Universe of Learning: Understanding the Origins and Diversity of Planets August 2, 2018 3:00 pm CT

Kay Ferrari: This is Kay Ferrari. On behalf of Jeff Nee, and Amelia Chapman from the Museum Alliance and Heather Doyle, and Rachel Zimmerman-Brachman and myself from Solar System Ambassadors, we welcome you to the first of our series of Universe of Learning programs for the next fiscal year. I’m going to turn the program over to Dr. Emma Marcucci who will be the facilitator for today. Welcome Emma.

Dr. Emma Marcucci: Thank you Kay. And thank you for all of the listeners now and listening to the recording in the future. Today we are going to have our NASA’s Universe of Learning telecon on “Understanding the Origins and Diversity of Planets”. We are excited to bring you this briefing on planetary formation. For those of you who were with us last spring, our last science briefing was in May – or, our last NASA Universe of Learning science briefing was in May - on star formation so now we’re going to look at planet formation.

Getting started on Slide 2 we have our standard NASA Wavelength list. There are our resources: some citizen science examples that we’ll go into in a little bit more detail in a second. There’s a couple of learning activities, the Active Accretion Learning Game just to let you know there’s some notes in this PowerPoint. This is still an educationally sound activity but some of the links have been updated so I put those updated links in the notes section.

1 We’ll be reviewing some of our exoplanet resources as well. We also want to highlight that it’s the 15th anniversary of the Spitzer Space Telescope which is done a lot of work in looking at planet formation looking at exoplanets. On the Wavelength list you’ll see links directly to Cool Cosmos and to the TRAPPIST-1 products. I also listed the general URLs for Spitzer. NASA Wavelength was having a few issues accepting some of the URLs so there are a ton of resources related to this topic so I highly encourage you to look at the images, the videos, the animations, the news releases. And then the last section on Wavelength is some selected press releases. These are some of the more recent press releases or some of the more kind of iconic results but it is not by any standard a complete list.

Going to Slide 3. This is our outline of the talk today. Our format is a little bit different than normal for those of you have joined us before. We’re actually going to start with our resources and then we will go into our two science speakers. They’ll each have about ten to 15 minutes to share their information and then we’ll have about ten to 15 minutes of discussion and questions at the end.

So getting started on Slide 4 I’m going to go over the resources. These resources are kind of some “Greatest Hits” or “Best of”. So these are resources that you’ve seen before if you’ve attended our science briefings. In the subsequent slides we have the briefing listed so you can look at it. Our first one, going to Slide 5, is Disk Detective. Disk Detective is a citizen science project. It’s hosted on the Zooniverse.org page and this was originally presented in September. I’m going to briefly go over how these work, but I encourage you to go back to those original presentations if you would like more information.

2 Going to Slide 6, Disk Detective. You are basically helping- this is the citizen science aspect - you are helping identify disks, types of disks. There are two parts to this. There are informational buttons at the top, those are circled in green. These will give you tutorials and how the program works. Then the circles and arrows in orange are the steps you take. So essentially what this Disk Detective is, you have an image and the target is in the center of that red circle. When you press Play it’s going to shift through different images, different wavelengths. You can put that on repeat and you can watch as many times as you’d like, but once you’ve watched it the options in the middle - which are currently grayed out once you’ve watched it they’ll be dark - you choose what describes the object. You can choose multiple options. Does the object shift in the circle? Are there multiple objects? Different factors that would affect what type of disk this is? Then you click Finish and you get the next option. It’s very easy to get started, you just jump right in. Again, more details are in that September briefing.

Going to Slide 7, our second citizen science resource is Exoplanet Explorers, also on the Zooniverse.org hosting site. We had a presentation on in January 2018. That was our live from AAS briefing. And that was actually the result of a paper [about] an exoplanet solar system that was found entirely through this citizen science project. So this was science done with this resource. We also, during our March 2018 Jessie Christiansen talked about this one in the resource itself in a bit more detail.

So going to Slide 8 this is what it looks like when you launch the activity, the resource. There is a pop up there in the middle that will walk you through the

3 tutorial of what you’re supposed to be doing. If we go to the next Slide 9 this is then what you’ll be doing once you’ve gone through that kind of mini tutorial. You can always pull the tutorial up and other information up on the right-hand side. Again, circled in green, that’s your informational button.

