The multibillion dollar HDST would be a game-changer, and if it advances beyond the concept phase, it would launch in the 2030s. With a mirror 25 times the size of Hubble's, HDST could delve deep into the universe's past to trace how gasses enriched with the elemental ingredients of life moved in and out of galaxies.
HDST also could examine dozens of Earth-like exoplanets that are too tiny for Hubble and its immediate successor, the James Webb Space Telescope, to see. HDST would scour their atmospheres for signs of alien life, perhaps finally answering whether or not we are alone in the cosmos.
The vision for the HDST was described in a July report spearheaded by the Association of Universities for Research in Astronomy (AURA), a consortium of global institutions that operate astronomical observatories.
The Kavli Foundation hosted a Google+ Hangout to learn more about HDST's promise from Julianne Dalcanton of the University of Washington, who was co-chair of the AURA committee, and committee member Marc Postman of the Space Telescope Science Institute. (Due to technical problems, committee co-chair Sara Seager, from the Kavli Institute at the Massachusetts Institute of Technology, was unable to join the Hangout.)
These scientists answered questions about how HDST will trace cosmic evolution, from the primeval rise of chemical elements necessary for life to the potential for alien life right in our cosmic backyard, as well as how to build such a powerful instrument.
More details about the participants are as follows:
- JULIANNE DALCANTON – is a Professor in the Department of Astronomy at the University of Washington and the other co-chair of the HDST study. Her research focuses on the origin and evolution of galaxies.
- MARC POSTMAN – is an Astronomer at the Space Telescope Science Institute (STScI) and served on the committee for the HDST report. His research interests include galaxy cluster and large-scale cosmic structure evolution and formation, along with large space telescope design and implementation.
- ADAM HADHAZY (moderator) – is a freelance science writer who chiefly covers astrophysics and astrobiology. He has a Master's degree in science journalism from New York University.
Below is a modified transcript of the discussion. Edits and changes have been made by the participants to clarify spoken comments recorded during the live webcast.
THE KAVLI FOUNDATION: What drew each of you to the High Definition Space Telescope (HDST) project and how will it impact your work?
JULIANNE DALCANTON: I’ve been a heavy user of the Hubble Space Telescope for more than a decade. It's a fantastic machine, and I still can't believe some of the things that we've been able to do with it. But with every machine that you use, you always reach the limit sooner or later. You always know what it could do better. The more you use the Hubble, the more exciting ways you find to use it, and the more it occurs to you about just how much more we could do if we had that next thing.
Now there's also a big element of paying it forward. I was in graduate school when the Hubble Space Telescope was launched. Shazaam! There it was, and I could use it, and I could do science, and it was fantastic. But these things don't magically appear. You don't go down to Walmart and pick up a telescope and then just launch it. It takes decades of planning in order to make this happen. And so, those of us who have benefitted from all of the work that our predecessors did really owe it to start thinking about what is the instrument that we want to have transforming astronomy decades from now, so that future generations of students will have the same experience that we had.
MARC POSTMAN: I have a very similar sentiment to Julianne. I remember the first Hubble image I got for my own research, which was so dramatically better than any of the ground-based data I’d had up to that time that I spent the entire day just staring at the image.
We've done great with Hubble, and James Webb is going to take us quite a bit further. But when you look about where we need to be in the 2030 era, you realize that as great as Webb will be, and as great as many of our big ground-based telescopes will be, there is still a lot of clarity and depth that we're going to need that we just won’t have a telescope for. So that’s why we are thinking about this one. In particular, if you really want to look for those Earth twins around other stars, you're also going to need a telescope that can really see very faint things. You're going to need a telescope that can see planets when they're very close to very bright things, like the stars they are orbiting, and be able to dissect these planets' light to see what they’re made of.
