"Aliens" for the purpose of this market must be living beings that have demonstrably existed on other planets for non-trivial periods of time before the creation of this market.

"Strong evidence" should mean that there is general, global consensus that these are actually aliens.

This market will resolve to YES if those creatures have DNA, meaning physiology that includes two polynucleotide chains that coil around each other to form a double helix. If multiple alien species are discovered at once, I'll wait 5 years following the initial discovery and resolve to YES if any of those creatures have DNA.

This could be from any cause, including panspermia, an earth species that left to live elsewhere a long time ago, weird alien abduction hybrid experiments, or just the universe only producing living species that carry hereditary information with DNA.

Otherwise, this market will resolve to NO. I will indefinitely extend the close date until the discovery of aliens.