# Do brown dwarfs have stripes?

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Brown dwarfs (BD) are often depicted with stripes.

brown dwarf Jupiter

Pictures of BD resemble Jupiter but brown dwarfs have even more stripes.

Question:

How do we know brown dwarfs have so many stripes?

I suppose it can differ depending on BD's temperature and mass. Probably only cold BD can have stripes.

Were the stripes observed? (by photometry, by transit or occultation, etc)

Or are the stripes result of theoretical modeling? Or just "artist impression" because of lack of information?

If result of modeling - do the stripes represent analogs of Hadley cell athmospheric circulation? Are they high and low pressure bands?

Do brown dwarfs have so many bands because of higher gravity?

A number of brown dwarfs have had 'surface maps' created using the light from those stars.

In 2013, observations of 2MASS J22282889-4310262, a brown dwarf 35 light years away, were published. These were made using the Hubble and Spitzer space telescopes and were able to show changing light patterns and distinct layers of material at different altitudes in the atmosphere. This provided evidence for textures but not necessarily banding in the atmosphere. I believe the Hubble has carried out other observations of brown dwarfs with the aim of determining their surface details.

In 2014 Luhman 16 A and B, a brown dwarf binary system, 6.5 light years from Earth, were imaged using the VLT CRIRES spectrograph. Luhman 16B was found to have patches perpendicular to the plane of rotation. Luhman 16A was found to be featureless at the frequencies observed.

Earlier this year, a paper was published describing how the VLT had been used again, this time employing polarimetry, to detect Jupiter-like banding on Luhman 16A.

The paper here describes modelling based on observations that indicate Jupiter-like cloud bands (page 13).

So there does seem to be mounting evidence that brown dwarfs have stripes. The accuracy of the artists' impressions is something we'll probably find out in the future.

UPDATE - January 2021

A new study of Luhman 16 A and B by Apai, Nardiello and Bedin has been published. They applied a 'novel photometric approach' to TESS data and found that we are viewing them at angles close to their equatorial planes and that they look 'strikingly similar to Jupiter'. The paper at the Astrophysical Journal is here but is paywalled.

Last update, I promise!

This is an image from the Apai, Nardiello and Bedin paper that was reproduced at Centauri-Dreams.org. The preprint of the paper is available for free download at Arvix.

## Astronomers Discover Brown Dwarf Covered in Stripes

Astronomers have found a distant brown dwarf, a celestial body that resembles a star, that’s covered in dark brown stripes — not unlike the clouds blanketing Jupiter.

It’s a bizarre find, but it’s not the first time that astronomers have seen a striped brown dwarf, Science Alert reports. However, the technique used by the Caltech astronomers, known as polarimetry, could provide a new tool for researchers trying to probe and understand the cosmos.

## Astronomers see Swirling Weather on the Closest Brown Dwarf

Brown dwarfs are the weird not-planets but not-stars in the universe, and astronomers have wondered for decades if their atmospheres are striped like Jupiter’s, or splotchy like the sun’s. A team of astronomers based at the University of Arizona used NASA’s TESS Observatory to find the answer: if you saw a brown dwarf for yourself, it would look more like a giant planet than a star.

Brown dwarfs are about the size of Jupiter, but much more massive. But they’re not quite massive enough to sustain nuclear fusion of hydrogen in their cores, so they don’t qualify as stars. They float around the galaxy largely undetectable, since they don’t emit copious amounts of radiation.

Still, they’re hot on the inside (generated by leftover heat from their formation), and cold on the outside (because, space), and so heat constantly flows outwards. And when heat flows, weather happens.

But weather can happen in all sorts of ways, like the striped bands of Jupiter, the chaotic swirlings of the Earth, or the random splotches of the sun. What kind do brown dwarfs have?

Astronomers with the University of Arizona turned to NASA’s Transiting Exoplanet Survey Satellite (TESS), which normally hunts for exoplanets, but is exquisitely tuned to also study brown dwarfs. They used TESS to observe the Luhman 16 system, a pair of orbiting brown dwarfs just 6.5 light-years away.

