Recent research proposes that the heliosphere—the Sun's protective bubble—resembles a deflated crescent, challenging earlier comet-tail models.
The heliosphere, shaped by solar wind particles, extends beyond Pluto's orbit before fading into interstellar space. It shields our Solar System from cosmic rays and other galactic threats. But defining its precise boundaries has long been a challenge.
Studying the heliosphere from within is inherently difficult. NASA's Voyager 1 and Voyager 2 probes, launched in the 1970s and now in interstellar space, provide crucial data, supplemented by missions like Cassini and New Horizons.
Scientists developed advanced computer models using this data to delineate the heliosphere's structure. "We focused on particles often overlooked in solar wind energy balances," explains Merav Opher, astrophysicist at Boston University.
These particles, neutral hydrogen atoms from interstellar space, penetrate the heliosphere unimpeded. Inside, solar wind ionizes them, altering their paths and serving as tracers for the boundary—essentially acting as a natural radar for NASA researchers.
Previous models depicted the heliosphere as comet-like, with a rounded leading edge and elongated tail. A new study in Nature Astronomy revises this view, describing it as a "deflated crescent," per NASA.
In the image above, yellow represents solar particles; red shows interstellar particles deflected around them.
This shape matters because the heliosphere isn't fully impervious—up to 25% of galactic cosmic rays reach Earth. "These rays may trigger DNA mutations driving species evolution," notes Opher.
