Wait, I'm confused. From the fine article:
"a rocky core surrounded by a layer of water in a "supercritical" state where it is both liquid and gas, and topped by a blanket of steam."
"the planet probably does not have a substantial atmosphere to carry the sun's heat to the unlit side."
If there's no substantial atmosphere, what's keeping the pressure on the water layer to keep it in a supercritical state and not boiling off at 2000C? Need a lot of pressure to keep water even partly liquid at those temps...