By carefully studying the change in brightness from the Luhman 16 binary as they orbited each other, they could determine the patterns in their atmospheres. The result: striped.

Jupiter gets its stripes from its rapid rotation. Plumes of warm material rise up from the interior, reach the edge of the atmosphere, cool off, and slink back down. The massive planet’s rotation stretches those plumes into rings, giving Jupiter its characteristic alternating stripes of up- and downward moving material.

Presumably something similar is happening in the Luhman 16 system.

“Knowing how the winds blow and redistribute heat in one of the best-studied and closest brown dwarfs helps us to understand the climates, temperature extremes and evolution of brown dwarfs in general,” said lead author Daniel Apai, an associate professor in the Department of Astronomy and Steward Observatory and the Lunar and Planetary Laboratory.

Further research will help astronomers uncover whether this is the status quo for brown dwarfs, or if each one is unique.

## Powerful Auroras Found at Brown Dwarf

Mysterious objects called brown dwarfs are sometimes called "failed stars." They are too small to fuse hydrogen in their cores, the way most stars do, but also too large to be classified as planets. But a new study in the journal Nature suggests they succeed in creating powerful auroral displays, similar to the kind seen around the magnetic poles on Earth.

"This is a whole new manifestation of magnetic activity for that kind of object," said Leon Harding, a technologist at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author on the study.

On Earth, auroras are created when charged particles from the solar wind enter our planet's magnetosphere, a region where Earth's magnetic field accelerates and sends them toward the poles. There, they collide with atoms of gas in the atmosphere, resulting in a brilliant display of colors in the sky.

"As the electrons spiral down toward the atmosphere, they produce radio emissions, and then when they hit the atmosphere, they excite hydrogen in a process that occurs at Earth and other planets," said Gregg Hallinan, assistant professor of astronomy at the California Institute of Technology in Pasadena, who led the team. "We now know that this kind of auroral behavior is extending all the way from planets up to brown dwarfs."

Brown dwarfs are generally cool, dim objects, but their auroras are about a million times more powerful than auroras on Earth, and if we could somehow see them, they'd be about a million times brighter, Hallinan said. Additionally, while green is the dominant color of earthly auroras, a vivid red color would stand out in a brown dwarf's aurora because of the higher hydrogen content of the object's atmosphere.

The foundation for this discovery began in the early 2000s, when astronomers began finding radio emissions from brown dwarfs. This was surprising because brown dwarfs do not generate large flares and charged-particle emissions the way the sun and other kinds of stars do. The cause of these radio emissions was a big question.

Hallinan discovered in 2006 that brown dwarfs can pulse at radio frequencies, too. This pulsing phenomenon is similar to what is seen from planets in our solar system that have auroras.

Harding, working as part of Hallinan's group while pursuing his doctoral studies, found that there was also periodic variability in the optical wavelength of light coming from brown dwarfs that pulse at radio frequencies. He published these findings in the Astrophysical Journal. Harding built an instrument called an optical high-speed photometer, which looks for changes in the light intensity of celestial objects, to examine this phenomenon.

The combination of results made scientists wonder: Could this variability in light from brown dwarfs be caused by auroras?

In this new study, researchers examined brown dwarf LSRJ1835+3259, located about 20 light-years from Earth. Scientists studied it using some of the world's most powerful telescopes -- the National Radio Astronomy Observatory's Very Large Array, Socorro, New Mexico, and the W.M. Keck Observatory's telescopes in Hawaii -- in addition to the Hale Telescope at the Palomar Observatory in California.

Given that there's no stellar wind to create an aurora on a brown dwarf, researchers are unsure what is generating it on LSRJ1835+3259. An orbiting planet moving through the magnetosphere of the brown dwarf could be generating a current, but scientists will have to map the aurora to figure out its source.