The steps that you’re doing: you’re looking at this light curve in the middle, circled in orange. Then you are selecting whether it seems to be a good match to the guide which is in the blue box on the right. You select Yes or No, you click Done, it brings up the next option. You may notice that in this particular example on the far left it says “Finished”. That means that they’ve had enough people look at this example to have kind of confidence in the finding. So you can look at different projects and ones that still need extra sets of eyes.

Going to Slide 10. Our third example that I’m going to run through today is Eyes on Exoplanets. This was originally presented in March 2017 by my colleague here Carolyn Slivinski. Eyes on Exoplanets is kind of an immersive interactive environment to explore space. You may be familiar with the NASA’s Eyes infrastructure, there’s Eyes on Earth, Eyes on the Solar System and then Eyes on Exoplanets.

So each one of these dots you see in this main picture is an exoplanet that’s been detected by one of our missions, either ground-based or space-based. The database that feeds Eyes on Exoplanets is directly linked to the main exoplanet archive database, so it is updated regularly. At the moment you download an interface and then that interface connects to the Internet to pull that data.

If we go to the next Slide 11, these are some of the examples. You can zoom along with your mouse. You can click on objects. When you click on an object, this is for example the TRAPPIST system in the center there kind of all

4 of those words in the very middle, you can get some information about the star, about the planet. If we go to the next page on 11 you’ll see these in a bit more detail. You can look at different views. You can view it from the star, from the planet, you can do some comparisons - how long would it take to travel there in a Ferrari or in a jumbo jet or at the speed of light. You can compare it to our solar system. You can turn on the habitable zone, so where is an area that liquid water might be possible? You can do a lot of exploration.

[Slide 11] The bar that’s on the right was the one that was at the top of the screen. You can always get Home so that’s your far left button. You can View From Earth. This is kind of a planetarium view; they actually sit you on Earth and you can look at the sky from that perspective. The third button in is the Latest Discoveries. So these are some of the most recent additions to the database. The middle button with the exclamation point are Weird Planets. These are oddly shaped planets or very hot planets, kind of some of the extreme unique planets that we’ve seen.

Next over you can toggle on Kepler. Going further over you can Search; for example you can search the TRAPPIST-1 system. The final button - or well, final is brightness settings - but the final blue button is you can look at different Exoplanet Missions. So these are all the missions that have looked for - have found exoplanets both ground-based and space-based. So it’s a very powerful tool. In the Wavelength list there is a video tutorial that video that’s linked there to help give you some context of seeing it in action since we can’t demo that on a telecon.

5 So that is it for resources. Are there any questions that you have before we jump into our science topic for today? If you have any questions please unmute and speak up. We do request that you just restrict yourself to one question for now so we make sure we have time for our presentations. All right well I don’t hear any questions so if you do have any questions please feel free to reach out to us at a later date. You can email Kay and she can coordinate with us to address those questions.

Starting on Slide 13 we are happy to have Dr. Farisa Morales join us. She is an Astrophysicist who hunts for planets at NASA’s Jet Propulsion Laboratory or JPL and is a professor at the California State University Northridge. She studies stars surrounded by planetary debris disks, the dusty ring-like structures home to colliding asteroids, sublimating comets that circle stars like the Sun and hint at planetary formation processes. She is going to be talking to us today about those planetary debris systems. Farisa, please take it away.

Dr. Farisa Morales: Hello. Can you hear me?

Dr. Emma Marcucci: Yes we can.

Dr. Farisa Morales: Excellent. Thanks for that introduction. I am happy to talk a little bit about how planetary systems form. If we go to Slide 14 the first thing I have there is a link for those that have PDFs of the presentation at the bottom of the page. If you click on that, that little animation what it does is that it starts out with a relatively uniform disk that is known as a primordial disk.

So the idea is that planetary systems form from a collapsing cloud, a molecular cloud. So a chunk of that cloud will collapse onto what is known as a protostar, so baby star. So due to conservation of angular momentum, the disk or that cloud begins to spin and flatten out into a disk. And if you run the

6 animation that disk eventually also becomes dissipated. Most of the material falls onto this proto-baby star, forming the star and then as the star ignites and begins to clear out its environment and push away the remaining hydrogen less than 1% or so. Initially about 1% to 10% is in the disk the majority again went into the star and then the disk becomes dissipated.

