Earth and its Moon are unique in the Solar System.
The subjects of the study by Will and her colleagues are just six fragments recovered from Antarctica. These fragments are all part of the, and consist of a very specific kind of rock: unbrecciated – that is, not a 'fruitcake' of multiple rock types, as many meteorites are – basalt from a volcanic plain on the Moon.
There the rock lay, until an impact massive enough to send lunar rocks flying to Earth. Such an impact would have to have been relatively large, gouging deep into the lunar surface to reach rock that had not been exposed for eons. The sub-millimeter glass particles in the basalt, the team found, retained isotopic signatures of helium and neon, like tiny time capsules. And these signatures were the same as the solar wind, but were detected in much higher abundances than expected.
The team found the isotope ratios of the neon were very similar to isotope ratios of neon in Earth's mantle plumes, deep upwellings of hot molten that sample reservoirs of material deep inside Earth that are likely undisturbed since the planet formed, 4.5 billion years ago. This similarity suggests that the gasses came from Earth, the researchers concluded.