We’ve spent the last few weeks talking about different ways astronomers are searching for exoplanets. But now we reach the most exciting part of this story: actually imaging these planets directly. Today we’re going to talk about the work NASA’s Spitzer Space Telescope has done viewing the atmospheres of distant planets.
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Announcer: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit Astronomy.SWIN.edu.au for more information.
Fraser Cain: Astronomy Cast episode 367, Spitzer Does Exoplanets. Welcome to Astronomy Cast, our weekly fact-based journey through the cosmos. We help you understand not only what we know but how we know what we know. My name is Fraser Cain and the publisher at Universe Today. With me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of CosmoQuest. Hi, how are you doing?
Dr. Pamela Gay: I’m doing well. How are you doing, Fraser?
Fraser Cain: Good. I wanna shamelessly self-promote something this week.
Dr. Pamela Gay: This is unusual in what way?
Fraser Cain: Are you kidding me? No. I never self promote. I –
Dr. Pamela Gay: No, I adore you. I just remember when your Phases of the Moon app came out, which is an awesome app, but you used that sentence a lot.
Fraser Cain: Yeah, so I’m now gonna shamelessly promote my Patreon Campaign. So you can go to Patreon.com/UniverseToday and you can kick us a couple of bucks every month. And that makes – that goes for making Universe Today. We remove all the ads from Universe Today from you. You get advanced access to all the cool videos that we’re doing. I’ll follow you on Twitter. I will – we shout out in the videos that we record your name.
And seriously, it makes a huge, huge difference. The ads suck and being a way that we can actually just work directly for the fans who love the stuff that we do, that means the world to us. And so this is the future. I think it’s just fantastic for all the people. I really wanna thank all the people that have already supported me. And I would love it if you could kick a couple of bucks our way. And –
Dr. Pamela Gay: And after you kick a couple of bucks to him, you need to also go sponsor the Patreon Campaign for learning space because we use Patreon to fund all of our teacher professional development. So you can help pay the salaries of Nicole Bracey and Nicole Glucci, whose name I finally know how to pronounce, and they will turn your money into helping teachers get science into the classroom. We will not follow you on Twitter. We will instead educate the world. It’s a different priority but we can keep up better with teachers than with Twitter.
Fraser Cain: And we are going to be doing a Patreon Campaign for Astronomy Cast shortly so stay tuned for that. And all hail Patreon.
Dr. Pamela Gay: Yes, yes.
Fraser Cain: If you’re a creator I highly recommend –
Dr. Pamela Gay: Cole Palmer, if you’re listening, thank you.
Fraser Cain: Yeah, absolutely. All right. Let’s get rolling with the show today.
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Fraser Cain: So we spent the last few weeks talking about different ways the astronomers are searching for exoplanets. But now we’ve reached the most exciting part of the story, actually imaging these planets directly. And today we’re gonna talk about the work that NASA’s Spitzer space telescope has done viewing the atmospheres of distant planets.
All right, Pamela, so we’ve talked about Spitzer a bunch of times. We’ve talked about Spitzer in terms of just infrared astronomy. We talked about the actual just the telescope and what happened with the telescope. But let’s really focus in on Spitzer’s work for observing extrasolar planets and then maybe what the future holds for this method of looking at the atmospheres of planets.
Dr. Pamela Gay: So I’d like to start by clarifying that when we say directly imaging exoplanets, what we mean is getting spectrum of their atmospheres. So Spitzer is allowing us to directly detect the characteristics of exoplanets from wind speeds to what their atmospheres are composed of. But we can’t look at a planet and say it’s blue or it’s green so –
Fraser Cain: No, that’s what I said. That’s exactly what I said.
Dr. Pamela Gay: So, yeah, the Spitzer space telescope launched back in 2003. We did an entire episode on the dude it’s named after. We did an entire episode on it. And it was originally designed to see very red waves of light, the far infrared. And to do that it needed the liquid helium onboard. And as it was designed to do, overtime it used up all of that liquid helium.
And in May, 2009 this glorious space telescope warmed up. But it only warmed up so far as it can still see into the infrared, just not as far into the infrared. And because they were planning for this to happen they designed the spacecraft with instruments that can still work now that it’s a little bit warmer. And some of those detectors include spectrographs that are capable of detecting atomic and molecular lines from other stars and apparently other planets.