The discovery reported in the July 30 issue of Nature could help scientists better understand how brown dwarfs generate magnetic fields. Additionally, brown dwarfs will help scientists study exoplanets, planets outside our solar system, as the atmosphere of cool brown dwarfs is similar to what astronomers expect to find at many exoplanets.

"It's challenging to study the atmosphere of an exoplanet because there's often a much brighter star nearby, whose light muddles observations. But we can look at the atmosphere of a brown dwarf without this difficulty," Hallinan said.

Hallinan also hopes to measure the magnetic field of exoplanets using the newly built Owens Valley Long Wavelength Array, funded by Caltech, JPL, NASA and the National Science Foundation.

## Brown dwarfs reveal exoplanets' secrets

Brown dwarfs are smaller than stars, but more massive than giant planets. As such, they provide a natural link between astronomy and planetary science. However, they also show incredible variation when it comes to size, temperature, chemistry, and more, which makes them difficult to understand, too.

New work led by Carnegie's Jacqueline Faherty surveyed various properties of 152 suspected young brown dwarfs in order to categorize their diversity and found that atmospheric properties may be behind much of their differences, a discovery that may apply to planets outside the solar system as well. The work is published by The Astrophysical Journal Supplement Series.

Scientists are very interested in brown dwarfs, which hold promise for explaining not just planetary evolution, but also stellar formation. These objects are tougher to spot than more-massive and brighter stars, but they vastly outnumber stars like our Sun. They represent the smallest and lightest objects that can form like stars do in the Galaxy so they are an important "book end" in Astronomy.

For the moment, data on brown dwarfs can be used as a stand-in for contemplating extrasolar worlds we hope to study with future instruments like the James Webb Space Telescope.

"Brown dwarfs are far easier to study than planets, because they aren't overwhelmed by the brightness of a host star," Faherty explained.

But the tremendous diversity we see in the properties of the brown dwarf population means that there is still so much about them that remains unknown or poorly understood.

Brown dwarfs are too small to sustain the hydrogen fusion process that fuels stars, so after formation they slowly cool and contract over time and their surface gravity increases. This means that their temperatures can range from nearly as hot as a star to as cool as a planet, which is thought to influence their atmospheric conditions, too. What's more, their masses also range between star-like and giant planet-like and they demonstrate great diversity in age and chemical composition.

By quantifying the observable properties of so many young brown dwarf candidates, Faherty and her team -- including Carnegie's Jonathan Gagné and Alycia Weinberger -- were able to show that these objects have vast diversity of color, spectral features, and more. Identifying the cause of this range was at the heart of Faherty's work. By locating the birth homes of many of the brown dwarfs, Faherty was able to eliminate age and chemical composition differences as the underlying reason for this great variation. This left atmospheric conditions -- meaning weather phenomena or differences in cloud composition and structure -- as the primary suspect for what drives the extreme differences between objects of similar origin.

All of the brown dwarf birthplaces identified in this work are regions also host exoplanets, so these same findings hold for giant planets orbiting nearby stars.

"I consider these young brown dwarfs to be siblings of giant exoplanets. As close family members, we can use them to investigate how the planetary aging process works," Faherty said.

## Astronomers Detect Clouds Swirling Around A Brown Dwarf

Astronomers have discovered a curious band of clouds swirling across the surface of a brown dwarf called Luhman 16A, similar to the stripes on the surface of Jupiter. The finding adds to the peculiarity of brown dwarfs – oddballs too big to be planets but too small to be stars. Although they are star-like in composition and formation, they lack the intense nuclear processes that happen inside stars.

Located just 6.5 light-years away, Luhman 16A is part of a pair with Luhman 16B, each weighing about 30 times the mass of Jupiter. They are the closest brown dwarf pair to Earth.

To identify the bands on the surface of Luhman 16A, the team used a technique called polarimetry. Polarimetry is the measurement of the polarization of light, a phenomenon that happens when light waves vibrate in a single plane. This is what’s used to create the 3D effect in cinemas (where we use special glasses to filter the light) and it has many applications in astronomy, from the study of planets to the research on the properties of the universe as a whole.

