Aurora stellaris

Today's topic falls into the category of "The More You Think About It, The Weirder It Gets," and comes to us courtesy of my writer friend Andrew Butters.

Before I get to the meat and potatoes of the story, two bits of background.

Auroras occur because of the solar wind, a powerful stream of particles (chiefly electrons and protons) emitted from the upper atmosphere of the Sun.  When they strike the Earth's upper atmosphere and interact with the various molecules in the air, this has the effect of exciting the electrons in the molecules (bouncing them to higher energy levels), and when those electrons fall back into the ground state, they emit the extra energy as light.  Because of the quantization of energy levels, each color (frequency) is associated with a particular transition in a particular element -- the commonest are reds and greens (from oxygen) and blues (from nitrogen).

Auroras on Earth are most often seen in high latitudes because of the shape of the Earth's magnetic field.  The slope of the magnetic field lines increases the closer you get to the poles, so at high latitudes it acts a bit like a funnel, creating spectacular displays in the Arctic and Antarctic regions.

Despite the fact that I feel like I feel like I live in the Frozen North (especially at this time of year), I've only ever gotten to see the auroras once.  It was about ten years ago, and we heard there was a solar storm and the "Northern Lights" were going to be seen a lot farther south than usual.  That night it was supposed to be crystal-clear -- also an unusual occurrence in this cloudy climate -- so once it was dark, my wife and I went across the street into the neighbor's field and watched for a while, with disappointing results of the "Is that a flicker?  I think that's a flicker" sort.

At some point my wife, who is clearly the brains of the operation, realized that we were looking for the Northern Lights, but we were facing south.  In our defense, there were fewer trees obstructing the sky in that direction, but it's still a little like the guy who was searching around the kitchen floor for his contact lens, and his wife joined him, but the two of them couldn't find it.  She finally said, "Are you sure you dropped it in the kitchen?"  And he responded, "No, I dropped it in the bathroom, but the light is better in here."

In any case, we turned around to the north...

.... and wow.

Over our rooftop and beyond the branches of the walnut trees was a light show like I've never seen before -- shifting curtains of green luminescence resembling some kind of gauzy emerald curtain.  It was spectacular.  We watched it for about forty-five minutes before it finally started to fade.

So if you're ever looking for auroras, make sure you're pointed the right way.

The second piece of background is that there is a strange astronomical object called a brown dwarf.  Brown dwarfs are almost-stars -- something on the order of twenty to eighty times the mass of the planet Jupiter.  Since the fusion of hydrogen into helium -- what powers stars' cores -- requires intense pressure to get started, there's a lower limit to the mass a star can have.  Below that mass, the gravity of its contents is insufficient to raise the pressure in the core to the point where fusion can begin, and what you end up with is something midway between a planet and a star.

Well, the link Andrew sent me is about a new discovery by the amazing James Webb Space Telescope -- of a brown dwarf, W1935, which has auroras.

On first glance, you might think, "why not?"  But remember how auroras are created.  They're caused by the interaction of a stream of high-energy particles with the atmosphere of a planet.

So where are the high-energy particles coming from?

Artist's illustration of W1935 [Image courtesy of artist Leah Hustak and NASA/ESA/CSA]

Even odder, the atmosphere of W1935 seems to have a temperature inversion -- a region of the atmosphere that warms, rather than cools, with increasing altitude.  Its upper atmosphere was glowing with the very specific infrared frequency given off when you heat methane.  So not only does it have auroras when there's no reason it should, there's some sort of a heat source that's creating convection in its atmosphere without it receiving an external heat input from a star.

"We expected to see methane, because methane is all over these brown dwarfs. But instead of absorbing light, we saw just the opposite: The methane was glowing," said Jackie Faherty, of the American Museum of Natural History, who led the study.  "My first thought was, what the heck?  Why is methane emission coming out of this object?...  With W1935, we now have a spectacular extension of a solar system phenomenon without any stellar irradiation to help in the explanation.  With the JWST, we can really 'open the hood' on the chemistry and unpack how similar or different the auroral process may be beyond our solar system."

So here we have one more example of a significant mystery out there in space, and yet another brilliant contribution to astronomy and astrophysics by the JWST.  It seems like every new cache of data opens up as many new questions as it solves old ones.  But that's the way it goes with science -- as Neil deGrasse Tyson put it, "As the area of our knowledge grows, so too does the perimeter of our ignorance."

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Strange new worlds

Since the discovery of the first exoplanet in January of 1992, astronomers have identified over 5,500 of them, with nearly a thousand of the systems analyzed having more than one detected planet.  It now appears that at least one of the variables in the Drake equation -- f_p, the fraction of stars that have planets -- is far higher than anyone might have expected. 