And in the disk there is what is known as planetesimals forming. So these are the building blocks of planets. If you go to Slide 15, another animation, let’s assume that some planets have formed and that there’s still debris around and so later as the system has become more mature and these planets are clearing out their environments around the star. They can also rotationally perturb the planetesimals that remain around them. And so if you run the animation you’ll see that there’s a couple of boulders that will collide and replenish the dust in the system.

So what’s happening now is this dust that is replenished is a second generation dust. So initially the planetary system formed from a hydrogenrich, gas-rich molecular cloud which had this primordial disk. But later the dust gets replenished and now it’s more like grains of silicon and ices that are replenished from this rotational perturbation.

If you go to the next slide which would be 16 also at the bottom you have a link there. And if you run that animation what you’ll see is that just fast forward, fast forward when you have a collision between two larger boulders and this is all happening - the initial formation of the planetary system is like the first 10 million to 30 million years which sounds like a lot, perhaps to

7 human beings, but due to the stellar lifetime this is very short when the star forms and in the first 10 million to 30 million years you have a planet forming.

But later, maybe 100 million years later, 200 million, within the first billion years I mean compared to the Sun the Sun is like 4.5 billion years now. So within the first gigayear. It’s reminiscent of the late heavy bombardment what the solar system went through where Jupiter and Saturn gravitationally perturbed each other and there was a lot of stuff thrown around it is believed, that’s the current consensus. So if you run this animation on Page 16 then boulders colliding against each other or comets sublimating their debris as they get thrown inward these debris gets spread out into arcs or rings that are much easier to see with space observatories like Spitzer Space Telescope for example because when all that dust is gathered into a planetesimal then it’s hard to see because most of the particles are trapped inside that boulder. But when it’s spread out now due to the surface area of this ring you can more clearly see them.

Slide 17 is a summary basically of when I talk about exoplanetary debris systems, I really mean for example we have there representative of Ceres on the middle right on the bottom right we have a representative of the Kuiper Belt. So Ceres for the asteroid belt, Pluto for the Kuiper Belt, comets, asteroids, the planets themselves, the tails of comets. So we have that also on the picture, and zodiacal dust. In general there’s interplanetary dust everywhere. So I mean everything including ourselves, on rocky Earth for example, we’re all debris.

In studying the debris, if you go to [Slide 18], what factors inform us of their architecture like what have we been seeing in the past decade or so. On [Slide 19] I show you on the left is a schematic of I said brightness versus a wavelength there. So that’s known as a black body curve. That’s what you

8 would expect to see, how bright is something versus wavelength for a point source.

So that curve peaks somewhere at some wavelength that corresponds to the temperature of that star. Now if you have a bunch of particles, that would be the bottom insert - bottom left-hand corner of that Slide 19 - if you assume that there’s a bunch of particles in thermal equilibrium with the star so just a very narrow ring and all the particles are at the same temperature because they’re the same distance, what you expect to see then from that system is it’s very, very far away and you cannot actually see the ring of debris. You’re going to see a Spectral Energy Distribution which is what the acronym at the top of the page means. SED means Spectral Energy Distribution.

The energy that we’re seeing from these rings they have another black body that’s peaking at colder wavelengths or meaning longer wavelengths, colder temperatures. So the superposition of these two black bodies the one from the star and the one for the debris is what you see at the bottom left-hand corner of the slide here, Number 19. I’m going to focus on that little white square in the middle of that superposition of two black bodies because that’s where the turnover happens, that’s where it’s no longer sort of spherical coming down but yet we have another hump, a little hump there due to the rings.

So now if you go to the right-hand side of that Slide Number 19 that’s real data. That’s what’s Spitzer Space Telescope saw and we published in 2009, that corner. So the gray line in the middle of the page diagonally coming down and there’s a label there “Star Model.” So that’s the star. Then we see in dark

9 what is known as the IRS data from 5 to 35 microns. Again this how much flux is in Janskys (Jy) for example versus wavelength on the bottom axis. The IRS spectra shows us how is peeling off the photosphere. It’s coming up and the later there’s also MIPS photometry. So we have those two diamonds on the plot there on the upper right-hand corner of this slide.

