In the absence of detailed information we consider a general structure, with a diameter of 1 km. It has a 250-meter radius inner core with an equation of state (EOS) consistent with granite (density 2.63 g/cc). This is surrounded by a 250-meter thick mantle with an EOS of tuff, a soft, porous rock that formed by the compaction of volcanic ash (density 1.91g/cc). The total mass is 1.05x10+15g or just over a billion tons (Fig 3), and the average density is near 2.

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