 Why did the alien separate when they go down to the surface instead of working together?
A gentle fancy for the Christmas Season—an oft-told tale with a wistful twistful of Something that left the Earth with a wing and a prayer. Earth was so far away that it wasn't visible. 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. Machines compiled dictionaries and grammars and began translating the major languages. The history of the planet was tabulated as facts became available. The course of the ship changed slightly; it was not much out of the way to swing nearer Earth. For days the two within the ship listened and watched with little comment. "We've got to make or break," said the first alien. "It's not what they've done," said Bal, the second alien. "I may remind you that in two months twenty-nine days we're due in Willafours," said Bal. They've had two world wars in one generation and that the third and final one is coming up you can't help feeling in everything they do." "The wrong diplomatic move, or a trigger-happy soldier could set it off. A meteor shower could pass over and their clumsy instruments could interpret it as an all-out enemy attack." "We'll just have to forget there ever was such a planet as Earth." Except for the one thing they lack, and that's quite odd, they seem exactly like us. "It is. "There is. "In a week we can't negate their entire history. "And then what? "And when we get to Willafours we'll be busy. 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. Atmospheric analysis showed that as far away as we were." "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." "Sitting there, wondering when it's going to hit them. There's so little time," Ethaniel said. Our machines translate their languages easily and I've taken a cram course in two or three of them.
 They thought they could cover more ground this way and talk to more people about maintaining peace.
 They want to take advantage of some alone time while they are not on their main ship.  They have different knowledge of these different areas, as they travel to the areas they know more about.  There is not space for two aliens in one small landing craft, so they must split up.  They thought they could cover more ground this way and talk to more people about maintaining peace.