Dave Koch talks about his powerpoint slides
From Night Sky Network telecon, November 16, 2006
David Koch: ... Tonight, I’d like to talk about the Kepler Mission which we have been working on now for five years as a formal NASA mission and probably 15 years since we’ve started thinking about how to do this mission.
SLIDE 3 If you go to your Slide 3, which is the overview for my talk, you can see that what I’m going to talk about first is what is a habitable planet. When we use that term, we really ought to be using a similar definition so we all know what we mean by that.
Then, I will talk about different ways to look for planets. There’s more than one way to skin a cat and there’s more than one way to find a planet. I’ll just briefly mention what has been discovered to-date about extrasolar planets.
And from that, I’ll launch into our Kepler Mission itself which uses transit photometry, I’ll describe the concept for the mission, and finally, some of the results that we expect at this point. This is what’s called a discovery mission. We’re out there to discover things that aren’t known, so it’s kind of hard to predict precisely what we’re going to find. But we will make an attempt at that anyways.
SLIDE 4 So, moving on then to Slide 4, what you need to do when you do an experiment or do an observation or design a space mission is you have to figure out what is important and how to look for it. And the way we went about this is to say we’re interested in finding habitable planets and tried to quantify in our minds what that meant. And that then tell us how you have to go look for planets.
So, the first thing when you talk about habitable planets, it might come to mind (Arnold Guthrie’s) old song about redwood forests and Gulf Stream waters and fields of wheat and things like that as being habitable. (Well, it will) certainly describe our planet. They’re not things that we’d probably be able to find in the near term.
But there are things that are important to get those coral beaches and palm trees and things like that, and that basically defines habitable forests. And among those things are, you need to have the right temperature, you certainly need to have some kind of an atmosphere -- you have to have air to breathe or - for plants to use as well.
Habitable also implies that you have liquid water on the surface of the planet; you certainly need light -- you can’t have a planet that’s floating out in free space without being near a star, so light is important.
Also, a secondary thing that we don’t always think about planets is that you need a radiation shield to protect you from both a solar (flaring) and galactic cosmic rays. So that’s an important part of a planet. And also, that atmosphere serves as a protection against asteroids.
So we’ll look at - a little bit about each of these aspects in the next few slides.
SLIDE 5 Going on to Number 5 then, there are quite a few things that affect the temperature of the planet and determine whether or not it can be habitable.
The first thing that comes to mind, and the most important thing, of course, is temperature of the star that the planet is orbiting. That determines the amount of radiation that falls on the planet.
And in conjunction with that, of course, is the distance the planet is from the star. It’s fairly obvious, I’m sure, to everyone on the phone tonight that the closer you are to the star, the hotter the planet gets, and the further you are, the colder the planet is. And that’s why Mercury, for example, and Venus are so hot, whereas Mars is a whole lot colder than the Earth. So, the distance from the star is important.
Also, what’s important is the shape of the planet’s orbit. If you have a circular orbit, of course the planet is at a constant distance from the star, and so, the heating of the planet is constant, whereas, if you’re in an elliptical orbit, the heating varies throughout the orbit. An extreme case, of course, is a comet which spends a lot of time very far from the Sun -- and it’s very cold. And then, as it gets into the inner solar system, it heats up and you get the beautiful long tail due to the evaporation of the gases and ices. And so, you can see that the distance changing in an elliptical orbit would create a very traumatic climate and maybe, in fact, destroy the climate on the planet. So, the shape of the orbit is very important to a planet being habitable.
Lastly, the thing that’s harder to get a handle on is the effect of the atmosphere that is surrounding that planet. Some atmospheres are not so good. For example, Mercury -- I’m sorry -- Venus has got a very thick atmosphere. It has a lot of greenhouse gases and the temperature on Venus is even much higher than on Earth than you would expect from just the fact that it’s slightly closer to the Sun, to the star.
Bruce Tinkler: Just to follow up on your initial premise. You were looking at defining habitable planet. And I know you won’t be able to determine this by your observations, but what impact do you see the orbital period - the rotational period of a planet having on whether or not it might be habitable?