What has come as an additional surprise is how varied these worlds are.  Having grown up on a steady diet of Lost in Space, Star Trek, and Star Wars, I kind of had exoplanets pictured as mostly Earth-like, with lots of big rocks and maybe an odd-colored sky:

The truth is, every new one we find holds some sort of surprise.  Some of the odder ones are:

• TrES-2b, which holds the record as the least-reflective planet yet discovered.  It's darker than a charcoal briquet.  This led some people to conclude that it's made of dark matter, something I dealt with here at Skeptophilia a while back.  (tl:dr -- it's not.)
• CoRoT-7b, one of the hottest exoplanets known.  Its composition and size are thought to be fairly Earth-like, but it orbits its star so closely that it has a twenty-day orbital period and surface temperatures around 3000 C.  This means that it is likely to be completely liquid, and experience rain made of molten iron and magnesium.
• 55 Cancri e, nicknamed the "diamond planet."  Another "hot super-Earth," this one is thought to be carbon rich, and that because of the heat and pressure, much of the carbon could be in the form of diamonds.  (Don't tell Dr. Smith.)
• PSR J1719−1438, a planet orbiting a pulsar (the collapsed, rapidly rotating core of a giant star).  It has one of the fastest rates of revolution of any orbiting object known, circling its host star in only 2.17 hours.
• V1400 Centauri, a planet with rings that are two hundred times wider than the rings of Saturn.  In fact, they dwarf the planet itself -- the whole thing looks a bit like a pea in the middle of a dinner plate.

The reason all this comes up is that we just had a new addition to the "weird exoplanet" list thanks to the James Webb Space Telescope.  It's called WASP-107b, and it has a number of bizarre characteristics.  First, it is "fluffy" -- that's actually how the astronomers describe it -- having one of the lowest overall densities of any exoplanet known.  It has about the mass of Neptune, but a diameter closer to that of Jupiter.

Second, it has a retrograde orbit -- it moves the opposite direction from the rotation of its host star and the revolution of the rest of the planets in the system.  Its orbit is highly eccentric (elliptical), and is actually tipped 118 degrees away from the ecliptic (the plane of revolution of the rest of the system).  Astrophysicists believe that it got this way because of interaction with the much more massive WASP-107c, but the truth is, they've never seen anything like it, so that's a surmise.

The atmosphere has high quantities of water vapor -- kept gaseous by the high temperatures (the upper atmosphere has an average temperature of 500 C) -- and sulfur dioxide.  A bigger surprise was that the "highly dynamic atmosphere" (scientist-speak for "wind speeds that would blow your ass into the middle of next week") creates clouds of superheated silicate sand.  The overall result is that being on WASP-107b would be like living inside a permanent pyroclastic flow.

"The fact that we see these sand clouds high up in the atmosphere must mean that the sand rain droplets evaporate in deeper, very hot layers and the resulting silicate vapor is efficiently moved back up, where they recondense to form silicate clouds once more," said study co-author Michiel Min.  "This is very similar to the water vapor and cloud cycle on our own Earth but with droplets made of sand."

"JWST enables a deep atmospheric characterization of an exoplanet that does not have any counterpart in our Solar System," added study lead author Achrène Dyrek.  "We are unravelling new worlds."

What's shocking is how bizarre some of these new worlds are.  It was natural enough to look at the planets in our own Solar System and assume that they kind of ran the gamut of planetary types -- thus the predominance of rocky worlds and gas giants with zillions of moons that you find in early science fiction.  What continues to astonish is just how wrong that was.  Wherever we look, we see an incredible variety of planets and star systems, and the great likelihood is that despite how many we've found, we've only scratched the surface.

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Look upwards

Since (surprise!) we've all once again survived the apocalypse, and Saturday September 24, 2022 turned out to be less of a "day to remember" than a "day I've already kind of forgotten," today I'm going to turn to one of my favorite topics, namely: space.

I've been continually wowed by the images coming in from the James Webb Space Telescope.  When it was first deployed, the astronomer and engineers responsible for it told us we were going to be blown away by the quality of the data it would send us, and if anything, that's been an understatement.  We've seen images of astonishing crystal clarity, not only photographs of galaxies further away than anything yet studied but detailed views of objects much closer to home.

It's one of the latter that prompted me to write today's post, because the latest posted image from the JWST is of the planet Neptune.  Just a couple of months ago I did an entire post on how generally weird Neptune is; a lot of our information on it is old, however, having come from the Voyager 2 flyby a little over thirty years ago.  Since then, we've had to study it from farther away, and a lot of what we've learned has raised more questions than answers.

So I was really eager to see what JWST would find out about the eighth planet.  And it's started out with a bang.  Check out this image, showing the planet with its rings and several of its fourteen moons:

[Image is in the Public Domain courtesy of NASA/JPL]

The rings are made of dark material -- this is actually the first time they've been directly observed since Voyager 2 (even the Hubble Space Telescope didn't have the optical resolution to see them).  The bright spots in the atmosphere are clouds of methane ice; the planet itself is not its usual deep cobalt blue because this image was taken in the near infrared range of the electromagnetic spectrum.

I find it deeply inspiring that despite the continuing turmoil down here on Earth, the scientists still have their eyes trained on deep space.  It also keeps us humble, you know?  Even as a child, when I'd look up at the sky through my little telescope, it always gave me a feeling of awe at how majestic, magnificent, and absolutely huge the universe was.

It reminds me of the words of Apollo 11 astronaut Michael Collins, about his experience of seeing the Earth from space: "The thing that really surprised me was that it [Earth] projected an air of fragility.  And why, I don’t know.  I don’t know to this day.  I had a feeling it’s tiny, it’s shiny, it’s beautiful, it’s home, and it’s fragile."

It's a perspective we all should have.

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