The sun is hot.
Well, YEAH, ‘cuz it’s the sun!
But its atmosphere is too hot.
What’s going on?
Hello!
I’m Ian O’Neill, space producer for Discovery News and today I want to take you on a journey
deep into the sun’s atmosphere.
As you’d expect the solar atmosphere or the “solar corona” is hot.
But it’s TOO hot -- a problem that solar physicists have been trying to solve for decades.
In fact, my own solar physics PhD thesis was based on this very same solar conundrum.
From observations we know that the sun’s outer layer, the photosphere, is around 6,000
degrees Kelvin or Celsius.
We also know that the core of the sun is a nuclear furnace bubbling away at tens of MILLIONS
of degrees.
So, you’d expect the sun’s corona to be cooler than the photosphere since it’s further
away from the core, right?
Wrong.
Just above the photosphere is the chromosphere which extends into the lower corona and something
weird happens.
The temperature of coronal plasma skyrockets to millions of degrees.
It just makes no logical sense and seems to violate some hefty laws of thermodynamics!
If you put your hand next to a hot lightbulb, you wouldn’t expect that, as you move your
hand away from the bulb, that the air would get HOTTER.
But with the sun, as you leave the photosphere and enter the corona, that’s EXACTLY what
happens, it gets hotter, not cooler.
So what’s going on?
And perhaps most importantly: why should we care?
The first theory is that magnetic waves travel from the sun’s interior, ripple through
the corona like vibrations along a guitar string and resonate with the solar plasma.
We’ve observed these waves in the corona and we have a pretty good idea that they have
a significant heating effect, but they’re not the whole story.
Another heating mechanism seems to be down to countless explosions in the corona, known
as “nanoflares”.
Although they are tiny when compared with solar flares like the X-class flare that caused
a radio blackout on Earth earlier this month, nanoflares certainly aren’t insignificant.
Each nanoflare is thought to explode with the energy of 240 megatons of TNT, which is
equivalent to 10,000 nuclear weapons going off at once!
Regardless of how active the sun is, countless millions of these eruptions are thought to
be crackling in the corona all the time, undoubtedly cooking the sun’s atmosphere.
But how much cooking is going on?
Researchers have now turned NASA’s NuSTAR X-ray observatory for help.
NuSTAR is designed to look for the highest-energy X-rays generated in the furthest-most reaches
of the universe by black holes and other crazy energetic phenomena.
It just so happens that, by pure luck, NuSTAR is also finely tuned to detect the X-ray signature
of nanoflares inside the sun’s corona.
Early NuSTAR results have produced one of the most beautiful images in modern astronomy
[[insert: http://www.nasa.gov/sites/default/files/thumbnails/image/pia18906-nustarsun.jpg]], proving that nanoflares crackle throughout
the corona.
Only time will tell whether these “nano” explosions have the oomph to bake the corona
to millions of degrees.
But why does all of this matter?
Space weather is born deep inside the corona.
Solar flares erupt and huge bubbles of magnetized plasma -- called coronal mass ejections -- are
launched from this region.
The more we understand the nature of the corona, the better we can understand how the sun’s
most violent explosive events impact Earth.
After all, solar storms are known to knock out satellites, garble communications and
even knock out power grids, wouldn’t it be nice to properly get to know where and
why these eruptions are born?
What’s your favorite solar mystery?
Let us know in the comments below, and subscribe for more DNews every day of the week!