A year ago, NASA's Parker solar probe flew closer to the sun than any satellite in history, collecting a spectacular treasure of data from the edge of the crown a million degrees from the sun. That data has now allowed solar physicists to map the source of a major component of the solar wind that continuously splashes the Earth's atmosphere, while revealing strange investments of magnetic fields that could be accelerating these particles to our planet, which they publish in the magazine 'Nature'.
These accelerated particles interact with the Earth's magnetic field, generating the colorful northern and southern lights. But also have the potential to damage the electrical network and telecommunications networks on Earth's surface, threaten orbiting satellites and perhaps endanger astronauts in space.
The more solar physicists understand about the sun's magnetic environment and how it throws the solar wind particles toward the planets, the better they can predict events and prevent damage.
"There was a great space weather event in 1859 that destroyed the telegraph networks on Earth and one in 1972 that activated the naval mines in North Vietnam, only because of the electric currents generated by the solar storm," recalls Stuart Bale, professor from Physics at the University of California and lead author of an article on the new results of the FIELDS probe experiment.
"We are a much more technological society than in 1972, communications networks and the electricity network on Earth are extraordinarily complex, so the great disturbances of the sun are potentially very serious he continues. If we could predict the space weather, it could shut down or isolate parts of the power grid, or shut down satellite systems that could be vulnerable. "
One of the main objectives of the Parker solar probe is to discover the source of the "slow" solar wind and how it accelerates in the hot atmosphere of the sun: the 1 million degree solar corona. The solar wind consists of charged particles, mainly protons and helium nuclei, that travel along the lines of the sun's magnetic field.
It is known that the so-called "fast" solar wind, with a speed of between 500 and 1,000 kilometers per second, comes from large holes in the solar corona at the north and south poles of the sun. But the origin of the "slow" solar wind, which is denser but about half the speed of the "fast" solar wind, is less understood.
Data from the first close encounter of the probe (the probe has had two other encounters during the closest approach, or perihelion, of its orbit around the sun) reveals a great deal of new physics.
"The first three meetings of the solar probe that we have had so far have been spectacular," admits Bale, the principal investigator of FIELDS.
"We can see the magnetic structure of the crown, which tells us that the solar wind is emerging from small coronal holes; we see impulsive activity, large jets or setbacks that we believe are related to the origin of the solar wind; we see instability (the gas itself is unstable and generates waves), and we are also surprised by the ferocity of the dust environment in the internal heliosphere, "he adds.
During each close encounter, the probe was parked for a week above a crown hole that transmitted solar wind particles along the magnetic field lines beyond the probe, giving the instruments on board the probe an unprecedented view of what was happening on the solar surface below.
Thanks to the extreme ultraviolet mapping of the sun by other spacecraft, such as STEREO, Bale and their colleagues they were able to track the wind and magnetic fields to a source, the coronal holes, which strongly suggests that these holes are the source of the slow solar wind. Coronal holes, which are related to sunspots, are cooler and less dense areas than the surrounding crown.
The unexpected was a series of turns in the magnetic field while passing through the spacecraft. During these periods, the magnetic field suddenly reversed 180 degrees and then, seconds to hours later, receded.
"These interruptions are probably associated with some type of plasma jets says Bale. My feeling is that these interruptions or jets are fundamental to the problem of solar wind heating. "
Another surprise was the dust that splashed the spacecraft repeatedly during each overflight in the perihelion, the point in the orbit where the spacecraft was closest to the sun. Probably smaller than a micron, which is one thousandth of a millimeter, the dust particles are probably remains of asteroids or comets that melted near the sun and left their dust trapped.
That dust is now orbiting the sun, and Bale suspects that much of it, when hitting the spacecraft, is ejected out by light pressure and destined to escape completely from the solar system.
Bale adds that studying the solar wind of the Earth is like studying the source of a waterfall near the bottom, where turbulence obscures what happens at the top.
"Now, with the Parker solar probe, we are getting closer and closer to the top of the waterfall, and we can see that there is an underlying structure – it highlights -. At the source, what we see is something that is consistent with jets impulsive. You have a small hole, a coronal hole, and the solar wind comes out in a gentle flow. But then, besides that, there are jets. When it reaches Earth it is all mixed. "
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