IT HAS long been a mystery why most lunar 鈥渟eas鈥濃�攚hich are actually
ancient lava flows鈥攁re on the side of the Moon nearest Earth.
Now researchers at the Massachusetts Institute of Technology and Brown
University in Rhode Island suggest that as the Moon solidified 4 million years
ago, radioactive heating near the core formed an unstable layer of lava. Because
of the small size of the Moon鈥檚 metallic core, says researcher Shijie Zhong,
only a single plume rose towards the surface, causing the asymmetry (Earth
and Planetary Science Letters, vol 177, p 131). He speculates that the
higher mass of the lava flows led to the 鈥渟ea side鈥� pointing towards the
Earth.
Zhong says that similar ideas may explain why Mars鈥檚 northern and southern
hemispheres are so different. 鈥淲e鈥檙e working on it right now,鈥� he says.
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