"I often think of polarimetric instruments as an astronomer's polarized sunglasses," said lead author Maxwell Millar-Blanchaer, a Robert A. Millikan Postdoctoral Scholar in Astronomy at Caltech, in a statement. "But instead of trying to block out that glare we're trying to measure it."

“Polarimetry is the only technique that is currently able to detect bands that don’t fluctuate in brightness over time,” added Millar-Blanchaer, whose study is published in The Astrophysical Journal. “This was key to finding the bands of clouds on Luhman 16A, on which the bands do not appear to be varying. This is the first time that it’s really been exploited to understand cloud properties outside of the solar system.”

The team cannot image the brown dwarf directly, but the technique is sensitive to cloud features. Combined with atmospheric modeling, the data from the polarimetry suggests that Luhman16A might rain silica. While not enticing weather, it is an expected one for an object with a temperature almost high enough to melt silver.

Next-generation telescopes such as the Extremely Large Telescope will be able to exploit this technique and push it far beyond the bounds of clouds to detect liquid water on the surface of a planet.

Illustration comparing the masses of planets, brown dwarfs, and stars. Credit NASA/JPL-Caltech/R.Hurt (IPAC)

## Two Failed Stars in Our Cosmic Neighborhood Seem to Have. Stripes?

Never appreciated for what they are, brown dwarfs are often compared to what they are not. Indeed, they’re stuck in a celestial no man’s land, classified neither as stars nor gas giant planets. As new research shows, however, comparing brown dwarfs to gas giants like Jupiter is more appropriate than we realized.

A new paper in The Astrophysical Journal provides evidence of stripes and polar storms on brown dwarfs, similar to the ones seen on Jupiter. Using a space-based satellite, a research team led by planetary scientist Dániel Apai from the University of Arizona was able to construct basic maps showing the upper atmospheric layers of two nearby brown dwarfs. The paper is shedding new light on these enigmatic objects, while paving the way for future research.

Brown dwarfs are often referred to as failed stars, which kinda sucks if you’re a brown dwarf, of which there are many in the Milky Way. Indeed, our galaxy is absolutely bursting with these objects, with research from 2017 estimating a population around 100 billion. That’s a lot of failures, but hey, we can’t all be stars.

Brown dwarfs are typically as big as Jupiter but much more dense, packing in between 15 to 80 times more mass. At the same time, brown dwarfs are lightweights compared to stars, featuring insufficient pressure at their cores to trigger nuclear fusion, which is how stars are born. These objects are quite dim and difficult to see with telescopes, making it difficult for astronomers to study surface features.

“We wondered, do brown dwarfs look like Jupiter, with its regular belts and bands shaped by large, parallel, longitudinal jets, or will they be dominated by an ever-changing pattern of gigantic storms known as vortices like those found on Jupiter’s poles?” said Apai in a statement .

To find out, the team used NASA’s Transiting Exoplanet Survey Satellite (TESS), a space-based telescope normally used to detect exoplanets. Apai and his colleagues used TESS to observe two brown dwarfs, Luhman 16A and Luhman 16B, which are relatively close to Earth at approximately 6.5 light-years away. Both are roughly the same size as Jupiter, but they’re considerably more massive, 34 times and 28 times respectively, and about 1,500 degrees Fahrenheit hotter. The scientists managed to record over 100 rotations of both objects.

The data acquired by TESS, plus some fancy algorithmic work, allowed the team to measure changes in the brightness of the two brown dwarfs as they rotated. The objects exhibited fluctuations in brightness as they spun around, making it possible to create rudimentary maps of their upper atmosphere.