Fraser Cain: And last episode we talked all about spectroscopic lines and how a spectrograph is laid out and how you build a room that you display the rainbow of the light from a star. Spitzer doesn’t have a room to do this so what is the instrument like on Spitzer?
Dr. Pamela Gay: Well, so different types of spectrographs have different purposes. The ones that we were talking about last week are extraordinarily high resolution in order to determine exactly how fast a star is or is not moving. This means that when we look at its lines we can use spectrographs like that. If there are two different versions of the same atom side by side, for instance different versions of lithium, we can see those differences. If there are two difference versions of a molecule like different versions of magnesium hydride, which I’ve studied in the past with a [inaudible][00:06:43] spectrograph, we can see those different versions.
That high, high resolution is what allows us to see little-ler, not little but little-ler planets yanking around on little stars and big planets yanking around on big stars and everything in between. But once we know there’s a planet there we can do something else. We can also start trying to separate out the light from the star and the light from the planet. And telescopes like the one that is used at Lasil for harps, they don’t really do that so much because the light from the star as seen in optical just totally drowns out the light from the planet.
But with Spitzer looking in the infrared, planets, they’re really good at absorbing heat and reradiating it in a variety of different ways. And stars aren’t usually quite as bright out in the infrared as they are in the, well, bluer wave lengths of light. So with Spitzer we have this fabulous combination of we’re looking in the colors that planets are brightest and stars are fainter. And this allows us to start to make out the light of the planet entwined with the light of the star.
Fraser Cain: It’s weird to think about that idea that the star is less bright. You know what I mean, right? Like because you just imagine, if it’s like a bright star it’s just gonna overpower everything we see because of its sunlight and because of its visible light. But, I mean, obviously stars do radiate in the infrared as well but they’re pushing a lot of that into the visible light, into the x-rays and so on. And so it’s actually quite funny that you can sort of split the difference between the brightness of the planet and the brightness of the star when you push into that infrared spectrum.
Dr. Pamela Gay: And this all goes back to – again, we did an entire episode on this – it goes into black body radiation. The color of light where an object gives off the most light is directly related to the temperature of that object. So this is partially why really hot stars are bluer and really cold stars are redder. Those wave lengths are where the peak intensity from the stars are.
Now with the black body intensity it’s kinda like it tapers off toward zero going towards longer and shorter wave lengths, and you have this beautiful asymmetric curve. We take advantage of that curve when we use the Spitzer space telescope. And we also take advantage of transiting planets. So you do have to have, not necessarily a planet that passes directly in front of the star, but you need a planet that passes directly behind the star.
Fraser Cain: Whoa. So it’s the opposite of a transit. It’s an opposite. What do they – then what do they call it when the star – eclipsing? What do they call it when the stars go in front of the –
Dr. Pamela Gay: The planet has been eclipsed by the star.
Fraser Cain: Has been – or an occultation?
Dr. Pamela Gay: Sorta kinda.
Fraser Cain: Yeah, like when – no, I guess not, when a moon passes in front of the star that’s an occultation. Anyway, so can you explain that then? So let’s explain that. Why when the planet passes behind the star can we tell what the planet’s atmosphere is?
Dr. Pamela Gay: Well, it’s because we have to do subtraction. And what we really need is that clean spectra of the star. We can observe the combined light of the planet and the star even if the planet isn’t directly in front of the star. So if they’re side by side as long as that planet is radiating both heat emission from – well, it absorbs it, it’s now giving it off like Jupiter does. Jupiter gives off more energy than it receives from the sun so you have a nice hot Jupiter. It’s giving off more light than it’s receiving and it’s heated up anyway so we have a nice really warm object.
Stick that right next to the star or in front of the star and you now have the combined spectra of planet plus star. Now we unfortunately aren’t in the situation where we can readily just go, let’s erase the star by looking strictly at the planet. That requires a chronograph. As we’ve discussed, we don’t really have super awesome chronographs yet. We’re getting there. There are a few good ones. We have some direct images of planets but not good ones.
So Spitzer doesn’t have a chronograph and so the best we can do is wait for that planet to duck behind the star. And when the planet is behind the star we’re not seeing any of its light. We get a clean spectra of just the star. We now take the spectra of star plus planet, subtract spectra of star, we are left with spectra of planet.
