Paris (AFP)
Under the Sun exactly ... The Parker probe, launched in 2018 to attack the mysteries of our star, approached its fiery crown, the outermost layer of its atmosphere, discovering "a surprisingly chaotic world".
"We found things that we did not expect at all!" Enthuses Matthieu Berthomier, of the French Laboratory of Plasma Physics, co-author of the work.
"Notably that the solar wind speed is not at all regular.It can increase very impulsively, sometimes 100/150 km per second.It is very strange," he told AFP.
The size of a car and protected by a very thick heat shield, NASA's Parker Solar Probe probe is the human construction that has come closest to the sun.
"We have been waiting for decades and decades to understand these mysteries," Nasa Chief for the Sun's study missions, Nicola Fox, said in a conference call.
The first observations of the probe feed four studies published Wednesday in the journal Nature and reveal a world that the University of Michigan describes as "surprisingly chaotic".
"We were shocked to see how different the wreath is when you watch it closely," said Justin Kasper of the University of Michigan, co-author of the work.
Since it was launched on August 12, 2018, Solar Probe has been racing towards the Sun (the probe holds the record for the highest speed per unit mass). His goal is to try to solve an old mystery: what is heating his solar corona?
The outermost part of the solar atmosphere is curiously 200 times warmer than the surface of the star. This extreme heat (more than a million degrees Kelvin) can not be generated by our star since, according to the laws of nature, the further we get away from the heat source, the lower the temperature.
"The crown thus finds a way to heat itself.We are trying to determine the physical processes that allow it," says AFP Alexis Rouillard, CNRS researcher at the Institute for Research in Astrophysics and Planetology, also co-author .
- Small solar storms -
If this mystery is not yet solved (there are still six years to probe that will be closer to the Sun in 2024), some of the observations received can learn a little more, especially on the enigmatic solar wind.
This flow of ionized particles released by the Sun originates in the upper layers of its atmosphere. It can be felt down to Earth, where its storms can disrupt the power grid or cause satellite failures.
"Earth's communication and power networks are now very complex, so the Sun's disturbance could be very serious," says Stuart Bale of the University of California, Berkeley. Understanding them would help to predict them.
According to Parker's observations, "the wind would not be a continuous, undisturbed laminar flow, but would, in large part, consist of small streams of chaotic material, like small thunderstorms," explains Alexis Rouillard. A surprise for astrophysicists.
"We also did not expect that these very sudden increases in the solar wind speed would be accompanied by a considerable increase in the density of the plasma particles, it can double," added Matthieu Berthomier.
Another unexpected discovery is the behavior of the magnetic field (which surely plays a role in the mystery of the heating of the crown). At times, the magnetic field suddenly reverses 180 degrees, then, a few seconds or hours later, turns around, reports a statement from the University of Berkeley.
And that's not all: "the solar wind was at times deviated quite significantly", the solar corona was turning faster than expected ...
"These observations will fundamentally change our understanding of the Sun and the solar wind and therefore our ability to predict space weather events," said Justin Kasper of the University of Michigan, co-author of the work.
Especially since the space car sends "data every 150 days", says Matthieu Berthomier. And this for almost six years.
© 2019 AFP