Tiny Alien World Challenges Planet Formation Theories by Orbiting Distantly from its Star

We're learning a little bit more about alien worlds and how they're created. Scientists have discovered evidence that an extrasolar planet may be forming quite far from its star--about the twice the distance Pluto is from our Sun. The new findings could reveal a little bit more about planets in far off galaxies.

This latest planet lies inside a dusty, gaseous disk around a small red dwarf TW Hydrae, which is a mere 55 percent of the mass of the sun. This disk is the closest one to Earth--only about 176 light-years away. Because planets and other rocky bodies can form from this disk of material, researchers were interested in studying it a bit more closely.

In order to do so, the astronomers employed the Hubble Space Telescope, making observations over a wide range of wavelengths from visible to near infrared. They then modeled the color and structure of the disk. In the end, they found a deficit of material--or a gap--in the disk. This gap was just slightly wider than necessary for a planet-opening gap, which seemed to point to the possibility that an exoplanet is actively forming in the area.

"TW Hydrae is between 5 and 10 million years old, and should be in the final throes of planet formation before its disk dissipates," said coauthor Alycia Weinberger of the Carnegie Institution in a news release. "It is surprising to find a planet only 5 to 10 percent of Jupiter's mass forming so far out since planets should form faster closer in. In all planet formation scenarios, it's difficult to make a low-mass planet far away from a low mass star."

Planet formation that occurs so far away from a low mass star like TW Hydrae is at odds with the conventional view. Under the most accepted scenario, planets form over tens of millions of years from the slow accretion of dust, rocks and gas. This accretion occurs most easily close to the central star, where orbital timescales are short. In fact, even under a disk instability scenario, in which planets can collapse quickly from the disk, it's not clear how such a low mass planet could form.

Yet this formation is occurring, despite the fact that theory says the exoplanet shouldn't even exist. The findings reveal how planets form and what conditions can result in planet formation. In addition, it shows what chemical constituents are available to new planets. The research could show a little bit more about the origins of the planets in our own solar system.