David Koch: Well, I would say that if a planet is gravitationally locked -- like, for example, the moon’s face is gravitationally locked to our earth -- that makes for very inhospitable kind of a planet. You - if you had that with a planet who - that faced - just one side face to the Earth, you would probably end up with solid ice on the back side of that planet and basically no liquids, no water or anything on the sun-facing side.
In terms of seeing orbital rotation periods that are considerably different than ours, let’s say, 48 hours or 200-hour periods or 2-hour periods, I really don’t know what that would do to the atmospheres or the surfaces of those planets. That’s a fun thing to speculate about and it will be even more fun to get to the stage where we can actually observe planets like that and get those kinds of measurements. We certainly won’t, but other future missions might be able to do that. If nothing else, at least measure the - start looking at cloud tops, telling you what the rotation period of the planet is once you get to have that kind of resolution for a space mission.
SLIDE 6 So, all of these properties basically define what we refer to as the habitable zone around each star. And if you look on Page 6 then, we have a plot there that was originally developed by Kasting, Whitmire and Reynolds where they talk about the Habitable Zone in this classic paperback in 1993. And the green band there shows where the Habitable Zone lies for different stars, where the star mass is shown on the left-hand scale and the labels there towards the left side of the plot are different types of dwarf stars.
And our Sun, of course, is a G2 star, so it would fit near where that says G0. And of course, our Sun is defined to have a mass of 1. (And at a Mass of 1) (then, I’ll show) where the planets in our solar system are in terms of distance from the star.
And you can see that there are two blue dots inside the Habitable Zone for our Sun, the inner one, of course, being Venus and Earth being right in the middle of that zone. Mars is right on the outside edge of that zone. Mars is just outside what we would consider the Habitable Zone for our solar system.
SLIDE 7 What are the important things, well, about an atmosphere -- going on to Page 7?
The composition of the atmosphere certainly is important. If you want to have life, you need free oxygen. But you don’t want too much of it either. You wouldn’t want a pure oxygen atmosphere probably. A lot of our atmospheres in Earth, it’s mostly nitrogen as you can see. And of course, you don’t want many toxic gases. You don’t want things like sulfuric acid or any kind of sulfur in large amounts in the atmosphere, or any other poisonous gases, of course, would not be very good.
The composition of the atmosphere affects its temperature. You can put in very small amounts of the greenhouse gases like water and CO2 and they affect tremendously than the amount of heat that is held in the atmosphere. The amount of ozone you have in the atmosphere, even though it’s a small percentage, has a great effect on the heating of the atmosphere.
And another aspect of having an atmosphere is that it helps you minimize the extremeness from day to night that you have on the planet. A good example of that is on the moon where you have no atmosphere to speak of. When you’re on the Sun side of the moon, it’s extremely hot. And of course, you get into any kind of shade even on the Sun side. Or, if you go to the backside of the moon, it goes - the temperature drops dramatically. Having an atmosphere helps you (calibrate) that temperature so you don’t have great extremes. As you know, everyday, our typical temperature extreme day to day, on average, is probably -- day to night -- not much more than 20 degrees.
The atmosphere also acts as an invisible protective shield for us as humans. It absorbs the cosmic rays from - the very high energy cosmic rays from the galaxy as well as charged particles from the Sun and solar flares, it absorbs the ultraviolet and it also protects us from micrometeoroids which come in at such high velocities they’ll put a hole right through the window in the Space Shuttle that’s in orbit above our atmosphere which would normally protect us. So, it's good to have that atmosphere. Another point is that the atmosphere, of course, transports water in the form of clouds and rain. So these are all important aspects for, having a habitable planet is to have something that can hold a nice, life-sustaining atmosphere.
SLIDE 8 Well, going to Page 8, it turns out that the size of the planet dramatically affects its habitability. That is, something that is very large or very small is not, by nature, going to be habitable. And the reason for that has to do with the mass of the planet.
