Newborn Planet Is Youngest Ever Found

James Owen
for National Geographic News
April 3, 2008
The youngest planet ever detected has been found developing inside a distant "womb of gas," scientists have announced.

The embryonic planet may only be a few hundred years old, providing a unique look at how planets are made, according to a team of astronomers led by Jane Greaves of the University of St. Andrews in Scotland.

"We were amazed when we found it," Greaves said, noting that the next youngest confirmed planet is ten million years old.

The newfound protoplanet, named HL Tau b, was discovered taking shape about 520 light-years away in the constellation Taurus.

HL Tau, the parent star, is itself in its infancy, since it's believed to be less than a hundred thousand years old. Our own sun, by comparison, has been blazing for more than 4.5 billion years.

The new planet is a "distinct orbiting ball of gas and dust, which is exactly how a very young protoplanet should look," Greaves said in a statement.

"The planet will probably take millions of years to settle down into its final form," she said. "So we really are seeing it very early—even a bit like the first cells that make up a human embryo in the womb."

Planetary Trigger

Despite its youth, the developing world is already a healthy size as planets go, Greaves noted.

"The protoplanet is about 14 times as massive as Jupiter and is about twice as far from HL Tau as Neptune is from our sun," she said.

That means HL Tau b will likely grow into a gas giant resembling a larger version of Jupiter.

Greaves' team made the surprise find while studying the protoplanet's parent star using radio telescopes at the Very Large Array (VLA) in New Mexico and the Jodrell Bank Observatory in England.

The VLA detected a concentration of rocky particles about the size of pebbles in the disk of material around HL Tau, which suggested a planet might be forming.

Evidence for the protoplanet was supported by longer-wavelength telescope readings at Jodrell Bank and by computer models.

The study team says the discovery bolsters the controversial theory that gas giants can form due to a rapid collapse of gas around a dense region in the dusty disk surrounding a star.

Known as gravitational instability, this process may have been kick-started in the case of HL Tau b by a close encounter with another young star about 1,600 years ago, the team reports.

(Related news: "Evidence of Huge Planetary Collision Found" [January 10, 2008].)

The new finding represents "a nice observation using complementary observational facilities," said Tom Hartquist, head of the Astrophysics Group at the University of Leeds in the U.K., who was not involved in the work.

"There's been a lot of debate recently about the role of gravitational instability in planet formation, so from that point of view [the new study] might be controversial," Hartquist added.

But given that the team has a theoretical model that explains their data, he said, "I think it's an important contribution to showing that gravitational instability does play some role [in planet formation]."

Brown Dwarf?

More should become clear as increasingly powerful telescopes provide better images of the protoplanet, Hartquist added.

"For instance, if gravitational instability is important, there should be a spiral structure that develops in the [star's] disk," he said. Previous models have suggested that instability in the disk would cause its gases to form into spiral arms.

What is certain, the astrophysicist said, is that the planet will never support life.

"It's just too far out [from its sun], too cold, and too massive," he said.

"It's almost massive enough to become a brown dwarf star," a type of star that ignites but is not massive enough to maintain hydrogen fusion after a few tens of millions of years.

Hartquist also noted that the planetary discovery underlines the international importance of astronomical facilities in the U.K. at a time when Jodrell Bank is threatened with closure due to funding cuts.

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