Unusual bets and prop wagers
What's the best bet on whether aliens will land before Christmas?
Direct answer
There is no evidence-based way to price such an event precisely; treat it as a novelty question rather than a sensible investment.
How to use this answer
This is a reasoned general answer rather than a confirmed bookmaker ruling or a claim about an event that has actually occurred. Exact cases need the facts supplied by the organiser or operator.
Novelty and prop markets depend on their written definitions. Find the precise wording, qualifying period and published result source; an ordinary sporting rule does not always decide how a novelty bet settles.
This is a practical or editorial answer; no universal operator rule is claimed.