Scientists are the first to simulate 3-D exotic clouds on an exoplanet

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An artistic depiction of the exoplanet GJ1214b. Credit: Wikimedia Commons user Tyrogthekreeper

Scientists have catalogued nearly 2,000 exoplanets around stars near and far. While most of these are giant and inhospitable, improved techniques and spacecraft have uncovered increasingly smaller worlds. The day may soon come when astrophysicists announce our planet’s twin around a distant star.

But size alone is insufficient to judge a globe. Though Earth and Venus are nearly identical in size, the latter’s surface is hot enough to melt lead. Astronomers must gather information about an exoplanet’s atmosphere, often through observing how the planet scatters or absorbs light from its parent star. But, that information is not always useful—as is the case with the exoplanet GJ1214b.

“When an exoplanet passes in front of its star, light can be absorbed at some wavelengths by molecules in the atmosphere, which we can analyze by looking at how light passes through the planet’s atmosphere,” said Benjamin Charnay, a postdoctoral researcher in the University of Washington Department of Astronomy. “But for this planet, when researchers previously looked with the Hubble Space Telescope, they saw almost no variation with wavelength of light.”

This “flat spectrum” for GJ1214b indicated that something in the planet’s blocked light, keeping scientists in the dark regarding its atmosphere. Charnay decided to computationally model what its atmosphere could be, based on the planet’s temperature and composition. In the process, as he reports in a new paper in Astrophysical Journal Letters, he and his collaborators became the first to simulate three-dimensional exotic clouds in the atmosphere of another world.

“It’s an important step in characterizing exoplanets,” said Charnay.

GJ1214b was among the first “mini-Neptune” exoplanets discovered, which are intermediate in size between Earth and Neptune. They’re the smallest exoplanets that can be studied with existing technology, and GJ1412b is in an ideal position.

“Most of the other mini-Neptunes that have been discovered orbit stars between 100 and 1,000 light years away,” said Charnay. “GJ1214b is quite close to Earth, just 42 light years away, and it orbits its star in just 1.6 days.”

That fast orbit gave scientists the opportunity to record the exoplanet’s flat spectrum, ruling out an atmosphere of simple hydrogen, water, carbon dioxide or methane. Instead, something high in the atmosphere was blocking light from penetrating farther down.

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