We believe from our theory of planet formation that the planets (secrete) from the gas and the dust that is left over in the solar nebula or stellar nebula. When the star forms, there are still these grains of dust and large amounts of gas still in the disk left over that eventually form into planets and if the planet formation process leaves a core that is too small that is less than about half the mass of the earth, at that point, you don't have enough surface gravity to hold on to a life-sustaining atmosphere and you end up with a planet something like Mercury or Mars. That's because their surface gravity is so small, they won't hold to a life-sustaining atmosphere.
Okay. Now, if you get bigger than a half an earth mass’s, you start accumulating gases; the heavier gases you hold on to easier. But if the mass of the final planet that forms out of the grains in the nebula is too large -- and by too large, I mean bigger than about 10 earth masses -- at that point, you have enough surface gravity to continue to hold on to the very abundant and light elements, hydrogen and helium. And once they start collecting on the planet in the atmosphere, the mass of that planet will grow tremendously and turn into something like a Jupiter or a Saturn which is almost all gas, almost all hydrogen gas with some helium. And that, of course, is not a - what I would consider a habitable planet. And so, the size of the planet, the size of that core that forms, determines whether or not the planet is habitable.
SLIDE 9 Moving on Page 9 then, if one wants to find habitable planets, based on the discussion I just had, you need - these are the key features that you incorporate in the design of your experiment or observations or space mission.
The first one is, picking the right kind of star to look at. You want something that is similar to our Sun, what we call solar-like star, and that is what we refer to as FG or K dwarf stars. Also, we call them main sequence stars. So that’s the kind of star you want to look at for planets.
The next thing is the orbital period, the orbits that these planets are in. You want them to be in the habitable zone. And for the particular type of star, you can look back at this figure and figure out what the orbit size is or the orbital period of the planet will be if it's in the habitable zone.
So, that means if you're building an experiment that can only look the great distance from the star, you'll miss the habitable zone. On the other hand, if your experiment can only find planets that are very close to a star, you miss the habitable zone. You want an experiment that can find the planets in the habitable zone.
And finally, you want an experiment that is sensitive enough or has enough precision to see a planet that is somewhere between a half an earth mass and 10 earth masses -- at least that small. Obviously, if you can find smaller planets, you'll find the bigger ones. But if you only can find big ones, that doesn't mean you're going to find the small ones.
But bottom of the page, I referenced an interesting provocative, if nothing else, book entitled, Rare Earth that has chapter after chapter on all of these little nuances that can affect whether or not a planet is habitable. It goes into both the astrophysical aspects as well as the biological aspects of whether or not the planet will be a habitable planet similar to earth. And depending upon your viewpoint, you could say, well, (earths) are common or having just the right kind of everything could be very unusual and very rare. And that, in fact, is what the Kepler Mission is designed to answer. The question is, are earths common or are they rare? Both answers are very important.
SLIDE 10 Moving on then to the next section on detecting extrasolar planets -- and by extrasolar planets, I mean planets that orbit other stars...
SLIDE 11 looking at Page 11, I have just listed there in a tabular form the various methods that people know about for trying to look for planets. Some of these have been very successful so far, some of these are very difficult to do and have yet to yield any results.
Really, the first extrasolar planet detected was by Alex Wolszczan, and he detected planets going around a pulsar. And with that method that was using radio astronomy and pulsar timing, he was able to find planets even as small as the moon.
But this is an unusual case. The pulsar is not a star that you would want to visit because of the lack of nice soft photons, sunlight so to speak, and the fact that it has a lot of high-energy radiation coming off of it.
So, that was interesting. It proved that, in fact, the ability to form planets, even after a supernova and the formation of a pulsar, was quite possible. That you had three forming in this system was a real indicator that the - our solar system probably is not unique. That was back in the early 90s.
Then, the next big breakthrough came by the first extrasolar, real extrasolar planet that was detected around a solar-like star. And that was by Michel Mayor and Didier Queloz back in 1995. And they found this planet we know now as 51 Pegasus. We refer to it as a hot Jupiter because it had a shockingly, surprisingly short orbital period of only four days going around its star which was a real surprise to everybody, all astronomers. Everybody just never expected that you would find something like Jupiter that close to a star. Its orbit is 20 times closer to this - to its star than the earth is to the Sun. That is, it’s at 120th of an astronomical unit.
