Planetary Pastry, First Course

“Morning, Al.  What’s the scone of the day?”

“No scones today, Sy.  Cathleen and one of her Astronomy students used my oven to do a whole batch of these orange-and-apricot Danishes.  Something to do with Jupiter.  Try one.”Great Apricot Spot 1
Cathleen was standing behind me.  “They’re in honor of NASA’s Juno spacecraft.  She just completed a close-up survey of Jupiter’s famous cloud formation, the Great Red Spot.  Whaddaya think?”

“Not bad.  Nice bright color and a good balance of sweetness from the apricot against tartness from the orange.”

“You noticed that, hey?  We had to do a lot of balancing — flavors, colors, the right amount of liquid.  Too juicy and the pastry part comes out gummy, too dry and you break a tooth.  Notice something else?”

“The structure, right?  Like the Spot’s collar around a mushed-up center.”

“Close, but Juno showed us that center’s anything but mushed-up.  <pulls out her smartphone>  Here’s what she sent back.”

GRS 1 @400

Credits: NASA/JPL-Caltech/SwRI/MSSS/Jason Major

“See, it’s swirls within swirls. We tried stirring the filling to look like that but it mostly smoothed out in the baking.”

“Hey, is it true what I heard that the Great Red Spot has been there for 400 years?”

“We think so, Al, but nobody knows for sure.  When Galileo published his telescopic observations of Jupiter in 1610 he didn’t mention a spot.  But that could be because he’d already caught flak from the Church by describing mountains and craters on the supposedly perfect face of the Moon.   Besides, the Jovian moons he saw were much more exciting for the science of the time.  A planet with satellites was a direct contradiction to Aristotle’s Earth-centered Solar System.”

“OK, but what about after Galileo?”

“There are records of a spot between 1665 and 1713 but then no reports of a spot for more than a century.  Maybe it was there and nobody was looking for it, maybe it had disappeared.  But Jupiter’s got one now and it’s been growing and shrinking for the past 185 years.”

“So what is it, what’s it made of and why’s it been there so long?”

“Three questions, one of them easy.”

“Which is easy, Sy?”

“The middle one.  The answer is, no-one knows what it’s made of.  That’s part of Juno‘s mission, to do close-up spectroscopy and help us wheedle what kinds of molecules are in there.  We know that Jupiter’s mostly hydrogen and helium, just like the Sun, but both of those are colorless.  Why some of the planet’s clouds are blue and some are pink — that’s a puzzle, right, Cathleen?”

“Well, we know a little more than that, especially since the Galileo probe dove 100 miles into the clouds in 1995.  The white clouds are colder and made of ammonia ice particles.  The pink clouds are warmer and … ok, we’re still working on that.”

“What about my other two questions, Cathleen?”

“People often call it a hurricane, but that’s a misnomer.  On Earth, a typical hurricane is a broad, complex ring of rainstorms with wind speeds from 75 to 200 mph.  Inside the ring wall people say it’s eerily calm.  The whole thing goes counterclockwise in the northern hemisphere, clockwise in the southern one.”

“So how’s the Great Red Spot different?”

“Size, speed, complexity, even direction.  East-to-west, the Spot is eight times wider than the biggest hurricanes.  Its collar winds run about 350 mph and it rotates counterclockwise even though it’s in Jupiter’s southern hemisphere.  It’s like a hurricane inside-out.”

“It’s not calm inside?”

“Nope, take another look at that Juno image.  There’s at least three very busy bands wrapped around a central structure that looks like it holds three distinct swirls.  That’s the part that’s easiest to understand.” GRS core

“Why so?”

“Geometry.  Adjacent segments of separate swirls have to be moving in the same direction or they’ll cancel each other out.  <scribbles diagram on a paper napkin>  Suppose I’ve got just one inside another one.  If they go in the same direction the faster one speeds up the slower one and they merge.  If they go in opposite directions, one of them disappears.  If there’s more than one inner swirl, there has to be an odd number, see?”

“So if it’s not a hurricane, what is it?”

“Got any donuts, Al?”

~~ Rich Olcott

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