Potential New Planet Breaks all the Rules

Tucked far away in the recesses of a highly elliptical orbit around the neighboring star TW Hydrae may be a planet.

According to a paper published in The Astrophysical Journal, the reason for the distance between the star and possible planet, which is estimated at 7.5 billion miles wide, is unclear, but could arise from a transition in the nature of the disk’s dust composition. Another theory states that it could be the presence of a planetary companion.

“The finding of interest here is that we discovered a gap in the disk around the tar known as TW Hydrae, and our calculations indicate that the gap may be harboring a planet of 6 to 28 times the mass of the Earth,” Hannah Jang-Condell, a University of Washington professor and co-author of the paper, said in a press release. “That’s a small planet. It’s not a ‘gas giant.’”

Jupiter, for instance, is 300 times the mass of Earth. More likely, the planet represents something more similar to Neptune, the researchers hypothesize.

Furthermore, because the possible planet is located so far from its star and heat source, it is probably similar to Neptune in temperature as well.

However, should it exist, the planet's orbit would challenge current planet formation theories that state planets form over tens of millions of years (TW Hydrae is believed to be between 5 and 10 million years old) from the slow, persistent accretion of dust, gas and rocks in a region close to the central star where orbital times are short.

The disk however, lacks dust grains in its outer regions, according to a report from the Space Telescope Science Institute (STSI) at John’s Hopkins University.

“Typically, you need pebbles before you can form a planet,” John Debes, an astronomer at the STSI and lead author of the study said in a separate press release. “So, if there is a planet there, and there is not even millimeter-sized dust – roughly the size of a grain of sand – farther out, the observation is inconsistent with traditional planet formation models.”

According to the STSI release, an alternative planet-forming theory suggests that a portion of the disk becomes gravitationally unstable and collapses on itself, causing a sort of expedited planet formation.

Jang-Condell, who ran nearly 200 possible models in an effort to try out different planets that could create such a gap, offered another possible scenario.

“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,” she said. “Maybe the composition of that disk is changing at that radius.”

Regardless of which theory is true, however, Jang-Condell said that, most of all, the researchers “just hope it’s a planet.”