Transcript: The Chandra X-Ray Observatory

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Fraser: Astronomy Cast Episode 192 for Monday May 31, 2010, The Chandra X-Ray Observatory. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well, how are you doing Fraser?

Fraser: Very well. Now you and I were just talking about this, but we just want to remind all of our listeners that we are going to be at DragonCon…

Pamela: Labor Day weekend…

Fraser: Labor Day weekend… in Atlanta, Georgia. It’s a great party. 20,000 people there… amazing costumes… we’re going to do a live show… we’re going to be on panels… we’re going to be, like, wandering around aimlessly… looking for people to go out for lunch with… So, yeah, if you’re going to be coming to DragonCon, we’re going to be there.

Pamela: And looking a little further ahead in time, for those of you who like to plan ahead, like we do, in October we’re going to be at the US Science and Engineering Festival. There’s a National Mall outdoor event on October 23 and 24, and I’ll be in a Galaxy Zoo booth, also with Moon Zoo and other Zooniverse projects, and Fraser and I are going to be doing a stage show event. So come and support the show, see the two of us live, and check out all the amazing exhibits. Anyone who’s anyone doing science is going to be at this amazing event letting you play with their science.

Fraser: We’re going to find out if we can translate a podcast to a stage show… that’s the question.

Pamela: I think we’ll be ok.

Fraser: My money’s on “yes.” Alright, let’s get on with the show. So the Chandra X-Ray Observatory is the third of NASA’s great observatories, sent into space aboard the space shuttle to view the universe in high-energy x-ray radiation. This is the territory of supernovae, super-massive black holes, and neutron stars–some of the most extreme places in the universe. Now I actually started Universe Today back in 1999, and so within like 3-4 months of when I started working on the website, Chandra launched on the space shuttle. So I have a real good connection… I’ve been reporting on Chandra now for like 11 years…

Pamela: That’s amazing…

Fraser: Yeah, I know… so as observatories go, this is the one that I’m actually quite familiar with, with a lot of its research, and so I’ve seen the things come out of it. But for those who haven’t been reporting on it for 11 years… and once again, last week we talked about Chandrasekhar the person, and now we’re going to talk about Chandra the X-Ray Observatory… Chandra the robot, based on the man. So, let’s go back in history and take a look at the concept of Chandra. What’s the idea here?

Pamela: Well, back in the ‘70s, NASA started putting together plans for a set of great observatories. They ended up with four different missions, the Hubble Space Telescope was the first to go up, then there was the Compton Gamma Ray Observatory, which I think says that there’s probably a fourth dude named Compton in our future. Next to go up was the Chandra X-Ray mission, and then Spitzer was the last of the great observatories. Now Chandra… the idea for the mission… and it was originally the AXAF mission… the absolutely unpronounceable acronym mission… it was really conceived and proposed to NASA in 1976. The idea was put forward by Riccardo Giacconi and Harvey Tananbaum and it was to fill a gap in our ability to understand the universe. There’s so many things that give off x-ray emissions… shocked gases, compressed gases in clusters, gas that gets heated up as it falls into black holes, all these things—they’re emitting x-rays. Stars emit x-rays. And we couldn’t see it! And not being able to get information is annoying, and so they started in the late ‘70s and through the ‘80s and ‘90s working to design this amazing telescope that allows half arc second resolution of x-rays. Just learning how to focus x-rays has been a challenge.

Fraser: Right, and we can’t see gamma rays because they’re blocked by the atmosphere as well. So, I guess that’s why the Compton Gamma Ray Observatory was put up. But unless you build a space telescope, you’re not going to be able to see any x-rays at all.

Pamela: Right. And so we had to figure out how to build, how to focus, how to understand all that was needed to detect x-rays. It took a while. A lot of the work was done at the Smithsonian Astronomical Observatory at Harvard, and today, in fact, Chandra Center is located in Boston with joint support from the Smithsonian, from MIT, and at the Chandra Center. But they figured it out, and the science that’s come out of this mission is truly amazing. When I started graduate school, black holes were one of those things that everyone knew existed. But…

Fraser: Mathematically….

Pamela: Right. And we all pointed at the same couple of binary systems saying, “That probably is a black hole.” As I imitate older, male faculty members… but there was no evidence, and that is so annoying! But with Chandra, we were finally able to start looking at things and say, “That’s the signature of a black hole.” And that was perhaps the first really amazing thing Chandra brought us.

