Spacecraft Investigates Source of Solar Wind
The solar wind, which is a constant and fast stream of charged particles emitted by the sun, is present throughout our solar system. It occupies the space between planets and is responsible for geomagnetic storms on Earth, which can interfere with satellites, as well as the mesmerizing auroras seen at high latitudes, known as the northern and southern lights.
But how the sun produces the solar wind has remained unclear. New observations from the Solar Orbiter spacecraft may provide an answer.
Scientists said Thursday that the spacecraft has detected numerous jets of relatively small charged particles that periodically eject from the corona — the sun’s outer atmosphere — at supersonic speeds for 20 to 100 seconds.
The jets emerge from structures in the corona called coronal holes, where the sun’s magnetic field extends into space rather than back to the star. They are called “picoflare jets” because of their relatively small size. They arise in areas a few hundred miles across—small compared to the enormous scale of the sun, which is 865,000 miles (1.4 million km) in diameter.
“We suggest that these jets could actually be a significant source of mass and energy for sustaining the solar wind,” said solar physicist Lakshmi Pradeep Chitta of the Max Planck Institute for Solar System Research in Germany, lead author of the study published in the journal. Science.
The solar wind consists of plasma – ionized gas, or gas in which atoms have lost their electrons – and is mostly ionized hydrogen.
“Unlike the wind orbiting the Earth, the solar wind is ejected outward into interplanetary space,” Chitta said.
“Earth and other planets in the solar system pass through the solar wind as they orbit the sun. Earth’s magnetic field and atmosphere act as shields and protect life by blocking harmful particles and radiation from the sun. But the solar wind is constantly spreading outward from the sun and blowing up a bubble of plasma called the heliosphere that surrounds the planets,” Chitta added.
The heliosphere extends about 100-120 times further than the Earth’s distance from the Sun.
The study’s data came last year from one of three telescopes for the Extreme Ultraviolet Imager on the Solar Orbiter, a solar-observing probe built by the European Space Agency and the US space agency NASA that will launch in 2020. The Solar Orbiter was about 31 million miles (50 million kilometers) away from the sun at that time – about a third of the distance between the sun and the earth.
“This discovery is important because it sheds more light on the physical mechanism of solar wind generation,” said solar physicist and study co-author Andrei Zhukov of the Royal Observatory of Belgium.
American physicist Eugene Parker predicted the existence of the solar wind in the 1950s and confirmed it in the 1960s.
“The origin of the solar wind is still a long-standing puzzle in astrophysics,” Chitta said. “The main challenge is to identify the dominant physical process that is powered by the force of the solar wind.”
Solar Orbiter is discovering new details about the solar wind and is expected to get even better data in the coming years by using additional instruments and looking at the Sun from other angles.
Zhukov said the stellar wind is a common phenomenon for most, if not all, stars, although the physical mechanism may vary between different types of stars.
“Our understanding of the Sun is much more detailed than our understanding of other stars in terms of its proximity and thus the possibility of more detailed observations,” Zhukov added.
