A giant hole on the Sun's surface has ejected a record amount of rare helium-3 gas into space. In October 2023, this gas was measured at a concentration 180,000 times higher than normal, marking a significant discovery that could unlock new insights into the Sun's mysteries.
Toward the end of October 2023, astronomers detected an extraordinary release of helium-3 from the Sun — the largest emission of this isotope ever recorded from our solar system's central star. Scientists traced its source to a solar jet emanating from the edge of a coronal hole, characterized by a burst of particles containing only light elements.
Astrophysicist Radoslav Bučík from the Southwest Research Institute in the U.S. explained: "This rare isotope is one neutron lighter than the more common helium-4 and is extremely scarce in our solar system. On average, there is only one helium-3 ion for every 2,500 helium-4 ions." He added, "However, solar jets appear to accelerate helium-3 preferentially due to its unique charge-to-mass ratio."
Helium-4 is the most common isotope of helium, accounting for about a quarter of the mass of all ordinary matter in the universe. Both helium-3 and helium-4 are believed to have formed in the early moments after the Big Bang, but helium-3 is much rarer.
In the solar wind, helium-3 typically makes up only about 0.002% of the composition. However, solar jets can enrich this isotope to concentrations nearly 10,000 times higher. On October 24–25, 2023, ESA and NASA's Solar Orbiter recorded helium-3 concentrations 180,000 times the normal level in the solar atmosphere — with the gas being ejected at much higher speeds than other materials.
During this period, solar observatories detected a large coronal hole on the Sun's surface. Coronal holes are temporary regions in the Sun's outer atmosphere (corona) where the magnetic field is open, allowing solar wind to escape more easily. These areas appear dark in ultraviolet and X-ray images due to their cooler, less dense plasma.
In these magnetically open regions, the solar wind can shoot charged particles into space at high speeds. At the edge of this particular coronal hole, Bučík and his team identified a solar jet — a highly focused plasma stream — as the source of the helium-3-rich particle event.
"Surprisingly, the magnetic field in this area was weak — more typical of quiet solar zones than active regions," Bučík noted. "This supports earlier theories suggesting that helium-3 enrichment is more likely in weakly magnetized, low-turbulence plasma."
What made this jet even more intriguing was its composition. Solar particle events that accelerate particles in or from the corona often include high levels of helium-3, but usually also feature elevated amounts of heavier elements like neon and iron.
In contrast, the October 2023 event showed no significant increase in iron levels. Instead, the flow was rich in elements like carbon, nitrogen, silicon, and sulfur. Only 19 other solar particle events with similar chemical profiles were recorded between 1999 and 2023.
This rarity could indicate that such events are indeed unusual — or, alternatively, that they are common but often go undetected because they're too weak or too distant from Earth to be observed. The Solar Orbiter, positioned halfway between Earth and the Sun, is ideally located to detect such subtle phenomena.
