Researchers using NASA’s James Webb Space Telescope have pinpointed silicate clouds in the atmosphere of a distant planet. During its 22-hour day, the atmosphere is constantly rising, mixing and moving, bringing warmer material up and pushing cooler down. The resulting changes in brightness are so dramatic that it is the most variable planetary mass object yet.
A team led by Brittany Miles of the University of Arizona also made extraordinarily clear detections of water, methane and carbon monoxide using Webb’s data and found evidence of carbon dioxide. This is the largest number of molecules ever identified at once on a planet outside our solar system.
Cataloged as VHS 1256 b, the planet is about 40 light-years away and orbits not one, but two stars over a period of 10,000 years. “VHS 1256b is about four times farther from its stars than Pluto is from our Sun, making it a great target for Webb,” Miles said. “This means that the light from the planet is not mixed with the light from its stars. Higher in its atmosphere, where silicate clouds swirl, temperatures reach a scorching 1,500 degrees Fahrenheit (830 degrees Celsius).
In these clouds, Webb detected larger and smaller grains of silicate dust, which are shown in the spectrum. “The finer silicate grains in its atmosphere may be more like tiny particles in the smoke,” noted co-author Beth Biller of the University of Edinburgh in Scotland. “Larger grains can be more like very hot, very small particles of sand.”
VHS 1256 b has low gravity compared to more massive brown dwarfs, which means its silicate clouds can appear and stay higher in its atmosphere where Webb can detect them. Another reason its sky is so turbulent is the planet’s age. It’s quite young in astronomical terms. Only 150 million years have passed since it formed – and it will continue to change and cool for billions of years.
In many ways, the team sees these findings as the first “coins” pulled from the spectrum, which researchers see as a treasure trove of data. In many ways, they have only begun to identify its content. “We have identified silicates, but a better understanding of which grain sizes and shapes correspond to specific cloud types will require a lot of additional work,” Miles said. “This isn’t the last word on this planet — it’s the start of a large-scale modeling effort to fit Webb’s complex data.”
Although all of the features the team observed had been spotted on other planets elsewhere in the Milky Way by other telescopes, other research teams typically identified only one at a time. “No other telescope has identified so many objects at once for a single target,” said co-author Andrew Skemer of the University of California, Santa Cruz. “We see many molecules in a single spectrum from Webb, detailing the planet’s dynamic cloud and weather systems.”
We’ll be able to learn a lot more about VHS 1256b in the coming months and years as this team—and others—continue to sift through Webb’s high-resolution infrared data. “There’s a huge payoff for a very modest amount of telescope time,” Biller added. “With only a few hours of observation, we feel like we have endless potential for more discoveries.”
What can happen to this planet in billions of years? Because it is so far from its stars, it cools over time and its sky can change from cloudy to clear. Scientists observed VHS 1256b as part of Webb’s Early Release Science program, which is designed to help transform the astronomical community’s ability to characterize planets and the disks where they form.