Fraser Cain: So what’s the process then? How do the astronomers choose which objects to point at? How do they know there’s gonna be a planet there to observe?
Dr. Pamela Gay: Well, they’re either looking at something where we already know there’s a planet via the transit method or it’s a survey object. A large number of scientists have said, I’m going to search – and this is why we originally started getting into this game with objects like 51 peg and the signus binary system – I’m going to look at sun-like stars or at least stars that are very high in metals. Metals make planets. And I’m just gonna look at them with the Doppler method to look for the wiggles that are related to a planet being there. Add in transit surveys, we have Crow, we have Kepler. Throw those in. Throw in the random person in their driveway with their 4″ reflector or refractor getting lucky with awesome photometry. And we’ve started to find planet after planet after planet.
Now we’re not in general going to do that sort of survey work using a space telescope. But once planets have been identified via some other means we can start doing follow-up observations with Spitzer. Now there’s also scientifically interesting objects that they’re going to be doing high resolution spectrograph – spectroscopy of.
And occasionally we get into really lucky situations where we knew there was one planet that we’d found via some method. And then once we start subtracting that star off we realize, wait, there’s other things there as well.
Fraser Cain: Right. I mean, so they typically identify the targets using some other method be it they use the transit method, the rate of velocity method, people find them from the ground. They find this candidate and then I guess if it meets a certain kind of criteria, they think, okay, this is the kind of thing that we can observe with Spitzer.
Dr. Pamela Gay: So ideally what they’re going to start by chasing is the hot Jupiters. These are the objects that are, well, like their name says, gas giants similar to Jupiter. But the hot part means that quite often they’re in orbits that are far smaller than the orbit of even Mercury.
Fraser Cain: Yeah, right.
Dr. Pamela Gay: So you’re looking at a Jupiter-like object snuggled up so closely to its sun that in some cases it actually raises title forces, waves on the surface of both the star and the planet.
Fraser Cain: Got it. And so what kinds of planets then has Spitzer taken a look at? I mean, there are some pretty crazy planets.
Dr. Pamela Gay: Well, there are some pretty crazy planets. You have – well, like I hinted to, you have these hot Jupiters that are so close to the planet that they’re orbiting that they actually essentially pull up a plasma wave from the surface of the star that as the planet orbits, this wave follows around on the surface of the star. You end up with planets that are essentially leaving behind tails of material as the radiation of the star they’re orbiting pushes off the planet’s atmosphere.
Then you also start finding things that we should’ve thought about as existing ahead of time but at least I know I never read about them in journal articles prior to reading about Spitzer observing them. You end up with what we look at as small rocky worlds for probably nothing more than the left-behind remnants of, well, a gas giant that is a gas giant no more.
Fraser Cain: That’s crazy. Yeah, I mean, the most recent – some of the most recent observations, right, I was mentioning at, right, that they’ve turned – or they found objects which are like mini Neptunes that have had the outer layers blasted away and turned into a super earth potentially.
Dr. Pamela Gay: Exactly.
Fraser Cain: So that’s just kinda mayhem. So, I mean, how do you get a planet that’s in that kind of an extreme environment – how do you get a planet that’s so close – I mean, I’m envisioning – I don’t know if you’ve seen these pictures of the rings from Cassini where you see these little shepherding moons that are moving within the rings. And they’re pulling this title, almost a gravity wave; they’re pulling ice particles towards the moon as it moves around. And then I guess as the moon moves away then the particles fall back into their place.
And I guess that’s the same thing, right, that as this planet is going around the star there is like this super tide that’s getting pulled up towards it. How do you get this?
Dr. Pamela Gay: I love it when you ask me questions that if I had a complete answer for I could say, hand me my Nobel Prize please. We don’t really know, is the answer. And when we first started finding hot Jupiters, I remember listening – I unfortunately can’t remember his name, it was an Israeli planetary theoretical planet model or awesome dude who was just like, we didn’t calculate this to begin with. This was not – to paraphrase horribly a conversation that occurred in the early 2000s, no one ordered this up.
We had kind of assumed the planets mostly form where they are or they migrate a little bit due to gravitational interactions. But this migrating all the way in toward the sun and stopping – it’s the stopping that’s the mystification part. So there are various ideas. One of the ones that I like the most – this doesn’t mean it’s the most likely, it’s just the one that – there’s a whole lot of them out there. We don’t know which is right.
