Solar wind is a continuous outflow of charged particles—primarily protons and electrons—from the Sun. While it can disturb GPS signals and other satellite systems, it also powers the spectacular auroras that illuminate Earth’s polar skies.
Recent observations suggest that solar wind may also be leaving its mark on the Moon’s surface and plays a key role in creating the heliosphere, the vast bubble of solar plasma that surrounds our entire solar system.
Hydrogen (≈90 %) and helium (≈10 %) make up roughly 98 % of the Sun’s composition and dominate the solar wind. The extreme temperatures in the corona strip electrons from these atoms, producing a fully ionized plasma—free electrons moving in concert with the positively charged nuclei.
At altitudes of about 1,300 miles (2,100 km) above the photosphere, the corona transitions into the solar wind. While the corona’s magnetic field keeps the plasma confined near the Sun, the field weakens with distance, allowing the charged particles to escape into interplanetary space.
Inside the corona, particle motions are relatively ordered, but once they cross the “source surface” at roughly 20 million miles (32 million km), their trajectories become more chaotic, giving rise to the high‑speed streams that define the solar wind.
Solar wind streams vary in speed: slow wind moves at 186–310 mph (300–500 km/s), whereas fast wind can reach 373–497 mph (600–800 km/s). Fast wind originates in coronal holes—regions of open magnetic field lines that act as conduits for plasma to stream outwards.
Slow wind’s origins are less understood but appear linked to the Sun’s magnetic cycle. When sunspot activity is low, slow wind typically emanates from the equatorial belt; during solar maximum, both slow and fast wind can be observed from nearly any latitude.
As the solar wind expands, it forms the heliosphere—a protective bubble that contains the Sun, Earth, Moon, and all other solar system bodies. The heliosphere is surrounded by the interstellar medium, a mix of hydrogen, helium, and dust.
The heliosphere’s outer layers include the termination shock—where the solar wind slows abruptly—and the heliopause, the boundary where the solar wind pressure balances that of the interstellar medium.
When solar wind particles collide with Earth’s magnetosphere, they are funneled toward the magnetic poles. The resulting excitation of atmospheric gases produces the aurora borealis and aurora australis.
While the Moon lacks a global magnetic field, recent data from the Lunar Reconnaissance Orbiter suggest that localized magnetic anomalies shield certain regions from solar wind, producing “lunar swirls”—dark or light streaks that reflect variations in surface composition.
Satellites are also vulnerable. Charged particles can cause single‑event upsets in electronics, degrade solar panels, and induce orbital decay, necessitating robust shielding and error‑correction protocols.
Solar wind is a continuous flow of charged sub‑atomic particles—primarily protons and electrons—emitted by the Sun.
The hot corona, beginning about 1,300 miles above the solar surface, expands into space. The weakening magnetic field beyond ~20 million miles allows the plasma to escape.
Hydrogen and helium dominate, accounting for roughly 98 % of its mass.
Solar wind can disrupt GPS and other satellite systems, but it also generates the stunning auroras that light up polar skies.
Charged particles are drawn toward the magnetic poles, energizing atmospheric gases and creating luminous auroras.
