The aliens' spacecraft eject a plume of plasma or gas during atmospheric entry in order to slow down for landing.


The shape of these spacecraft are like rounded out, fat coins, which appear to have anti-matter-like propulsion but it is speculated they were launched through a huge railgun, in order to give them a boost. In the vaccuum of space, with no air resistance, so they were able to go on for a while before they engaged the engines.

These spacecraft are disposable, "one-shot-deals," like humanity's first 30 years' spacecraft so that cannot be reused. Upon atmospheric entry, they maintain their tight cluster to center forces for a beachead, and then they eject gas or plasma out of their crafts in order to slow down for landing.