The Great Exoplanet Debate, part 7: Questioning Exoplanet Missions
watch the video here: https://connect.arc.nasa.gov/p68qflmgnhk/?launcher=false&fcsContent=true&pbMode=normal
Sara Seager: I agree, in terms of where planets come from and when they're formed in the relation to the debris disks that you see, its going to be phenomenal. So we hope that you, if that's what you’re doing, will actually find some really great things for us.
And I just wanted to be pessimistic again. Not for you, but because there is a misconception of why can't we just do better things from the ground. And actually the part we haven't mentioned yet is the atmosphere is really bad, we don't like it at all. Even though we want to find one like that.
Vikki Meadows: We want to breathe it.
Sara Seager: Yeah, we want to breathe it, that's a problem. The best analogy is like when you are swimming in a pool, you look up and you can never see anything really clearly. And adaptive optics is a great way to try and get rid of that. To decode what the atmosphere is doing. But I just wanted you to know that the reason we can't reach Earths is because we don't have enough information to decode the atmosphere. And that really is in the form of a bright star. You need an extremely bright star in order to get enough information going through the atmosphere to know what the atmosphere is doing. Now you could imagine a laser, because there are laser guide stars, generating a really bright star on your own, but the cost of generating a star bright enough would probably be like the cost to put a space mission up to begin with. So we don't think it can reach Earths, but in the terms of the waves of new exoplanets science, I believe that direct imaging is the next wave. And we're actually going to wait to see what it can help us understand about planet formation.
Eric Ford: And also, even if you could find some technology to overcome the variables of doing great adaptive optics, you still have the issue the atmosphere has a lot of water, carbon dioxide. And so it would be very difficult to get the sort of life signatures that you'd be looking for and disambiguate with the Earth's atmosphere.
David Grinspoon: Wow, you stumped us.
Sara Seager: Well, you didn't stump us. So Juno is going to Jupiter and measure the gravitational moments. Hopefully resolve whether or not Jupiter has a core and what the internal structure of Jupiter is. So that may be helpful for us, but again from exoplanets, we're not going to be getting gravitational moments. It’s not really clear what the connection would be to understanding a population of exoplanets and what their internal structure is, versus just wanting to learn about planets for the sake of understanding fundamentals.
Audience: But if Juno is going to understand the formation and evolution of Jupiter, if you're doing a lot of complex modeling of exoplanets, is that going to improve the models and help when you are doing more theoretical modeling?
David Grinspoon: In an indirect way of course. Any understanding of planets, and you know Juno going to help us hopefully understand magnetic fields and how dynamos generate magnetic fields more. And that relates to atmospheric evolution. And so it’s all related. This is Astrobiology; we're all one. But as far as you know, I think, the reason why there was that silence is that it’s in that indirect sense. I don't think that exoplanet people are thinking of that as really a mission that very directly helps them.
Sara Seager: Right, it won't help us directly, but indirectly in terms understanding models of our biggest planet, our biggest sign post. It will be useful that way. But it doesn't have a direct connection, unfortunately.
Eric Ford: The diversity of extrasolar planetary systems is so big that even if the planetary community did a great job of understanding every planet in our solar system, we would still have a humongous task ahead of us.
David Grinspoon: Okay, a question from Shawn.
Dirk Schulze-Makuch: That is absolutely right.
David Grinspoon: Yeah, it may seem like an uphill battle, but of course part of the Decadal process is these townhall meetings. And if we show up and flood the townhall meetings with people that are really passionate exoplanet missions, then I think that would have an effect. Another question.
Audience: Lucy Ziurys, University of Arizona. So I hear this this talk about [how] we'll be able go see molecules in these atmospheres. So I want to know, really over the next ten years, what kind of spectral resolution you can really obtain, realistically. And what spectral features do you really think you can identify conclusively in a planet...
Sara Seager: Are you talking about a habitable planets, or in any atmospheres?"
Lucy Ziurys: Let's just say any atmospheres just to start with. Then you can go to habitable.
Sara Seager: Yeah, good question.
Vikki Meadows: Well, at the moment we can, using transit transmission, detect molecules like CO2, methane, water, in these atmospheres. For JWST we were hoping to get a habitable planet and we would go again after things like CO2 and water vapor and potentially oxygen that’s in the wavelength band. Might be quite challenging. But again, many of these observations to get a single molecule could be several hundred hours. So, it’s challenging.
Lucy Ziurys: Just for the next decade. How well can you do?
Vikki Meadows: Well JWST will be the only thing that can do a habitable Earth-like planet or Super-Earth-like planet in the habitable zone.
Sara Seager: Well, I don't know. I mean, the best example now, let’s leave the hot Jupiters aside. There's this planet GJ 1214b, which is kind of a mini-Neptune. Some people call it a Super-Earth, whatever. But in that case, things have really been happening from the ground. Although it’s only one object for now. As we speak, pretty much anyone with any big ground-based telescope is trying to look at this thing. And in terms of spectral resolution, they just clued in to the fact that one or two transits won't cut it. And they need like ten or fifteen; they could really make progress in identifying molecules. Now which molecules? Water is a good one to think about because water is very spectroscopically active and it’s ubiquitous. The other ones that have been mentioned are maybe methane. The spectral resolution may be, I don't know, twenty.
Vikki Meadows: Filter bands.
Sara Seager: Yeah. People are trying to do spectrophotometry. So its sort of a more in-depth discussion, but I think it will be really great from what we can do from the ground on bright objects. We just need more Super-Earths to be discovered that we can actually observe.