Asteroids may well be the source of Earth’s water, yet I’m beginning to have second thoughts.
It is becoming clear that the early Solar System’s small bodies have had a complex and interesting history; and it is certainly true that, back in the early history of the Solar System, there was a period in which the sheer number of asteroids hitting Earth might have been high enough to make this explanation fit. What I can’t see is how Earth’s water could have been delivered by asteroids without being diluted by an equal influx of comets, altering the deuterium to hydrogen ratio again.
Instead, we should probably look towards Earthly solutions. Geologists have recently suggested that rocks deep in the Earth’s mantle may have provided a refuge for water, which would then be released when plate tectonics carried them up to the surface. Rosetta may have travelled six billion miles to tell us to look closer to home.
CHRIS LINTOTT co-presents
The Sky at Night