The one I like the most is you have the sun, when it’s very young it’s a blasting evil little star screaming in x-rays and other shades of light. And it blasts out the solar nebular around it as part of ending the star formation. So basically you have stuff collapsing. Stuff collapsing star at night. Star starts giving off light. The light pressure then starts pushing stuff away so the in fall stops.
You then have cleared out at least some of the region around the star. Around that you have the solar nebula, stellar nebula if it – whatever you wanna call it. We always call it a solar nebula. And planets are forming in that. And for reasons we can’t fully articulate, some of these planets are not pleased to stay where they are and they start migrating towards that star.
And either they stop because they stop absorbing matter and stop having frictional interactions when they hit the inner rim of that planetary disk and we have no real observational evidence of things clearing a spiral instead of clearing the ring, they stop for some reason.
So for some reason, it probably has to do with frictional dynamics, they get dragged in and then they stop and don’t fall in for reasons we don’t fully articulate. One of the theories put forward is the sun cleared up that [inaudible] [00:18:57] region.
Fraser Cain: Or magic.
Dr. Pamela Gay: Yeah, something devised in a computer. If you’ve read Cybermage, magic is mediated by servers and I’m good with that.
Fraser Cain: And a lot of these planets are also tidally locked to their stars, right, and so they get these ferocious winds that blast across the planet too.
Dr. Pamela Gay: And what’s awesome is with Spitzer they’re actually able to get a sense of how wide the atmospheric lines are. And the cool thing with rotating worlds, rotating stars, things that rotate is as that rotating object, one side of it’s going to be coming towards you and being blue shifted. The other side’s going to be moving away from you and being red shifted. And of course the middle is moving perpendicular to you so there’s no shift perceived.
And this whole rotating body ends up creating a thickening, a broadening of that spectra line and it gets broader the faster that sucker is spinning or the faster the winds are blowing, the faster the convective cells in the atmosphere. And we can see that and we can see, oh dear God, I don’t want to be on that world.
Fraser Cain: That’s amazing. That’s crazy that you can detect –
Dr. Pamela Gay: It’s awesome.
Fraser Cain: I know it’s awesome, right, that you can detect the speed that it’s rotating, the speed of its winds, how long it takes to go around, the composition of its atmosphere, what it’s probably made out of based on the atmosphere and all this kinda stuff without really – as we said, you’re not looking at it. You’re just having all of these indirect observations based on its spectra. And this is – like spectroscopic analysis has gotta be just the greatest tools that astronomers have at their disposal.
Dr. Pamela Gay: It’s also the most boring set of images you can possibly look at.
Fraser Cain: Just looking at these lines [inaudible] [00:20:53] –
Dr. Pamela Gay: I studied – as I said, I studied magnesium hydrate stars. And you can go read the paper. It’s in ADS. And that was by far the most boring thing I’ve done in my entire life. And I studied variable stars.
Fraser Cain: Right. That sounds a little brighter. Now it’s a little dimmer. Now it’s a little brighter. Now it’s a little dimmer. Yeah.
Dr. Pamela Gay: Right. So what’s awesome about this is beyond just being able to say, wow, that world has really fast convective cells in its atmosphere. We can also say, wow, that planet – we can start to see water. We can start to see – we haven’t yet found free oxygen in the atmosphere but this has actually led to a whole body of research on what chemical composition, what chemical fingerprint in an atmosphere means there’s life.
And I actually have a bet with Seth Shostek, who periodically forgets we had this bet because it was over dinner and there may not have been only food consumed. But Seth Shostek from the study institute and I have a bet on I say we’re going to find life on other worlds first by detecting the chemical composition in a world’s atmosphere rather than by detecting radio waves.
Love the Allen telescope. It does more science than just listening for little green dudes. But I really believe it’s in telescopes like Spitzer that we’re gonna find life on other planets.
Fraser Cain: And you and I, we’re in complete agreement and this is why –
Dr. Pamela Gay: Yeah.
Fraser Cain: — we have advocated for literally the entire time that we have being doing Astronomy Cast together that there should be some kinda super powerful telescope designed to observe the atmospheres of distant worlds.