Since then - since that wonderful discovery, we now know of about 200 planets orbiting other stars. And these, of course, are all much, much larger, much more massive than earth. Many of them are even bigger than Jupiter. Most of them are in very-short-period orbits although some now had been found with longer-period orbits. It takes a lot longer to detect these than the ones that are orbiting in matters of days, weeks or months.
Astrometry, the third one I list there, that's an old method that people have tried for years and years and years, hoping to find planets around the nearest stars, for example the Bernard’s star. Some - at one point, people thought there might be a planet orbiting it because of its little wiggle.
And astrometry uses the same method people have used for years to look for binary stars. You look for the little wobble of the star compared to some distant background star and hope that you find one with a tiny wobble that would be due to a planet. This method is, you know, has been tried for years. But nothing has been found with it yet.
The other message is transit photometry. I'm going to talk about it. Actually, it has been successful now. We’ve - people have found transiting giant planets from the ground. Also, about a month ago, they announced the - that the Hubble Space Telescope was able to detect about 16 of them in a cluster near the galactic center.
And another mission that - besides Kepler that is a space mission that is designed to look for planets is what is called the COROT Mission that’s coming up this - next month, they’re supposed to launch. It’s a European mission.
It is similar to Kepler in principle but, its capabilities are a lot less. It’s a much smaller telescope, it’ll look - going for a few months in any one direction in the sky, so it’s not going to find planets in the Habitable Zone.
We can also find giant planets using reflection photometry. We’ll do that with Kepler as well.
Two other methods. Microlensing has been trying to find planets for years -- one possible detection there -- and direct imaging which eventually is hoped to actually image the disk of a planet, is being studied. Those missions are very difficult to do and very costly. And they’re on the horizon, but they’re not something that we’re able to do at this time. They’re quite expensive space missions.
Just as an aside, there is a Web site that you can learn about all of the planet detections to-date. That’s the extrasolar encyclopedia and the URL is quite simple -- it’s xlplanet.eu, xlplanet.eu). You can go there and it lists all the detections of all the planets with all the details assigned to them.
(Sarah Jurado): I was wondering if there is another mission planned to look at a different part of the sky because I know you that when you were answering the other question, you said that, you know, you have to study the stars on the ground so you’ll know what stars you’re looking at. And that’s why you can’t point the telescope. I was wondering if you are planning on building another telescope maybe to point at the southern sky.
David Koch: We certainly aren’t planning that. I will say the COROT Mission that I mentioned that’s being flown by the European, it’s a different kind of mission plan. It has two aspects. one is to look at planets, the other is actually look at rotations of stars. That’s where the name comes from.
And they - well, the way their mission plan is set up is they will - they have a smaller field of view and they will be looking for something like two or three years-long mission.
…will look for (about) four months at a field and then move to a different field.
The net result is they will only be able to find planets that have shorter-period orbits. So things like few weeks, maybe a month at most. They won’t be able to find planets (unintelligible) habitual home, (you know), (those things) that have (longer periods), (maybe years).
They, therefore, can start looking in - they’re looking in the other places of the sky and get statistics of a different fashion from what we can get.
SLIDE 12 So, going on to Page 12 now, talking about the Kepler Mission, the reason Kepler is able to detect planet is because of the method that we used. The radio velocity method which is being used to-date and found - has found more than 200 planets is used - can be used for giant planets but it’s not sensitive enough to find Earth-like planets especially Earth-like planets in a one-year orbit. The method is much more sensitive for the more massive planets and for the planets that are very close into their star.
So, the method we use is photometry, that is, looking for transits. And we’ve designed the Kepler Mission - we optimized it to detect habitable planets in the Habitable Zone of solar-like stars. That’s the way we designed all the parameters for the - optimizing for that approach.
SLIDE 13 Looking on Page 13, I created a little graphic here using the picture of our own Sun. You can even see some spots on it in a few places. And on the left, to scale, I put Jupiter, the disk. We won't see that from the Earth, but if you were looking from some distant part of our outer solar system, you would see Jupiter in contrast to the Sun .and you can tell it’s very noticeable. The area of Jupiter is about 1/100 the area of the Sun, so when Jupiter crosses the face of the Sun, as is viewed by some distant observer, the brightness of the Sun would decrease by about 1% during that period of time and there would, in fact, be very abrupt change in brightness as Jupiter crossed the (line); it would stay fairly constant across the disk and then jump up again in brightness when Jupiter left.
