The Sun may look like a calm, glowing sphere from Earth, but its atmosphere is an extremely dynamic environment filled with powerful magnetic fields and superheated plasma. Among the most important processes driving this activity is magnetic reconnection—a phenomenon that can suddenly release enormous amounts of stored magnetic energy and trigger powerful solar eruptions.
A recent observation by NASA’s Parker Solar Probe (PSP) has provided an unusually close look at this process. Researchers led by Patel used data collected by the spacecraft during a major solar eruption on 5–6 September 2022. The spacecraft passed directly through a region where magnetic field lines were reconnecting in the solar corona, allowing scientists to measure the plasma involved in the process.
The observations offer a rare opportunity to connect theoretical models of magnetic reconnection with actual measurements from the Sun’s atmosphere.
What Is Magnetic Reconnection?
Magnetic reconnection occurs in highly conductive plasmas, such as those found throughout the solar atmosphere. The Sun’s plasma is strongly influenced by magnetic fields, and these fields can become twisted, stretched and compressed as the solar atmosphere evolves.
When magnetic field lines pointing in opposite directions are brought close together, their configuration can change. The field lines effectively break and reconnect in a different arrangement. During this process, magnetic energy that has accumulated in the field can be converted into other forms of energy, including the kinetic energy and heat of the surrounding plasma.
This release can be extremely powerful.
Magnetic reconnection is therefore considered a major mechanism behind several explosive solar phenomena, including solar flares and coronal mass ejections (CMEs). These eruptions can send huge quantities of energetic particles and plasma into space.
Understanding how reconnection begins, develops and continues is important not only for solar physics but also for understanding plasma processes throughout the universe.
A Rare Opportunity Near the Sun
For many years, scientists have studied magnetic reconnection at the Sun primarily through remote observations. Telescopes and spacecraft can observe changes in the solar atmosphere, magnetic structures and energetic emissions from a distance.
However, remote observations have limitations. They show scientists what is happening in the Sun's atmosphere, but they do not always provide direct measurements of the plasma flowing through the reconnection region.
This is where the Parker Solar Probe offers a major advantage.
Launched in 2018, PSP was designed to travel extremely close to the Sun. Its instruments can directly measure properties of the solar wind and plasma in regions that were previously inaccessible to spacecraft.
During the major solar eruption on 5–6 September 2022, PSP encountered a reconnecting current sheet in the corona. A current sheet is a relatively thin region where magnetic fields change rapidly across a small distance and where magnetic reconnection can occur.
Instead of simply observing reconnection from afar, PSP effectively flew through the reconnection region and sampled its plasma directly.
Reconnection Continued Long After the Flare
One of the most significant findings from the study was the duration of the reconnection process.
The solar flare reached its peak before PSP made its measurement. Yet, approximately 24 hours after the flare peak, the spacecraft still detected a distinctive flow of plasma known as a reconnection exhaust.
A reconnection exhaust is produced when plasma is rapidly accelerated away from the reconnection region. Detecting this signature provides important evidence that magnetic reconnection was still actively taking place.
Researchers confirmed the continued reconnection using remote-sensing observations from the Solar Orbiter spacecraft.
This is particularly important because magnetic reconnection associated with solar eruptions is often expected to operate over much shorter periods. The study found that the process continued far longer than the typical timescales of a few minutes to several hours.
The observation therefore suggests that fast magnetic reconnection can remain active for an unusually extended period during a major solar eruption.
Measurements Match Computer Simulations
Another important result came from comparing the PSP measurements with numerical simulations.
Scientists use computer models to reproduce magnetic reconnection under different plasma conditions. These simulations help researchers understand how magnetic fields rearrange themselves and how energy and plasma are transported during the process.
In this case, the plasma parameters measured by PSP inside the reconnection region were consistent with numerical simulations.
This agreement is significant because it provides an important connection between theory and direct observations.
Scientific models of magnetic reconnection are built on physical principles and mathematical calculations. However, observations are essential for determining whether those models accurately describe what happens in nature.
The PSP measurements provide a valuable test of these theories under real solar conditions.
A Bridge Between Different Plasma Environments
Magnetic reconnection is not unique to the Sun. Similar physical processes occur in many plasma environments.
Scientists study reconnection in the Earth's magnetosphere, in laboratory plasma experiments and in distant astrophysical systems. It is also relevant to energetic phenomena occurring throughout the universe.
However, the physical conditions in these environments can be very different. Direct measurements from the solar corona can therefore provide an important reference point for understanding reconnection more broadly.
The new PSP observations help establish a connection between three important areas: theoretical models, laboratory experiments and natural plasma systems in space.
Because PSP is measuring the plasma close to the Sun, its observations can also help researchers understand how processes occurring near the solar surface eventually influence the solar wind that travels throughout the solar system.
Why the Discovery Matters
Solar eruptions are not merely interesting astronomical events. They can affect the space environment around Earth.
Powerful eruptions can accelerate particles and release enormous amounts of plasma into interplanetary space. When these disturbances reach Earth, they can contribute to space-weather events that affect satellites, radio communications, navigation systems and other technologies.
Understanding magnetic reconnection is therefore part of the larger effort to understand how solar eruptions develop and how their energy is transported through space.
The September 2022 observation gives scientists a new set of measurements that can be used to improve models of these processes.
Most importantly, the study demonstrates the value of combining different types of observations. PSP provided direct measurements of the plasma, while Solar Orbiter supplied complementary remote observations. Numerical simulations then provided another way to test whether the observed plasma behavior was consistent with theoretical expectations.
A New Window Into the Sun
The Parker Solar Probe's encounter with the reconnecting current sheet represents an important step forward in solar physics. Rather than observing magnetic reconnection only from a distance, scientists were able to examine the plasma within the reconnection region itself.
The discovery that fast reconnection continued about 24 hours after the flare peak challenges the idea that such processes necessarily operate only for short periods. The agreement between spacecraft measurements and numerical simulations also provides stronger evidence for the physical models used to describe magnetic reconnection.
These observations will help researchers refine those models and better understand how magnetic energy is converted into heat, motion and energetic particles during solar eruptions.
As PSP continues its journey through the Sun's environment, it is expected to encounter more extreme and scientifically valuable plasma conditions. Each encounter can provide another piece of the puzzle surrounding the Sun's powerful magnetic activity.
Ultimately, the observations from September 2022 show why getting closer to the Sun matters. By directly sampling the plasma where magnetic reconnection occurs, Parker Solar Probe is turning theories about the Sun's most powerful energy-release processes into testable, measurable science.
Reference: Patel, R., Niembro, T., Xie, X. et al. Direct in situ observations of eruption-associated magnetic reconnection in the solar corona. Nat Astron 9, 1444–1454 (2025). https://doi.org/10.1038/s41550-025-02623-6
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