An SwRI-led study identified particles accelerated to extremely high energies by magnetic reconnection near the Sun. As NASA’s Parker Solar Probe (trajectory shown in green) crossed the heliospheric current sheet, it encountered merging magnetic islands (blues) and protons accelerated toward the Sun, establishing reconnection as their source, distinct from unrelated solar processes. Credit: JHUAPL.
New research from the SwRI has found that particles are energised by magnetic reconnection in the nascent solar wind.
The research offers insights into processes that heat the solar atmosphere and accelerate the solar wind, and identified a new source of energetic particles near the Sun.
These definitive observations were made by instruments aboard NASA’s Parker Solar Probe, which detected the powerful phenomena as the spacecraft dipped in and out of the solar corona.
These new results offer fresh perspectives on how magnetic reconnection could heat the solar atmosphere, which then transitions into the solar wind, and also how solar flares accelerate a small fraction of charged particles to near-relativistic speeds.
Southwest Research Institute (SwRI) scientist Dr Mihir Desai, lead author of a new paper about this research, said: “Through the SwRI-led Magnetospheric Multiscale mission, scientists made the first direct detection of the source of magnetic reconnection near Earth, observing how this explosive physical process converts stored magnetic energy into kinetic energy and heat.
“Now Parker has made direct observations of how magnetic reconnection at the heliospheric current sheet (HCS), where the interplanetary field reverses its polarity, energises charged particles to extremely high energies.”
Trapped energetic protons
As Parker crossed the HCS, scientists discovered a sunward-directed reconnection jet and sunward-propagating highly energetic protons, establishing their origin from HCS reconnection sites and not from unrelated processes at the Sun.
Within the core of the reconnection exhaust, Parker detected trapped energetic protons a thousand times greater than the available magnetic energy per particle.
Desai said: “These findings indicate that magnetic reconnection in the HCS is an important source of energetic particles in the near-Sun solar wind.
“Everywhere there are magnetic fields there will be magnetic reconnection. But the Sun’s magnetic fields are much stronger near the star, so there’s a lot more stored energy to be released.”
Magnetic reconnection — when magnetic field lines converge, break apart and reconnect in an explosive physical process — energises particles and generates high-speed flows.
At the heart of space weather, reconnection is responsible for powerful solar events, such as solar flares and coronal mass ejections (CMEs), and drives disturbances in Earth’s space environment.
Such disturbances produce spectacular auroras but can also shut down electrical power grids and disrupt satellite-based communication and navigation systems.
Desai said: “Reports from the American Meteorological Society indicated that the powerful solar events in May 2024 wreaked havoc with farmers when extreme geomagnetic storms disrupted the precise GPS-guided navigation systems used to plant, fertilise and harvest rows of seeds, causing an estimated loss of up to $500 million in earning potential.
“Parker’s access to this new data is critical, particularly as we remain in the midst of a very active solar cycle.”
Parker was able to make these measurements due to its record-breaking proximity to the Sun, flying through its corona up to three times a year.
Of particular interest is understanding how the Sun’s atmosphere heats up and accelerates the solar wind.
Understanding these processes can also help scientists develop ways to predict and mitigate the effects of solar flares and CMEs, as well as provide new insights for laboratory fusion research.
The study is published in The Astrophysical Journal.
