Eggsteroids are objects in Angry Birds Space, they act similarly to the Golden Eggs in the other games, but it automatically teleports the birds via a wormhole instead of just being collected.
In some levels, the Eggsteroid can't be obtained, these being Utopia 4-30 and Cosmic Crystals 7-30 after defeating the bosses, Fat Pig and Alien Pig.
They are golden egg-shaped asteroids with small craters on them, they are a bit larger than The Eggs and Golden Eggs.
As said above, they can be found as Golden Eggs in some of the levels, but can't be obtained at the levels said above.
They were normal Eggs found in Space, but the pigs started stealing them. One of them, the master, King Pig stole one from a peculiar cubic bird, the Ice Bird, angering him and making Red and his flock enter a wormhole that led them to space, transforming them into Super Heroes.
Ice Bird retrieves the Eggsteroid several times, but a pig always steals them, such as Fat Pig, that ate it, and Alien Pig, that transformed it into source for his Crystalizer UFO, all defeated later.