The Eggsteroid is located on level 5-3 of Angry Birds Space Red Planet. Zoom out and you will see the Rover on the extreme right of the level. Waste Terence then use the Lazer bird to reach the Rover. Once you hit the egg you’ll immediately be transported via a wormhole to the level.
This level is rather complex and Foreman wears the shield, so he is very hard to pop.
One strategy 3-starring this level is to fire the Ice Bird toward the southern geyser to freeze the northern structure. Then blast the southern structure with Bomb to fling debris all over the place, clearing the level.