“We can thus advance research in astrophysics”: NASA’s Parker probe has succeeded in getting as close as possible to the Sun

Never has a scientific machine sent by humanity come so close to our star. On Tuesday, December 24, at 12:53 p.m. Paris time, NASA’s Parker Solar Probe (PSP) solar probe passed 6.2 million kilometers from the surface of the star, a small distance on the scale space.

At that time, Parker was the first space mission to penetrate the Sun’s corona, the outermost layer of its atmosphere, at a blazing speed of 690,000 km/hour, a speed that would reach Washington to Tokyo in less than a minute!

PSP had been successfully launched on August 12, 2018 from Cape Canaveral, Florida. To get this close to the Sun, the probe traveled for six years and made increasingly rapid loops using Venus’ gravitational assistance seven times. Parker had to wait for his 22nd passage to approach the Sun in this way. It will return at a similar distance on March 22 and June 19.

While the probe explored the solar corona, its 11.4 centimeter thick carbon heat shield had to endure temperatures exceeding 900°C, the satellite’s core remaining permanently turned towards the interstellar medium, which itself is freezing. Thus its four scientific measuring instruments, weighing 50 kg for a 700 kg probe, remained close to ambient temperature, at around 29°C.

Two major scientific enigmas to be solved

What is the Parker probe doing in the solar corona, this outer part of the Sun’s atmosphere which extends over several million kilometers? The mission aims to better answer two of the major scientific questions opened in the middle of the 20th century.

The first of these two questions is why the temperature of the solar corona exceeds 1 million degrees while it is only 5,500 °C on the surface of the star. To explain this temperature difference, Thierry Dudok de Wit, professor of physics and researcher at the Laboratory of Physics and Chemistry of the Environment and Space at the University of Orléans who manufactured one of Parker’s magnetometers, thinks that several mechanisms contribute to heating the solar corona.

” First of all, he explains, magnetic reconnection, a very important phenomenon in plasma physics, via which recombining magnetic field lines release their energy to heat and accelerate the plasma; then the waves, omnipresent in the solar corona, can also communicate part of their energy to the plasma; finally, the large number of eruptions, frequent on the surface of the Sun and all the more numerous as they are small, means that their contribution becomes important. »

The second puzzle to solve is to understand how solar storms emanating from the corona, despite the force of gravitational attraction which should hold them back, bombard the planets of the solar system including the Earth with floods of particles. Moreover, the mission is named after Eugene Parker (1927-2022), an American astrophysicist who played a major role in the theory of the solar wind, the existence of which he predicted in 1957.

“Advancing research in astrophysics”

“For fundamental researchspecifies Thierry Dudok de Wit, understanding the solar wind, its origin and its acceleration allows us to better understand the wind and the crown of the stars, to which we will never have access. Thanks to in situ measurements, we can advance research in astrophysics. »

If these solar winds, once arriving in the Earth’s atmosphere, offer the marvelous spectacle of the Northern and Southern Lights, they can also cause magnetic disturbances and jam terrestrial communications. Thus, in 1989, a solar flare caused Quebec’s power plants to shut down for nine hours.

“Solar activity, explains Thierry Dudok de Wit, disrupts the operation of satellites and radio communications. It also has implications for power grids, astronauts, satellite orbits, aircraft crew, etc. All this is part of space weather, which has become a discipline in its own right with the increased presence of man in space and, unfortunately, its militarization. »

In a few years, when Parker runs out of fuel, it should receive reinforcement from the Solar Orbiter probe, launched in February 2020 and managed by the European Space Agency, to study the processes at the origin of the solar wind. This machine will remain 33 million kilometers from the Sun, but it is equipped with more instruments, in particular to observe its poles, one of the last regions of the star still poorly understood.

The two missions complement each other and a good number of scientists work on both at the same time. For Thierry Dudok de Wit, “ PSP can be compared to a Ferrari which goes as close as possible to the Sun, but is lightly equipped. Solar Orbiter is like a minibus: better instrumented, but going less close and not penetrating the solar corona ».