The Sciences

Exoplanet's Surprising Detour Reignites Astronomical Debate

80beatsBy Veronique GreenwoodSep 27, 2011 5:09 PM


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When Fomalhaut b was announced in 2008, images showed it following a clear orbit around its star.

What's the News: Even if you don't know an exoplanet

from an exoskeleton, you probably saw the gorgeous images of Fomalhaut, aka "Sauron's Eye," making their way around the web in 2008

. A tiny, bright dot in the star's surrounding dust cloud had moved, showing itself to be a planet---the first planet beyond our solar system to actually be seen, rather than detected with nonoptical instruments. Cue the champagne! But new pictures show something odd: Fomalhaut b, as the planet was named, is veering off in an unexpected direction. Does this mean it's not a planet after all, or is there another explanation?

What's the Context:

  • Fomalhaut b showed up in two different images taken by the Hubble Space Telescope in 2004 and 2006. In the intervening years, the object had moved, appearing to sweep out an orbit through the star's dust cloud.

  • But Fomalhaut b is kind of weird, as exoplanets go. It's very bright, way brighter than astronomers would expect from a planet that size, and it's also not visible in the infrared spectrum in pictures taken from Earth, which is kind of fishy---astronomers think the planet is young, so it should burn bright in infrared, but it hasn't shown up yet. The planet's brightness, at least, astronomers think, might be from a layer of dust that's accrued around it, like the rings around Saturn.

  • Additionally, its status as the "first directly observed" exoplanet has ruffled some people's feathers, in a scientific community where excitement about new planets has reached a fever pitch. Ray Jayawardhana, an astronomer at University of Toronto, says that if dust is behind the brightness, technically speaking it's not the planet that's been directly observed. "They continue to call it a directly imaged planet," he told Eric Hand of Nature News. "I think it's time to stop doing that."

Not a Planet?

  • Now, a new observation taken in 2010 and presented by Paul Kalas of UC Berkeley at a recent conference shows that the planet isn't continuing along what scientists thought was its path. It looks like it's continuing on into the dust instead.

  • Jayawadhana takes that as an indication that it may not be a real planet, he tells Nature News, which has a fascinating rundown of the science---and scientific politics---involved.

  • Fomalhaut b's clear orbit, which appeared to have cut a path through the star's dust cloud over the eons, was one of the reasons astronomers dubbed it a planet. Although it's possible that the orbit just happens to have some instability built in, if the object takes a substantial detour, that is a potentially serious strike against planethood.

Not So Fast:

  • The new image was taken with a different camera than the one that recorded Fomalhaut b in 2004 and 2006, Kalas notes. The high-resolution channel Kalas and company used then was not replaced when the Advanced Camera for Surveys broke, so the new image is taken with the Space Telescope Imaging Spectrograph.

  • That difference in instrumentation, for now, means that it's possible that Fomalhaut B's veer is just an artifact.

The Future Holds: Kalas is going to get another chance to snap a picture of the planet next summer. That should help resolve whether this anomalous movement is real---and thus give greater insight into Fomalhaut B's celestial status. [via Nature News


Image courtesy of ESA, NASA, and Paul Kalas

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