###### Something Big Just Slammed Into Jupiter

An amateur astronomer in Texas captured a rare sight earlier this week when an apparent meteor…

The scientists detected patterns consistent with high-speed winds running parallel to the equator. This was taken as evidence of atmospheric stripes similar to the ones seen on Jupiter. The associated winds, the authors speculate, are churning the atmosphere and delivering heat into the bowels of the brown dwarfs. The scientists also spotted signs of vortices in the polar regions, again similar to what’s seen on Jupiter.

“Wind patterns and large-scale atmospheric circulation often have profound effects on planetary atmospheres, from Earth’s climate to Jupiter’s appearance, and now we know that such large-scale atmospheric jets also shape brown dwarf atmospheres,” said Apai.

This discovery is a huge boost for scientists who study brown dwarfs. Should similar features appear on other brown dwarfs (this study presents a small sample size of two, so more work will be needed to validate these results), it’ll allow scientists to more meaningfully study the origin, climates, and temperatures of brown dwarfs. Looking ahead, the team is hoping to drill further down and study things like clouds, storms, and winds on brown dwarfs.

Excitingly, the technique used by this team could be used to map other distant objects, including Earth-like exoplanets.

Senior staff reporter at Gizmodo specializing in astronomy, space exploration, SETI, archaeology, bioethics, animal intelligence, human enhancement, and risks posed by AI and other advanced tech.

## If these brown dwarfs spun much faster they'd tear themselves apart

Astronomers have found three brown dwarfs — objects more massive than planets but less so than stars — that are the most rapidly rotating of any known. These beasts spin so dizzyingly fast they rotate about once per hour.

That's phenomenal. Think of it this way: They are about the same size as Jupiter, but that giant planet in our solar system spins once every ten hours. These objects spin ten times faster.

#### More Bad Astronomy

Or how about this: Standing on Earth's equator you'd experience a sideways velocity due to Earth's spin of about 1,700 kilometers per hour. Standing on the equator of one of these brown dwarfs that you'd be moving more like 375,000 kph!

Whoa. In fact, they're spinning so rapidly that the centrifugal force outward is nearly equal to their gravitational force inward. In other words, if they spun much faster they'd literally fly themselves apart.

Diagram showing relative masses and sizes of planets, brown dwarfs, and stars. The star shown would be an extremely low mass red dwarf, which can be roughly the same size as Jupiter though much denser. Credit: NASA/JPL-Caltech

Brown dwarfs are fascinating objects. They are sometimes called “failed stars”, which I think is unfair (who's to say they aren't really successful planets?). They form like stars, collapsing from interstellar clouds of gas and dust, but don't quite get enough mass to create sustained nuclear fusion in their cores (which is what defines a star). They're hot when they first form, and slowly cool off over time.

Generally speaking they have a mass range of roughly 13–75 times the mass of Jupiter anything lower mass than that is more like a planet, and anything more massive is a star. Weirdly, though, a quirk of physics keeps them pretty small. If you add mass to an object like Jupiter it doesn't get bigger, it gets denser. So a massive brown dwarf is only a bit bigger than Jupiter, but far more massive, making them on average denser than iron! They're weird objects, these brown dwarfs.

In some ways they look like planets, and can have storms in their upper atmospheres. These can be bright features, and as the brown dwarf rotates we see it come into and out of our view. Now, brown dwarfs are too far away to see as anything other than dots in our telescopes, but as a bright spot rotates into view we see the dwarf get brighter, then dimmer again as the storm rotates away onto the far side. So, by monitoring their brightness we can determine their rotation speed.

… but of course it's not that simple. What if there are two storms on opposite sides of the dwarf? If we thought they were a single storm we'd mistakenly calculate a rotation speed two times faster than it really is.

To check for that, astronomers took spectra of the brown dwarfs. This breaks the light up into individual wavelengths (think of them as color). Some atoms and molecules in the atmosphere absorb and emit light at pretty specific colors, and these show up as a raised blip or a narrow dip in the spectrum.