Fraser: So how did Chandra get up into space, then, because, I mean, you’re…

Pamela: I did skip a step. We do need to launch the mission, don’t we?

Fraser: Yeah, yeah… sorry, don’t mean to rein you in, there…. it’s very exciting… I can’t wait… but let’s at least talk about how it made it into space.

Pamela: It was actually launched on the space shuttle Columbia. The early great observatories were all designed for space shuttle launches. The original thought was to grab them, bring them back down to Earth, do things to them, and take them back up periodically. With Hubble, it got left up there and continued to be serviced by the space shuttles, most recently last year, but with Chandra there were some changes to it towards the end of the design cycle, and it was actually put into a highly elliptical orbit that would cause it to spend most of its orbit out beyond the Earth’s radiation belts. The Van Allen radiation belts are actually fairly damaging to the instrumentation on Chandra. They actually had to remove one of the instruments from the focal plane when going through the Van Allen Radiation Belt to help protect it from getting zotted by too many rays. So it’s now in an orbit that takes it a third of the way to the moon once per orbit and then cycles back closer to Earth and that’s usually when we get the data, but it can’t be serviced. But remarkably enough, this mission that was planned for five years has had an extended mission and has now planned to go for ten years… well it’s already surpassed ten years actually, it’s now 10 years and 10 months along… it’s estimated that it has at least a 15 year life expectancy at this stage. So that’s pretty amazing… it’s another one of those missions that was built and built well and is extending far beyond what was hoped for initially.

Fraser: Alright, now you can talk about the science.

Pamela: Thank you! So it allowed us to find where are the black holes.

Fraser: Right, but I mean obviously black holes are black… they absorb all the radiation—I’m assuming even x-ray radiation so how can Chandra see a black hole?

Pamela: Well, the neat thing is when you shock gas hard enough, it gets hot. And hot gas starts emitting in the x-rays. And so when we look towards black holes, we see both material that’s getting destroyed as it falls in… it flickers in the x-ray, and also, much more interestingly, we end up seeing these bubbling shock waves of material around black holes where, as you look in, you’ll see it literally looks like soap bubbles in the x-ray where when the black hole was active… when it was feeding… when something was getting destroyed… the process of having the matter get sucked in is highly energetic. It’s highly luminous as well, and all that light pressure, that radiation pressure, can clear out bubbles, and these bubbles… the edge of the bubbles pushing outwards shocks the gas that the bubble is hitting. So you have radiation pressure going outwards, just like air going into bubble gum. And the edge of the shock bubble is where the radiation is colliding with the interstellar material. And these beautiful bubbles are found in our own galaxy, they’re found in other galaxies, allowing us to know not only do we have the black hole Sag A star which Chandra discovered from its x-ray emission before we were able to image the stars orbiting so closely to it, but we’re also able to see these same amazing really cool structures in other galaxies.

Fraser: So, if I understand correctly, we’ve got a super-massive black hole, it’s feeding on material, the material is crushed around it so tightly that it’s becoming like a star around it… nuclear fusion is getting going, and what you end up with is the light pressure blowing out of this mutant star… this temporary star… and that’s blowing out cavities around the super-massive black hole.

Pamela: Right. This is talked about as black hole blow-back. And there’s some really, really amazing images in the Chandra galleries.

Fraser: And so this is some of the more exciting stuff… you’ve got black holes, you’ve got these high energy x-rays streaming out of the neighborhoods around them, but some of the even more significant discoveries are not quite as exciting, as you said. It’s like hot gas…

Pamela: Well, yeah, but it’s hot gas jetting out of black holes…

Fraser: Right, or galaxies colliding together…

Pamela: And clusters colliding!

Fraser: Right.

Pamela: One of the coolest discoveries to come out of Chandra, and this is one of the ones that actually in some ways may have sounded the death knell for modified Newtonian dynamics, the alternative to dark matter in theories trying to… well no, it’s not that there’s invisible stuff, it’s that we don’t understand gravity… No, we understand gravity, and we know we understand gravity because the images from Chandra allow us to look at clusters, and the important one here is the Bullet cluster. And when you look at it you can see shocked gas from where the two clusters are starting to collide. But then you can also see these orbs of dark matter imaged via gravitational lensing. So you look very carefully at the images and measure the distortions in the background galaxies and by looking at the distortions you can figure out, well, this was distorted by dark matter, this wasn’t distorted by dark matter. So by combining Chandra which gives us the gas, and by looking at gravitational lensing of background galaxies, we can map dark matter and gas and we can see that the two are segregated… they aren’t together. And this is just a fabulous result… we know dark matter is stuff because of Chandra.