The bottom right hand corner of that slide has another similar plot. But what I’ve done there is I’ve subtracted the contribution of the star. So if you subtract the contribution of the star you have the excess emission only and now you see that it’s clearly these two - the warm and the cold which is represented here in blue and red emission from two rings of debris. So one ring of debris was not good enough, you needed two rings of debris to reproduce the data.

So back in 2009, 2010, 2011 we’re finding - if you switch now to Slide Number 20 - I did the same exercise on a lot of these sources and we’re finding that the temperature of the warm dust tends to pile up at around 190 degrees Kelvin and the cold dust tends to happen around 60 degrees Kelvin. So that’s what the histogram is showing you on the upper part of Slide Number 20. So in blue there the warm dust at around 190 Kelvin. The bottom part of that histogram is just A type stars; the number of A type stars is like two to three times more massive than the Sun where the histogram above that for solar type stars, so sunlike stars. And it doesn’t matter if it’s the more massive more luminous stars or solar type stars, the temperature of the dust tends to be the same. It’s not the size of the ring, but the temperatures. So the temperature horizon where this dust tends to accumulate.

We go then to Slide Number 22. So Slide Number 21 is basically telling us so then, you know, where do we go from there? We have evidence of two belts. Herschel Space Observatory which was an infrared mission complementing

10 Spitzer Space Telescope but longer wavelength than prepared by the European Space Agency but NASA contributed as well. On Slide 22 you see that we found lots of doughnuts, doughnuts all over the sky. Face on, and edge on and so on. What we’re seeing here for the Herschel contribution is that we’re seeing at colder wavelengths than what Spitzer could see the size of the rings of the Kuiper Belt. There’s several of them that I am showing you on that slide and that comes from a paper we published in 2016, so it’s relatively recent.

Moving on to Slide 23, now that we have all this information I had to adopt realistic grain property because black bodies was just not cutting it for how the Spectral Energy Distributions, the SEDs, were behaving. And so on Slide 24 I talk a little bit about these icy grains inclusion matrix particles versus core mantel particles and I found that they were behaving about the same. And so the idea here is that we’re mixing water, ice, and nitrogen, amorphous carbon, rocky silicate material. So we make up these dirty ice grains using their optical constants and compute their emissivity properties in the computer. We put them in what we call a synthetic model. So on Slide 26 we have an SED model is that what you have also, Carol and Emma? On 26 I’m showing you here a cartoon of the model because Emma and Carol said I could not show you equations. So here is cartoon version of a belt. Imagine there a central star, a warm inner belt and a cold outer belt where we’re going to put in those icy grains. And if we do that, then going to Slide Number 27 now we see data that you saw before, very similar on the left-hand side of the slide where we have a star coming down, the IRS spectroscopic data from Spitzer. And then the diamonds in black, green and red on that upper left-hand

11 corner of the slide, one of the sources, they have these phone number names so it’s HD159492 and so on. So I mean we started several of these so there were 70 of these sources debris disks that I was pursuing.

The blue curve going through the data is the sum of a star, a rocky inner belt and an icy outer belt. The pink curve is the sum of only rocky material which doesn’t cut it. And the green curves on there are pure black bodies which again are not a good enough fit. So on the bottom right-hand corner you see a zoom out of the excess emission and how the blue curve goes really nicely through the data telling us that now that we know the size of the rings of the outer Kuiper Belt that they are icy.

So again informing of how these planetary systems are forming, their structure, the composition. If you go to Slide 28 we have a similar result. It’s just another source where icy grains are more likely. The black diamond is a little higher than the blue curve, which tells me perhaps that the grains are more pure water ice then I put in here. It was a three to one ratio - I put in three parts water, one part ammonia, and then amorphous carbon and so on. So it’s just telling me that there’s probably cleaner water in that specific debris disk.

