We have “touched the Sun”. NASA made the announcement on Tuesday, December 14, reporting that the Parker Solar Probe had approached our star in an unprecedented way. At a speed of 500,000 km / h, the machine launched in August 2018 reached the solar corona, arriving 15 million kilometers from the surface of the Sun. She crossed a symbolic border called the Alfvén border. In other words, Parker Solar Probe has entered the direct vicinity of our star. This is a historic feat since never before has a man-made object come so close.
In fact, the probe broke its own record in October 2018 when it approached 42.73 million kilometers from the sun. And it’s not over: the probe keeps approaching our star (it is now 13 million kilometers from it). Franceinfo summarizes what Parker Solar Probe could reveal to Earthlings.
The mechanisms of the astonishing warming of the solar corona
It’s an enigma that has puzzled astrophysicists for decades: why is the temperature around the Sun much higher than that of its surface? Normally, the temperature should dissipate as it moves away from our star, but this is not what is observed. In fact, the temperature on the surface of the Sun rises to 5500 ° C while it reaches 1 million ° C in its corona, the outermost part of its atmosphere. This crown is visible during solar eclipses, as shown in this photo where it appears in a gradient from white to gray.
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Scientists agree, for the moment, to say that the solar corona is heating up by itself and that different mechanisms are in play. Parker Solar Probe is still too far away to collect data allowing to identify those really at the same time. ‘work. “We have not yet arrived in the area where the heating is occurring”, specifies to franceinfo Thierry Dudok de Wit, researcher at the Laboratory of physics and chemistry of the environment and space of Orleans (Loiret), directly involved in the Parker Solar Probe mission.
Scientists will know more when the probe is closest to the Sun in 2025, about 7 million kilometers from its surface. Cautious, Thierry Dudok de Wit believes that the conclusions will not arrive before “several years”.
The dynamics of solar flares
Our star generates a solar wind. This stream of particles, very weak, “is a plasma, that is to say a gas made up mainly of electrons and protons but also of ions”, explains the Paris Observatory. But the Sun also experiences jolts. It then rejects large quantities of materials. We speak of coronal mass ejections (CME), more commonly known as solar flares. Our star then expels much more energetic particles at very high speed.
When these particle expulsions reach the Earth, they give rise to the aurora borealis (or australis, depending on the hemisphere in which the observer is located). If the eruptions are more violent, we speak of solar storms. “The rashes are often small, however sometimes there are large ones”, clarified on France 3 Center Val-de-Loire Thierry Dudok de Wit. They can then disrupt the functioning of electrical and electronic devices on Earth, affecting in particular our GPS installations and our means of communication via radio, internet or our laptops.
These phenomena are taken seriously by the scientific and international community due to our increasing use of these technologies. “Transpolar flights sometimes lose all contact with the ground during these eruptions”, illustrated Thierry Dudok de Wit. The strongest solar storms could have dramatic consequences. That of July 23, 2012, extraordinarily powerful, could have “send contemporary civilization back to the 18th century” if it had occurred a week earlier, Nasa said in 2014.
Understanding the dynamics of our star’s winds, and producing solar weather forecasts anticipating the frequency and intensity of eruptions, is therefore essential. And Parker Solar Probe’s observations are proving to be as decisive as necessary because the first results, published in 2019, had already provided important elements, going against the most consensual hypotheses.
“The specialists all imagined the solar wind as a fluid escaping relatively quietly and evenly, in all directions. But we found that it is anything but that.”
Thierry Dudok de Witto franceinfo
“The elements that constitute the solar wind should have a very precise behavior in terms of displacement and speed. However, we find near the Sun that it very different from what we observe near the Earth”, specifies Thierry Dudok de Wit. “It’s the whole point of having an instrument on site”, he insists, and go into the crown, “zone which marks the difference between the moment when the wind is really connected to the Sun and when the wind escapes in a free way”.
Valuable information about the stars
If the Parker Solar Probe observations only concern our Sun, they can also help to better understand other stars, underlines Thierry Dudok de Wit.
“The researchers observed that the corona rotates faster than expected around the Sun, which could affect our more general understanding of the rotation of stars.”, explained the CNRS, in 2019, after the publication of the first results. However, the study of the rotation of stars is decisive for calculating their age, as recalled in April by the French Atomic Energy and Alternative Energies Commission (CEA).
“It’s interesting because we are not only looking to see things through the lens that interests us, but to draw conclusions that go far beyond our domain”, concludes Thierry Dudok de Wit.