Fraser: Right, and that there are situations where the dark matter can be separated from the galaxy and the gas that’s in the galaxy so that you can actually see it as a separate entity. So that whole idea of not understanding gravity has just gone out the window.

Pamela: And we’ve now seen this in multiple different clusters. In addition to the Bullet cluster we can also see it in the ever-so-poetically-named MACS J0025.4 -1222. And we can also see it in a much more mixed-up way in Bell 520. So all these different systems are showing us evidence of where the dark matter and where the gaseous materials are located by using Chandra to give us the gas content.

Fraser: And I think one of the other things that’s really interesting is when astronomers will use several of the great observatories to do some of their images. So they’ll take an image of the same part of the sky in x-ray and then they’ll merge that with images from Hubble and then they’ll merge that with images from Spitzer and you get almost like three different colors in one image; but it’s not colors, it’s three different wavelengths that are telling you completely different things. So you see the gas with Spitzer, you see the visual stars with Hubble, and then you can see the dense objects or the colliding gas or the hot gas areas thanks to Chandra. And when you have these working together, it tells a much better story.

Pamela: And I know there’s a lot of people out there who don’t like false color, but the combined images of the great observatories scientifically paints such a new and interesting picture… especially when looking at supernovae… where we’re able to see for the first time the neutron stars in the centers, and the gas jets they’re emitting, and the materials around them. That was one of Chandra’s first targets was actually looking at just supernovae and giving us a new view on these well-known objects. What we learned was really, really astonishing. Go out, look at a supernova. Look at it again in the Chandra galaxies. Cas A is another example of these amazing systems where we see so much for the very first time. The Crab Nebula is really my favorite.

Fraser: Yeah, well and I think one interesting one as well is supernova 1987a which was in the Large Magellanic Cloud, and it only happened… what… 25 years ago… right?

Pamela: Yeah.

Fraser: I remember when it happened… it was in the news.

Pamela: Our good friend Phil Plait researched it.

Fraser: Oh really? I didn’t know that! And so we can see it year after year expanding… this shockwave bubble expanding out from where this supernova exploded. And you can see the hot gas… these filaments and knots of hot gas where the supernova is colliding with the nebula that’s around it because the supernova exploded in a star-forming nebula and is now clearing out a lot of space and starting new solar systems and forming them… so you can imagine these knots of gas might be denser pockets… the locations of future solar systems.

Pamela: And there’s some really fabulous things even with much more… in some ways simpler systems… there’s the Cat’s Eye Nebula for instance. Looking at it you can start to see again the high-energy shocked gas and this is a cooler system with a white dwarf. And it really lets you see where are the shocks, and that’s information we didn’t used to have. It makes for much more fascinating images. But, the thing I think a lot of us forget, and so far we’ve managed to forget it for 18 minutes, is Chandra’s also gotten pointed back at the earth. You can use Chandra to start to observe aurora and it can be used to see exactly what’s happening as these high-energy particles from the sun are interacting with our own atmosphere.

Fraser: That’s pretty cool.

Pamela: It’s very, very cool.

Fraser: I know that the x-rays that Chandra gathers are so valuable that they’ll even use the time in between, so when Chandra is slewing from one target to another, it has to sort of go past all this other space and all of that data is actually made available to astronomers as well. As it moves the track is maintained and any x-rays that happen to bounce into its detectors along the way, they’ll use that as well. They’re actually starting to piece together whole sky surveys, thanks to some of the random data that Chandra has gathered.

Pamela: The serendipitous observations….

Fraser: Yeah, I mean with Chandra… especially with x-rays… you really need to focus on one target, wait a long time, and gather all those precious photons at that high energy.

Pamela: Proposals are written for kiloseconds…

Fraser: For kiloseconds… I don’t understand…

Pamela: So you say, “I need 16 kiloseconds on object. That means you need 16 thousand seconds observing something.

Fraser: So… several hours.

