The Sun's Corona, A Fiery Halo, Is Still a Mystery to Scientists

The Sun's Corona, A Fiery Halo, Is Still a Mystery to Scientists
By Paul Sutter, Astrophysicist | August 17, 2017 03:23pm ET

The sun's outer atmosphere, called the corona, ejected streams of material in February 2000, as imaged by NASA's Solar and Heliospheric Observatory (SOHO).


Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at COSI science center. Sutter leads science-themed tours around the world at AstroTouring.com. Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

There are many things we don't understand in this universe — and some of those things sit right in our own backyard. Not our literal backyard, of course, but in one case, at the very heart of our solar system: the sun itself. Total solar eclipses offer a crucial chance to learn more about this star's unusual outer atmosphere.

Over the past century, scientists have puzzled out the process of nuclear fusion that has powered the sun for billions of years, detected neutrinos emanating from those fiery reactions in the core, modeled the process of energy transfer via conduction and predicted the fate of the sun as a white dwarf billions of years from now.

But the corona is something else. The thin, tenuous outer atmosphere of the sun extends millions of kilometers past the photosphere, what we usually think of as the sun's visible "surface." That makes the corona thicker than the main body of the sun itself, for those of you keeping track. [Total Solar Eclipse 2017: Here Are the Best Live-Video Streams to Watch]

The corona is so dim that it's usually totally overwhelms by the light emitted from the photosphere. But during a total solar eclipse, that light is conveniently blocked, giving us the spectacle of a moon embraced by a fiery halo. The corona is finally allowed its moment to shine. For those of you lucky enough to find yourselves on the path of totality on Aug. 21 (boldly assuming it won't be cloudy that day), you'll get to see this rare sight with your own eyes.

Did I mention that the corona has a temperature of over a million Kelvin? That seems like an important detail. That's roughly the same temperature as the sun's cacophonous nuclear core, and it's way, way hotter than the bulky mass of the rest of the sun.

Of course, you wouldn't feel that heat if you swam through it. The corona is incredibly thin, and its temperature is a measure of the average speed of the particles that comprise it. High temperatures mean that a single particle will slam into you like a bullet, but if there are hardly any particles around to begin with, you'll barely feel a warm breeze.

So how does the corona get so hot, despite extending far beyond the surface of the sun? Well, scientists are not exactly sure. It might have something to do with magnetic fields, though. We know that as a spinning ball of charged particles, the sun carries some pretty hefty magnetic energy. Those magnetic fields get warped and twisted and, eventually, can burst apart, releasing tremendous amounts of stored energy in the process.

It's this cycle of twisting-and-releasing magnetic field lines that scientists think is responsible for sunspot cycles and solar weather like flares and coronal mass ejections.

Does this process of releasing stored magnetic energy feed the flames of the corona? Its intensity does seem to be linked to the sunspot cycle, which is an important clue. But the detailed physics have bedeviled scientists for decades, despite extensive study and simulation.

(More at link:  https://www.space.com/37832-corona-of-the-sun-is-a-mystery.html )

I happened to take a trip with my brother and girlfriend to the path of totality this time, down on the Oregon coast. It was simply amazing. Even after seeing thousands of photos of the event, nothing compared to seeing it with my own eyes. I tried to take lots of photos with a decent DSLR but failed. Nothing even approached what my eyes had seen. It reminded me tremendously of mental hallucinations seen in my youngsterhood, messing around with LSD and psilocybin. But it was real, and beyond beautiful.

Aditya-L1: India's solar mission sends first photos on way to Sun
Published
7 September
https://www.bbc.com/news/world-asia-india-66738230

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India launches Aditya-L1 solar observatory, its 1st-ever sun probe
News
By Mike Wall published September 02, 2023
The mission will tackle some of the sun's biggest mysteries.

Fresh off its success at the moon, India is now headed for the sun.

The nation launched its first-ever solar observatory today (Sept. 2), sending the Aditya-L1 probe skyward atop a Polar Satellite Launch Vehicle (PSLV) from Satish Dhawan Space Centre at 2:20 a.m. EDT (0620 GMT; 11:50 a.m. local India time).

The PSLV deployed Aditya-L1 into low Earth orbit (LEO) as planned about 63 minutes after liftoff, sparking applause and high fives in mission control.

"Congratulations, India, and congratulations, ISRO [the Indian Space Research Organisation]," Jitendra Singh, India's Minister of State for Science and Technology, said shortly after deployment on ISRO's launch webcast.

"While the whole world watched this with bated breath, it is indeed a sunshine moment for India," Singh added.

The successful launch followed on the heels of another big milestone for India: On Aug. 23, its Chandrayaan-3 mission became the first to land softly near the moon's south pole.

Chandrayaan-3's lander-rover duo are expected to conk out in a week or so, when the harsh lunar night falls at their touchdown site. But Aditya-L1's long journey has just begun.

Related: Facts about the sun's age, size and history

a rocket rises into a blue sky atop a conical pillar of flame.

India's Aditya-L1 solar observatory rises into the sky on Sept. 2, 2023 atop a PSLV rocket. (Image credit: ISRO)
A long road to a good sun-viewing spot

Aditya-L1 won't stay in LEO forever: After a series of checkouts, it will use its onboard propulsion system to head toward Earth-sun Lagrange Point 1 (L1), a gravitationally stable spot about 1 million miles (1.5 million kilometers) from our planet in the direction of the sun.

That destination explains the latter part of the mission's name. And the first part is simple enough: "Aditya" translates to "sun" in Sanskrit.

The 3,260-pound (1,480 kilograms) observatory will arrive at L1 about four months from now, if all goes according to plan. But the long trek will be worth it, according to the ISRO.

