[dredmorbius]

For those curious, 9.7 g/cm^3 would roughly match the densities of Thulium (9.321), Bismuth (9.807), Moscovium (>9.807), Lutetium (9.84), or Lawrencium (>9.84). Several of those are short-lived radioactive elements, however.

Going up the scale slightly are Actinium (10.07), Molybdenum (10.22), and Silver (10.501).

My suspicion is that there's possibly a core of Lead (11.342) or Thorium (11.72) (both fairly abundant on Earth, and stable), though Mercury (13.5336) and Tungsten (19.25) give some interesting possibilities, surrounded by a crust (or ocean) of less-dense materials.

Oh, and surface temperature is ~1,200°C.

Quite a conundrum.

Elements listed by density (at standard temperature & pressure: 100 kPa & 0°C): <https://www.thoughtco.com/elements-listed-by-density-606528>