Cosmic Vision from the European Space Agency

Ben - The National Astronomy Meeting gives people an opportunity to find out what others are working on and where the science might take us in the future. Mark McCaughran, from the European Space Agency or ESA, was at the meeting to explain ESA's Cosmic Vision of their plan to commission and support space missions over the coming years.

马克-宇宙六世sion is a programme which we put together in the last few years in the European Space Agency to provide some structure, some top level science guidance of the sorts of questions the community would like to see answered. Then we opened up an announcement of opportunity for people to actually propose actual missions against those questions in 2007. Space flight of course takes a long time to put missions together, but also, we've gone through a whole evaluation process to look at studying the mission, see what's feasible time-wise, cost-wise, and what the best science is. So we started with 65 missions in total and we're now down to the final 6 or 7. Out of which, we're still doing a shootout. It's kind of a technical shootout, looking at what's feasible on the right time scale. We want to get these things launched quite quickly - relatively, 2017, 2018. And so we don't want to do lots of technology development. You can think of crazy things that might take until 2030 to do and we want to get some missions in the pipeline because we have missions in this decade flying but we have a bit of a gap towards the end. And so, we want to get these things going.

Ben - So what were the questions that we think we want to answer?

Mark - Well, there are a whole range of questions starting from how does the sun work, how does the sun influence our lives every day, the weather in which we have space weather but also the weather on the surface of the planet. Of course, that's of great importance to many people as it relates to climate change. But then going to the other end of the universe, looking at the overall cosmological appearance of the universe, why is the universe the way that it is, how has the universe evolved to the state that it's in, what's the fate of the universe. But then there's all the things in between. How were stars born? How do planets get born around stars? How do they evolve? What are their chances of finding the conditions for life and maybe even life elsewhere? And then in our own solar system, is life unique in the solar system? Can we go to Mars? Can we go to the oceans of Europa under the ice crust there and are the conditions right for life there? So it's a kind of an overarching set of science questions. Many of the missions will approach many of those questions.

Ben - And so, was it split evenly? Did you say "we have this much resources, we have this many questions. We want to make sure we give X resources per X question."

Mark - Yeah. That's a very good question and in fact, more traditionally rather than per question, you would've seen it allocated in the past per discipline. But there was no precondition set on this. In fact, this time around, the astronomers are in the ascendant, they've got out of the M class missions, the medium class missions we're studying, they've got 3 of those, 3 out of the 4, and 2 of the L class missions, the large missions, those are astronomy or astrophysics related. That sounds like the planetary people are doing very poorly but of course, they've got other things which they're doing including going to Mars with NASA. That's not something that was in the cosmic vision process. That's a separate program at ESA. So the whole Martian exploration is going on in tandem in parallel.

Ben - So what's the difference between a medium class mission and a large class?

Mark - The amount of money is different between the two of them and originally, the M missions started off at 300 million Euros brought in from ESA. We had to look at that again and now, we think that to make sense out of those missions, the science goals that they propose as asked but also that the community felt were the best ones, probably going to cost us about 450 million. We expect then money to come in from the member states of ESA as well, European countries who contribute building bits of the payload, building parts of the instrumentation, maybe roughly 150 million more so about 600 million for one of those. The L missions have a contribution from us of about 650 million, but they will be actually - all three of those which we're looking at at the moment would be in tandem with United States, Japan, and other collaborators. And so, those are much bigger missions overall, up to 2 billion, for example, for our Jupiter mission, EJSM. So, the amount of resources is larger there, but also, we expect them to do more stuff. So the M missions are supposed to be very focused science goal experiments if you like - let's pick one question, let's get an answer to it, let's do it as well as we can. The Ls are generally more observatory style missions where you're going to look at a whole broad range of questions with a suite of instruments or go and do outer solar system exploration which is very expensive to do. It takes a long time to get there.

Ben - And so, what are the ones that you've considered? You said you've whittled it down to a short list.

