"That's no moon, it's a rogue planet"

An artist's conception of a free floating planet without a host star. Note that this is a Jupiter-sized giant planet, which are far less likely to be orphaned in interstellar space. (Image Credit: NASA/JPL-Caltech)

An artist's conception of a free floating planet without a host star. Note that this is a Jupiter-sized giant planet, which are far less likely to be orphaned in interstellar space. (Image Credit: NASA/JPL-Caltech)

We have eight planets in our solar system (let's save Pluto for a another time). But what if I told you there might have been even more early on in the formation of our solar system? And that now these planets are orphaned in interstellar space.

In October, at the Division for Planetary Sciences (DPS) meeting in Pasadena, astronomers announced that there may be as many as seven or eight orphaned Mars-sized planets per star. 

Thomas Barclay and Elise Quintana at the NASA Ames Research Center ran dynamical simulations of a solar system. First, they ran the simulation without gas giants like Saturn or Jupiter. Then, they introduced a couple of gas giants. There were a results. First, gas giants act as big bullies. When gas giants are present, more material gets dynamically disturbed and flung out of the system. Second, they found that there's a mass limit to which types of planets are ejected from the system. Surprisingly, planets larger than Mars seldom escape.

The gas giants left to right: Jupiter, Uranus, Saturn, and Neptune are the big bullies of the solar system. This becomes especially apparent when stacked up side by side to scale. (Image Credit: Wikipedia Creative Commons, Lmspascal)

The gas giants left to right: Jupiter, Uranus, Saturn, and Neptune are the big bullies of the solar system. This becomes especially apparent when stacked up side by side to scale. (Image Credit: Wikipedia Creative Commons, Lmspascal)

In the past, astronomers have mostly found gas giants in interstellar space. It now appears that this may be an observational bias. In other words, our instruments are better and finding bigger things (makes sense). For instance, we found the alphabet soup planet 2MASS J1119-1137 95 light years away in the constellation Hydra which is 4-8 Jupiter masses. It's huge!

But now theory has proposed a new model. How do we look for these smaller Mars-sized outcasts? With the Wide Field Infrared Survey Telescope (WFIRST), which will launch in the 2020s. Infrared surveys are really good at finding warm small planets in the cold expanse of space.

This telescope will help us determine if there are truly more rogue planets in this galaxy than stars. So stay tuned - the future of science is now!