The Mothership is the assumed home of the Aliens from Independence Day. It is as large as an entire planet and is where larger Alien ships are released from the bottom of the ship.
The Mothership is as large as an entire planet. The space where other Alien ships enter is in the shape of an upside down triangle. There is one circle on each side of the Mothership that sinks in and two large spikes on the bottom of the ship. On the very bottom of the ship, City Destroyers are released.
The inside of the Mothership is most certainly "alien" in appearance. The inside of the ship is covered with aqua colored glowing lights and there are several towers where other Aliens may actually live since there is no proof that the Aliens have their own planet. There is a section of the Mothership where more Aliens prepare for "invasions" in Troop Transports and where the Alien Supreme Commander inspects Alien Attackers.
The Mothership is assumed the home to all of the Alien race. The Aliens would arrive near a planet in the Mothership which would detach City Destroyers to inspect the surface of the planet.
In the film Independence Day, the Mothership was not seen until near the ending of the film when Steven Miller and David Levinson tried to sneak into the Mothership in a captured Alien Attacker. Steven and David planet i virus and bomb into the Mothership which caused it to explode, killing the Alien race once and for all.