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This summer, humanity undertakes its first mission to touch the Sun: a spaceship will be launched in the outside atmosphere of the Sun.
The NASA Parker Solar Probe probe, named after Eugene Parker, a physicist from the University of Chicago who first predicted the existence of the solar wind, will directly sample the particles solar and magnetic fields to try to solve some problems. the most important questions that arise in the field of solar science today. Among these questions: What is the origin of solar wind and how is it sped up to speeds of up to 1.8 million miles per hour?
The solar wind fills our entire solar system. When gusts of solar wind arrive at Earth, they can trigger a dazzling dawn, but also expose astronauts to radiation, interfere with satellite electronics and disrupt communication signals such as GPS and radio waves. The more we understand the fundamental processes that drive the solar wind, the more we can mitigate some of these effects.
In 1958, Parker developed a theory showing how the sun's hot crown – then known to be millions of degrees Fahrenheit – is so hot that it overcomes the gravity of the sun. According to the theory, the material in the crown continually extends outward in all directions, forming a solar wind. A year later, the Soviet satellite Luna 1 detected solar wind particles in space, and three years later, observations were confirmed by the Mariner 2 spacecraft.
Mariner 2 detected two separate currents solar wind: a slow current moving at about 215 miles per second and a fast current flowing through the space at twice that speed. Then, in 1973, the origins of the fast solar wind were identified. Radiographic images of the crown taken from Skylab, the first inhabited space station in the United States, have revealed that the rapid wind is emerging from the coronal holes, which are dark and relatively cold regions of the Sun
. in many ways, a bigger mystery, "said Jim Klimchuk, a solar physicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland." It offers great promise to reveal a new fundamental understanding. "
The origins and mechanisms of slow solar wind acceleration remain mysterious. This is a fierce debate that has been going on for decades between scientists.
But we are not without clues. NASA's Ulysses mission, launched in 1990 to fly over the poles of the Sun, observed that during periods of minimal solar activity, the slow solar wind is confined to the Sun's equator where Parker Solar Probe will fly . As the solar cycle progresses to its maximum, the structure of the solar wind goes from two distinct regimes – fast to the poles and slow to the equator – to a heterogeneous and inhomogeneous flux.
The Debate on the Origins of the Slow The solar wind articulates around a distinction between what is called the closed crown and the open crown. The closed crown designates the regions of the Sun where the magnetic field lines are closed, that is, connected to the solar surface at both ends. Helmet-shaped light streamers – large loops that form on magnetically active regions, shaped like a knight's pointed helmet – are one example. Plasma, or ionized gas, that travels along closed loops of a helmet streamer is mostly confined to the area near the Sun.
The open crown, for its part, refers to regions where the magnetic field lines are anchored. in the sun at one end only, extending into the space of the other, thus creating a road for the solar material to escape in the space. The coronal holes – the coldest regions at the source of the fast solar wind – are the habitat of open field lines.
By the time the slow solar wind leaves the solar corona, it is also flowing over open magnetic field lines, the only way to get so far from the Sun. But theories diverge on whether it started or whether it was born on closed field lines to move to open field lines somewhere.
The theory of expansion factors, for example, says that the solar wind slow lines, just like the fast wind. Its (comparatively) slow speed results from the expanding path it takes to get out of the crown, as the magnetic field lines line the edges of the flutes of the helmet. Just as the water flowing through a pipe slows down as the pipe expands, the plasma that flows through these magnetic channels expands and forms the slow wind
Other theories claim that the slow solar wind comes from closed field lines and then passes to open field lines. As a result, the slow wind forms when the open field lines of the coronal holes strike the closed field lines at the edges of the helmet flutes, explosively re-forming in an event called magnetic reconnection. Like a train that changes lanes after the operator has toggled a switch, the plasma that was on the closed field lines of the streamer suddenly finds itself on an open field line, where it can escape to the space
on the closed field lines is supported by evidence that he has already faced the extreme types of heating that we know.
"It's not the temperature of the plasma when we measure it, but the temperature history of this plasma" Aleida Higginson, a researcher at the University of Michigan working at Goddard . "We can say that the slow solar wind was a lot warmer in the past." In addition, the particular mixture of elements that make up the slow solar wind corresponds well to those observed in the closed crown – but not with the plasma we know has always been on open field lines.
Current efforts to test these spacecraft theories near Earth are stalled by the large distance between their measurements and the origins of the solar wind (many can arrive in 93 million miles). The key is getting closer, bringing the solar wind back to its source – and Parker Solar Probe will do just that.
"If we can measure the slow solar wind, and find that it comes from the border between magnetic open and closed Parker Solar Probe instruments will collect evidence downstream of the magnetic reconnection – a telltale sign that magnetic reconnection gives rise to the slow solar wind, "said Klimchuk
. Open-field theory is at play. Specific types of reconnection twist the resulting magnetic field in different ways, and Parker's instruments will measure twists in these fields very early, before they had a lot of time to be deformed.In addition, close-up images of the nascent solar wind will tell us how the coronal structures evolve as they propagate towards the This will help us answer a long-standing question about whether the solar wind is a continuous or intermittent flow.
For Scientists who need data to test their theories, accurate measurements of the magnetic fields of the solar corona will be invaluable. "That's why Parker's mission is so important," said Higginson. "It all comes down to understanding the detailed magnetic structure on the Sun."
Learn more:
Send your name to the sun aboard the NASA Parker Solar Probe
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