Newly Clocked Exoplanet Spins a Whole Day in 8 Hours

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Time flies on beta Pictoris b, a behemoth gas planet orbiting a young neighbor star about 63 light-years from Earth.

A day there lasts just eight hours, making beta Pic b a faster spinner than even Jupiter, which rotates in 10 hours. Pic b is the first planet beyond the solar system to have its rotational rate clocked, scientists said in an article published in this week's Nature.

"Technically, what is interesting is that it was so easy to do these observations," lead researcher Ignas Snellen, with Leiden University, Netherlands, wrote in an email to Discovery News.

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"We devised a new technique that combines very precise spectroscopy with high-contrast imaging," Snellen added, referring to a technique that splits light into its component wavelengths for chemical analysis.

By studying the telltale fingerprints of carbon monoxide in the planet's atmosphere, Snellen and colleagues figured out that Pic b was rotating -- shifting the carbon monoxide measurements along with it -- at a rate of about 15.5 miles, or 25 kilometers, every second.

"We came up with these observations as a kind of test for the method," Snellen wrote. "It will be extremely powerful with the next-generation of telescopes, like the European Extremely Large Telescope, and may even allow us to probe Earth-like planets in the habitable zone of nearby stars."

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The discovery bolsters theories that the mass of a planet directly correlates to its spin, with bigger planets rotating faster than their smaller siblings. Until now, however, scientists had observational evidence only from planets in our solar system.

Scientists suspect Pic b, which is still warm and young, is just ramping up. Over the next hundreds of millions of years, it is expected to cool down and shrink to about the size of Jupiter.

If its angular momentum stays the same, the planet should spin up to about 25 miles (40 km) per second, Snellen notes in the Nature paper.

"This eventual spin velocity agrees remarkably well with the solar system trend," University of Arizona astronomer Travis Barman noted in a commentary on the research, also published in Nature.

"The number of directly imaged giant planets will soon increase substantially, and many of these planets will be excellent targets for spin measurements in the near future," Barman noted.

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