Demon

From Galactic Fleets Wiki

Uninhabited planets are not currently usable for production and can not be terraformed.

This includes planets that are Gas Giants, Demons, or Barren.

The Gas Giant is a planet more like Jupiter and is often brightly colored.

Demons are often close to stars and are too hot to be inhabited.

Barren planets are bereft of atmosphere and are, well, barren.

While scans of planetary systems will show you potential hostile ships in a system, they will not show you ships in orbit around planets, including uninhabited ones. So you should fly ships to check them periodically to see if ships are hiding there.