On the right there, if you look closely, there’s a tiny black dot right of center of the solar disk. And that is what would appear to be Earth or Venus to scale. It is 1/100 the radius of the Sun or basically one part in 10,000 of the area of the Sun. And it’s, you know, you’ll have to look close to see it even on the page. It’s virtually impossible to measure that change in brightness of the Sun when the planet crosses the disk. It would be - it’s a very difficult thing to do. It’s not an obvious change in brightness. But that’s what we are able to do with the Kepler Mission.
The method actually is quite robust because we’re not just looking for a single transit, we’re looking for multiple transits. The first transit tells you, hmm, maybe there’s something there.
You then wait for the thing to come around again; you don’t know when it’s going to come. But the second time it cross - you see it crossing the star, you have a possible period. If it’s truly a planet orbiting that star, you look for one more period later and it has got to be there precisely at the right time as the previous period. And what we do, in fact, in our mission is we ask for four transits as a way of checking.
Now, not only does the period have to be precisely correct when it does this, but the change in brightness, each time it does that, has to be the same because neither the star nor the planets changed in area. So, the change in brightness has to be repeatable.
The orbit plane didn’t move, so the duration of the transit has to be same each time and that duration for - just to give you an idea how long a transit lasts, if you were to look at the Earth transiting the Sun from some distant place in our galaxy, you would see that across the center of the Sun, it takes about half a day.
And you can think of it this way. The Earth moves about 1 degree in its orbit per day. And that is - it’s 365 days to go around, so it’s 1 degree per orbit, one degree per day. And the angular size of the Sun at the distance of the Earth is half a degree. So it takes about half a day for Earth to cross the disk of the Sun. So that’s take kind of time duration of the transit that you have to be looking for. And you can derive all that from Kepler’s law by the way. So, that’s the principle, the method we used.
SLIDE 14 Going on to Page 14 then, the question is how, do we do it with the Kepler Mission? Well, I’ve already said we’ve optimized it to look for Earth-like planets in one-year orbits. And the way we do it is we look at 100,000 stars continuously and simultaneously. We measure the brightness of 100,000 stars every half hour simultaneously.
We take that data with our telescope and we look at the same set of stars for the entire four-year mission. You can't look in one place, you know, one day in another place in another day because if you blink, you’ll miss a transit. So you have to look in the same place in the sky.
And the way we do this is with a Schmidt telescope. As astronomers, you’ve probably heard of Schmidt telescopes. They’re - they have a special property of being able to look at a wide field of view in the sky, wide for telescopes that is.
Our field of view is over 100 square degrees. And to put that in context, think of the field of view of the Hubble Space Telescope. If you took a grain of sand between your fingers and how held it arm’s length, that’s how much of the sky the Hubble Space Telescope can view at any one time. It’s not a whole lot.
But Kepler, if you take your open hand at arm’s length and hold it up, that’s how much of the sky Kepler views at any one time. In fact, the gaps between our CCD modules, as you can see in the little diagram on the right there, those gaps are so big that you can put the full moon in between the CCD modules and not touch two modules. So it’s a fairly - a really large piece of sky.
(John Gallagher): Open hand?
David Koch: …hold your open hand at arm’s length, that covers about 100 square degrees in the sky.
Another comparison I use is that the dipper on the Big Dipper is about 50 square degrees. So, it’s like double scoop. It’s two dips from the Big Dipper. So it’s about how much of the sky we look at.
The next thing is the photometric precision of the telescope, of the photometer, of the CCDs has got to be good enough to see that tiny transit. And we’re designing this instrument - this photometer to have a noise level of less than 20 parts per million.
Now, the reason for that is -- you go back to few slides -and you saw the size of the Earth relative to the Sun is one part of 10,000. That’s - actually, it’s a little bit smaller than that even.
