Incursion into the solar corona

The Parker Solar Probe mission was able to get closer to the Sun, which has a core temperature of around 15.5 million degrees.

By Vahé Ter Minassian Posted today at 06:00

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"Atlas Collection of the cosmos". It's a shot of hell. It shows the disk of the planet Mercury diffusing its light through the clouds of a sort of brilliant, almost dazzling geyser: nothing less than a "coronal jet", one of the puffs of plasma gasped by our star, the Sun !

Conducted on November 8, 2018 exactly, this extraordinary image of the most internal regions of the solar system is the first to have been broadcast by the Parker Solar Probe mission after its passage closer to the Sun. Two days earlier, this NASA spacecraft had broken several records by flying over the surface of the star at 343,000 km / h at an altitude of just 25 million kilometers.

The feat is big. "It has been expected for more than sixty years by specialists in gravi-physics"recalled NASA's Nicola Fox a month later when the first data arrived on Earth. In fact, astrophysicists had long hoped to plunge their instruments into the solar corona, the upper part of the atmosphere of our star. But in front of the complexity and the cost of such a project, they had each time given up. The only exceptions are the German-American Helios 1 and Helios 2 probes, which, from 1974 to 1986, made observations from orbits which, beyond Mercury, made them 46.5 and 43.5. millions of kilometers from the Sun (0.31 and 0.29 astronomical unit, 1 astronomical unit corresponding to once the Sun-Earth distance).

The Parker Solar Probe mission went a lot further. Launched August 12, from the base of Cape Canaveral (Florida), the probe has used, at the beginning of October 2018, the gravitational attraction of Venus to tighten its orbit and approach the Sun. Ceasing as planned all communications with the Earth, it operated for several days in an automatic mode before sending, on November 16, a signal indicating that its four sets of instruments had not been damaged by this passage in the vicinity of our star.

These instruments are loaded, by their measurements in situ, to answer various questions from astrophysicists about the solar corona, which extends for millions of kilometers beyond the chromosphere. Why is its temperature - which in some places reaches two to three million degrees - much higher than that of the surface (6000 ° C)? What is its exact role in the generation of "solar winds" and the nature of the high energy particles that pass through it?