Pamela: Right. So for instance when I was observing galaxy clusters with the McDonald Observatory 107-inch, we could get pretty good observations in 900 seconds of fairly distant… admittedly by local standards… so something a couple tenths of a Z away… clusters… 900 seconds, there’s all your galaxies, move on, find your next cluster. But to look at closer objects and end up using sometimes many, many more seconds to get at the x-ray data… you’re literally counting one photon at a time.

Fraser: And so what do you think is the connection between the observatory and Chandrasekhar? Why was it named after him?

Pamela: Well, a lot of the really cool objects that are getting observed with it are the types of things that, well, Chandra’s theories explained why they’re possible and why we should go looking for them. The white dwarf inside of the Cat’s Eye Nebula, the many different neutron stars, the pulsars, all of these objects… he’s the one that predicted these. And then black holes… he’s the person who figured out that well, if this mass gives you neutron stars then this greater mass… oh, oh dear… this collapses even more. These are his objects and these are the objects detected by the Chandra Observatory.

Fraser: And, so the last thing I’d like to talk about is how exactly does Chandra work? Because we’ve talked a bit about x-ray observatories in the past… With a visible light observatory you’ve got a mirror, and photons come in and they’re focused by this mirror and you use a CCD camera to record the image. But I know that x-rays are much higher energy and they’re trickier to get a hold of.

Pamela: Yeah, that would be an understatement.

Fraser: So how does Chandra do that when mirrors don’t work?

Pamela: What they do instead is they have nested cylindrical surfaces, and these nested surfaces slowly, using basically grazing incidence angles, reflect the light… getting it down to the detector. So the light comes in, it reflects off the inner edges, goes to a slightly better angle, gets focused a bit more, until it finally hits the detector.

Fraser: So, it’s like you’re nudging it.

Pamela: You’re nudging it ever so carefully.

Fraser: Right, because there’s no way to actually make them bounce, but you can just change their angle a little bit. So then would you say that we’re not actually… it’s not like we’re focusing a huge area, like you might with say Hubble or a like great big observatory, you’re mostly just getting a little more focus than you would…

Pamela: They actually are able to focus the telescope very, very well, it’s just a different technology. So with Hubble you are going to get tenths of an arc second. But with Chandra you’re still getting half an arc second of resolution, which is better than most ground-based telescopes can get. The telescopes on an average night, not a great night, not a horrible night, but an average night at McDonald we were looking and 1-2 arc seconds of good sky seeing. So here, Chandra is getting better than that, and it’s getting better than that with x-rays. This is one of the profound things about Chandra Observatory is when we first started building x-ray observatories in the ‘70s, you basically pointed and said that giant area of the sky, there’s x-rays there somewhere. There’s been a billion fold increase, literally, in sensitivity and resolution combined that allow Chandra to count individual photons coming off of distant objects and resolve them at the same resolution that you get from the best ground-based telescopes under average conditions.

Fraser: So you said that Chandra will have maybe a 15 year life span, and we’re ten years into it… What’s going to be next? What will replace Chandra? Because this is something that you’ve got to have an x-ray observatory going…

Pamela: So we want Chandra to keep working… it would be awesome, but we do have to plan for the future. And being scientists, we do want to eventually get even better data… we do want to be able to collect more photons in less time and at higher resolutions. So right now there’s a joint mission being planned named the International X-Ray Observatory… it’s a joint mission between the European Space Agency, NASA, and JAXA which is the Japanese space agency. And they’re hoping to launch it around 2020. Now the thing to remember is that everything in NASA is in flux right now, and strangely everything seems to be set for 2020, so expect that date to slide, expect that name to change, expect anything to be possible.

Fraser: Humans landing on the moon… finding Earth-sized planets with their x-ray observatories….

Pamela: Yeah, that one’s not going to happen. But if you put a comma in there, I’ll go with it. Finding Earth-sized planets, finding a better x-ray observatory. Yeah, let’s go with that.

Fraser: So the replacement could go up in 2020.

Pamela: We’re hoping…

Fraser: Right. And it will be more better.

Pamela: Yes.

Fraser: Cool. Alright, well that explains everything. Thanks a lot, Pamela!

Pamela: Well, it’s been my pleasure, Fraser.

Transcript: The Kepler Mission

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Fraser: Astronomy Cast Episode 190 for Monday May 17, 2010, The Kepler Mission. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing ok… it’s been an amazingly stormy, scary, awful weather day but we finally got to record.