If you go to Slide 29 another similar result and so over and over and over we saw these things that the outer belt is icy. So moving on to Slide 30, what I mean to show you there is basically a conclusion that Spitzer saw both warm and cold components of debris around relatively mature stars that are in the process of forming their planetary systems. The warm dust was wellcharacterized with the IRS spectroscopy. Herschel confirmed that there’s an outer belt and it shows us the result location which helps us pin down the composition of the grains. So there, number five on Slide Number 30 is

12 pointing out that it’s revealed that there is water ice on these outer belts similar to what we see here in the solar system.

I then began to inquire about the gaps because there’s belts and so what’s between the belts? We have four gas giants here. So on Slide Number 31 I’m letting you know that I went planet hunting. Slide 32, a picture of the Keck Observatory’s primary mirror on the upper left-hand corner and the bottom right there I am outside at 40% the oxygen, 14,000 feet high, on the top of Maunakea, a dormant volcano in Hawaii.

If you click again, if you go to the next slide, then that’s what the data looks like on Slide Number 33. That’s very simple, not a lot of reduction on that data. But you can see there’s an interesting point source there at 2.9 arc seconds from the star already, more or less at the right location between the belts where you would expect for these debris systems to have perhaps giant planets right? So these we call candidate planets because we don’t know if they are planets. It could be a background source, right? So we have to go back and confirm. The way we do this is that we use these large, large telescopes on the planet, this is a direct imaging technique.

On Slide 34 there’s a few cutouts of what adaptive optics is. Thanks to adaptive optics, which is a deformable mirror in the path of the light - so in the upper left-hand corner this is taken from a video - there’s also a video if you want to watch it there’s a link at the bottom of Slide 34. The light comes in - this is for the Gemini Observatory but it’s the same way for Keck. The

13 light comes into the primary, bounces off the secondary mirror back down through that hole in the primary mirror into the optics box.

As the light gets bounced around, on the second upper right-hand corner of that slide there’s a little gray-looking triangle inside the optics box, that’s a DM, a deformable mirror. And that deformable mirror when you close the loop it changes its shape to catch the photons where they were supposed to have fallen. The way it’s done is that the atmosphere is monitored outside the telescope. Then the deformable mirror does its job and what you end up with is a million times better resolution than you had before. So thanks to this adaptive optics technique we have been able to detect faint companions to these interesting dusty stars.

So on Slide 35 for example we reported in 2015 that we found brown dwarfs. Here’s a brown dwarf published. And Slide 36 we’re reporting last month the detection of a white dwarf. So we’re finding all kinds of things and lots of candidate exoplanets, we’re finding also brown dwarfs and white dwarfs. And on Slide 37 I thank you for your attention.

Dr. Emma Marcucci: Well thank you very much. That was great information. For anyone who is interested in those equations that she mentioned, the slide jump between 24 and 26 is because there’s a hidden Slide 25 which has those equations on it.

Dr. Farisa Morales: There you go.

Dr. Emma Marcucci: Yes. So as a reminder we’re going to have our next speaker and then we’ll do questions at the end. If you have a question, please make a note on a piece of paper and maybe what slide number it’s noted on and we will come back to those after our next talk. So going to Slide 38 -- there we go, all right -- so our second speaker is Dr. Hilke Schlichting. She is a professor in Earth Planetary

14 and Space Sciences and in Physics and Astronomy at UCLA. Her research interest lay in the intersection of astrophysics and planetary science. Her work combines exoplanet research with the study of our solar system to take advantage of the powerful synergy to develop a comprehensive understanding of planetary formation. Hilke, please take it away.

Dr. Hilke Schlichting: Thank you very much for the very kind introduction. It’s a great pleasure to have this opportunity to share a little bit about the origin and the recipe of planets and exoplanets. With that let’s move on to Slide 39. On this slide first of all unfortunately the X and Y axis labels don’t seem to have come out so what’s plotted on the x-axis is period and date, and what is plotted on the y axis is size in Earth sizes. So the Earth would actually be the second tic on the y-axis on the figure.

Every little blue point that you see corresponds to one of the planetary candidates that has been reported by NASA’s Kepler mission. To me this plot, although maybe it reveals that I’m a true geek, is truly fascinating because it has this amazing information. What it’s telling us is that first of all our universe is full of planets. So every little blue point is one of the planetary candidates that has been discovered. And then it tells us actually that planets live in spaces and sizes where we actually don’t have planets in our solar system.

