* Astronomy

Some planets beyond our solar system might be rocky like Earth, but lack its gooey metallic middle, a new study suggests. Such 'coreless' terrestrial planets would not have magnetic fields, which would make them inhospitable to life as we know it.
Rocky planets were once thought to consist of three main layers: a thin solid crust, a viscous, rocky mantle and a solid or molten iron core.
This layering, or differentiation, is thought to have occurred early in the solar system's history, when collisions between rocky bodies and the decay of radioactive isotopes melted the interiors of large objects, allowing dense material to settle towards their centres.

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