Fraser: Yeah, during the summers we always have to do our recordings in between tornado warnings. In fact if people go back through our archive, it’s like… oh, yeah… in the summer… tornadoes… and then, you know, the year before… It’s like your summer pastime is to somehow get work done while nature is trying to tear your city apart.

Pamela: Yes… this is why backup systems and laptops with 9-hour batteries are both useful things, and if you can couple it with a 3G wireless, you can weather it out in the basement.

Fraser: Ok, stop shilling for the networks…. unless they want to pay us, then we’ll shill for them. Alright, so last week we studied Kepler, the man. This week we take on Kepler, the mission. Launched in March 2009, this is the spacecraft designed to search for Earth-sized planets orbiting other stars. So we’ll take a look at the history of this mission, the launch, and the science gathered so far. I like this kind of one because the spacecraft is already up, it’s safely launched, it’s operating, it’s already got some science data… the best is yet to come, so we can both talk about things that have already happened but also predict the future, which is always great. It’s also, as I mentioned in the last episode, it’s not that connected to Kepler, except that you learn a lot about planets.

Pamela: Well, yeah… he’s kind of the originator of the whole planet idea… so, yeah, it’s cool.

Fraser: So then let’s go back to the history of the mission and the science that’s coming together here.

Pamela: Well, the idea for the Kepler mission actually originated in the 1980s. The idea probably originated well before that, but they started pulling together the science team, assigning roles, writing up white papers, that sort of work in the 1980s. Then, it finally got funded, got put through, lots of ideas detailed… we have another tornado warning, if you heard that ding in the background.

Fraser: Focus, Pamela, come on… stick with things that are really important here…

Pamela: They started pulling together the really good team in the ’80s and ’90s, these things got funded. I’ve been able to find papers back in the early 2000s detailing what they planned to do. They originally had a planned launch date for 2007, but as happens with many NASA missions, there were budget cuts, there were budget delays, there were mission delays… yeah, they finally launched in March 2009. Today we have this fabulous mission, and the biggest thing that didn’t survive all the way through the multi-decade process from conception to birth was the radio transmitters flexible gimbals. So, instead of being able to point their radio receiver without having to move the mission… they actually lose one day a month of being able to collect data just in sending data back to the planet Earth.

Fraser: Everything else is intact.

Pamela: Yeah, and it’s doing great science.

Fraser: I can remember, actually, when I first started Universe Today… so we’re talking 11 years ago now… I can remember writing articles about the upcoming plans for the Kepler mission. I mean early, early on… early 2000…. so it has definitely been around for a long time. So, lets talk about the purpose and see if we can somehow connect it to Kepler the person. What is the purpose of the Kepler mission?

Pamela: It is to discover planets by looking at planetary transits and more importantly to discover planets as small as the planet Earth. The way it’s doing this is it’s looking at a field of stars in the direction of the constellation Cygnus. So, if you know how to find the summer triangle, right now you can go out and look up and look in the same direction that Kepler’s looking in. And in this fairly crowded field of stars it has picked out… well, it hasn’t… the science team has picked out a hundred thousand stars that they’re studying, taking new images every 30 minutes, and looking to see… do any of these stars have the dimming that you expect to get when a planet passes in front of the star, blocking a small fraction of its light.

Fraser: So they say they’ve got a 100,000 star targets, but they’re focused in a very tight region of space, so the spacecraft is not really having to… it’s not turning up, down, left, right, and all the way around… it’s really just zooming around in this one little spot of the sky. But it can’t gather the whole space at once, can it?

Pamela: No, it’s actually getting all 100,000 stars all at once!

Fraser: Oh, wow! Ok…

Pamela: And that’s… and one of the things that causes me a bit of sadness is that they could actually be collecting data on a whole lot more stars… it’s a 10-degree field of view… this mission has a giant mosaic of detectors that are looking at a large chunk of the constellation Cygnus…

Fraser: Right, that’s like 20 times the size of the moon… so measure a circle 20 times as big as the moon, and that’s the space… and it’s just staring at that whole space all at the same time.

Pamela: Right, and it’s taking image after image… co-adding them as needed, to allow us to see all of these stars. But it actually has even more stars in its field of view than just those 100,000, and it would be kinda weird if a mission had exactly 100,000 stars in its field of view anyways. But the reason it’s only looking at these 100,000 is it has to pick and choose how much data it can save because it has to keep all of its data stored up on its hard drive until that once-a-month download of data, and then that download is limited in time to how much time they can get on the Big Ear… the network of radio telescopes that we use to communicate with various space missions. So if there was unlimited time on the Big Ear dedicated to Kepler, we could be looking at even more stars than we’re currently looking at.