TKF: That’s a good segue into how sharp the High Definition Space Telescope’s cosmic vision will be compared to the Hubble Space Telescope's. Here we see some simulated images of the same galaxy located 10 billion light years from Earth. On the left-hand side is how this distant galaxy looks through the Hubble Space Telescope. It’s all chunky and pixilated. Now, on the right-hand side, a super-Hubble Space Telescope can see the galaxy’s whirling spiral arms in exquisite detail, plus make out a dwarf galaxy off to the right. With sharper images like this, what kinds of questions will the High Definition Space Telescope allow us to answer that we don’t have the ability to answer currently?
DALCANTON: The question is where do we start and where do we end. We can talk about what the High Definition Space Telescope might transform for days.
TKF: Let's hone the question then to how a next, next, generation space telescope could someday answer the question of, “Are we alone in the universe?” How will looking back, deep into cosmic time, help us learn more about actually how life arose in the universe?
POSTMAN: One of the things that we can credit Carl Sagan for making us all aware of, is that every atom and molecule in our own body was once in the center of a star somewhere. All the atoms heavier than, essentially, hydrogen and helium were made in the cores of stars. So the main ingredients for life are all created in the cores of stars, and also during the phase when stars end their lives. The big question of how life is distributed throughout the cosmos is intimately tied to how do those atoms, like carbon and oxygen and nitrogen, get out into interstellar space. How do they form solid bodies on which life can ultimately take root, and what's the big connection between that astronomical process and then the biological processes that lead to life?
Understanding that whole story is what we're trying to do here. There are key bits in galaxy evolution that we think happened, but we don't know for sure because we haven't directly observed them. One of those key processes is how does gas that carries those elements away from stars like oxygen, nitrogen, and carbon, how does that enriched gas tend to leave galaxies and stars, and then fall back into them? Following that flow is something we'd love to be able to do, and we’ve been doing it a little bit with Hubble, but only in very small bits and pieces. HDST would allow us to visualize that whole process directly.
DALCANTON: The story goes back even further. It's not just the processes that happen near a star in the evolution of stars, but how did we even get stars in the first place? We only got stars because enough material made it into a galaxy and got close enough that it combined together into stars. That takes us further and further and further back into time. Now, James Webb will revolutionize our view of some of the very youngest, most distant galaxies. But that still leaves billions of years of cosmic time over which we're trying to understand the processes even leading to the step of getting the stars you need to host planetary systems, and to build the elements you need in order to develop planetary systems.
So with the precision of the view that you would get with HDST, we can actually resolve out the scale over which regions turn into stars. Right now, as you could see in the Hubble image, they were just these pixelated, blurry regions. These regions were a little blue in color, so we're pretty sure that's a region where stars form. But with HDST, we should be able to resolve out the actual subunits of the little regions, and galaxies, where stars form. We'll also be able to do that absolutely anywhere it occurs in the universe it occurs, which is remarkable and transformative.
TKF: What are some of the biggest engineering and technical hurdles to building a super-Hubble?
POSTMAN: One of the key things we want to do is to be able to image Earth-sized planets in habitable zones around other stars in the galaxy. A habitable zone is this region which allows water to exist in a liquid state on the surface of the planet, and we think that's important for making the probability of life a lot higher. To be able to do that you're looking for a very faint planet, a planet like the Earth. If we were to go 50 light-years away from Earth and look back at the Sun, the Earth only shines by reflective light, and we'd see this little star that was the Sun, and then we’d see a tiny dot that was 10 billion times fainter than the Sun sitting right next to it. That would be the Earth.
So the challenge for looking for life is we've got to suppress the bright glare of a star that's 10 billion times brighter than the planet you're trying to see. One of the big technical challenges is to build an instrument able to do that, and such instruments are called coronagraphs. Right now the state of the art of coronagraphs is they can probably do that starlight suppression by a factor of 10 million instead of 10 billion. So there's a bit of a step there—almost a factor of a few hundred in performance that we need to get to that level. Now, there's been a lot of progress made. People think they know how to design devices that will do this. So we need to now take it from the conceptual phase to actually building something.
