Seems like quite a few Class M planets.
“Seems like quite a few Class M planets.”
Humans have spent millions of years living in this biosphere; where we share similarities with every fungus, bacteria and virus. Every 150 pound human is carrying 5 pounds of bacteria, fungus and viruses. Actually, that 150 pound human has more non-human cells than human cells because that 5 pounds of cells are so much smaller than human cells. Our highly evolved immune systems keep the alien growths in check and balanced.
Now, imagine we go to another world that has evolved totally different analogs of bacteria, fungus and viruses. Those aliens will be right at home in our wet, nutrient filled bodies. Our immune systems won’t recognize them and we’d shortly be sprouting growths like forest fungi inside our eyelids. We wouldn’t make it a month on this new world.
Mankind will NEVER walk freely and unprotected on a life containing alien world. Science fiction whips up wonderful worlds and aliens. But if we ever meet them for real, no matter how “nice” they are; their bacteria will kill us; and vice versa.