Because a close fly-by probe is something we know how to do, and is a much more affordable and achievable goal than a mission that would have the true goal of confirming life on Europa.
Such a mission would involve landing on an outer solar system body with no atmosphere, penetrating 10-15 miles of ice, and directly sampling liquid water for microbes. That's a huge undertaking that would cost a lot more than $5B. If any part of that failed, it would be a pretty bad look for NASA and those who voted to fund it, and a negative result still wouldn't mean there is no life.
I certainly think that's something we should be attempting to do in the future. But an initial close flyby mission is something we know we can do with a high probability of success, and data gathered from such a mission could build support for a more extensive follow-up in the future. The data gathered might even make that future mission less expensive and more likely to succeed by mapping likely places where the ice is thinner, or where tectonic activity pushes water to the surface.
And hey if a microbe in a plume of water happens to land in a collection receptacle on this mission, that's just an incredible bonus without setting the mission up for disappointment.
Such a mission would involve landing on an outer solar system body with no atmosphere, penetrating 10-15 miles of ice, and directly sampling liquid water for microbes. That's a huge undertaking that would cost a lot more than $5B. If any part of that failed, it would be a pretty bad look for NASA and those who voted to fund it, and a negative result still wouldn't mean there is no life.
I certainly think that's something we should be attempting to do in the future. But an initial close flyby mission is something we know we can do with a high probability of success, and data gathered from such a mission could build support for a more extensive follow-up in the future. The data gathered might even make that future mission less expensive and more likely to succeed by mapping likely places where the ice is thinner, or where tectonic activity pushes water to the surface.
And hey if a microbe in a plume of water happens to land in a collection receptacle on this mission, that's just an incredible bonus without setting the mission up for disappointment.