The Sun is the most energetic particle accelerator in the solar system.

It accelerates electrons to nearly the speed of light and shoots them into space, flooding the solar system with so-called "solar energetic particles."

Researchers are now using the Solar Orbiter to determine the sources of these high-energy electrons and to track the relationship between the phenomena we see in space and actual events on the Sun.

They found two distinct types of SEE (solar energetic particle) events, each with a different story:

One is associated with strong solar flares (explosions in smaller regions on the solar surface),

and the other is related to large-scale eruptions of hotter gas in the solar atmosphere, called "coronal mass ejections," or CMEs.

The paper's authors said: "We observed a clear distinction between 'impulsive' particle events and 'gradual' particle events. In 'impulsive' events, these high-energy electrons are ejected from the solar surface through solar flares;

while in 'gradual' events, which are associated with longer-lasting coronal mass ejections (CMEs), these events release a broader stream of particles over a longer period."

A clearer connection.

When scientists knew that there were two types of SEE events, the Solar Orbiter was able to measure a large number of events and get closer to the Sun than other missions, revealing how they form and leave the surface of our star.

Solar flares observed by EUI and STIX

Metis observing a coronal mass ejection

"We can only determine the time and location where these particles begin on the Sun by using multiple instruments to observe hundreds of events at different distances, and by being so close to our star, we can measure the particles in their 'raw' early state," said one of the researchers.

"This is the first time we have clearly seen the connection between high-energy electrons in space and the related events on the Sun," added a co-author.

"We measured the particles in the field using the cosmic ray particle detectors on the probe—that is, the Solar Orbiter actually flew through the electron stream—while using more spacecraft instruments to observe what was happening on the Sun."

Instruments on the Solar Orbiter

Researchers detected SEE events from different distances from the Sun.

This allowed them to study the behavior of electrons as they traveled through the solar system, answering long-standing questions about these high-energy particles.

When we see a flare or a coronal mass ejection on the Sun, we usually observe a noticeable delay between what happens on the Sun and the release of energy electrons into space.

In extreme cases, these particles seem to take several hours to escape.

"The results indicate that this is at least partially related to the way electrons propagate in space—either a delay in release or a detection delay, as the electrons encounter turbulence and scatter in different directions, so we cannot detect them immediately. These effects accumulate the further away from the Sun they go."

The space between the Sun and the planets in the solar system is not empty.

A stream of charged particles continuously flows out from the Sun, dragging the Sun's magnetic field. It fills the space and affects the movement of the energy electrons; electrons cannot move freely but are constrained, scattered, and disturbed by this wind and its magnetic field.

Protecting Earth.

Crucially, this discovery is important for our understanding of space weather, and accurate predictions are essential for keeping our spacecraft operational and safe.

Of the two types of SEE events, one is more important for space weather: the one associated with CMEs, because it often contains more high-energy particles, causing greater damage.

Because of this, being able to distinguish between these two types of high-energy electrons has great significance for our predictions.

"Knowledge from the Solar Orbiter will help protect future spacecraft, enabling us to better understand the high-energy particles from the Sun that threaten our astronauts and satellites," said the researcher.

Looking ahead, the European Space Agency will pioneer a revolutionary approach, conducting operational observations of the "side" of the Sun for the first time, revealing continuous insights into solar activity.

Reference: SCIENCE & EXPLORATION

Double trouble: Solar Orbiter traces superfast electrons back to Sun

Images from the European Space Agency

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