Many science fiction plots use the idea of a deserted world wandering through space completely separated from its parent star. This dramatic set is a good place for intense action, but is it realistic? Even those worlds were out there, could we find them? A NASA press release claims not only are they there, but these worlds may even outnumber stars.
A forming solar system is a violent place. As the planets form around the young star, they start gravitationally pulling on each other. These tugs can send planets careening through the solar solar system, colliding into each other, or ejected from the system entirely. It's the planets that escaped that a team of astronomers from New Zealand and Japan were looking for.
Planets are not easy to find. The biggest problem is how small they are. The Earth may not seem like a small place, but compared with the vastness of space it is nothing more than a speck of dust. Normally we look for exoplanets by seeing the planet affect the light coming from their parent star in some way. So how could astronomer find these roaming worlds separated from their parent stars?
The team of scientists used a 5.9 foot (1.8 meter) telescope to get their data. However, I would be surprised if any telescope could see even a large planet separated from its host star, so the astronomers got some help from gravity. When light passes through a lens, the speed the light is traveling changes. That then causes the light to chage direction. When light passes by a massive object, like a star or planet, that light is bent around the object changing its direction. The bigger the object the greater the effect. This effect allows astronomers to used massive objects in space, or even clusters of them, as natural lenses. This is called microlensing. This allowed the team to watch discover these planets as they magnified the light of background stars.
I really like this study for several reasons. They found something very exciting in these wandering worlds. They gave us a starting point in trying to figure out just how many of these lonely planets there are. They also were creative in discovering them using a subtle and elegant effect. Finally, they had their results confirmed by another independent team of astronomers before publication. This is kind of science that gets me excited do research and teach each day.