An asteroid is on collision course with Earth and it's up to the player to prevent the inevitable catastrophe. "Mission Asteroid" is the third text adventure with graphical illustrations by Sierra. But due to its easy difficulty level it was released as number zero in Sierra's Hi-Res Adventure series. The game's parser only understands simple one- or two-word commands.

There is a terrible tragedy about to happen to Earth. An asteroid, is speeding through space directly toward Earth. This particular asteroid was one of many revolving about the Sun between the orbits of Mars and Jupiter. Somehow, this asteroid jumped its orbit and is now threatening the life of every living soul on Earth. The only way to stop the asteroid is to blow it up in space before it gets to Earth. As an astronaut, you are assigned the duty of rocketing to the asteroid and blowing it up.