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This post is not about short people of a particular colour, who are ill. This is about Brown Dwarfs, stars that are forever stuck in puberty – too massive to be a planet, and not massive enough to ignite nuclear fusion like “normal” stars that go on to live “star” lives (you know, burning hot and shining bright, possibly giving energy to planets / moons-full of life-forms, like our Sun).

A new study of 44 such brown dwarfs has revealed that, like planets, the brown dwarfs too have weather systems. For obvious reasons, the weather there is a bit “unearthly”. On Earth, the majority of storms and lightning are somehow related to water. But the brown dwarfs are far too hot to have any kind of water-based weather. Yet, they still do have clouds, and storms, and lightning, and you get the picture.

An artist’s rendition of the weather on a brown dwarf. Credit: NASA/JPL-Caltech/University of Western Ontario/Stony Brook University

(See, I did say “you get the picture”. Get it? Please don’t kill me.)

So what are these storms made of then? The clouds and the rain they rain are believed to be made of hot sand, salts, and even molten iron! To give you some idea, iron melts at 2,800°F (1,538°C). So, imagine a real hot, burning furnace, and add lightning to it. I think this image fits the context.

So how did astronomers see such violent weather on these “failed stars”? Well, clouds moving across the surface of a planet, or star in this case, result in variation of the brightness of the light emanating from that surface. In the case of planets, it is the light that they reflect (coming from their star), while in the case of these brown dwarfs, it’s the light they generate themselves. Even though the light from the dwarfs is not very bright compared to normal stars, our instruments can still pick up the variations in it, as clouds block some of it for some time, and then move to some other part of the surface, leading to changes in brightness over time.

Although out of the 44 brown dwarfs under study, only about half showed direct evidence for these brightness variations, scientists still think most or all of the dwarfs must be “weathered”. This is because it’s likely that not all of them were aligned perfectly with the line of sight from Earth – some of them would be aligned such that the storms would either be hidden or always be in view; for detection of weather patterns, the key is change in brightness. For example, if a storm were to always cover the surface of the dwarf, the light from the dwarf would be reduced. But since we never get to see that same dwarf being any brighter, we can’t say whether this is because it’s covered by a storm, or because it’s just less bright by itself (by not being massive enough, and hence, by not producing enough energy).

So, the point is, we can assume that almost all brown dwarfs weather such weather.

And it turns out that Santa was extra pleased with the astronomers’ efforts! In addition to the above, they also discovered that some of these dwarfs rotated more slowly than any previously observed! They have a couple of theories as to why that might be – different formation histories, undetected planets tugging on the dwarfs (gravitationally) and slowing them down over time, etc. As always, they need more observations and data to say anything conclusively.

The observations were made with the Spitzer Space Telescope, which takes images in the infrared spectrum and was ideally suited for the job. This was in part because of the thermal-imaging capabilities (as used by night-vision goggles, and also by the “predator” in the Arnold Schwarzenegger movie, Predator), and partly because of its orbit – it orbits the Sun, instead of the Earth. This allows it to make observations of such faint stars, which would otherwise be next to impossible to see, because of the background glare from the Earth.

All this information not only helps the astronomers understand brown dwarfs better, but also their little cousins, the gas giants, like Jupiter. Perhaps these observations may one day be able to explain what’s really going on with Jupiter’s Great Red Spot, which has been in existence for over 400 years!

Great Red Spot, as spotted by Voyager 1 in late 1970s. Credit: NASA (http://photojournal.jpl.nasa.gov/catalog/PIA00014) [Public domain], via Wikimedia Commons

 And you thought the recent “polar vortex” was bad!


— Shivang Gupta


– News release