be called mongoids. It’s much less of a mouthful and I imagine that Dr. Hans Zarkov would approve, if he were real.

  4. Good to see that all rouge planets aren’t like Mondas!

    I suspect that the surplus of star-less planets is due to the huge supply of dirigible planets left over after the last inter-galactic war.  They were supposed to be sold off at duly authorised Army Surplus stores but they bring such low prices that I wouldn’t be surprised if unscrupulous operators have just been dumping them.

  5. I’m amazed at the surface temperature — I had assumed it would be frozen like an asteroid.

    It seems to me that anything with a surface temperature like that could potentially support life — both homegrown (like our own Archaea bacteria) and potentially supporting a human population deriving power and food from heat alone (though of course a potential colony would need a lot of insulation or to be build a fair distance away to prevent us from burning up…).

    1. Paraphrasing from Wikipedia:
      If in fact the planet is part of the “AB Doradus moving group”, the age of the planet will be between 50 and 120 million years.
      Which I’m guessing would explain the observed temperature:  younger planet = hotter planet.
      Also, at 4-7 Jupiter masses, it’s gonna take a while for a beast of that size to shed its’ “birth heat”, to coin a term.

  6. I figured it was the homeworld of the wormfaces after it had been separated from its star in _Have_Space_Suit_Will_Travel_.

    1. Loved that book as a boy.  I had to edit it on the fly when I read it to my children, though – they didn’t grow up during the space race, so the math and chemistry stuff was boring and offtopic to them.

      It wasn’t as bad as Tom Swift, or Beloved Belindy, though – try reading one of those to a child of color.  You have to either massively revise on the fly, or constantly stop to explain… “No, honey, Johnny Gruelle wasn’t a racist, it’s just that he was purposely invoking the ‘mammy’ stereotype to address an audience in a time when racism was commonplace and accepted.  Belindy isn’t stupid, she’s… what?  What does ‘invoking’ mean?  Ok, uhm…..”

    2. Probably not. Remember that  wormface travels at 1G when not in a hurry. His people keep their spacecraft at standard temperature and pressure with an earth like atmosphere. They would be completely at home on earth, not on a super-jovian gas giant.

      But crossing the streams for a moment, John Varley’s Invaders were a gas giant species with a fetish for dolphins…

  7. Men are from Mars, Women are from Venus, Ann Coulter and Rush Limbaugh are from an far-out, overheated planet where the sun never shines.

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