How are all the Eggsteroid levels opened

Angry Birds Nest has a post with analysis of the announcement video:

• At first glance, the video suggests that the Red, Black, and [now-green] Big Brother birds all have the same abilities as before, though newly-designed.

• The Blue birds have the same ability, though they seem a bit stronger than in the original apps.

• There also seems to be a purple-colored bird (we are not going to speculate as to its name right now), whose ability is to redirect and accelerate. Personally, I believe this is a new ability of the existing Yellow bird.

• There is also a new “icy” bird (again, no speculation as to name), whose ability is to freeze its contact area on a structure.

This seems to be accurate based on this newer post describing all of the birds in detail, which I won't reproduce.

Edit: Based on playing the game just now, it appears that the blue birds don't speed up as mentioned in the latter post (but not the first). Possibly it was just confirmation bias on ABN's part since there's a nice rocket-like glow when they split apart. As well, all birds show a plot of the first part of their trajectory.

These levels are under Eggsteroids. From the screen containing all the planets, if you scroll over to the 4th planet, you'll see the Eggsteroids levels. Clicking on the planet will show you any unlocked levels and allow you to replay that level. These appear to be comparable to the Golden Egg levels of the earlier games.