The "Alien Monsters" Yu Saint mentioned was, in essence, just a general term. It referred to anything that could potentially threaten the astronauts and put their lives in danger.
This included potentially living Aliens, as well as autonomous defense robots, automated sentry systems, and a whole range of similar entities. Of course, actual Alien Monsters were also on the list. Earth had even considered possibilities like spaceships that transformed into giant robots, or biological ships that morphed into giant amoebas or biomechanical Monsters, and had developed countermeasures for each.
"After all, they are a civilization from the same era as the Immortal Gods. They were soaring through the Starry Sky thousands of years ago. It wouldn't be the least bit surprising if their defensive measures, or even their individual lifespans, surpassed several thousand or even ten thousand years. Speaking frankly and humbly, our Earth Civilization is really just a junior to those civilizations."
