How do meteorites reveal the early Sun's activity?
Solar wind gases, solar flare tracks and isotopes made by solar radiation in meteorites record that the young Sun was far more active than today.
The young Sun was very different from today's. Like other young stars, it rotated faster and produced stronger flares, more intense ultraviolet and X-ray radiation, and a powerful solar wind. Meteorites hold several kinds of evidence for this.
Solar flare tracks. Energetic particles from solar flares leave microscopic trails of damage in crystals. Some grains in regolith breccias and in primitive meteorites have very high densities of such tracks, suggesting intense irradiation while they lay on asteroid surfaces or drifted in space.
Solar wind gases. Regolith breccias contain gases implanted by the solar wind. Some meteorites contain more solar gas than expected from today's solar wind intensity, perhaps reflecting a stronger early wind.
Radiation-made isotopes. Beryllium-10, a radioactive isotope that is not made in stars but can be produced by high-energy particles hitting other atoms, appears to have been present in some CAIs. This suggests that intense radiation from the early Sun produced it in the nearby disc. Lithium-7 and other isotopes are also studied for similar effects.
X-wind models. Some scientists have proposed that CAIs and chondrules formed close to the young Sun, where magnetic activity lifted them and then threw them outwards in a wind, although this model is debated.
Understanding the early Sun's activity matters for the evolution of planetary atmospheres. A more active young Sun could have stripped atmospheres from small planets and altered chemistry in the disc. Meteorites thus provide unique evidence about how stars like the Sun behave in their youth.