Orphan planets? What a sad thought. A planet all alone floating through space, no "parent" star and no "brother or sister" planets in a nice "home" of a solar system. For a long time astronomers didn't think many orphan planets existed, but new research suggests that Orphan planets may be even more common than stars! (There's 400+ BILLION stars in just our galaxy!)
Artist's conception of an orphan planet
Orphan planets, or planets in general outside our solar system, are not something we can point a telescope at and directly observe. Astronomers have to get crafty and find other ways of detecting these bodies. To find normal planets, astronomers watch a star for a long time, and if they see a periodic dimming of the star then they assume there is a planet orbiting around it (even though we can't directly see the planet.) Finding orphan planets is a bit more difficult though, because these planets are dark and cold and not orbiting a star. We can, however, use a trick I've discussed before, called gravitational lensing, to find such planets. Long story short, if you have a planet floating through space, lets say 20 light years away, and it passes in front of a cluster of stars say 100 light years behind it, instead of dimming the stars, the planet will bend the stars light around it and the cluster will actually look brighter! So if we suddenly see a short brightening of a star cluster, or other distant object, and there is no real explanation for it, an orphan planet may have crossed our path. Astronomers have just announced the discovery of 10 Jupiter sized orphan planets ~15,000 light years away!
Where did these orphan planets come from? The leading theory is that they formed around a star with other planets, but were kicked out of the system soon after forming by gravitational forces of the host star and other planets. So they're pretty much planet rejects that are given up at birth and become orphan…. Wow that's dark. I promise the next post will have a happier vibe to it!
Image credit: NASA/JPL-Caltech