Fraser: Right, so then let’s kind of imagine this mission… it’s pointing at this spot in the sky… it’s gathering all this light… it’s seeing all these stars… Some of them are going to be constant in their brightness, and others are going to be changing in brightness, right? But there’s going to be a whole bunch of reasons… there’s going to be variable stars, there’s going to be novae, there’s going to be all kinds of things going on, right?

Pamela: So they’re initially actually looking at a larger number of stars… First of all they surveyed the field very well from the ground, eliminating all of the variable stars they knew about… didn’t observe any of those… and then during their early parts… the first tens of days of the mission, they looked at over 140,000 stars and eliminated over 40,000 stars because they weren’t ideal candidates. They were either binary stars that just weren’t discovered, they were variable stars that weren’t discovered, they were stars that were not your classical pulsating nice regular easy-to-look-at variable, but were rather stars that had flare activity… all of these things… the properties of the star were erasing any potential to find planets. So they weren’t useful for planet-searching science… they were still useful for lots of other science. That science is now going to be based on a very short window of data… and that’s ok… we’re still getting good results.

Fraser: And they’re using the transit method, right? This is the method where you’re looking at the star and the planet happens to pass directly in between this star and Earth and slightly dims the amount of light that we see coming from that star in a very specific pattern as that planet dims… you know, passes in front of the star… dims the star, then goes behind the star, then we see another pattern… that’s what they’re looking for. And they’ve used other… they’ve used like Spitzer and they’ve used other methods for finding planets in this way.

Pamela: Right. And this is actually going to be an amazing set of data because we can detect transits from the planet Earth. In fact if you have a good 4-inch telescope with a really good, really sensitive detector you can make observations of some of the planetary transits that we already know about. The catch is, well, there’s only a few stars that are bright enough that we can see the tenth of a percent… the hundredth of a percent… if we’re lucky the one percent dimming that occurs with planetary transits. Most of the transits are so faint that if you have a star that’s not very bright to begin with, and you’re looking for a very slight change in its brightness… that’s really hard to detect. So by sticking the mission in space, you don’t have to worry about atmospheric effects, you can constantly watch objects around the clock, but mostly you avoid the effects of our atmosphere. You can end up with a fake planet just by clouds passing by.

Fraser: So, how sensitive is Kepler? And let’s put that in context in what’s been found already using other techniques, or using the transit technique, what will it find… hopefully…

Pamela: We know that it can find planets the size of the planet Earth…

Fraser: Wow…

Pamela: They’ve been able to cross-correlate the early results and look at things that we know exist, and based on the things that we know exist and the signal-to-noise… planets the size of Earth can be found.

Fraser: In the same orbit as Earth?

Pamela: In the same orbit as Earth…

Fraser: Right. And so… but from what I understand so far, it’s kinda like you’re grabbing the low-hanging fruit… it’s harder and harder to notice the smaller planets moving in front of the star and to get that pattern. It’s easy to catch the big ones that are moving… the mega-Jupiters that are moving really close to their world because they’re going to darken the star quite significantly and we’re going to see it fairly often so you can start to pick out that pulse almost… but the Earth-sized planets… you can imagine, you’d only detect Earth moving in front of our star once a year, and you’d need to confirm that for several years before you’d have a good candidate.

Pamela: So you’re hitting on two different problems that we have to deal with. And one of the problems is that planets like Earth… they don’t cause that much of a dimming of the star that they’re passing in front of. So, that in itself is hard to detect. The planet Mercury, for instance, causes a transit depth of 0.0012 percent. Jupiter causes a 1.01 percent. So Jupiter… even with the orbit it’s at… that’s a whole lot easier to detect. Now, in addition to the “it’s hard to detect because it’s just not wiping out enough light from the star,” the other issue is… they want to have ten repeating transits before they confirm an object. Four is pretty good, ten is ideal. With four, that means you’re waiting four years before you’re able to confirm a planet like the planet Earth. You have to wait for four transits.

Fraser: Right, so you see a little blip in the data and you’re like… ok, let’s come back in a year and see if it happens again.

