On March 26, 2022, the ESA/NASA Solar Orbiter spacecraft made the first of its close perihelion passages. The spacecraft flew closer to the Sun than the inner planet Mercury, achieving its closest approach at just 32% of the Earth’s distance from our star. Being that close to the Sun, the images, movies and data returned were spectacular. They show powerful flares, breathtaking views across the solar poles, and a curious solar ‘hedgehog’ — the most eye-catching feature seen during this perihelion; it stretches 25,000 km (15,534 miles) across the Sun and has a multitude of spikes of hot and colder gas that reach out in all directions.
Solar Orbiter is a collaborative mission between the ESA and NASA to study our Sun. Launched on February 10, 2020, it carries ten scientific instruments.
Its main science goal is to explore the connection between the Sun and the heliosphere.
The heliosphere is the large ‘bubble’ of space that extends beyond the planets of our Solar System. It is filled with electrically charged particles, most of which have been expelled by the Sun to form the solar wind.
It is the movement of these particles and the associated solar magnetic fields that create space weather.
To chart the Sun’s effects on the heliosphere, the results from Solar Orbiter’s in-situ instruments, which record the particles and magnetic fields that sweep across the spacecraft, must be traced back to events on or near the visible surface of the Sun, which are recorded by the remote sensing instruments.
This is not an easy task as the magnetic environment around the Sun is highly complex, but the closer the spacecraft can get to the Sun, the less complicated it is to trace particle events back to the Sun along the ‘highways’ of magnetic field lines. The first perihelion was a key test of this, and the results so far look very promising.
On March 21, 2022, a few days before perihelion, a cloud of energetic particles swept across Solar Orbiter. It was detected by the Energetic Particle Detector (EPD).
Tellingly, the most energetic of them arrived first, followed by those of lower and lower energies.
“This suggests that the particles are not produced close to the spacecraft. Instead, they were produced in the solar atmosphere, nearer the Sun’s surface,” said EPD principal investigator Dr. Javier Rodríguez-Pacheco, a researcher at the University of Alcalá.
“While crossing space, the faster particles pulled ahead of the slower ones, like runners in a sprint.”
On the same day, Solar Orbiter’s Radio and Plasma Waves (RPW) experiment saw them coming, picking up the strong characteristic sweep of radio frequencies produced when accelerated particles — mostly electrons — spiral outwards along the Sun’s magnetic field lines. RPW then detected oscillations known as Langmuir waves.
“These are a sign that the energetic electrons have arrived at the spacecraft,” said RPW principal investigator Dr. Milan Maksimovic, a researcher with LESIA at the Observatoire de Paris.
Of the remote sensing instruments, both EUI and the X-ray Spectrometer/Telescope (STIX) saw events on the Sun that could have been responsible for the release of the particles.
While the particles that stream outwards into space are the ones that EPD and RPW detected, it is important to remember that other particles can travel downwards from the event, striking the lower levels of the Sun’s atmosphere. This is where STIX comes in.
While EUI see the ultraviolet light released from the site of the flare in the atmosphere of the Sun, STIX see the X-rays that are produced when electrons accelerated by the flare interact with atomic nuclei in the lower levels of the Sun’s atmosphere.
Exactly how these observations are all linked is now a matter for the researchers to investigate.
There is some indication from the composition of the particles detected by EPD that they were likely accelerated by a coronal shock in a more gradual event rather than impulsively from a flare.
“It could be that you have multiple acceleration sites,” said STIX principal investigator Dr. Samuel Krucker, a researcher at FHNW.
Adding another twist to this situation is that the Magnetometer instrument (MAG) did not register anything substantial at the time. However, this is not unusual.
By combining data from all instruments, the scientists will be able to tell the story of solar activity from the surface of the Sun, out to Solar Orbiter and beyond.
And that knowledge is exactly what will pave the way for a future system designed to forecast the space weather conditions at Earth in real-time.
In the lead-up to perihelion, Solar Orbiter even got a taste of how such a system might operate.
Source link: https://www.sci.news/astronomy/solar-orbiter-perihelion-images-sun-10826.html