If the brown dwarf spins rapidly, these features get smeared out due to the Doppler effect, where light gets shifted a bit in wavelength as an object approaches or recedes from us. When an object spins, part of it moves toward us and part moves away, so the overall effect is to broaden the spectral features in wavelength.

Comparison of the rotation speeds of a brown dwarf, Jupiter, and Saturn.

The astronomers used the Spitzer Space Telescope to examine 25 bright brown dwarfs to look for various properties. Three of them displayed the ridiculously fast rotation speeds. If you're keeping track at home their names are 2MASS J04070752+1546457, 2MASS J12195156+3128497, and 2MASS J03480772−6022270. I'll just leave those alphanumeric salads there for you. But the astronomers found rotational periods (the brown dwarfs' “days”) of 1.23, 1.14 and 1.08 hours, respectively.

The record before this was 1.41 hours, so these are clearly winners.

I'll note that the measured rotational speed in km/hr may actually be higher! This number depends in part on how they're tilted with respect to us if we're seeing them more pole-on their real velocity is even higher.

How close are they to breaking up due to their high spin speed? That's harder to know. It depends on their mass and radius the bigger they are the more outward force they generate at a given speed, but the more massive they are the higher their gravity is and the harder it pulls material toward the center, offsetting the rotation. Still, the scientists found that they appear to be spinning at about half the speed necessary to fly apart. That's impressive.

In fact when they look at known spin rates of brown dwarfs, there appears to be a cluster of them near this top rate. That may be because ones that spin faster do in fact lose material, which slows their spin. So this may be about as rapidly as we'll ever see any brown dwarf spin.

Another effect is that a spinning object will flatten out at the equator, becoming oblate, like a beach ball someone is sitting on. This can be easily seen with Jupiter and Saturn, and in fact Saturn is the most oblate object in the solar system due to rotation it's about 10% smaller through its poles than across its equator. Doing the calculations, the astronomers find the brown dwarfs are about 5-8% flattened.

Overview of the discovery of three super-fast rotating brown dwarfs. Credit: NOIRLabAstro

Again, impressive, given their surface gravity is about 100 times Earth's. If they weren't spinning, standing on the equator I'd weigh over 7 tons! But due to their spin I'd only feel my weight being a little more than it is now (um, considerably less than 7 tons). Maybe twice as much, so not bad.

So why do they spin this rapidly? It's possible they were born rotating rapidly, as material fell onto the objects and they grew, increasing their spin. Maybe ones at this end of the rotation scale collided with and absorbed other objects (other brown dwarfs or planets) which spun them up. It's hard to say.

The first brown dwarfs were only discovered in the 1990s, and we're still learning about their basic properties. That's reflected in the fact that they can still surprise us! I hope there are still lots more such surprises to be found. In science, that's generally the way to bet.

## How does a brown dwarf die?

It should decay much faster than black holes of similar mass. There should be some spontaneous fusion too.

The brown dwarfs outer layer will eventually solidify. Much longer than billions of years. Deeper down should become metallic hydrogen. Phase transitions usually generate heat.

At low temperature the metals can precipitate and rain out of solution. The falling droplets release energy because they are denser and they are falling down a gravity well. That will generate heat and delay surface cooling.

The word "death" has always bothered me with regard to stars. In what sense is a star "alive".

About as alive as my laptop, which is in the process of dying on me apparently.

Electron degeneracy also holds up planets.
Three gas giants possess internal heat - all except Uranus.

Would Uranus freeze at 1 bar level if it were in outer solar system?

Electron degeneracy also holds up planets.
Three gas giants possess internal heat - all except Uranus.

Would Uranus freeze at 1 bar level if it were in outer solar system?

I have no idea about Uranus.

Planets are mainly supported from pressure produced by thermal motion of the atoms and molecules within.
Some degeneracy is present, but not to the extent of that within the dwarf stars, where the density is the deciding factor for its radius, regardless of temperature.
As a planet cools, motion of the mass within the interior does occur, as cooler material, being more dense will tend to flow towards the interior, producing mass displacement currents, or convection currents with regards to heat flow.

