Yes, EARTHS is a Scrabble word!

Letter values in Scrabble US: E 1, A 1, R 1, T 1, H 4, S 1.

Is it a valid word?

EARTHS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the 3rd planet from the sun; the planet we live on
the loose soft material that makes up a large part of the land surface
the solid part of the earth's surface
the abode of mortals (as contrasted with Heaven or Hell)
once thought to be one of four elements composing the universe (Empedocles)
the concerns of this life as distinguished from heaven and the afterlife
a connection between an electrical device and a large conducting body, such as the earth (which is taken to be at zero voltage)

Also: dry land, solid ground, terra firma, worldly concern, earthly concern.