Astronomers discover sand clouds in the atmosphere of a failing star

New observations from the James Webb Space Telescope have given us direct confirmation that some alien worlds have clouds of rock.

The telescope has directly detected silicate clouds in the atmosphere of a brown dwarf – the first time, according to an international team of astronomers, that such a detection has been made in a planetary-mass companion outside the solar system.

The full findings, according to the team, are the best spectrum yet for a planetary-mass object. These results might not only help us better understand these so-called “failed stars,” but represent just a taste of what the JWST can do.

The article has been submitted to AAS journals and is available on the arXiv preprint server while it goes through the peer review and publication process.

We’ve seen JWST take a direct image of an exoplanet before, but a brown dwarf is a slightly different fish.

These objects are what happens when a small star doesn’t accumulate enough mass to start hydrogen fusion in its core, and they occupy the mass regime between larger planets and smaller stars.

However, at about 13.6 times the mass of Jupiter (sorry Jupiter, you tried) brown dwarfs can fuse deuterium or heavy hydrogen – hydrogen with a proton and a neutron in the nucleus, instead of a single proton.

The pressure and melting temperature of deuterium is lower than that of hydrogen, which means that brown dwarfs are a bit like “lite” stars.

This means that unlike exoplanets, brown dwarfs emit their own heat and light. It is much less than that of the stars, of course, but it can be detected directly, especially in the infrared wavelengths in which JWST specializes.

Observations obtained by a team led by astronomer Brittany Miles at the University of California, Santa Cruz come from a brown dwarf about 72 light-years away called VHS 1256-1257 b, first described in 2015.

It has a mass about 19 times the mass of Jupiter and is relatively young, with a reddish-hued atmosphere.

This hue has already been attributed to clouds in young brown dwarfs. So the team took infrared spectra to see if they could determine the composition of the brown dwarf.

It works because different elements absorb and re-emit light at different wavelengths. Scientists can look at the spectrum to see darker and brighter features, and determine what causes them.

The team found that the atmospheric composition of VHS 1256-1257 b was similar to that of other brown dwarfs studied in infrared wavelengths, but much brighter.

“Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several parts of the JWST spectrum based on comparisons of brown dwarf spectra patterns, molecular opacities, and atmospheric models,” the researchers write in their paper.

The characteristic of carbon monoxide, according to the researchers, is the clearest ever seen. And they also detected, as they hoped, clouds – hypothetical long clouds of silicate particles in a thick layer, with a submicron grain size. These are likely minerals such as forsterite, enstatite or quartz, the team notes.

This finally seems to confirm that young brown dwarfs may be surrounded by uneven silicate clouds that influence brightness variability.

This gives us a tool for interpreting observations of brown dwarfs in the future, and something to look for in future observations, the researchers note.

“These initial results from the JWST’s first scientific observations are groundbreaking and can also be obtained for many other nearby brown dwarfs that will be observed in future observing cycles,” they write in their paper.

“This observatory will be a pioneer, pushing our understanding of atmospheric physics in planetary companions, brown dwarfs and exoplanets for years to come.”

The research has been submitted to AAS journals and is available on arXiv.

Astronomers discover sand clouds in the atmosphere of a failing star

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