Images from Sun's edge reveal origins of solar wind

Images from Sun's edge reveal origins of solar wind
Conceptual animation (not to scale) showing the Sun's corona and solar wind. Credit: NASA's Goddard Space Flight Center/Lisa Poje

Ever since the 1950s discovery of the solar wind - the constant flow of charged particles from the sun - there's been a stark disconnect between this outpouring and the sun itself. As it approaches Earth, the solar wind is gusty and turbulent. But near the sun where it originates, this wind is structured in distinct rays, much like a child's simple drawing of the sun. The details of the transition from defined rays in the corona, the sun's upper atmosphere, to the solar wind have been, until now, a mystery.

Using NASA's Solar Terrestrial Relations Observatory, or STEREO, scientists have for the first time imaged the edge of the sun and described that transition, where the solar wind starts. Defining the details of this boundary helps us learn more about our solar neighborhood, which is bathed throughout by solar material - a that we must understand to safely explore beyond our planet. A paper on the findings was published in The Astrophysical Journal on Sept. 1, 2016.

"Now we have a global picture of solar wind evolution," said Nicholeen Viall, a co-author of the paper and a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "This is really going to change our understanding of how the space environment develops."

Both near Earth and far past Pluto, our space environment is dominated by activity on the sun. The sun and its atmosphere are made of plasma - a mix of positively and negatively charged particles which have separated at extremely high temperatures, that both carries and travels along lines. Material from the corona streams out into space, filling the solar system with the solar wind.

The details of the transition from defined rays in the corona, the sun’s upper atmosphere, to the solar wind have always been a mystery. Using NASA’s Solar Terrestrial Relations Observatory, or STEREO, scientists have for the first time imaged the edge of the sun and described that transition, where the solar wind starts. Credit: NASA’s Goddard Space Flight Center/Genna Duberstein

But scientists found that as the plasma travels further away from the sun, things change: The sun begins to lose magnetic control, forming the boundary that defines the outer corona - the very edge of the sun.

"As you go farther from the sun, the drops faster than the pressure of the material does," said Craig DeForest, lead author of the paper and a solar physicist at the Southwest Research Institute in Boulder, Colorado. "Eventually, the material starts to act more like a gas, and less like a magnetically structured plasma."

The breakup of the rays is similar to the way water shoots out from a squirt gun. First, the water is a smooth and unified stream, but it eventually breaks up into droplets, then smaller drops and eventually a fine, misty spray. The images in this study capture the plasma at the same stage where a stream of water gradually disintegrates into droplets.

Images from Sun's edge reveal origins of solar wind
Views of the solar wind from NASA's STEREO spacecraft (left) and after computer processing (right). Scientists used an algorithm to dim the appearance of bright stars and dust in images of the faint solar wind. This innovation enabled them to see the transition from the corona to the solar wind. It also gives us the first video of the solar wind itself in a previously unmapped region. Credit: data from Craig DeForest, SwRI

Before this study, scientists hypothesized that magnetic forces were instrumental to shaping the edge of the corona. However, the effect has never previously been observed because the images are so challenging to process. Twenty million miles from the sun, the solar wind plasma is tenuous, and contains free-floating electrons which scatter sunlight. This means they can be seen, but they are very faint and require careful processing.

In order to resolve the transition zone, scientists had to separate the faint features of the solar wind from the background noise and light sources over 100 times brighter: the background stars, stray light from the sun itself and even dust in the inner solar system. In a way, these images were hiding in plain sight.

Images of the corona fading into the solar wind are crucial pieces of the puzzle to understanding the whole sun, from its core to the edge of the heliosphere, the region of the sun's vast influence. With a global perspective, scientists can better understand the large-scale physics at this critical region, which affect not only our planet, but also the entire solar system.

