You have to have sufficient skill points over all. A higher Tier (generally) is worth more than a higher rank in the lesser Tier, but it's not absolute, ie: Rank 9 in Tier 1 is worth more than Rank 1 in Tier 2.

The Aliens do not wander, nor will they pursue. They are also leashed atm, so that you can explore for now. Poke them at your own peril though. The leash will also be coming off soon, probably by Monday.