Hubble Captures Planet Formation 7.5 Billion Miles From Host Star
June 13, 2013

Hubble Captures Planet Formation 7.5 Billion Miles From Host Star

Lee Rannals for — Your Universe Online

Astronomers using NASA's Hubble Space Telescope say they have discovered evidence of a planet forming 7.5 billion miles away from its host star.

The exoplanet is under construction about 176 light-years away from Earth in the constellation Hydra the Sea Serpent. The suspected planet is orbiting the diminutive red dwarf TW Hydrae.

"It's so intriguing to see a system like this," said John Debes of the Space Telescope Science Institute in Baltimore, Maryland. Debes leads a research team that identified the gap. "This is the lowest-mass star for which we've observed a gap so far out."

Planets are thought to form over tens of millions of years. A planet 7.5 billion miles from its star should take more than 200 times longer to form than Jupiter did, which is at a distance of 500 million from the sun. However, what complicates the story more is the fact that TW Hydrae is just 8 million years old and is only 55 percent as massive as our sun.

"If we can actually confirm that there's a planet there, we can connect its characteristics to measurements of the gap properties," Debes said. "That might add to planet formation theories as to how you can actually form a planet very far out."

The disk around the star lacks large dust grains in its outer regions. Observations have shown that dust grains roughly the size of a grain of sand are not present beyond about 5.5 billion miles from the star.

"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," Debes said.

The team wrote in The Astrophysical Journal that the planet is between six and 28 times more massive than Earth. If the suspected planet were orbiting in our solar system, it would be about twice Pluto's distance from the sun.

Coauthor Alycia Weinberger of the Carnegie Institution and principal investigator of the observations said it is surprising to find a planet only five to 10 percent of Jupiter's mass forming so far out since planets should form faster closer in. She said it is difficult to make a low-mass planet far away from a low mass star.

“If the mass of this suspected planet is as low as it seems to be, this presents a real puzzle. Theory would say that it cannot exist," said Carnegie astrophysicist Alan Boss, who works on disk instability models.

TW Hydrae has been a hot topic in the last week. Astronomers said during a press conference at a meeting of the American Astronomical Society that this star helped gain a little insight into our own Sun's past. The team said based on TW Hydrae observations they were able to conclude that our Sun was active and "feisty" during its infancy.