Exoplanet VHS 1256 b (NIRSpec and MIRI Emission Spectrum)

Ready to look for clouds and molecules on a distant planet?

A research team led by Brittany Miles of the University of Arizona used two instruments known as spectrographs aboard the James Webb Space Telescope, one on its Near Infrared Spectrograph (NIRSpec) and another on its Mid-Infrared Instrument (MIRI) to observe a vast section of near- to mid-infrared light emitted by planet VHS 1256 b. They plotted the light on the spectrum above.

First, let’s look for silicate clouds in Webb’s data. Based on observations of many other exoplanets by many telescopes, the researchers know to look for signatures of clouds in particular areas in the spectrum. Signatures of silicates appears before and after 10 microns, a particular wavelength of infrared light.

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.

The combined evidence of fluctuations in the planet’s brightness over time and the different cloud layers in the spectrum point to turbulent weather on VHS 1256 b. “These detections reflect that the planet’s cloud patterns change fairly rapidly,” explained Beth Biller of the University of Edinburgh in Scotland. If the researchers were to take more, and longer, observations of the planet, they would see the spectrum shape shift as the locations of the clouds move, reflecting that the clouds are rapidly shifting through the planet’s atmosphere during its 22-hour rotation.

But these aren’t like clouds high in Earth’s atmosphere. These clouds are hot – akin to the temperature of a candle flame. Earth’s upper atmosphere is thin and would feel extremely cold.

The researchers also made extraordinarily clear detections of water, methane and carbon monoxide with Webb, and found evidence of carbon dioxide. It’s too early to tell what this combination of molecules might mean, though, since the data need to be fully modeled. “Webb’s high-resolution data are stressing our existing models,” notes Polychronis Patapis of ETH Zurich in Switzerland. “Existing models can ingest one or two features, but not as many as Webb has shown us of this target.” This is an extraordinarily exciting moment for researchers – it means there is an amazing amount to learn as they revamp models to fit these data.

Webb’s observations of VHS 1256 b highlight many of its technical strengths. Not only do its instruments detect a wide range of near- and mid-infrared light, Webb’s position in space means that the telescope can observe more infrared light than is accessible on Earth – and it captures the details in high resolution. (Earth’s atmosphere filters out some near-infrared and all mid-infrared light.) “Webb has effectively doubled the wavelength range that we’re able to capture,” said Brittany Miles of the University of Arizona, the paper’s lead author. “To top that off, we only needed seven hours to capture the spectrum, which is practically overflowing with details.”

VHS 1256 b is about 40 light-years away in the constellation Corvus. It orbits not one, but two stars, which are tightly orbiting one another. The planet lies about four times farther from its stars than Pluto is from our Sun. Although a single day on this planet is 22 hours long, it takes 10,000 years to complete a single orbit or year.

The planet’s clouds were confirmed with data from the Webb Telescope.

MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (the MIRI European Consortium) in partnership with JPL and the University of Arizona.

NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and micro-shutter subsystems.