Venus is only somewhat smaller than Earth. If radioactive isotopes are fueling Earth's interior heat then it seems like that should be so with Venus.
What Venus doesn't have is a significant moon or rotation/spin.
With rotation I think Venus would have some magnetic field.
Makes me think tidal friction is a greater contributor to internal heat than is generally cited.
To create a surface inhabitable planet several low probability events all must intersect.
1) Must be large enough rocky body to sustain internal heat (molten core).
2) An early binary collision is needed to provide spin (for magnetic shielding) & hopefully a stable moon for additional tidal friction.
3) The planet's [stable] orbit must be clear of other rocky debris.
4) There needs to be a good supply of organic, volatile chemistry & water.
Any planet close to Earth's properties is quite rare.
Mars has spin but a chilled core.
Venus is about the right size but without spin & perhaps a bit too close to the Sun.
An intelligent species wouldn't burn the life bridge it was standing on before it at least had an accessible replacement.
Still waiting for that intelligent species to show up.
Waiting for Godot...
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