Parker Solar Probe and Solar Orbiter team up to tackle 65-year-old sun mystery

A new groundbreaking measurement made by the Solar Orbiter spacecraft and the Parker Solar probe brings scientists closer than ever to solving a longstanding mystery surrounding the sun. Oddly enough, our host star's atmosphere, or corona, is staggeringly hotter than the solar surface despite being further away from the obvious source of the sun’s heat — and this is a puzzle that has troubled physicists for about 65 years. 

The collaboration between these two instruments was made possible when the Solar Orbiter, operated by the European Space Agency (ESA) performed some space-based gymnastics. These maneuvers allowed the spacecraft to observe the sun and NASA’s Parker Solar Probe at the same time. Ultimately, that allowed for simultaneous solar observations between the two, which together indicated that turbulence is likely heating the solar corona to incredible temperatures.

"The ability to use both Solar Orbiter and Parker Solar Probe has really opened up an entirely new dimension in this research," Gary Zank, co-author of a study on the results and a researcher at the University of Alabama in Huntsville, said in a statement.

This team-up could finally solve the so-called "coronal heating mystery," which revolves around that heat discrepancy between the corona, made of wispy and nebulous electrically charged gas called plasma, and the sun’s surface, or photosphere. 

Related: Scientists may finally know why the sun's outer atmosphere is so freakishly hot

Two views of the sun captured by the Solar orbiter spacecraft show the blazing hot corona  —  the sun’s outer atmosphere normally hidden by light from the sun’s surface. (Image credit: ESA)

What is the coronal heating mystery?

The corona can reach temperatures as great as 1.8 million degrees Fahrenheit (1,000,000 degrees Celsius), while 1,000 miles below it, the photosphere only reaches temperatures of around 10,800 degrees Fahrenheit (6,000 degrees Celsius).

That is a troubling fact because the sun’s core, where the nuclear fusion of hydrogen to helium occurs, is where the vast majority of the sun’s heat comes from. This is like air about one foot above a campfire being hotter than  air  one inch away from the flames. 

The discrepancy in heat also means there must be another heating mechanism at play  directly on the corona. Until now, that mechanism has evaded scientists, but turbulence in the atmosphere of the sun significantly heating coronal plasma has long been considered a plausible explanation. However, that hypothesis had been impossible to investigate with data from one spacecraft. 

Satellites can investigate the sun in two ways: they can get up close and personal, making in-situ measurements like NASA’s Parker Solar Probe does, or they can make more remote investigations like the Solar Orbiter. The Solar Orbiter studies the corona from around 26 million miles (42 million kilometers) away from the sun, while the Parker Solar Probe braves the blazing hot plasma of the sun as it passes around 4 million miles (6.4 million km) from the solar surface.

But, there is a trade-off between the two approaches. 

Remote sensing can see broad details about the sun, but suffers when it comes to making observations of what physics is at play in coronal plasma. On the other hand, in-situ observations can measure that plasma in greater detail but tend to miss the bigger solar picture.

That means uniting the large-scale measurements of events on the sun from the Solar Orbiter with the detailed observations of the same phenomenon by the Parker Solar Probe could present us with the total picture of the sun with  all intricate details filled in  —  the best of both worlds. 

This isn’t as straightforward as it sounds, however. To facilitate this team-up, the Parker Solar Probe would have to be within the field of view of one of the Solar Orbiter’s instruments as the two observe the sun from their relative positions.

How scientists achieved the 'best of both worlds' to potentially solve a solar mystery

A team of astronomers, including Italian National Institute for Astrophysics (INAF) researcher Daniele Telloni, discovered that on June 1, 2022, the two solar observatories would be within touching distance of the desired orbital configuration to engage in such a team-up.

As the Solar Orbiter would be looking at the sun, the Parker Solar Probe would be just off to the side, only a little bit out of view of the ESA spacecraft’s Metis instrument  —  a device called a "coronagraph" that blocks out light from the photosphere to image the corona and is ideal for large-scale, distant observations.

An illustration shows the Solar Orbiter needing to perform a maneuver to catch the Parker Solar Probe and the sun at the same time.   (Image credit: ESA/NASA/Robert Lea)

To perfectly line up the two spacecraft and get the Parker Solar Probe in view of Metis, the Solar Orbiter performed a 45-degree roll and was then pointed slightly away from the sun. 

The data that was collected as a result of this well-planned maneuver authorized by the spacecraft’s operation team paid off, revealing turbulence that could indeed be transferring energy in the way solar physicists had theoretically predicted would be causing coronal heating. 

