'Zombie' planet: Weird world may be back from the dead

Victoria Jaggard, physical sciences news editor

(Image: ESA; Hubble, M. Kornmesser; and ESO, L. Cal?ada and L. L. Christensen)

Is the Hubble Space Telescope a planet reanimator?

The orbiting observatory first revealed the exoplanet known as Fomalhaut b, but soon afterward astronomers pronounced the world dead, writing it off as a blob of dust. Now NASA claims to have brought Fomalhaut b back to life as a shrouded planet.

Fomalhaut is a bright, young star about 25 light years from Earth. It is surrounded by a disc of debris most likely left over from the star's formation - the perfect place to spawn planets.

In 2008 astronomers using Hubble data announced that a bright object was orbiting in a gap in the disc, a sign of a planet carving its way through the debris. The discovery was hailed as the first exoplanet portrait made in visible light.

But follow-up tests began ushering the planet toward its deathbed. No other telescopes, including Hubble's infrared cousin Spitzer, could find Fomalhaut b in images.

What's more, the original data from Hubble said that the planet varied wildly in brightness and orbited at an unexpectedly fast clip based on its position in the debris disc. This led astronomers to conclude that the bright object was no planet, just a clump of wandering dust.

Thayne Currie, an astronomer at the University of Toronto, wasn't ready for Fomalhaut b to give up the ghost. His team applied new analytic techniques to the original Hubble data and collected fresh observations from the Subaru Telescope in Hawaii. They used a similar image-processing method as the researchers who discovered Fomalhaut b to filter out the light from the star and make any planets easily visible. They also employed a more advanced technique. Neither filtering method showed brightness variations for the object.

"Honestly it is unclear to us exactly how the original authors ... got that result in the first place," Currie said in an email to New Scientist. The new data also show the object moving at just the right speed for it to be a planet.

The team thinks the best explanation is that Fomalhaut b is a planet a bit more massive than Jupiter that's engulfed in a cloud of dust. "It could be shrouded in dust because the planet is still surrounded by a swarm of small, boulder- to asteroid-sized planetesimals that are colliding and thus making dusty debris," Currie said. The dust would explain why the planet continues to be undetectable with current infrared telescopes. It's also possible the colliding bodies are moons in the making, he added.

Their work may not be the nail in the coffin, though, as researchers need more data to back up Fomalhaut b's revived planethood. And if the new model is correct, Fomalhaut b just lost one of its biggest claims to fame: the light from the object would be coming from the shroud of dust rather than the planet itself, which would mean it's no longer among the handful of worlds that have had their picture taken.

Journal reference: arxiv.org/abs/1210.6620

Source: http://feeds.newscientist.com/c/749/f/10897/s/24e28096/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A120C10A0Czombie0Eplanet0Eweird0Eworld0Emay0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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