Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:
CORONAL HEATING PROBLEM
This is the Sun. He’s kind of a big deal, and he knows it.
The interior of the Sun is several million degrees Celsius. By comparison, the surface of the Sun is quite chilly. It’s only a few thousand degrees. Still, if you were standing on the surface of the Sun, you wouldn’t last long.
But before you launch yourself into space to escape the heat, there’s something you should know: as you fly away from the Sun, passing through the corona, the temperature starts getting hotter again. It’s not quite as hot as the interior, but still… we’re back into million-plus degree heat.
If that doesn’t make sense to you, that’s okay. It doesn’t make sense to me either, or anyone else. Astro-scientists have been baffled by this for decades now. They call it the coronal heating problem.
I first heard about the coronal heating problem back in 2014, when I was starting my research for what became the 2015 Mission to the Solar System. To be honest, it’s not something I’ve spent a lot of time thinking about since then. Every once in a while, it comes up again and I think, “Oh right… so they still haven’t figured that out yet?”
But as you may heave heard last week, NASA’s on the case. Their newly named Parker Solar Probe is going to skim very close to the Sun and try to figure out what the heck’s going on.
Parker is scheduled for a launch window in July/August of 2018. Its mission is expected to last until 2025. So hopefully a decade from now, whenever I’m reminded of the coronal heating problem, it won’t be a problem anymore, and I’ll be able to think, “Oh right… they finally figured that out!”
Planet Pailly 
Whenever I hear or read about this issue, I always wonder how we know the temperatures of those zones. The Parker probe will be the first one to actually get anywhere close to the corona.
The sun is the most difficult place to reach in the solar system, and not because of the temperature. The Parker probe, despite being launched on a Delta IV Heavy, is going to need several years and numerous gravity assists for its orbit to graze within six million kilometers.
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I’m guessing we measure the Sun’s temperature with spectroscopes or something. It would be kind of a let-down if it just turns out we just measured wrong.
As I recall, you did a pretty good post once on how difficult it is to get to the Sun.
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Yeah, stars’ temperatures are measured spectrographically.
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Makes sense to me.
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Interesting. I knew that spectroscopy could be used to detect a star’s chemical properties, to measure a its relative motion, and its distance, but I didn’t know it could measure temperature. Apparently they can do so by measuring the peak wavelength (i.e. color range) and plugging it into something call Wien’s Law, something derived in the 19th century. https://en.wikipedia.org/wiki/Astronomical_spectroscopy#Temperature_and_size
Thanks James. I actually had forgotten about that post.
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I remember that post of yours being a bit of an eye opener for me. I think I knew getting to Mercury was tricky, but I hadn’t given much thought about how to get to the Sun.
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For any interested parties: it was a post debunking an urban legend about NASA accidentally sending a spacecraft into the sun: https://selfawarepatterns.com/2015/05/11/nasa-has-never-accidentally-sent-a-probe-into-the-sun/
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I never knew this… interesting stuff 🙂
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Yeah, it is a very weird thing. Hopefully it’ll start making sense to us soon.
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It’ll probably be useful too!
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I could be totally wrong, but I’ve heard that there isn’t really a surface to the Sun. It’s all one giant ball of gas that gets continuously less dense all the way out to the heliopause. What we see as the “surface” is just a visual artifact, where the density of the gas becomes low enough for photons to begin escaping without bumping into something. I’m going to have to do some research now to find out how much truth there is to that.
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No, I think you’re right. By surface, I merely mean top-most layer, a.k.a. the photosphere.
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I hadn’t heard of the Parker probe. Another thing to read about.
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It should be a very interesting mission!
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