The turbulence drives coronal heating in a way that is similar to what happens when coffee is stirred here on Earth. Energy is transferred to smaller scales by random movements in a fluid or gas — coffee and plasma  —  and this converts that energy to heat. In the case of the corona, plasma is magnetized, and that means stored magnetic energy can also be converted to heat. 

The transfer of magnetic and movement or kinetic energy from larger to smaller scales is the very essence of this turbulence, and at the smallest scales, it allows the fluctuations to interact with individual particles, mostly positively charged protons, heating them. 

That isn’t to say the mystery of coronal heating is "case closed," however. Solar scientists still need to confirm the mechanism that has been hinted at by these results and by the collaboration between the Parker Solar Probe and the Solar Orbiter. 

"This is a scientific first. This work represents a significant step forward in solving the coronal heating problem," Solar Orbiter Project Scientist Daniel Müller said.

The team’s research was published on Thursday (Sept. 14) in the Astrophysical Journal Letters. 

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Robert Lea
Senior Writer

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

  • Classical Motion
    I never thought of it as a mystery. I think it's due to the property of the atmosphere and density. The atmosphere of Sol is much different than ours. Our atmospheric particles are neutral. The acceleration from collision is very quick and short. If we lower the density, the speed of the particles does not increase.

    But the Sun's particles are electrified, and the acceleration can continue until another collision. In the Sun's liquid, this high density insure short travel and limited V. But up in the rarefied atmosphere....the particles has a longer path and acceleration duration for a higher V than down in the liquid. Thus much greater V of the atmospheric particles. And thus a higher temp.

    It never puzzled me.
  • commonsensephycist
    Admin said:
    The Parker Solar Probe and the Solar Orbiter may have finally solved a solar puzzle that has troubled scientists for decades.

    Parker Solar Probe and Solar Orbiter team up to tackle 65-year-old sun mystery : Read more
    Seriously??!! How does anyone take science seriously these days I mean everyone whose ever done it knows you put your hand right above the flames of a camp fire, that it's insanely hot compared to sticking ypur hand thru the flame, I mean ypu don't need a degree to understand the sun is no different. Heat is heat and the surface of a campfire flame is no different (except in temperature) to surface of the sun. I truly laugh at some of the articles written saying stuff like this one. You could asked me a decade ago and I'd say well heat rises therfore heat coming off the sun is of course hotter than the surface. Just like red hot coals are hotter than the surface etc. of a flame, just like the core of the sun(red hot coals) is hotter than the surface etc. Common sense should tell everyone in science that the Universe is not chaos, there's an order to it. Yet still science argues about order and chaos.. I'm starting to think it's all just one big game to these people drip drip information to let the public think " wow their making progress" when in reality their not, their just guessing because in my opinion looking thru a telescope is only a quarter of the way there when trying to understand or mathematically solve the universe..

    Hey science ask me anything and I bet I can answer it without all the fat you guys leave on it trying to act like a degree in something we haven't even figured out yet is an accomplishment

    The problem with science these days is they keep asking why,why,why instead they should be asking how,how,how. Why does gravity act like a force pulling in whatever direction, or why is space so empty compared to the "models" that say it should be more full.. Why are things so far apart, why did we just settle on the big bang when it doesn't make sense at all, why is space moving at different speeds in different directions. Most of all why was Omohomoa such a big deal when it was only a dang rock, and why won't governments of the world let us tell the public about Extraterrestrial life. I mean stop with the dumb how's and start with the why's..
  • Classical Motion
    From what I have read, the only way one can understand energy and mass and thru the study of statistics....with the concepts of math and information. At least this is the only strategy that is being used at the present time. And the way all theories are addressed as.

    Personally I believe it to be a huge failure. It restricts and limits intellect. But that's easy for me to say because I have no skin in this game.

    I think our very fundamental concepts about energy, mass and light, and don't forget gravity.....all are mis-understood. I don't think physicality needs math or information. Life might, but not physicality. Life is the only singularity detected.

    I am satisfied with the latest classical theories but others are just as satisfied with these modern math concepts of time and space. Although I fail to concept them myself.

    I think we're just as fundamentally ignorant as thousands of years ago. We just have much more comparative knowledge, not fundamental knowledge. More statistics.This knowledge gives us technology, but only more questions and mysteries about the fundamentals.

    Your post reminded me of a song, tell me why baby, why baby, why baby why. I was thinking, how baby, how baby, how baby how.

    I believe it to be done with and via structure. That's how. I think all physicality has structure....even force.

    But some believe the idea of structure at these minute scales is non-existent. Too small for physical structure.

    So the new denies the old, and the old denies the new.