Dr. Pamela Gay: Yeah.
Fraser Cain: Build this telescope, answer the question. Don’t you wanna know the answer to this question? Just build us a telescope, please.
Dr. Pamela Gay: And James Webb space telescope will have the capacity to go beyond what Spitzer’s doing and do the job better with bigger mirror, yeah.
Fraser Cain: Yeah. So, yeah, [inaudible] [00:22:56] talk about next, right? Yeah, so let’s talk about James Webb. That’s the next – it’s gonna – I mean, with Spitzer it’s been – there haven’t been a lot of observations, right, there haven’t been a lot of planets they’ve really been able to observe with Spitzer. James Webb is gonna take us to the – it’s not like Kepler delivering thousands and thousands of planets, right?
Dr. Pamela Gay: Well, Kepler’s discovery discovered the planets mission. Spitzer is a follow up on just the right ones and get extraordinary amounts of data. So the way to think of it is going along and identifying with a metal detector where all of the bits of metal on the beach are and dropping a little piece of plastics saying, hey, there’s a piece of metal here. And then where the biggest pieces of metal are, someone else comes along and digs up, well, Black Beard’s treasure, I don’t know.
Fraser Cain: Yeah, exactly. So let’s talk about James Webb and maybe some other methodologies that can use this technique to find the same thing.
Dr. Pamela Gay: So with Spitzer space telescope it’s a .85 meter, a 2’9″ mirror. So that’s a fairly small, yeah, 2’9″, yeah, it’s like [inaudible] [00:24:12] –
Fraser Cain: Yeah, [inaudible], yeah.
Dr. Pamela Gay: Yeah, it’s not big. I – my hair is probably about that length. So with the James Webb space telescope you’re looking at a multi-meter mirror that you and I could probably – the two of us manage to span across. That’s a bit bigger. And –
Fraser Cain: Yeah, it’s a gigantic – have you ever seen the model, the [inaudible] –
Dr. Pamela Gay: I saw it with you. We were both there together.
Fraser Cain: Oh, right, right, right. I always forget. That’s right, we were there together at the model and it was gigantic and [inaudible] –
Dr. Pamela Gay: Yeah, so when we were at South by Southwest a couple of years ago and we posted a bunch of photos of it.
Fraser Cain: That’s right. I remember now.
Dr. Pamela Gay: Sorry, I had to make fun of you.
Fraser Cain: Yeah.
Dr. Pamela Gay: So, yeah, if you go see, as Fraser and I have done together –
Fraser Cain: — together as a team.
Dr. Pamela Gay: — the James Webb space telescope is big. It’s slated to be – I’m looking up the number – it changed size at one point and I wanna not lie about how big it currently is slated to be. And I was going to [inaudible] [00:25:19] I looked up the number. It’s currently slated to be 6.5 meters across and I believe that that number will actually stick. And –
Fraser Cain: So that’s – I mean, Hubble is 3 meters? No. No, 1.6 meters, 2 meters? It’s around that area, Hubble.
Dr. Pamela Gay: Right. So this is substantially bigger.
Fraser Cain: — bigger, yeah. And bigger means better, like better –
Dr. Pamela Gay: Yeah, something like that.
Fraser Cain: That math sorta holds, yeah.
Dr. Pamela Gay: So in this case the bigger means better actually does apply. It doesn’t always apply. Harps is on a small telescope. It does awesome work. But with James Webb it takes what Spitzer’s able to do with the small mirror and goes, hey, we can see fainter stuff which means that they can look at the same stars but at a greater distance and increase the number of stars that we’re going to be able to see and detect the planets on.
So, you still have the problem of the planet needs to be transiting. You still have the problem of the planet needs to be hot enough and you don’t have a coronagraph. But the number of things that you’re able to now look at because you can see fainter objects, which means you can see things that are further away, it’s gonna increase our sample size. It’s gonna increase the number of things we’re able to look at. It has that spectrograph onboard. I believe it’s of a higher resolution. The truth will be in the pudding once the sector’s launched and hopefully deploys correctly. It better deploy correctly.
But this is – both Spitzer and James Webb space telescope are telescopes that in the long history of instruments like Hubble and ground-based instruments like Palomar even, these are systems that are designed to answer a myriad of fundamental questions. Hubble was put up to help figure out the expansion rate of the universe and what the heck planetary nebula are, as well as many other things. But Planetary nebula was a real problem when Hubble launched. We just couldn’t understand them.
