For the purpose of this answer, I'll assume a non-sentient organism roughly like a whale lands on Earth. Obviously not a tool-using species, no clothing, etc. The animal is large enough that there is no question of a prank, and different enough that investigation shows a non-Earth origin.
We are not alone in the universe!
So far extraterrestrial life are theories and clues, not hard facts. Ordinary people might be exited if the news reports of possible life on Mars, but if the life is microscopic, long dead, and not proven, the excitement won't last. If there is a complex organism like the space whale, that makes other sentient species appear much more likely. When will they come visit? Should we look for them?
Scientists would get a chance to look at an extraterrestrial organism. There is enough to give thousands of scientists a slice. Does the space whale use something like DNA? If so, it is a double helix? Which acids? What is the propulsion system? Rocket engines? Lightsails? Something else, unexplained by present-day science?
- Grab it and keep it under wraps. The advantages mentioned above are too valuable to just give parts away. Only carefully chosen scientists get a look and all reports are classified top secret.
- When was it detected, and what does that say? What if it had been a mile-wide rock and not a 1,000-ton whale? Who voted for and against their latest funding request?