According to the resolution criteria, I would say that that market should trade much much higher than OP's hypothetical market. Any governmental agency stating that "Extraterrestrial life exists" would count. NASA/Seti finding evidence of algae on an exo planet or Io or something counts.

I agree, it needs to be more specific. Like:

"NASA, ESA, and Roscosmos all confirm definitive concrete proof, and publish this proof, for the presence of organisms, or technology created by organisms, which originated from outside Earth's atmosphere, and was present within Earth's hill sphere at some point since 1900."

Which has already happened. Clinton basically announced the discovery of life on mars back in the 90s.

https://www.youtube.com/watch?v=pHhZQWAtWyQ