EXPLAINING how Earth ended up with enough water to form oceans has always been a sticking point for planetary scientists. Now, two of the latest models of planetary formation show that water could have accumulated rather easily on terrestrial planets. In some scenarios, planets could have started out with so much water that it would be impossible to find even the scraps of dry land that dotted Earth in the 1995 movie Waterworld.
Most models of planetary formation have assumed that sunlight could penetrate the solar nebula, the disc of dust and gas from which the planets formed. This…
