 What is the aliens' mission?
But this vast distance did not mean that isolation could endure forever. Instruments within the ship intercepted radio broadcasts and, within the hour, early TV signals. "It's not what they've done," said Bal, the second alien. There's nothing in this region of space our people want," said Ethaniel. "And how long can Earth last? They went much closer to Earth, not intending to commit themselves. For a day they circled the planet, avoiding radar detection, which for them was not difficult, testing, and sampling. "What's worse is that I now find they also have missiles, range one thousand miles and upward. They either have or are near a primitive form of space travel."
 Bal and Ethaniel are on a mission to Willafours.
 Bal and Ethaniel are on a mission to Earth to set up an interstellar trade route.  Bal and Ethaniel are on a mission to Willafours.  Bal and Ethaniel only have one week to save the Earth, but that is their mission.  Bal and Ethaniel are on a mission to steal the big bomb from the humans.