Now, one part in 10,000 is 100 parts per million. The change of brightness due to the Earth is actually 84 parts per million. So, having the noise at 20 parts per million means that we will have a 4 sigma detection. That is, the signal is four times the noise for the transit. And then, of course, we add transits together and that improves our signal-to-noise.
The mission itself is launched on a Delta II rockets into what we call a heliocentric orbit so that it’s not orbiting the Earth anymore. It actually leaves Earth and goes into orbit around the Sun and basically is trailing behind the Earth as the Earth goes around the Sun. So, it’s a slightly different orbit than the Earth. But that way, we don’t have a problem with the telescope being blocked by the Earth at some point in its orbit as it goes around the Sun as it goes around the Earth because we’re looking at one place in the sky always. And being in Earth orbit, that would - you can't do that. You would end up with the Earth blocking part of the sky on every orbit.
SLIDE 15 Going on into Page 15, we showed what we call the photometer. Photometer meaning we took a telescope and put the CCDs at the focal plane and the combination of the two is what we call a photometer. You could think of it as a photometer with 100,000 data channels coming out of it. It’s really what it’s doing.
And right now, we’re already building this - the Schmidt corrector. And the primary mirrors have been polished. We’ve received them and they’re - we’re about to get them (coated) with the special (coatings) that you put on space optics.
The CCDs that make up the focal plane, we’ve had all of our flight CCDs for over a year already. The electronics to process the CCD data, right now those electronics are being built. The electronic boards already have the parts stuffed on them and we’re into testing of those. The whole photometer itself should be completed, integrated as a unit and tested through all of its tests about a year now, next November.
And just to point, this is going to be the ninth largest Schmidt ever built, comparing it to all the ground-based Schmidts and it’s going to be the largest telescope ever launched beyond Earth orbit. Of course, subtle change when the James Webb Space Telescope is launched and built because it goes on beyond Earth orbit.
SLIDE 16 Slide 16 just shows you some of the CCDs that we have (in hands) literally. And for comparison, a typical CCD in a digital camera is about the size of your fingernails. So, you can see what a fingernail is compared to the CCDs that we’re flying on the Kepler Mission.
SLIDE 17 Going on to Page 17, it shows of the photometer then mounted in the spacecraft. The spacecraft provides the power from the solar cells. It provides the telemetry sending the signals down on the ground on a high gain antenna. And the signals for commands come up on the Omni antenna.
The avionics are - it’s a fancy term for electronics that control both the spacecraft and the photometer. And there’s a solid (unintelligible) recorder and some star trackers and the radiator -- that big thing on the side is needed to cool our CCDs; we passively cool them to about minus 95 centigrade.
SLIDE 18 Slide 18, we show you where in the sky we’re actually going to look. And if you look at that slide, you can see Vega is on the right side, Deneb on the left and the field of view is right between those two stars which form the Summer Triangle. One side of the Summer Triangle goes right through our field of view, so it should be an easy part of the sky for people to walk out their backdoor in the summer and point out and say, that’s where we’re looking for planets.
(John Cox): My question is, how did you choose that area of space to look?
David Koch: Okay, (John). You know, that’s a very good question. You might say, why pick any, you know, why pick a particular place?
And the reason - it has to do with the geometry. It’s not because we said there - that is a better place to find planets (than) some other place in the sky). It has to do with the geometry of the spacecraft, the launch vehicle and the orbit.
And the way it works is the following:
When you put a telescope in space, you need a sunshade. And that sunshade - it lengthens the size of the telescope and defines how close to the sun you can look.
The length of that sunshade is defined by the envelope of the launch vehicle. And when we look at this, we found that the closest you could get to the sun at any time, the biggest sunshade, (allowed us) 55 degrees angle away from the sun.
So, if you want to look continuously at one place in the sky, what that told us is you have to look above 55 degrees ecliptic latitude. You’d need to have to be above - at plus 55 ecliptic latitude or below 55 - minus 55 ecliptic latitude looking in the Southern Hemisphere, southern sky.
