An alien world just 70 light years from Earth is one of the strangest we’ve found yet.
It rings 20 Jupiter masses, has temperatures that can quickly melt aluminum, and has a 10,000-year orbit around not one but two stars. And, oh yeah: It’s ravaged by a constant storm of sand.
Astronomers have used the James Webb Space Telescope to obtain the most credible observations yet of the planet-mass object, revealing rolling clouds of silicate grains circulating in the atmosphere of the world named VHS 1256 b.
The discovery, was published last year on the preprint server arXiv, has gone through peer review process and will appear in The Astrophysical Journal Letters.
In addition, the team identified many of the components of VHS 1256 b’s atmosphere. These include unequivocal detections of methane, carbon monoxide and water, with additional evidence for carbon dioxide.
“No other telescope has identified so many features simultaneously for a single target,” says astrophysicist Paul Mollière at the Max Planck Institute for Astronomy in Germany. “We see many molecules in a single spectrum from JWST that describe the planet’s dynamic cloud and weather systems.”
VHS 1256 b is something of an enigma. Its mass borders on the boundary between giant planets and brown dwarfs”failed stars” that are not massive enough to fuse hydrogen but can fuse the heavier hydrogen isotope deuterium in their cores, which has a lower fusion temperature and pressure than hydrogen.
It is believed that the two types of objects form quite differently. Brown dwarfs typically form as stars, collapsing from a dense knot of material into a cloud of gas and dust, then sucking in more material to grow. Deuterium fusion is an intermediate step as the star grows, but some stars – the brown dwarfs – stop growing at that point and remain as they are.
On the other hand, planets are thought to form from the bottom up, from the material left over after a star has formed, clumping together to grow into a planet. That material is usually considered to be quite close to the star. The wide orbital separation between VHS 1256 b and its two suns suggests that it formed by cloud collapse, but it is not diagnostic.
Theoretically, planets can also form from the cloud collapse model; the estimated minimum mass for a cloud collapse object is a Jupiter. The dividing line between a planet and a brown dwarf is therefore the mass limit for deuterium burning, meaning that the exact nature of VHS 1256 b is unknown.
But it is the great distance that made such spectacular observations possible.
“VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, making it an excellent target for Webb,” says astronomer Brittany Miles from the University of Arizona, who led the international research team. “That means the planet’s light is not mixed with light from its stars.”
JWST’s observation range is the infrared and near-infrared, the range that includes thermal radiation. And VHS 1256 b is very young, only 150 million years old, and still quite hot from the formation process. Its atmosphere, where the sand clouds can be found, reaches 830 degrees Celsius (1,526 degrees Fahrenheit).
This heat, along with its low gravity, is what makes its sky so turbulent. Scientists analyzed the light detected by JWST and studied the spectrum in minute detail to pick out the features produced by different elements that absorb specific wavelengths.
This is how they identified the various gases they found in the object’s atmosphere – and the ever-changing sand clouds, likely composed of enstatite, forsterite or quartz.
So detailed was the data that researchers were able to identify different sizes of grains as well, from finer grains like smoke particles to larger grains like sand. These larger grains, the researchers hypothesized, are too heavy to remain in the upper atmosphere and rain back down into the interior, as smaller particles ascend.
This produces a dramatic variation in the world’s brightness over its 22-hour day, suggesting that silicate clouds may be a common mechanism for making such variations in brown dwarfs. The team believes the observations can easily be replicated for other brown dwarfs, which could help us learn more about these strange objects.
And VHS 1256 b has given us a lot to chew on.
“We have isolated silicates, but better understanding which grain sizes and shapes match specific types of clouds will require a lot of additional work,” says astrophysicist Elisabeth Matthews from the Max Planck Institute for Astronomy.
“This is not the last word on this planet—it’s just the beginning of a large-scale modeling effort to understand JWST’s complex data.”
The research has been published in The Astrophysical Journal Letters.
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