Gritty, swirling clouds of silica surround exoplanet VHS 1256 b

If you’ve ever been to the beach on a windy day, you’ve likely been treated to the not so fun feeling grains of sand hitting your face. That unpleasant experience would a walk in the park compared to what scientists have now discovered is happening in the atmosphere of the exoplanet VHS 1256 b.

A team of researchers using the James Webb Space Telescope (JWST) found that the planet’s clouds are made up of silicate particles that range in size from tiny specks to small grains.  The silicates in the clouds are swirling in nearly constant cloud cover. Silicates are common in our solar system and make up about 95 percent of Earth’s crust and upper mantle.

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During VHS 1256 b’s 22-hour day, the atmosphere is continuously rising, mixing, and moving. This motion brings hotter material up and pushes colder material down, the way hot air rises  and cool air sinks on Earth. The brightness that results from this air shifting is so dramatic that the team on the study say it is the most variable planetary-mass object known to date. 

The findings were published March 22 in the The Astrophysical Journal Letters. The team also found very clear detections of carbon monoxide, methane, and water using JWST’s data and even evidence of carbon dioxide. According to NASA, it is the largest number of molecules ever identified all at once on a planet outside our solar system.

VHS 1256 b is about 40 light-years away from Earth and orbits two stars over a 10,000-year period. “VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, which makes it a great target for Webb,” said study co-author and University of Arizona astronomer Brittany Miles, in a statement. “That means the planet’s light is not mixed with light from its stars.” 

The temperature in the higher parts of its atmosphere where the silicate clouds churn daily reach about 1,500 degrees Fahrenheit. JWST detected both larger and smaller silicate dust grains within these clouds that are shown on a spectrum

A chart of the emission spectrum on exoplanet VHS 1256 b.
There is likely a layer of very small grain silicate clouds higher up in the atmosphere. These silicates are finer, more like smoke particles, and are responsible for creating the plateau near 10 microns. Somewhat larger grain clouds are likely a bit deeper. Some particles in these clouds may be about the size of small grains of silt. CREDITS: IMAGE: NASA, ESA, CSA, Joseph Olmsted (STScI) SCIENCE: Brittany Miles (University of Arizona), Sasha Hinkley (University of Exeter), Beth Biller (University of Edinburgh), Andrew Skemer (UC Santa Cruz).

“The finer silicate grains in its atmosphere may be more like tiny particles in smoke,” said astronomer and co-author Beth Biller of the University of Edinburgh in Scotland, in a statement. “The larger grains might be more like very hot, very small sand particles.”

[Related: JWST has changed the speed of discovery, for better or for worse.]

Compared to more massive brown dwarfs, VHS 1256 b has low gravity, so its silicate clouds can appear and remain higher up in its atmosphere where JWST can detect them. It is also quite young as far as planets are concerned, at only 150 million years old. As with most young humans, it’s going through some turbulent times as it ages. 

The team says that these findings are similar to the first “coins” pulled out of a treasure chest of data that they are only beginning to rummage through. “We’ve identified silicates, but better understanding which grain sizes and shapes match specific types of clouds is going to take a lot of additional work,” said Miles. “This is not the final word on this planet – it is the beginning of a large-scale modeling effort to fit Webb’s complex data.”

While these features have been spotted on other planets in the Milky Way by other telescopes, only one at a time was typically identified, according to the team. They used JWST’s Near-Infrared Spectrograph (NIRSpec) and the Mid-Infrared Instrument (MIRI) to collect the data and says that there will be much more to learn about VHS 1256 b as scientists sift through the data.

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