Pamela: Yeah. And that’s a long wait. So right now they’re releasing stuff based on… their confirmed planets are all 3, 4, 5 days… but the longer ones… we’re going to have to wait. All of the planets so far announced are between 3 and 5 days of period.

Fraser: I want my science now!

Pamela: Well… sorry. But at least we know it’s coming. That’s the cool thing is we know it’s coming. And just today… that’s one of the cool things about… we meant to record yesterday… ended up recording today… today Kepler released 706 probable candidates for exoplanets. They think that probably only half of these systems will actually pan out to have exoplanets, but several of them could be multi-planet systems. Prior to today, we only had 460 candidates. We’ve more than doubled the number of possible planets that we know about just with one mission. Fifty years of work produced less results than the few months that Kepler’s been orbiting.

Fraser: This is the whole point… you build a really specialized tool, gets results. So then kind of looking forward, what can we expect from Kepler? How long is it supposed to operate for?

Pamela: It has a several-year mission. As with many NASA missions I’m reluctant to say exactly how long it’s going to last.

Fraser: But is it going to be one of those situations where like… well, you know, it was supposed to last now, but we’ve kept it alive another ten years.

Pamela: That’s kind of what I’m hoping for. It’s current mission length is 3 ½ years, and one of the problems that we’re going to deal with is its orbital period is 372.5 days, which means it’s lagging behind the planet Earth, orbiting the sun, and over time is going to drift further and further away from us. If they extend this mission it’s just going to keep drifting, which means that the radio signals coming from it are going to get fainter and hard to catch. But that’s not as big a problem as… well, should this mission choose to do like the Mars Exploration Rovers, which is harder for a spacecraft, but should it choose to behave like that it’ll eventually drift behind the sun.

Fraser: Right, or like SOHO… there’s a lot of missions that have definitely outlived their timeline, but it’s not like Spitzer where it’s got a set amount of coolant and then when that runs out, that part of the mission has to end. Or, like Deep Space 1 that had a set amount of Xenon for its ion engine, and when that ran out you really couldn’t navigate or maneuver anymore, or like Phoenix is a good example… designed to land on the north pole of Mars, but when the Martian winter set in, it got crumpled by several meters of ice and snow… this is one of those situations where they’ve got a set timeline, but there’s no real reason why the spacecraft can’t last longer than that.

Pamela: It’s working in optical wavelengths… 400 – 865 nanometers. It will have the standard… it could eventually, well it will eventually run out of thruster fuel, but we’ll see how long it lasts. They can be conservative… NASA always finds ways to surprise us and keep things going. But it’s currently scheduled for 3 ½ years, and we’re all going to hope that it just keeps on going and going and going…

Fraser: So then let’s say we take all the data that Kepler kind of pulls together, what does this tell us about the Milky Way… about the nature and number of planets?

Pamela: Well right now we’re only looking at a set of stars that are in the same orbital type that we’re in. One of the things that gets talked about is well maybe planets don’t form as well towards the center of the galaxy, maybe they form differently at different distances from the center. So, we’re looking at a set of stars that are in similar orbits to our own sun, and what we’re hoping to be able to say when we’re done is that this is the frequency at which star of these different types and these different… well, spacings in binary systems, have planets. One of the things that I’m really hoping will come out of this is a new model for planetary formation. Growing up, I like everyone else learned the solar nebula model… you end up with rocky worlds close to the sun then gas giants beyond that then icy giants beyond that and then out at the edge there’s the Oort cloud. Well, we now know that gas giants like to hug their stars. But where do the rocky worlds live? If you have rocky worlds, do the gas giants stay further out? How exactly do we build models to explain all the crazy varieties of solar systems that we’re finding? This may give us the data that’s needed to answer those types of questions.

Fraser: Right, so you can really get a sense of what does a typical solar system actually look like? What are the possible configurations that you can have? Could you have giant planets up front… rocky planets in the middle… or like what we have, the other way around… or if you have giant planets up close maybe you can’t have rocky worlds… and so on and so forth.

Pamela: Right.

Fraser: And then what percentage of stars just have planets? What percentage of stars have giant planets? What percentage of stars have… because if we took the Drake equation, we could theoretically fill in one number and call it a day, right?