Mark - Well we have on the M side, the medium missions at the moment, we have 3 full M's if you like. They're full scales ones. One is called Euclid and that's a dark energy mission. It's going to be looking at this mysterious stuff that appears to be accelerating the universe rather than the universe slowing down as you might expect. The second one is a mission called Plato and Plato is designed to go and look for planets around nearby stars and it does it by watching for so-called transits. If you get the alignment just right, a planet orbiting a star will go in front of the star as seen from your telescope or from the earth and it will make the brightness of the star drop very slightly for a day or so as it transits across for a few hours. So that's 2 out of 3. Third one is solar orbiter, looking at the sun and looking how the sun impacts our environment, and to get the best possible view on the sun, you want to get much closer to the sun. And so, rather than sitting out at the distance of the earth like our current mission, Soho does. Solar orbiter will be going into just a third of that distance. So a much closer in. But also, it's going to rise up above the plain of the planets so we can look down at the sun. Not exactly from above but from a high enough angle that it can see what's happening at the poles of the sun. So those are the three big M's and the last one is a thing called SPICA. And SPICA is actually a Japanese mission and it's a lot like our Hershel space telescope which we launched a year ago. But the big difference to Hershel which is doing fantastic stuff, SPICA is designed to be actually cooled down. The telescope will have refrigerators on it and cool the telescope down to just 6 degrees above absolute zero, so minus 200 - and see if I can do the math - 267 degrees C. And that reduces the background, the emission of telescope itself, and it makes all the instruments much more sensitive. So it's like a super Hershel and we would be contributing the actual telescope plus one of the instruments. So those are our four M's.

Ben - And the L class, the large missions?

Mark - Well there, we have three missions which are effectively all in collaboration with the United States with NASA. One of them is called EJSM, the Europa Jupiter System Mission, going off to Jupiter, studying Jupiter in great detail, but also, flying two orbiters, one around Ganymede and one around Europa. And that's to study those very interesting moons. Those moons have water oceans, we think, under very thick crusts of ice and so, very interesting environments potentially for life elsewhere in our solar system.

The second one is called IXO, the International X-ray Observatory, and this is a big collaboration again with NASA and we're joining forces to build a much bigger telescope which will collect much fainter x-ray photons from the high energy sky, from places like black holes, the extreme environments in our universe where very violent events take place.

Then finally, we have a mission called LISA and LISA's slightly less conventional than the other two. LISA is designed as a mission to detect gravitational waves. So the influence of gravity spreading through the universe from violent events like black holes merging, very high energy events where as the material is converted from matter into energy, you get ripples in the space time. LISA does this in a very interesting way. It puts three space crafts in the solar system, 5 million kilometres apart in the triangle and as these gravity waves pass through the LISA constellation, the three arms between the space craft will change length very slightly as the space time is distorted. And we have this incredibly high precision measurements, measuring this 5 million kilometres to nanometres. So 10^-9of a metre over 5 million kilometres and we do that on three arms simultaneously and by actually seeing how the arms change length, differentially, we can even work out where in the sky that object is. We can go and find it and say, "Right there, at this moment in time, two black holes have just merged and we see this fantastic ringing signal, this big "bong" as the two black holes merge together. So LISA's really odd. Of course, it's also predicated on something we've never detected which is gravity waves.

Ben - They all sound incredibly interesting. They're all answering really important and interesting questions. How do you choose which ones to support?

Mark - Well fortunately, we don't. That's why we have a whole community of scientists who we have in our advisory structures and we consult them and we try to place science foremost. These are very difficult decisions and people have to struggle with their own conscience sometimes and say, "Well, this is the one I really like because this is the area where I work in. I can take a big enough picture and see that this other mission is the one we should be going for." So we have a whole series of committees of working scientists - active people who make recommendations. They pass those recommendations to us and we try to look at them in terms of the programmatics, how long will it take to build, who will we collaborate with, the technologies we need to develop that we don't have yet. So fundamentally, it's a whole series of difficult decisions to make. All of these things, we would like to do. So we're always rejecting good ideas but in fact is a very positive process because it means that you have a robust check that you're doing good stuff.

Ben - Mark McCaughran, explaining ESA's Cosmic Vision.