Loner planets, 05.23.11

Researchers recently gathered evidence for the existence of at least 10 free-floating planets that are roughly the same mass as Jupiter.

The Microlensing Observations in Astrophysics (MOA), a joint project between Japan and New Zealand, and the Optical Gravitational Lensing Experiment (OGLE) survey group, made the discovery using telescopes that scan the center of the Milky Way galaxy. By measuring light as one star or planet passes in front of a distant star, the scientists can narrow down the possibilities of what the object may be. From the data they have gathered, they have discovered at least 10 free-floating planets (planets that do not orbit any particular star). Not only that, but based on census-style calculations, they say that for every star in our galaxy, there could be at least two such wandering worlds.

Image credit: NASA/JPL-Caltech.

So where did they come from? Several theories have been formed, and both seem equally plausible. One theory is that the planets were thrown out of their solar systems in the early centuries after their creation, due to the turbulence of all the new gravitational fields. Since they are not orbiting any one particular star, they have dropped into their own stable orbits around the center of the Milky Way.

The other theory regards how the planets formed. Brown dwarfs, a classification of stars, are extremely cool for stars (about the same temperature as a fresh cup of coffee), and are about as small as planets. Could these loner planets have formed the same way as those stars, or did they form the same way as the other planets and just get separated from the rest of their solar system? The researchers say both theories are just as likely.

 Credit: NSF.