The other challenge that goes hand-in-hand with coronagraphs is that you need the telescope to be very stable and not be changing its mirror positions, or its alignment, while you're doing that starlight suppression. It's remarkable how stable the telescope has to be, and that’s also, probably, another factor of a hundred improvement over where we are today in terms of current stability on space telescopes. So I think those are the two biggest challenges that we have to overcome.
TKF: Taking a viewer question—how are we going to get a mirror that is around 12 meters in diameter, as is proposed for the High Definition Space Telescope, up into space?
POSTMAN: The bit about the big mirror is not as much of a challenge, it's a technical detail.
DALCANTON: Marc has talked about some of the technical challenges in the project, but one of the things, while discussing it that we tried to look at were ways that we could take advantage of things that NASA already knew how to do. JWST is being built out of a collection of hexagonal mirrors that fit together like puzzle pieces to make one larger mirror. But the problem is you can't make a single mirror that’s any bigger than the width of the interior of your rocket. So with the launch of JWST, it's going to be folded up and then tucked inside a rocket. There are other ways you could do this if you had a bigger rocket. But the concept with HDST is just to put more hexagonal segments around something that's like JWST, then you fold it up and it unfurls in space.
POSTMAN: With the kind of rockets that are even available today, we already have a design using the same sort of unfolding mechanism that James Webb uses that would allow you to build a mirror like what Julianne just described and launch it in an existing rocket using the same kind of deployment scheme that James Webb will use. While we haven’t actually done that yet, it's a technology that's very derivative of something we already know how to do.
TKF: How could the High Definition Space Telescope be used for studying objects in the Solar System, such as the moons of Jupiter and Saturn that might harbor subsurface oceans?
DALCANTON: The Solar System is a very dynamic place and it's an incredibly interesting place. So in planetary astronomy, the best thing you can do is send probes to go off to visit things and get really close to it, like with the beautiful pictures we've seen of Pluto recently, and orbiters around Mars. For things like studying oceans on the moons of Jupiter, it would be great if we could actually go there, but that takes a long time.
"With HDST, we would have the resolution to watch anything in the Solar System even without going there. You could actually get to about 25 kilometers, I think, in terms of resolution on Jupiter, and could see features the size of Manhattan at the orbit of Jupiter. So you could see geysers, you could see volcanoes."—Julianne Dalcanton
The telescope is also very sensitive at ultraviolet wavelengths of light. We think that in the same way we have Northern Lights and aurorae on Earth, we see the same phenomena happening on other planets. With HDST, you can actually watch that occur with exquisite resolution.
I don't think HDST is a substitute for actually visiting the planets and NASA should continue to have a strong planetary program. But at the same time, you would be able to see phenomena, I think, that would help motivate us where we want to go to next in the Solar System.
With HDST, we would have the resolution to watch anything in the Solar System even without going there. You could actually get to about 25 kilometers, I think, in terms of resolution on Jupiter, and could actually see features the size of Manhattan at the orbit of Jupiter. So you could see geysers, you could see volcanoes.
POSTMAN: Yeah, I think that's right. The other thing is, we know New Horizons just flew by Pluto and it’s now heading out beyond Pluto to a couple of other very distant things we call Kuiper Belt objects. They are probably the most pristine, original material of which the Solar System was created. So being able to understand how many things like that are out there, and what they're made of is very key to understanding the Solar System. These objects are very faint and they’re very small, so you either need to go there, like New Horizons is doing, which you can't do that often, or you need a big telescope to try to see them. Studying those very distant and small bodies that are orbiting beyond Pluto is another area where HDST would really be able to do some very interesting observations.
TKF: Taking a step back, why are we talking about a telescope that won't launch until the 2030’s at the soonest? We could have five US presidents before this telescope is ever going to enter space. Why do the AURA report now?
