About 3 - If we’re talking about intelligent alien life, then hell yeah. There’s no way of knowing what kind of technologies and scientific knowledge they could share with us, but it’s bound to be worth a lot.
If we’re talking about non-intelligent life… well, the economic benefits are less evident.
About 1 - maybe success could be determined by a panel of top scientists - xeno-biologists, physicists, chemists, etc. - who could vote which team has either succeeded, or at least gotten close to success.
About 2 - I don’t think there’s any way of knowing that in advance. But maybe we could a long-lasting competition - decades long, if needed - with an open prize purse just waiting for someone to pick it up?
@TerryMulligan - Do you think this kind of a model might work?