So the three green dots that you see in the lower right-hand corner is actually our solar system. So the little green one at the bottom is Mercury, and then

15 you have Venus and Earth is the most right one if you wish. And so what’s really fascinating to me is that we found all these planets but they live in a space where basically where we don’t have planets at all in our solar system. So their typical orbital periods are less than 90 days, so they’re inside the orbit of Mercury. And their typical sizes are actually sort of in between Earth and that of Neptune. So that red line you see going all the way across is actually the radius of Neptune.

Those planets we actually nicknamed them or named them Super-Earth are Mini-Neptune because they are in the size between Earth and Neptune, are actually as of today the most common planets that we know of in our galaxy. So for somebody like me it’s truly fascinating trying to understand planet formation to understand where these planets come from, how did they form and why don’t we have one of those on our own solar system. I guess if you go to Slide 40 and 41 you have a little cartoon of the Super-Earth and the Mini-Neptune. We’re really trying to figure out what they are and where they formed? Did they form there where we see them, did they form further out and where they moved inward or did they do some sort of combination of these two?

And finally, the reason why we care about this so much is of course we want to understand our own formation and also want to understand how common or how rare is our solar system. And on that note I would like to remark that you will notice that sort of the lower right-hand corner is pretty empty of blue points. And to first order that’s not because there are no exoplanets there it’s to first order right now at least because those planets are the hardest to find. And so we may still be able to fill that space significantly. Keep tuned for that. And then actually the new mission that was just launched TESS and that started science operations last week actually may help fill some of that space in the future.

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So what’s the yield so far? The yield so far if you go to Slide 42 shows you a histogram basically the fraction of stars that has at least one of those planets as a function of planet size. And so if we do a simple exercise of adding up those planets, what we find is that if you will take planets that are bigger than Earth and smaller than Neptune if you add up these percentages, you know, 16% plus 20% plus 20% what we find is that about roughly every other star in the night sky or in our galaxy has at least one planet around it that in size bigger than the Earth and that orbits within 100 days.

To me this is a truly amazing result because it means when you tonight look up into the night sky you should think to yourself that every other star that you see has a planetary companion around it, on such a short orbital period where our own solar system would not have any. So we right now are in the other bin - the other 50% of stars that would show up as having no planets at all. So planets are truly ubiquitous. I guess that’s a wonderful thing because it gives us the opportunity to learn a lot about them and our origin.

Then of course we’re not only interested in finding planets, we want to characterize them. One final note: the planets that Kepler discovered, they’re almost all sort of in the same patch of our sky and that was because -- and you can see that on Page 43 -- that’s because Kepler basically surveyed one location. And so they’re this cone that is highlighted there. But now with the new TESS mission we are looking all over in the sky. So we’re going to get a good census in all the directions not just in one specific one. We don’t truly expect a huge change there but it’s always good to double check.

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Moving on to Slide 44. The next thing after finding planets of course we want to study them. We want to find out what they’re made of, could they harbor life? Would they be a good place to visit? The very first thing we can do is we can measure both their radius and their mass.

Kepler and TESS give us the radius, because those planets transit in front of their stars, so they blocked some of the stellar light. And by how much of the light they block tells us basically their radius. Then we can use additional methods to constrain or determine their masses. If we have both of those, we basically can calculate their average density which tells us something about their bulk composition. Or we can put them on a plot like the one shown on Slide 44.

So what I’m showing here is those lines correspond to planets, to hypothetical planets that I can come up with, made out of a single composition. So for example I could make a planet that’s entirely made out of rock on my computer, and that’s shown by the red line. So if my planet will be entirely made of rock if I measure its mass and its radius it should fall on this line. I can repeat this exercise for water which is shown by the blue line and so on and so forth. Now I can overplot the actual measured masses and radii of some of my exoplanets and this way I can actually get a first idea of what these planets may be made of with no other additional information.