Well, we - the - between the north and the south, the reason we picked the north is we have to do follow-up observations of the stars, we have to classify the stars we’re looking at and all of our research team members have access to telescopes in the Northern Hemisphere, not the Southern Hemisphere. So that told us we look at the northern part of the sky.
Then, the final question is, in that part of the sky, where do you have the richest star field? And all you have to do is pull out your Star Atlas and you can see that, you know, the real rich star field that you have is where the galactic plain rises above 55 degrees ecliptic latitude. And that is the single region in the sky then that matched all of our design criteria.
So it wasn’t that we think there are more planets in this place in the sky than any other place. It’s the best region for the geometry problem that we had to solve.
SLIDE 19 As far as results -- going on to Page 19 -- we don’t know what we’re going to find. We can tell you what we can detect, we can tell you how small the planet can be that we can find, but we don’t know what’s out there. This again is a discovery mission.
We can speculate what we might find. And the way we speculate is we make the assumption that all stars, like our Sun -- dwarf stars -- have planets and they - let’s presume that they are - have solar system, something like ours. That is, they have rocky planets the inner part of the solar system and there’s a reason why. Why? Because a planet formation, you would expect rocky planets in the inner solar system. They may have gas giants in the outer system, and there’s reason for planet formation theory to expect gas giants to be in the outer solar system.
And if you then assume that these rocky planets are in orbit, like Earth or Venus in the Habitable Zone, if that’s the case and presuming every - one of the planet - stars we look at would have a planet, then we would expect something like 50 planets that are exactly the size of the Earth. If the planets are no bigger, we could detect 50 of them.
If the planets, on average, could be larger, then we could find several hundred planets quite easily. And when you start getting to having multiple planets in the system, that is, like we have Venus and Earth in the same system, then you would even have a probability of about 12% that you might even see more than one planet transiting a given star. And we’re hoping for that kind of exciting result.
If you have lots of planets like Earth and Venus in shorter-period orbits, they’re easier to find, the probability they form a transit is greater. And chances are, if they’re common, then we’ll see thousands of terrestrial, that is, Earth-like planets.
As far as giant planet go, because of the detections of 200 planets already, we know the statistics of giant planets in short-period orbits. And we expect, just based on that statistic, that we’ll see over 100 giant planets in inner orbits. And if you have the size of the planet from the changing the brightness and then you do the radio velocity measurement and get its mass, you can then calculate the density of that planet. And we expect to be able t6o do that for several dozen planets.
The results that we get probably will be a mix of the - what I’ve described above. And the other thing is that we expect a large enough number of planets with our system that if, in fact, the number of planets are rare and we get a no result, that would be a significant result too because we were expecting some much larger number -- and if you only found a few, that would tell you something significant as well, that there aren’t - terrestrial planets are not common.
SLIDE 20 The last few slides are just programmatic information. Slide 20 shows you a little bit about of schedule - launch is scheduled for November of 2006 and we expect to get results. We don’t have to wait four years. We should, after the first few months, be able to tell a lot about planets with short-period orbits by, let’s say, a year after launch.
(Ken Cramer): I’m wondering sort of about the life time. After you’ve looked at this for four to six years, would you then point it to another spot in the sky? And what is the ultimate life time?
David Koch: Okay. We’re funded - the baseline mission is for four years, and we’re hoping that the mission is working, that we’re getting results. And if that’s the case, there’s a very high chance that they will continue - NASA will continue to operate it for at least two more years.
Ultimately, there - we have one consumable. There’s a small amount of hydrogen fuel on board that we need to take out the torquing of the spacecraft due to the solar pressure from the sun. And that - right now, we have sized the fuel tank for that to give us - let’s see. I’m trying to remember how we described it.
It supposed to give us 100% confidence of getting four years. That is, if you put in all the worst-case of scenarios and they all add up together, you would last four years.
Nominally, we ought to be able to get to six years. And I believe that we - we then picked a fuel tank which is a very special piece of flight hardware that has a lot of design and heritage to it. They come in standard sizes. And we’ll just take the next standard size up from our minimum requirements.
If we do that and we fill it to its capacity, we probably can operate for 12 years. That’s probably stretching it.