Some how the heat does flow from the interior of a dwarf star to the exterior, and this discussion has produced more questions on the actual mechanism.

## Bands of Clouds Swirl Across Brown Dwarf's Surface

Astronomers have detected what appear to be bands of clouds streaking across the surface of a cool star-like body known as a brown dwarf. The bands, resembling those that stripe the surface of Jupiter, were discovered using polarimetry, a technique that works in the same way that polarized sunglasses block out the glare of sunlight.

"I often think of polarimetric instruments as an astronomer's polarized sunglasses," says Maxwell Millar-Blanchaer, a Robert A. Millikan Postdoctoral Scholar in Astronomy at Caltech. "But instead of trying to block out that glare we're trying to measure it." Millar-Blanchaer is lead author of a new study on the findings, accepted for publication in The Astrophysical Journal. The observations were made using the European Southern Observatory's Very Large Telescope (VLT) in Chile.

While evidence for bands of clouds on brown dwarfs has been seen before, this discovery represents the first time that these features have been inferred using the polarimetry technique.

"Polarimetry is receiving renewed attention in astronomy," says Dimitri Mawet, professor of astronomy at Caltech and a senior research scientist at the Jet Propulsion Laboratory, which is managed by Caltech for NASA. "Polarimetry is a very difficult art, but new techniques and data analysis methods make it more precise and sensitive than ever before, enabling groundbreaking studies on everything from distant supermassive black holes, newborn and dying stars, brown dwarfs, and exoplanets, all the way down to objects in our own solar system."

The brown dwarf in the new study, called Luhman 16A, is part of a pair that together represents the closest known binary brown dwarf system to our solar system, lying at a distance of 6.5 light-years away. Discovered by NASA's Wide-field Infrared Survey Explorer (WISE) in 2013, each orb weighs roughly 30 times the mass of Jupiter. Brown dwarfs form from collapsing clouds of gas in a similar fashion to stars but they lack enough mass to ultimately ignite and shine with starlight.

Previous observations with NASA's Spitzer Space Telescope found that three other brown dwarfs had signs of cloud banding, and previous studies of the partner brown dwarf to Luhman 16A, called Luhman 16B, have inferred the presence of large cloud patches. But all of these previous measurements looked at how the brightness of the objects varied over time and did not measure polarized light. In the new study, the VLT's NaCo instrument was used to study polarized light from both of the Luhman brown dwarfs.

"Polarimetry is the only technique that is currently able to detect bands that don't fluctuate in brightness over time," says Millar-Blanchaer. "This was key to finding the bands of clouds on Luhman 16A, on which the bands do not appear to be varying."

The researchers explain that, although they cannot image the brown dwarf itself, their measurement of the amount of polarized light coming from it allows them to infer the presence of cloud bands through sophisticated atmospheric modeling. Their observations do not allow them to specify exactly how many bands of clouds are rotating around on Luhman 16A, but according to their models, the answer could be two.

Their models also show that the patches of clouds would have stormy weather similar to that on Jupiter.

"We think these storms can rain things like silicates or ammonia. It's pretty awful weather, actually," says co-author Julien Girard of the Space Telescope Science Institute.

In the future, the team hopes to extend this work to measurements of planets around other stars, called exoplanets.

"Polarimetry is very sensitive to cloud properties, both in brown dwarfs and exoplanets," says Millar-Blanchaer. "This is the first time that it's really been exploited to understand cloud properties outside of the solar system."

With next-generation ground-based and space-based telescopes, this same method can also be used to study those exoplanets with the potential to host life. Polarimetry is very sensitive not only to atmospheric properties, says Millar-Blanchaer, but also the type of surface a planet has, so it may be used one day to detect liquid surface water, a sign of habitability.

The study, titled, "Detection of polarization due to cloud bands in the nearby Luhman 16 brown dwarf binary," was funded by the National Science Foundation, NASA, and the European Research Council.