Fraser Cain: Still don’t have that fully figured out either but, you know –
Dr. Pamela Gay: But we’re a lot closer.
Fraser Cain: Yeah.
Dr. Pamela Gay: James Webb space telescope is going to help us get back to the beginning of the universe when it comes to looking at galaxies forming. But it’s also going to help us with the nearby universe, helping us understand the formation of planets, the atmospheres of planets. And when I say planets I finally get to mean things more than a few light years away.
Fraser Cain: Yeah, yeah, it looks – are there any potential ground-based observatories that are gonna do this work as well?
Dr. Pamela Gay: Well, what you start to run into with ground-based is as you look further and further into the infrared our atmosphere becomes a insert-all-the-expletives.
Fraser Cain: Right.
Dr. Pamela Gay: We have –
Fraser Cain: [Inaudible][00:28:00] wall.
Dr. Pamela Gay: Yeah, we have these evil things known as water molecules in our atmosphere. And it gets a little bit easier when you get into the high altitude deserts where most of the moisture in the atmosphere is below you and not actually there because you’re in the desert.
Fraser Cain: Um-hum.
Dr. Pamela Gay: Even in Hawaii though at high altitude where you’re looking down at oceans and clouds, even there it’s substantially better but it’s still there. So you really have to be up in space just like Spitzer. The problem with space is you eventually run out of helium and you do require helium cooling on these systems. But there are long-term missions you can do just by blocking light. And James Webb has that amazing and weird solar shield. And when it deploys it will keep everything in shadow and hopefully keep everything cool.
Fraser Cain: They’re gonna be busy with – James Webb’s gonna be busy so don’t count on it being – spending a lot of time looking at planets. It’s got that whole look back to the very edge of the observable universe job as well. So [inaudible][00:29:13] –
Dr. Pamela Gay: Dark energy, dark matter, dark planets.
Fraser Cain: Proto planets, peering through gas and dust to see the center of the galaxy. Yeah, it’s got some jobs to do so looking for asteroids –
Dr. Pamela Gay: But hopefully it will
Fraser Cain: — cold [inaudible] built objects, finding more planets in the solar – anyway, James Webb’s gonna be busy. Take a number.
Dr. Pamela Gay: Oh, yeah. Yeah, but hopefully like Hubble, it will live long enough that it eventually will start being able to do the science because there’s something bigger and better on the horizon.
Fraser Cain: Right. And so really what we’re saying is, someone should build a coronagraph-equipped infrared telescope capable of –
Dr. Pamela Gay: We’ll take a 3 meter.
Fraser Cain: — capable of analyzing the atmospheres of distant worlds. Put that in the hands of Pamela and we will find your aliens, okay?
Dr. Pamela Gay: And I will find an actual infrared observer to do all of the work.
Fraser Cain: Yeah, yeah, yeah, that person [inaudible] –
Dr. Pamela Gay: I’ll just fill out the paperwork.
Fraser Cain: We will deliver you aliens.
Dr. Pamela Gay: I’m a paper pusher.
Fraser Cain: Okay? We will deliver you aliens. Do you not wanna know if there are aliens? Get us a telescope.
Dr. Pamela Gay: Or at least trees. Or at least trees.
Fraser Cain: Alien trees, sure.
Dr. Pamela Gay: We can find the ants out there.
Fraser Cain: Yeah, perfect.
Dr. Pamela Gay: If there’s an ant we can see it, or at least we can see the oxygen.
Fraser Cain: All right. Well then, even if we don’t get our telescope, we’ll see you next week.
Dr. Pamela Gay: Sounds good, Fraser.
Fraser Cain: Thanks, Pamela.
Announcer: Thanks for listening to Astronomy Cast, a nonprofit resource provided by Astro Spear New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at AstronomyCast.com. You can email us at firstname.lastname@example.org, tweet us at AstronomyCast, like us on Facebook or circle us on Google Plus. We record our show live on Google Plus every Monday at 12:00 pm Pacific, 3:00 pm Eastern or 2000 Greenwich Meantime. If you miss the live event you can always catch up over at CosmoQuest.org.
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Duration: 32 minutes