The search for extrasolar planets has been heating up lately, and astronomers have been locating hundreds of new worlds at an amazing rate, including a nearby beauty that may not be that different from Earth (as well as many that are unbelievably different).  Until now all of the planets that we have eyeballed have one thing in common – they orbit a star – however a recent study has found ten roaming giants that do not appear to be gravitationally bound to anything.

A new result from astronomers who have spent years peering toward the center of the Milky Way has led to a startling conclusion: there may be billions of Jupiter-sized planets wandering the space between the stars, unbound by the gravity of a parent sun. In fact, there may be nearly twice as many of these free floating planets as there are stars themselves in our galaxy, and they may even outnumber planets orbiting stars!

The discovery was made using a technique known as microlensing:

Instead of looking for tell-tale blips of light near stars, or the effect of planets on their parent stars, microlensing looks for the effect of the planet on background stars that are far more distant than the planet itself.

It’s a little weird, and is due to gravity warping space. Imagine me sitting on a flat floor, rolling marbles away from me in all directions. If you’re sitting a few meters away, you can only catch the marbles that are aimed at you. But if there’s a dip in the floor between us, some of the marbles I roll that might have otherwise passed you will get their path diverted toward you as they curve around the dip. You get more marbles!*

The same thing with light and gravity. A star emits light in all directions, but we only see the small amount of light headed our way. If a massive object like a planet gets between us and the star, the gravity of that planet can warp space, causing light we otherwise wouldn’t see to bend toward us. We see more light: the star gets brighter! This is called a gravitational lens. If that massive object is a planet moving in space, then we the starlight get brighter as the planet moves between us and the star, and then fainter as the planet moves on. The way the light changes is predicted by Einstein’s equations of relativity, and can be used to find the mass of the planet doing the warping.

There’s lots more over on the Bad Astronomy blog, so go check it out if you’re interested.

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4 Responses to “Who needs a sun anyways?”

  1. I love the Bad Astronomy blog, they do a fantastic job of discussing the science of astronomy – particularly fascinating events – in laymans terms but without coming across as condescending, or needlessly dumbing down the topic. One of my favorite blogs :)

    I suppose it stands to reason that there would be many orphaned planets tooling about the universe, ones that where never snared by a stars gravity well. It would certainly be a lot more difficult to keep tabs on them, though, without the handy star as a reference.

    • It stands to reason that some exist – astronomers have long theorized that planets could be ejected from a solar system for a number of reasons – but the fact that there might be way more orphaned planets than planets that orbit stars is a little bit startling to me.

      • Ah, but it’s oh, so promising for storytelling potential, hm?

        Great article, by the way. Thanks for the links!

      • Jack McDevitt has a story about a colony on an ejected planet/moon system that is held in tidal lock to its gas giant. Although that forms a small part of the book, it is really interesting to see how he thought about a society without a sun, and without the regular passing of days and seasons.

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