OK, here's what Weiler said at today's press briefing:
The delay will mean something else. It's an opportunity. David Southwood, who is the director of science at ESA, my counterpart there, back in July we had our annual bilateral meeting. David and I in a private meeting started chatting about the fact that they had now orbited Mars, they have a very successful Mars mission right now. They have large ideas of what they'd like to do. But as is the case in the United States, these missions get more and more expensive. The easy stuff has been done....when you get into orbiting and landing things, that's when it gets tough, and it gets expensive. So David and I sort of talked about the possibility that maybe we ought to think about NASA and ESA getting together and come up with one Mars architecture, one Mars program for the Earth, so to speak. So we started talking about that, he took that back to the European Space Agency. Just by curiosity we had another meeting yesterday, just before this about the final decision here, and I shared this information with him. He has now gotten approval, and I am allowed to say this, that in the future NASA and ESA are going to work together to come up with a European-U.S. Mars architecture. That is, missions won't be NASA missions, they won't be ESA missions, they will be joint missions. We need to work together. We'll never, ever do a sample return mission unless we work together. We both have the same goals scientifically; we want to get our science communities together and start laying out an architecture. We now have that time, for all the wrong reasons, but we now have that time. We don't have to rush to come up with some idea for 2016. They've got some ideas, we've got some ideas. Let's work together. We know how to land things on Mars; they know how to orbit things on Mars. They have launch vehicles, we have launch vehicles. So this makes eminent sense to both of us. We have committed to each other to get our communities to start working toward that goal.
Later on, he was asked a followup question, and he said:
There isn't a lot of meat on the bone, other than that David and I at the top of our two science agencies have agreed that we [can't] keep fooling ourselves. Nationalism is great; it's nice to put our logos on our missions. But these missions are getting complex and expensive. We have the same scientific goals. They want to send rovers to Mars, they want to do a sample return, they want to search for life. The goals -- not surprisingly, Western Europe and the United States seem to think alike when it comes to science on Mars. Isn't this the right time, especially now, considering that the 2016 mission ideas are now up in the air because those missions will be impacted. ESA has some ideas for a mission in 2016. We could probably do a heck of a lot better mission if we did it together than if we continued to compete with each other. We've got technologies and know-how that they don't; they've got technologies and know-how that are special. Let's work together. What a thought. This just solidified -- we kind of reached the decision without much thought -- it was kind of a no-brainer yesterday, as I reflected to Dave what we were about to tell you today.
David and I are both realists; we recognize that scientists will like to say that missions cost X, and by the time engineers touch them, they're X times 2 and by the time cost analysts get involved it's X [times] 3. A sample return mission is not going to be done for three billion or four billion. That's like saying JWST can be done for a billion. When the experts look at a sample return mission the number comes out to between six and eight billion dollars. And that's not surprising what our rover's going to cost. ... David and I agree ... that we ought to do it together, as a U.S.-western European mission. And it's probably in the early 2020s.
It has long seemed obvious to The Planetary Society that there ought to be closer cooperation between NASA and ESA on planetary exploration, for exactly the reasons Weiler outlined: missions are getting more complex and expensive as their goals get more challenging, and NASA and ESA have similar science goals anyway. We can do much more ambitious missions together than we can do separately. I'm sure I speak for all Planetary Society members when I say "Hallelujah!" at this announcement.