Pamela: And this will allow us to fill in a lot of the numbers that don’t pertain to biology… and to do it very accurately. One of the things that I remember watching evolve scientifically is the idea of well, what metallicities of stars can have planets? What temperatures of stars can have planets? It was thought that the smallest stars couldn’t form planets, and the largest stars probably couldn’t form planets because they had massive outflows when they were young. And now we’re finding exceptions to everything we ever thought. But somewhere there’s got to be a parameter space of planets vs. no planets. We know that globular clusters, for instance, show no signs of having planets. This will help us start to get a handle on these things. And one of the interesting results that’s already come out is we’ve learned that stars aren’t as violent as we’d thought, in some cases. There was concern about just what fraction of stars show violent flare activity, the type of high-energy outbursts that prevent life forming on planets. We’re now finding that these outbursts don’t occur at the same rates that we’d worried. These outbursts are also the type of thing that make it hard to detect planets. So Kepler looked at this and we found more candidates for looking at planets and thus more candidates for systems that wouldn’t squelch life… and that’s a cool result.

Fraser: Will Kepler be able to help answer the life question at all?

Pamela: Not by itself. But the thing with Kepler is that it’s only detecting transiting planets. And transiting planets are the only type of planets whose atmospheres we can study. So if we start looking at these worlds that transit in front of their stars with telescopes that are capable of doing spectroscopy, we may be able to pick out the atmospheric lines of those planets from the stars’ stellar spectra and say this world has oxygen. And you only get free-ranging oxygen in an atmosphere if you have plants or some sort of microbial life. Otherwise it likes to form organic molecules. So we could conceivably, thanks to Kepler, find planets whose atmospheres we study with something else, that we start finding signs of pollution of plants, of all sorts of different things…

Fraser: Does that spacecraft exist? That tool?

Pamela: Sort of… Spitzer works for the biggest planets. It’s actually been able to detect atmospheres previously. And depending on the planet, once James Webb gets launched it will be able to aid in the battle. But a spacecraft dedicated to looking spectroscopically at stars with planets… that’s not up there yet. Although it would be really neat if someone planned it and launched it…

Fraser: We should call it like the Terrestrial Planet Seeker… or something like that…

Pamela: Right, right… we’re just going to keep saying that until someone builds it.

Fraser: We’re just going to keep nagging until somebody makes the Terrestrial Planet Finder and puts it back on the books and launches it and finds life… doesn’t anybody want a Nobel prize?

Pamela: It would be cool…

Fraser: Yeah, anyway… most important scientific discovery ever…

Pamela: Wouldn’t you rather be able to look at a planet and understand its industrial based on its atmosphere rather than catching random hard-to-make-sense-of and highly controversial radio signals that might get blamed on atmospheric noise?

Fraser: But you can see the Kepler mission helping even the SETI… because all these planets are known to be Earth-sized worlds orbiting other stars, so let’s just point SETI at them.

Pamela: Even more than that, just finding that there’s a planet… it could be that one of these Jupiters that we find out in the habitable zone, it’s not necessarily capable of sustaining life on its own because it’s a gas planet… it could have moons… it could have Endor with its own civilizations growing up on the moon.

Fraser: Hmmm…. yeah. I think there’s going to be a lot of data that’s going to come out, and there’s going to be so many interesting stories… I can see “First Solar System Resembles Our Own Solar System Found,” and it’s going to be with many of the same kinds of planets and the same kinds of orbits…. and hopefully then that will really spark a whole other layer of research of funding and so on… this is just to whet people’s appetite, I think…

Pamela: And the small planets look like they may be in the candidate list. And this is one of the amazing things, and a bit controversial as well, is they’ve found so many planetary candidates that they’ve released half their data early. The scientists behind Kepler were able to get a special dispensation and were given an extra 6 months to release their data beyond the one year that you normally get with a NASA mission. And they realized that we have 706 candidates, and they released 306 of those out to the public. Anyone who wants to can start following up on these objects. And they kept the 400 best for themselves. So 6 months from now hopefully we’ll be able to see what’s so amazing that they held it back, because the hints in the preprint that’s up on ArchiveX… they’re already pretty amazing. The average size is half-Jupiter.

Fraser: And this is what we’ve said… they’re just getting going… it’s all about the period… the length of time these planets are taking to go around their star. So they’re finding the quick ones… but now that we’re more than a year into the mission, they’re starting to find the slower ones. This is going to get pretty exciting. Alright Pamela, well I think that covers the Kepler mission… hopefully everybody understands it and will then know what they’re looking at when they read space websites talking about it, so that’s great… thanks Pamela.

Pamela: It’s been my pleasure.