The reason for this is that young planets retain heat from their formation, and only gradually cool.

This is a young planet, not all that stable.

When Earth was in its early formation, evidence suggests that numerous comets and other bodies smashed into the young planet.

He says the young planet was hot at its center rather than cold.

One could scarcely expect to find real consciousness on a planet so young, but there may be the first stirrings of intelligence here.

Venus must be still very hot as young planets radiate heat.

I poked at it with a stick, a social gesture probably older than this young planet.

It will also be possible to see very young planets in formation, while they are still hot.

It was a young planet compared to Earth.

In its place were comfortably middle-aged stars surrounded by young planets.