Time Until Impact
Cities with an observatory report the presence of an asteroid in its solar system, which is necessary to detect asteroids at extreme range. Asteroids known to be on a collision course with a world will cause an event log alert in the city report.
The asteroid is always marked as enemy, and can thus be targeted from a fire control station by both AI and avatars. It will also appear on the Unit list for attack and follow orders.
Depending upon the size of asteroid to impact a world, devastation could range from destruction of all cities to complete annihilation of the world body.
The largest asteroids are absorbed by gas giants harmlessly.
Moons and rings left behind when a planet is destroyed become asteroids immediately. All cities on moons are destroyed.
The goal is to develop the needed technology to get into space and blowup the asteroid.
You will only be able to see and attack the asteroid once it physically spawns in the system, which is 8 hours before the impact time.
The asteroid will slowly break down into smaller pieces as it is damaged.
Haxus visited the homeworld of Tamunshin to help with an asteroid, however they were unable to destroy it before the impact. Haxus recorded a video of the impact which can be seen here: http://hazeron.com/Playlists/Scenes%20of%20Hazeron/AsteroidImpact.mp4
Also, this was discussed in this thread on the forums: http://hazeron.com/mybb/showthread.php?tid=2062