"A satellite placed in the halo orbit around the L1 point has the major advantage of continuously viewing the sun without any occultation/eclipses," ISRO officials wrote in an Aditya-L1 mission description. "This will provide a greater advantage of observing the solar activities and its effect on space weather in real time."

Indeed, another sun-studying spacecraft is already at L1 — the Solar and Heliospheric Observatory (SOHO), a joint NASA-European Space Agency mission that launched in December 1995. (Several other spacecraft, including NASA's James Webb Space Telescope, are at Earth-sun Lagrange Point 2, which is a million miles from Earth, in the direction away from the sun.)

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Solar flares, the coronal heating mystery and more
Once it's settled in at L1, the solar probe will use four three science instruments to study the particles and magnetic fields in its immediate surroundings and four others to scrutinize the sun's surface (known as the photosphere) and its atmosphere.

This work will help scientists better understand solar activity, including the dynamics of solar flares and coronal mass ejections (CMEs), ISRO officials say. Flares are powerful flashes of high-energy radiation, and CMEs are huge eruptions of solar plasma.

Both types of outburst can affect us here on Earth. Intense CMEs that hit our planet, for example, trigger geomagnetic storms that can disrupt satellite navigation and power grids. (As a side benefit, such storms also supercharge the gorgeous light shows known as auroras.)

Aditya-L1 will also tackle the "coronal heating problem," one of the biggest mysteries in heliophysics. The corona — the sun's wispy outer atmosphere — is incredibly hot, reaching temperatures around 2 million degrees Fahrenheit (1.1 million degrees Celsius), according to NASA.

That's about 200 times hotter than the solar surface, which is "only" 10,000 degrees F (5,500 degrees C) or so. It's still unclear what is responsible for this startling and counterintuitive discrepancy. (Why would it be hotter away from the sun's core, where the energy-producing nuclear fusion reactions are occurring?)

Aditya-L1 has other science goals as well. For instance, the mission also aims to more fully flesh out the solar wind, the stream of charged particles flowing constantly from the sun, ISRO officials said. Aditya-L1 will measure the composition of the solar wind and attempt to determine how it is accelerated.

And Aditya-L1 will do all this work on the cheap: The mission's price tag is about 3.8 billion rupees, or $46 million US at current exchange rates. That's in the same ballpark as Chandrayaan-3; India's first successful moon-landing mission costs about 6.15 billion rupees, or $74 million US.


More at link: https://www.space.com/india-launches-aditya-l1-first-solar-probe
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India's Aditya-L1 solar observatory captures 1st gorgeous views of the sun (images)
News
By Sharmila Kuthunur published 2 days ago
The spacecraft has exited Earth's sphere of influence and is about a month away from reaching its cosmic accommodations at L1.



The SUIT payload onboard Aditya-L1 spacecraft captured the sun's full disk on first light earlier this week (Image credit: ISRO)
The SUIT payload onboard Aditya-L1 spacecraft captured the sun's full disk on first light earlier this week (Image credit: ISRO) (Image credit: ISRO)
An instrument onboard India's first sun-studying observatory has officially opened its scientific eyes and sent home beautiful images of our star.

The pictures, captured earlier this week by a payload named SUIT (short for Solar Ultraviolet Imaging Telescope), reveal a handful of features on the sun's surface, including a few sunspots, a solar "plage" and some silent, inactive areas.

It is a "lifetime opportunity to conceive a space telescope & get to see its first light observations," Durgesh Tripathi, SUIT's principal investigator, said in a post on X (formerly Twitter) on Friday (Dec. .

Related: India's Aditya-L1 sun probe spots 1st high-energy solar flare

Scientists turned on the instrument on Nov. 20, according to a statement by the Indian Space Research Organisation (ISRO), which is operating the Aditya-L1 solar observatory in collaboration with multiple institutions located in Ahmedabad, Pune and Kerala.


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The sun, of course, is a roiling ball of plasma. So rather than a solid, rocky surface like Earth's, the sun's visible "surface" is really a thin envelope of hydrogen and helium called photosphere. It is about 62 miles (100 kilometers) thick and home to sunspots, or dark, planet-size regions of intense magnetic fields from which powerful solar flares blast out. Sometimes, these plasma jets travel toward us, like those that spurred a recent "cannibal" solar storm that initiated gorgeous auroras around the world.

Aditya-L1's latest images capture four clear sunspots, including one very close to the sun's equator. Our star appears to be calmer to its left, labeled in the image as "quiet sun." Below the equator, you'll notice another feature called the plage, a very hot region usually seen in the chromosphere, which is the layer of the sun's atmosphere above the photosphere but underneath its corona.

The Aditya-L1 spacecraft lifted off on Sept. 2 from India's spaceport in Sriharikota on a four-month journey to L1 orbit, a vantage point in space approximately 1 million miles (1.5 million kilometers) from Earth. From this region, the probe can observe the sun continuously and also remain somewhat stable by using minimal fuel and requiring just a few orbital maneuvers.

The spacecraft flung past the sphere of Earth's gravitational influence in late September; it will reach its final cosmic accommodations later this month or early next. Then, its seven science instruments are expected to begin studying how solar wind particles behave after blasting from the sun, while also monitoring our star for upcoming solar flares.

The mission team has started switching on other payloads onboard Aditya-L1 too. Last week, for instance, ISRO announced the Aditya Solar wind Particle Experiment (ASPEX) instrument, meant to study the composition of solar wind by in-situ observations, was performing as expected. On Friday (Dec. , another payload designed to monitor solar wind was also turned on and declared to be in good health, the space agency said in a different statement.

Scientists hope to use data from this mission to predict solar flare activity and their companions, coronal mass ejections.

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