Now, in terms of would we look somewhere else or not, the answer is we probably would not because the value of the science we have continues to increase with staying on the same field. Also, we had to expend a lot of effort doing ground-based observing of that star field to understand what the stars were that we look at. We don’t - we can’t just swing around to some other place of the sky and start taking data. It would almost be a blind search at that point. So, for that reason as well, we would stay.
And finally, if you’re looking at things like the previous question, you know, asked about spots on stars, if you can go six years or more, you actually are starting to get into looking at the full cycle of - at least the solar cycle is 11 years so that you’re starting to get beyond five and six years or seen most of a full cycle of solar-like stars which would be also very interesting science.
SLIDE 21 Slide 21 shows you the large team of scientists working on this. And I will say there’s even a much larger team of engineers. Mostly aerospace and also at JPL who are working on this. So, it’s a big - a real team effort to do this kind of space mission.
(Ray Shapp): Hello. My question is, you didn’t talk about other (science missions) will do, but I assume what such precision photometry that you’ll be getting information about star spots and stellar activity cycles, that sort of thing?
David Koch: Oh, absolutely, (Ray). We - the thing is we can’t - we have not emphasized that aspect to the mission.
That aspect to the mission does exist. And we do have some key members who will be doing a different kind of science with the data. We have one group that will be doing what’s called a stereo seismology. That is, looking at the oscillations in the stars. It has been done for the sun. And from the oscillation periods, they can derive the density and the composition. That is, the ratio of heavy metals to hydrogen in the star. So, that - that’s one program. And they can do it for the brighter set of stars, about the 5000 brightest set. That’s one program that we’re doing.
Another one is we’re going to try to do astrometry to get the distances to the stars. One of the things we need to know is how far away the stars are. And the things, well, like you mentioned with spots, people will be able to hopefully derive rotation periods for the stars, stellar cycle periods.
An interesting side line to that is something called the Maunder Minimum. Four hundred years ago, there were no spots and the weather got very chilly, the Thames River in London froze over, it got so cold, the glaciers and the Alps came very low in the valleys. We don’t know how often that happens for our sun.
And if you look at a large set of solar-like stars, you can ask yourself what the percentage of them that are in Maunder Minimums are and that might help us predict when our next ice age is headed our way.
SLIDE 22 And then on the last slide, it’s just a summary of what I talked about. And what I didn’t put on there is the Web site for the Kepler Mission is kepler.nasa.gov. I kept it simple for people to remember.
So, that’s a ... sketch of what we are doing with the Kepler Mission here at NASA.
(Marni Berendsen)What are the follow-up missions for this after we do find some candidates? Do we have any firm missions planned yet?
David Koch: There are a number of different followups that you can do. We’re expecting that once you know where a planet is orbiting a star, that you can use things like the new planned James Webb Space Telescope to do a spectroscopy on that planet and tell you something about the atmosphere. And then, there are other bigger missions that are in the planning that haven’t been funded yet that can do some follow-up work.
They won’t necessarily look at the things that Kepler is looking, but will tell - those follow-up missions, first one is called SIM and the other is called Terrestrial Planet Finder. It’ll tell them how to design and optimize their design of the mission to optimize the results that they can get on planets.
Now, what those will do is get masses of the planet. We only get the size. They can only get the mass. So the combination of those two missions are quite complementary in terms of understanding things about the planets.
Marni Berendsen moderating
[Attending telecon:]
Bill All: Greenville, North Carolina with Carolina Skies Astronomy Club.
Joan Chamberlain: Astronomical Society of Northern New England in Maine.
Sue Moe: North Eugene High School Astronomy Club, Oregon.
Sarah Jurado: The Society of Physics Students at University of Toledo, Ohio.
Barbara Geigle: Berks County Amateur Astronomical Society in Warren, Pennsylvania.
Bruce Tinkler. Amateur Telescope Makers of Boston. We’re at the clubhouse in Westford.
John Wakefield: Houston Astronomy Club with 15 students from Planetary Astronomy class at the Montgomery College in Woodlands, Texas.
Ray Shapp: (Dr). (Dale Jerry) from NJIT, New Jersey Institute of Technology, hosting-9 folks listening in.
END
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