‘Shooting stars’ discovered in the Sun’s corona

The research will be published in a special issue of Astronomy & Astrophysics devoted to SolO’s first near perihelion to the Sun.

A team of astronomers from various European institutions led by Northumbria University in Newcastle has discovered “shooting stars” on the sun. Observations from the European Space Agency’s Solar Orbiter (SolO) have revealed never-before-seen “shooting star” phenomena or meteor-like fireballs occurring within the spectacular plasma displays known as coronal showers. The work will be presented this week at the National Astronomy Meeting (NAM 2023) by lead author Patrick Antolin, Assistant Professor at Northumbria University.

Although not actual water, coronal rain is a condensation process in which some of the burning material from the sun accumulates due to sudden, localized drops in temperature. The corona, which is the outermost part of the sun’s atmosphere, is made up of gas at temperatures of a million degrees, and rapid drops in temperature produce superdense clumps of plasma that reach 250 kilometers across. These fireballs plummet toward the sun when gravity pulls them at more than 100 kilometers per second.

The research will be published in a special issue of Astronomy & Astrophysics devoted to SolO’s first near perihelion to the Sun. It is currently available on the arXiv preprint server. In the spring of 2022, SolO sailed very close to the sun at a distance of only 49 million kilometers, one third of the distance between Earth and the sun, allowing for the best spatial resolution ever obtained of the solar corona.

Along with the first super-high-resolution images of coronal shower clusters, SolO observed heating and compression of the gas immediately below them. The resulting increase in intensity below the clumps indicates that the gas is heated up to a million degrees, lasting a few minutes as they fall. On Earth, “shooting stars” occur when meteoroids, or objects in space that range in size from dust grains to small asteroids, enter our atmosphere at high speeds and burn up. Only some meteors reach the ground without breaking up, and those that do can produce huge craters.

But the sun’s corona is thin and low in density and doesn’t remove much material from the clumps, so scientists believe that most “shooting stars” reach the solar surface intact. Their impacts have never been observed before, and observations of SolO have revealed that this process can produce a brief, strong glow with an upward surge of material and shock waves that reheat the gas above. “Shooting stars” and meteorites in Earth’s atmosphere are characterized by a trail behind the meteorite’s path, which is formed when hot material below removes parts of the object, a process called ablation. The same is true of comets that orbit the sun. However, ablation does not occur in the solar corona due to its magnetic field. Instead, the infalling gas is partially ionized and follows magnetic field lines, which act like giant tubes channeling the gas. The compression and heat underneath prevents the clumps from producing tails and makes the phenomenon much more difficult to capture on the Sun.

Lead author of the project, Patrick Antolin, says: “The inner solar corona is so hot that we may never be able to probe it in situ with a spacecraft. However, SolO orbits close enough to the sun to detect small-scale phenomena occurring.” within the corona, such as the effect of rain on the corona, allowing us a valuable indirect probe of the coronal environment that is crucial to understanding its composition and thermodynamics. Just detecting coronal rain is a huge step forward for solar physics because it gives important clues to major solar mysteries, such as how it heats up to millions of degrees.”

sources: https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202346016