To be fair, we don't need to find little green men in a UFO. It's sufficient to e.g. find fossils of extinct microorganisms on Mars, which is a slim possibility that's a goal of the Mars Sample Return mission.

These markets also have low volume at reasonable prices. If you bought $10K of "no" right now for next year, you would only get an 8% return, not 10%. You could execute better trades to get better prices, but the odds also become more sane over the year. The S&P 500 is also up 18% YTD (13% YoY for the last 5) and you can buy as much of that as you want.