Solar wind gases
Solar wind gases are atoms from the Sun implanted into the surfaces of grains exposed on asteroids, the Moon and other airless bodies.
The Sun constantly blows out a stream of charged particles called the solar wind. On airless bodies such as asteroids and the Moon, these particles hit surface grains and become embedded in their outer layers, just tens of nanometres deep. They include hydrogen, helium, neon and other noble gases with the Sun's own isotope ratios. These are solar wind gases.
In meteorites, abundant solar wind gases are a hallmark of regolith breccias. Their grains once lay at the very surface of their parent body before being buried and compacted into rock. Measuring the gases tells researchers that a meteorite was part of a soil-like layer on an asteroid.
Solar wind gases are also valuable to solar physics. NASA's Genesis mission collected solar wind directly between 2001 and 2004 and returned samples to Earth, confirming that the Sun's oxygen isotopes differ from those of Earth and most meteorites. Lunar soils and regolith breccias preserve a much longer record.
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