New work on lunar samples reveal a shared source for water in the deep interior of both Earth and Moon.
A watery double-planet: Luna and Terra
Science Magazine recently published a paper that reports that minute quantities of water contained in lunar volcanic glass appear to be identical in isotopic composition to terrestrial water. According to subsequent press reports, this finding revolutionizes our understanding of the origin of Earth and Moon. But does it?
Water is a simple molecule, made up of two hydrogen atoms and one oxygen atom. However, these atoms are not all made the same – they always contain the same number of protons and electrons but the number of neutrons they contain varies. In particular, some naturally occurring hydrogen contains an extra neutron and hence has twice the mass of normal hydrogen. This “heavy hydrogen” (called deuterium, for its atomic weight of two) is much less abundant than its lighter version. Planetary scientists use the amounts of deuterium, relative to normal hydrogen, as a measure of the provenance of the material, i.e., where it formed relative to the Sun.
Ultimately, substances that have identical deuterium/hydrogen ratios are presumed to have come from the same source. ...