Images from Sun's edge reveal origins of solar wind
Computer-processed data of the solar wind is shown. Credit: data from Craig DeForest, SwRI

Such observations from the STEREO mission - which launched in 2006 - also help inform the next generation of sun-watchers. In 2018, NASA is scheduled to launch the Solar Probe Plus mission, which will fly into the 's corona, collecting more valuable information on the origin and evolution of the .

STEREO is the third mission in NASA Heliophysics Division's Solar Terrestrial Probes program, which is managed by Goddard for the Science Mission Directorate, in Washington, D.C.


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More information: The Astrophysical Journal, DOI: 10.3847/0004-637X/828/2/66
Journal information: Astrophysical Journal

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Sep 01, 2016
No conjecture, no assumptions, so statement of theory as though it is fact,
.. a pretty definitive and graphic description of what the sun "is", ie. "not a solid ball in space, not a ball of fire", when, in fact, the sun is a solid ball in space. What we see is composed of an iron mantle surrounded by a relatively thin neon plasma layer. NASA is in denial.

http://www.thesur...sun.com/

RNP
Sep 02, 2016
@baudrunner

No conjecture, no assumptions, so statement of theory as though it is fact,
..in fact, the sun is a solid ball in space. What we see is composed of an iron mantle surrounded by a relatively thin neon plasma layer. NASA is in denial.

http://www.thesur...sun.com/

This is clear nonsense. You only have to glance at the spectrum of the Sun to see that it is composed of a large number (most) of the chemical elements and neon is only a tiny, tiny fraction of the material in the "outer layer".

You can get an idea of how we know this from http://www.columb...0Ex.html

....and the results of the measurements from http://hyperphysi...omp.html

Sep 02, 2016
Too bad the guy who discovered helium in the Sun by its spectrum didn't know it's just iron and neon there; it would have saved him from his discovery. It would have saved those who found hydrogen there too from their efforts.

With all the solar wind, one wonders how does hydrogen still stick to the Sun.

Sep 02, 2016
how does hydrogen still stick to the Sun.

Gravity. Look it up. Fascinating stuff.

Sep 02, 2016
how does hydrogen still stick to the Sun.

Gravity. Look it up. Fascinating stuff.

Hydrogen atoms (ions actually) have a speed that probably would allow them to leave the Sun in some billions of years if hydrogen is very rare on the Sun (compared to iron and neon). In the same way Earth loses hydrogen to outer space. The problem is that the Sun still has a lot of hydrogen, which indicates it may actually be composed of H, not Fe or Ne.

Sep 02, 2016
if hydrogen is very rare on the Sun

Luckily the sun is 73.5% hydrogen. (Fe and Ne together account for less then 0.3%)

In the same way Earth loses hydrogen to outer space.

Earth's gravity is far lower than that of the Sun.

Just looking up the numbers: Mean velocity in the sun corona is (calculated from Maxwell distribution) 145km/sec. Escape velocity of the sun is 618km/sec. From the distribution you can calculate how much of that has enough energy to escape. This comes out to a mass loss of 10^9 kg per second.
The sun clocks in at a mass of 2*10^30kg.

https://en.wikipe...Emission

So, the time until the sun would loses 1% of its mass by this emission alone would be 2*10^19 seconds (i.e. roughly 10^11 years...which is roughly 60 times longer than the expected lifetime of the sun from formation until it goes red giant)

So in short: No. It would not have lost most its hydrogen long ago.


Sep 02, 2016
I was talking about baud's affirmation that the Sun is composed of Fe and Ne. I think if that had been the case, the solar wind would have taken away H from the Sun. But that is not the case. You have a point though.

Sep 09, 2016
I never said that the sun is composed of Fe and Ne. I said that what we see is a massive iron mantle surrounded by a thin neon plasma layer. That is what we see. These suns often cool down to become red dwarf stars as they lose mass during more dynamic phases. Eventually it might become a dark body, ie a brown dwarf, then lose stellar properties altogether and be just a lump in space. A mostly iron one. Boring, huh?

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