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Few locations within the photo voltaic system get hotter than the surface of the sun. But opposite to expectations, the tenuous tendrils of plasma within the outermost layer of its environment—often called the corona—are far more searing than its floor.
“It could be very complicated why the photo voltaic corona is farther away from the solar’s core, however is a lot hotter,” says University of California, Berkeley house sciences researcher Jia Huang.
The photo voltaic floor lingers round 10,000 levels Fahrenheit, whereas the skinny corona can get as sizzling as 2 million levels. This conundrum is called the coronal heating problem, and astronomers have been engaged on fixing it because the mid-1800s.
“Simply talking, fixing this downside may assist us perceive our solar higher,” says Huang. A greater understanding of photo voltaic physics can also be “essential for predicting space weather to guard people,” he provides. Plus, the solar is the one star we will ship probes to—the others are just too distant. “Thus, understanding our solar may assist perceive different stars within the universe.”
A short historical past of the coronal heating downside
During the 1869 total solar eclipse—an alignment of the solar, moon, and Earth that blocks out the majority of the solar’s mild—scientists had been in a position to observe the faint corona. Their observations revealed a characteristic within the corona that they took as proof of presence of a brand new ingredient: coronium. Improved theories of quantum mechanics over 60 years later revealed the “new ingredient” to be plain previous iron, however heated to a temperature that was increased than the solar’s floor.
[Related: We still don’t really know what’s inside the sun—but that could change very soon]
This new clarification for the puzzling 1869 measurement was the primary proof of the corona’s excessive temperature, and kicked off many years of examine to grasp simply how the plasma received so sizzling. Another approach of phrasing this query is, the place is the vitality within the corona coming from, and the way is it getting there?
“We know for positive that this downside hasn’t but been resolved, although we’ve many theories, and the entire [astronomy] group continues to be enthusiastically engaged on it,” says Huang. There are presently two primary hypotheses for a way vitality from the solar heats the corona: the movement of waves and an explosive phenomenon known as nanoflares.
Theory 1: Alfvén waves
The floor of the solar roils and bubbles like a pot of boiling water. As the plasma convects—with hotter materials rising and cooler materials sinking down—it generates the solar’s immense magnetic field. This magnetic subject can transfer and wiggle in a particular sort of wave, often called Alfvén waves, which then push round protons and electrons above the solar’s floor. Alfvén waves are a recognized phenomenon—plasma physicists have even seen them in experiments on Earth. Astronomers suppose the charged particles stirred up by the phenomenon may carry vitality into the corona, heating it as much as surprising temperatures.
Theory 2: Nanoflares
The different doable clarification is a little more dramatic, and is sort of just like the solar snapping an enormous rubber-band. As the solar’s plasma tumbles and circulates in its higher layer, it twists the star’s magnetic field lines into knotted, messy shapes. Eventually, the strains can’t take that stress anymore; as soon as they’ve been twisted too far, they snap in an explosive occasion known as magnetic reconnection. This sends charged particles flying round and heats them up, a occurring known as a nanoflare, carrying vitality to the corona. Astronomers have observed a few examples of nanoflares with trendy house telescopes and satellites.
The coronal heating thriller continues
As is often the case with nature, evidently the solar isn’t merely launching Alfvén waves or creating nanoflares—it’s greater than doubtless doing each. Astronomers simply don’t know the way usually both of those occasions occur.
[Related: Hold onto your satellites: The sun is about to get a lot stormier]
But they may get some simple solutions quickly. The Parker Solar Probe, launched in 2018, is on a mission to the touch the solar, dipping nearer to our star than ever earlier than. It’s presently flying by some outer components of the corona, offering the primary up-close have a look at the actions of particles that could be accountable for the intense temperatures. The mission has already passed through the solar atmosphere once, and can maintain swinging round for just a few extra years—offering key data to assist scientists settle the coronal heating downside as soon as and for all.
“I’d be very assured that we may make huge progress within the upcoming decade,” says Huang.