POSTMAN: These are big, multibillion dollar projects, and they take a lot of planning, and in some cases technology development. NASA's doing more than one thing at a time, and so, it has to spread out how it invests its science funding—it can't all go to one project. As a result, these things do tend to take a couple of decades to go from the initial concept phase, to the initial design phase, to the construction phase and, ultimately, to launch and operations. I wish we could do it quicker, but we have lots of things that will keep us busy in the interim, so I think given that reality, you have to start now to think about what you want 20 years from now.
DALCANTON: I think another area where it really helps is in terms of if you have an idea of what your goal is you can start developing the technology now. So in the same way you're not going to retire until you’re in your 60s or 70s, barring the lottery, you start making plans now about what you have to do, such that you can eventually reach this goal at some time in the future.
TKF: How will the High Definition Space Telescope be our best scope yet at finding evidence of little green men, women, or whatever, and even better than the biggest ground-based observatories we'll have in the 2030s?
POSTMAN: HDST will be a significant advance over any telescope we have now or even on the ground in the next decade, and there’s a number of reasons. One of which is in order for ground-based telescopes to achieve their clarity they have to correct for the atmosphere, which is making the starlight twinkle. Every 10 or 20 seconds it does something different, and you don't have that in space. Even if scientists can correct for that, that correction on the ground is just not enough to be able to do that kind of one-part-in-10-billion, starlight glare suppression that you'll need to do to see an Earth-like planet around many different kinds of stars. HDST will have that stability, and capability, to see hundreds of star systems.
Now, it's not to say the ground won't be able to observe some stars in this manner. The ground probably will be able to study pretty cool stars—and by "cool" I mean low-in-temperature stars, small stars—and perhaps detect the planets in habitable zones around there, but only for maybe a handful of cases.
If we're trying to actually look for life, if you look at Earth's spectrum, you can see our climate in the atmosphere. You also see these signatures that life is present—you find evidence for oxygen, and methane, and water all coexisting in the spectrum the same time, which is a pretty strong indicator that there's some biological process going on. If you're on the ground looking through that same atmosphere that's full of these biosignatures, you have to first subtract all Earth's biosignatures out of the way before you see the ones on the exoplanet. That's not easy to do, especially if you're looking at another planet like the Earth. If you're in space, you don’t have that problem because you're well above the atmosphere.
Then once you're in space, the number of planets you can look really increases dramatically as you make your telescope bigger. So we thought about a telescope that would be able to find dozens of potential Earth-like planets around other stars, and that's why we picked the size we did for HDST.
DALCANTON: Just to add in, we would have loved HDST to be 20 meters across, or 30 meters across, but at some point you just can't pack it in to rocket. There's only so many suitcases you can put in your trunk, and there's only so much mirror you can fold up inside a rocket.
"The 'Carl Sagan Space Telescope' is something I’ve contemplated. He was one of the first people to think about studying the atmospheres of the planets in our Solar System, and then how that might be useful for looking at planets in other star systems. So it's certainly a very worthy namesake for such a telescope."—Marc Postman
TKF: There's time for one last question here, and this may be the hardest one, so just warning you. Most major space telescopes are mainly named after famous scientists like Edwin Hubble, Enrico Fermi, Lyman Spitzer, or important figures in space research like James Webb, a former NASA administrator. If you were to offer suggestions for the High Definition Space Telescope's official name down the road, what would be your top choice?
DALCANTON: I would think "Sagan" would be a contender.
POSTMAN: I would agree. The "Carl Sagan Space Telescope" is something I’ve contemplated. He was one of the first people to think about studying the atmospheres of the planets in our Solar System, and then how that might be useful for looking at planets in other star systems. So it's certainly a very worthy namesake for such a telescope.
DALCANTON: I've come to exactly the same conclusion. I think that’s a very natural name. The only question is if something like this wasn't to launch until the 2030s, someone else may have snatched up the Sagan name beforehand. I don't know if we can save it that long.
TKF: I think it does have a nice ring to it, the "Sagan Scope," or even the "Super-Sagan Scope!" We’re going to go ahead and wrap up. Thank you very much for your time today.