A planet is likely forming around the star TW Hydrae and the alien world is not where it should be, according to current theories of planetary formation.
The Hubble Space Telescope has photographed a debris ring around the star which contains a gap where a new planet appears to be forming. Remarkably, that ring is located 7.5 billion miles away from the star, over 80 times further away than the Earth orbits from the Sun, or twice the distance of Pluto.
Theories currently hold that planets far from their stars will sweep dust and debris from their path slowly, as they have slow orbital velocities and the concentration of material far from a star is sparse. Calculations show that such a planet should take two billion years or more to form, but the star itself, TW Hydrae, appears to be just right million years old. That is two million years less than it took Jupiter to form, which is sixteen times closer to the Sun than this planet is to its parent star.
The red dwarf star, about half the mass of the Sun, lies 176 light years from the Earth, in the direction of the constellation Hydra (The Sea Serpent). The disk surrounding it is 41 billion miles across, and the gap is 1.9 billion miles across.
TW Hydrae was imaged with the near infrared camera and Multi-Object Spectrometer aboard Hubble, and the results compared to earlier photographs taken by the orbiting observatory.
The planet forming within the gar is estimated to be between six and 28 times the size of Earth. If a planet in our solar system were orbiting as far from the Sun as this new planet is from its star, it would orbit out past the Kuiper Belt, where comets wait until they are nudged in to our inner solar system.
To add another puzzle to the mix, observations by the Atacama Large Millimeter Array in Chile have measured the size of the grains of debris in the disk, and found nothing larger than grains of sand within two billion miles of the gap.
"Typically, you need pebbles before you can have a planet. So, if there is a planet and there is no dust larger than a grain of sand farther out, that would be a huge challenge to traditional planet formation models," John Debes of the Space Telescope Science Institute, lead author of the study, said.
Not all astronomers are convinced that the gap in the dish around TW Hydrae is a planet, however.
"Since its [gap is] very circular, it could just be some kind of warp in the disk, a discontinuity in the shape of the disk at this point. Maybe the composition of that disk is changing at that radius," Hannah Jang-Condell of the University of Washington said.
Results of the finding were presenting in the June 14 issue of The Astrophysical Journal.
