James Webb detects grainy, turbulent clouds over a distant planet

An article available on the prepress server arXiv.organd already accepted for publication by The Astrophysics Journal, describes an extraordinary discovery made thanks to observations by the James Webb Space Telescope on a remote planet about 40 light-years from Earth.

According to data collected by the equipment and analyzed by researchers at the University of Arizona in the USA, the exoplanet VHS 1256 b contains silicate clouds in its atmosphere.

These clouds, according to the scientists responsible for the study, move steadily upwards and sideways throughout the planet’s 22-hour day. This turbulence pushes hotter material up and pushes cooler material down.

The brightness changes in VHS 1256 b are so drastic that, according to NASA, it is the most variable planetary mass object known to date.

Led by Brittany Miles, Ph.D. in astronomy, the team also made remarkably clear readings of water, methane and carbon monoxide with Webb’s data and found evidence of carbon dioxide. This is the largest number of molecules ever identified simultaneously on a planet outside the Solar System.

According to Miles, this distant world orbits not one, but two stars over a period of 10,000 years. “VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, making it a prime target for Webb,” he said. “This means that the planet’s light is not mixed with the light from its stars.”

Higher up in its atmosphere, where silicate clouds churn, temperatures can reach 830 degrees Celsius.

Within these clouds, the telescope detected increasingly larger grains of silicate dust, which are shown in a spectrum. “The finest silicate grains in your atmosphere may be more like tiny particles in smoke,” noted study co-author Beth Biller of the University of Edinburgh in Scotland. “The larger grains might be more like very hot, very small particles of sand.”

Because VHS 1256 b has low gravity, its silicate clouds can appear and remain higher up in its atmosphere, where Webb is able to detect them.

Another reason its skies are so turbulent is the age of the planet. In astronomical terms, it’s quite young: it’s only been 150 million years since it formed, and it will continue to change and cool for billions of years.

“We have identified the silicates, but a better understanding of which grain sizes and shapes correspond to specific cloud types will require a lot of additional work,” said Miles. “This isn’t the last word on this planet—it’s the start of a large-scale modeling effort to accommodate Webb’s complex data.”

All of the features observed by the team had already been observed on other planets in other parts of the Milky Way by other telescopes, however in these cases only one was identified at a time. “No other telescope has identified so many features at once for a single target,” said co-author Andrew Skemer of the University of California, Santa Cruz. “We’re seeing many molecules in a single Webb spectrum detailing the planet’s dynamic clouds and weather systems.”

There will be much more to learn about VHS 1256 b over the coming months and years as this team – and others – continue to sift through Webb’s high-resolution infrared data. “There’s a huge benefit to a very modest amount of telescope time,” Biller added. “With just a few hours of observing, we have what appears to be endless potential for further discoveries.”

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Source: Olhar Digital