For many years after Apollo, the binary accretion model was settled on as the best hypothesis for explaining the Moon's origins, even though it was known to be flawed. Then, at a conference in Kona, Hawaii in 1984, a compromise model was composed that accounted for all of the observed discrepancies. Originally formulated by two independent research groups in 1976, the giant impact model supposed that a massive planetary object the size of Mars had collided with Earth early in its history. The impact would have melted Earth's crust, and the other planet's heavy core would have sunk inward and merged with Earth's. The superheated vapor produced by the impact would have risen into orbit around the planet, coalescing into the Moon. This explained the lack of water, as the vapor cloud was too hot for water to condense; the similarity in composition, since the Moon had formed from part of the Earth; the lower density, since the Moon had formed from the Earth's crust and mantle, rather than its core; and the Moon's unusual orbit, since an oblique strike would have imparted a massive amount of angular momentum to the Earth–Moon system.