Dark discussion ahead for Europe and US

Euclid should launch in 2019

It couldn't have been planned better. Just as the Nobel committee was announcing its physics award would go to the research that identified the "accelerating expansion of the Universe", delegates to the European Space Agency were sitting down in Paris to approve a mission to investigate "dark energy" - the very thing thought to be pushing the cosmos apart at a faster and faster rate.

Saul Perlmutter and Adam Riess of the US and Brian Schmidt of Australia will share the Nobel. The trio studied a particular type of stellar explosion, or supernova, and found that the most distant of these objects were receding quickest.

This observation led to the theory that some mysterious, gravitationally repulsive dark energy must be behind the rising expansion of the cosmos - although we don't really have the foggiest idea what that is.

Esa's Euclid telescope will endeavour to get some answers. It will launch in 2019 and map the spread of galaxies and clusters of galaxies over 10 billion years of cosmic history.

Euclid will look in detail at the way those structures have grown through time to get some sense of how dark energy is working.

What's interesting from the perspective of this column is that it is Europe and not America that is launching this space mission.

Dark energy is one of the most pressing problems in astrophysics today and, given its role in identifying the problem, you would have thought it would be the US announcing such a mission.

They certainly have the concept on the drawing board - it's called the Wide-Field Infrared Survey Telescope, or WFirst. And a recent influential panel identified WFirst as the top priority mission for the coming decade.

But one of the US space agency's (Nasa) other missions is keeping it from being implemented. That other mission is the James Webb Space Telescope, which is costing so much money ($8.7bn total cost) it has forced the Americans to delay WFirst until perhaps the 2020s.

Saul Perlmutter was in philosophical mood when the BBC spoke to him about the issue. The University of California, Berkeley, researcher is part of the team that is defining WFirst.

"I'm still optimistic on WFirst and I'm also very supportive of the Euclid mission and we're doing our best to make sure it happens as well," he said.

"As a scientist, you feel a sense of team spirit for your country but you also have a sense of team spirit for the international community.

"We need to make sure someone is taking the ball further down the field. We'd love to be in the position where we could lead and play a big role in making the next steps possible; but whenever we falter, we hope that others will be there to take up the slack, and at the moment it seems like Europe is doing a good job."

What must be particularly tough on Perlmutter is that Euclid - unlike WFirst - will not use his supernova technique to investigate dark energy.

The European mission will instead study the influence of dark energy by looking for subtle distortions in the way galaxies appear as they line up on the sky, and by measuring the patterns in the three dimensional distribution of galaxies through time.

What will be interesting to see now is whether Perlmutter's and colleagues' Nobel triumph provides the impetus to find the money to build WFirst sooner (one should state that Perlmutter's colleagues included many collaborators, including Europeans). One can imagine that there will be some political pressure in Washington to accelerate the project, to ensure the US is the one "carrying the ball downfield". Certain members of the Senate are trying to do just this, urging Nasa to find a way to get going on WFirst as soon as 2013.

The alternative, of course, is that the Americans could simply ask to get onboard with Euclid. In the past, Esa has offered Nasa a 20% partnership in the telescope, and one of the simplest ways it could contribute is by providing the infrared detectors needed by Euclid's instruments. This technology is not available in Europe.

"The door is always open to the Americans, and we are ready to co-operate with them if they come with a reasonable proposal," Esa's director of science Alvaro Gimenez told me.

"What we wouldn't accept is a position where the Americans delayed or jeopardised the mission.

"Our baseline at the moment is to get the infrared detectors from the US company that makes them. We are developing this technology also in Europe, but it would be easier to keep the schedule if we procure them in the US."

The US is unlikely to be offered more than a 20% role because to give greater participation starts to unpick all the definition work that's been done to date, and risks delaying the launch. Would the US accept just a 20% role in Euclid? It's not a position of "leadership", but then pragmatism may demand that on this occasion America accepts what is going, according to Bob Nichol.

The Portsmouth University researcher is part of the Euclid team and one of the few Europeans involved in drawing up the WFirst concept.

"The mission we are scoping out for WFirst is phenomenal," he told me. "But it's a very different beast to Euclid and it's a much more expensive beast than Euclid.

"As a scientist, it's great to sit in a room and speculate on what we could build; it's very different when you read the newspapers about the financial crisis and the Greeks not being able to pay their mortgages.

"When reality bites, I think Euclid may be the mission for the times we are in."

There are about 8-9 months before Esa has to tie down the details of who's involved in Euclid and issues the instructions to start work on building the mission. It's a short window for the Americans to make an important decision.