For more than few thousands of years needed to explore the earth. Men lived with different belief about his territory from time to time. If we take Alexander the Great, he did not know land mass of Australia or America in his life time. As per his awareness India is the south end of the world from Greek. His world was 40% to 50% less than the world we have today.
Ancient man might have thought few 1000 miles were his world. That much alone he could move(walking). As per the year grows boundary is expanding.
Now earth is almost discovered completely. Nothing is left in the earth surface un-noticed. All sort of human civilization in the contemporary world discovered and many were erased from the earth by the discoverers.
Now it is time to explore space. Exploration to the space and neighborhood planets. We have not found any similar planets so far like earth. The distance in space is beyond imagination. Only unit is Light Years. So far man has not invented anything to move at the speed of light or faster than light. But may be in the future, man will invent such thing and travel in the space to find fellow living beings. Or some other living being from space may also try to reach earth.
At least this time, let us not behave like our past explorers. Earlier we killed the citizens of the new land being discovered. Red Indians in America, Aborgins in Australia, and many tribal were wiped out ruthlessly. Now in the Space exploration, Man should not repeat the same violence. Let the other living being live with its culture and belief. Since we are able to reach them, we may be technically advanced in our weapons. So let us stop eliminating living beings in outer space if we come across any. If aliens reached us, God knows whether they let us exists or eliminate, God only knows.
Before reaching outer space, are we allowing fellow human beings to co-exists in our current contemporary. Many civilizations are being crushed slowly. Nation eats another nation, Religion kills another religion. Society eats another society. Language eats another language. First, we have to stop the brutality here, in the earth. Developed countries are a threat to developing and under-developed countries. Military powers are trying to dominate non-military power countries. No end for Big Fish eating Small fish. We have to realize where we are leading this earth and change it positively.