Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Alien Planet Pack Free.
Alien Planet Pack v1.1
Update 1.1: Reset all prefabs position to 0,0,0 Fixed small import materials issue.
Assets to create your own Alien Planet environments! The assets are optimized for mobile and VR.
Includes 4 examples scene to get you started:
_All props, spaceships and terrains assets are using only a single texture/material.
_Include 4 different skyboxes
_6 spaceships designs with movable parts, effects and 3 skins each.
_Alien structures/ruins with 2 set of skins.
_Models range from 40 to 650 triangles.
_Particle effects: Snow fall, dust clouds, rain fall, glow, gas cloud, jets, etc….