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From NASA Parker solar probe is about to go to another close encounter with the sun, where investigators hope the spacecraft will solve a long-standing solar mystery: outdoor atmosphere of the sun millions of warm degrees (Fahrenheit or Celsius), while the surface is only around 6,000 degrees Fahrenheit (3,300 degrees Celsius)?
One theory says that this spectacular heating comes from small magnetic waves back and forth between the surface of the sun and the upper atmosphere. A new study based on a previous NASA mission suggests that the key lies in a region of the sun called preferential heating zone.
"Whatever the physics behind this overheating, it's a puzzle that has set us back for 500 years," said Justin Kasper, lead author of this new research, professor of space and climate science. climate at the University of Michigan, and principal investigator for the SWEAP instrument (Solar Wind Electron Electrons Alphas and Protons) aboard the probe, said in a statement. "In just two years, Parker Solar Probe will finally reveal the answer."
Related: NASA's Voyager 2 became interstellar the same day a solar probe hit the sun
According to what scientists know so far about this overheating, it's a strange process. Some chemical elements heat up at different temperatures and some heavy ions (or charged particles) become even hotter than the core of the sun.
All this warming makes the solar atmosphere, also called corona, balloon above the sun's surface. This atmosphere is visible during total solar eclipses, when the moon passes in front of the sun. For a few moments during these events, the crown shines in the sky.
In the overheating zone is also a phenomenon called Waves of Alfvén, which are small magnetic waves in an electrically conductive fluid (such as plasma) in a magnetic field. At the edge of this overheating zone, the solar wind (a constant stream of charged particles emanating from the sun) moves quickly enough to escape the waves. But below that, the particles of the solar wind are ping-pong and accelerate because of the waves bombarding them from all directions.
What scientists really want to know is how much this heating extends over the sun's surface. While Parker was not yet close enough to the sun to reach it, researchers were using decades of observations of the solar wind. NASA Spaceship, which was launched in 1994 and still works. Scientists have focused on the observation of helium, a common element of the sun.
The scientists followed the temperature of helium at different altitudes above the sun. The rate of temperature rise in this element decreases as the solar wind ions collide. Scientists have discovered that the overheating zone ends between 10 and 50 solar rays above the sun's surface.
Further analysis however suggested that the outer edge could be connected to the point of Alfvén, the distance above the surface at which the particles of solar wind escape the sun. Previous research has shown that the point of Alfvén can go up and down when the sun becomes more or less active.
Thus, Kasper and his co-author examined Wind's data year by year. What they found surprised them: the outer limit of the overheating zone and the point of Alfvén "moved in a completely predictable parallel manner, despite completely independent calculations," said Kasper.
These two lines will continue to move as Parker Solar Probe is getting closer and closer in the sun, so the researchers also calculated when the spacecraft would intersect these boundaries. This moment, when the probe can return data from these crucial regions, should occur in 2021 – giving scientists a completely new look at our sun.
A paper about research was published Tuesday, June 4 in The Astrophysical Journal Letters.
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