What is really striking is that many of them actually have radii that are so large that we know that they must have some sort of component of their total mass in hydrogen and helium – in some sort of light gas that basically can give them a large radius without changing their mass too much. So a little bit similar like Uranus and Neptune, that both have roughly 10% of their total mass in hydrogen and helium. Then of course we also found some that

18 actually are fully consistent with being some sort of rock iron mixture which will be closer to the Earth.

Here I would like to remind everyone when we talk about planetary atmospheres here, those atmospheres are extremely different from the atmosphere that the Earth has. Our own atmosphere, although it’s super important, only makes up about 1 millionth of our total mass. It’s a tiny amount of mass. It has basically an extend or a scale height that’s only about .1% of our radius. So we would not be able to see that if you would look at an Earth as an exoplanet. If you wanted to put it on this plot it would just show up as it pure rock and iron mixture.

But if you add about 1% of the total mass in hydrogen and helium you increase the radius so much that we can easily see that. So that’s why we are pretty confident that a significant fraction of these exoplanets actually must have hydrogen and helium envelopes. That’s super interesting understanding their formation because it must mean they must have formed in these initial gas disks that we just heard about so they formed rather quickly before the hydrogen and helium dissipated.

I would love to share many different things with you but I picked one specific topic because I think it highlights sort of the diversity. So one thing that we got very interested in is to explain the large diversity we see in composition. I should say that to the very first order most planets look like they’re formed with hydrogen helium envelopes, which is actually quite different from the

19 terrestrial planets that we have in our solar system. But even and then in some cases you can strip those and lose them.

But there is even in addition to that there is a lot of diversity. If you now move to Slide 45 we’ve been trying to highlight here. Unfortunately the axis here also got messed up. So on the x-axis is mass in Earth masses and on the y-axis you have density in grams per centimeter cubed. These points all correspond to the various exoplanets of which we have discovered densities. One thing that was very striking to us is the fact that if you take a given planet mass, say seven or eight Earth masses, we find a spread in density and biocomposition that ranges from less than a gram per centimeter cubed to more than 10 grams per centimeter cubed. So there’s more than one order of magnitude spread in density.

You may say well that’s not such a big deal because if you look at the Earth and compare that to Jupiter, we also have a pretty big spread in density. However, the Earth and Jupiter are extremely different in mass. Jupiter is much, much more massive - 200 times more massive than the Earth so those are very different types of planets. What’s remarkable for the exoplanets is that a given mass planet can look like a rocky core or basically like Uranus and Neptune. So what’s going on? How can we understand this? I think for comparison I plotted our solar system planets on this. So if you go to Slide 46 there’s the Earth, 47 there is Mars - there is Venus and then 48 is Neptune. So if you for our solar system if you pick a given mass planet, they basically have the same density. Earth and Venus have almost the same density so do Uranus and Neptune. Also Jupiter and Saturn are almost the same density. So this is not true for the exoplanets.

So what happened? What’s different? This is a particularly interesting question because we see this variation in densities even in a given exoplanet

20 system. If you pick one multiple planet system - Kepler showed us that planets like to have companions. So often when we find one planet we find several and they’re often extremely different. And so we’re wondering how on Earth is that possible?

One of the ideas that we proposed is actually that these systems have late instability - actually when the gas just goes away basically the gas is good at dampening the orbit, when the gas just goes away you have a phase of impact and those impacts basically can strip the hydrogen helium atmosphere very effectively. Once you do that you can convert a planet that had a very low density, because it has a lot of hydrogen and helium into one that looks essentially like a rocky core. The nice thing is that’s a little bit analogous to our own solar system, where basically our Earth had this very late giant impact that basically led to the formation of the Moon and our final assemble stage actually also comes from a giant impact. So it didn’t have such a big effect on the Earth atmosphere because our Earth atmosphere is not hydrogen and helium, it’s as you know much heavier gases, but if you have a hydrogen helium atmosphere this is a very good way of removing that.

So let me conclude. Super-Earths and Mini-Neptunes are the most abundant planets that we know of today in our galaxy. About 50% of stars have one of those close-in exoplanets on orbital periods roughly less than 100 days. About actually 10% of stars have an analog to our Jupiter, so a gas giant on an orbital period that’s the same as our Jupiter or a distance of roughly five Earth-Sun units. So that could be one way in which you could ask the question how common and how rare is our solar system? So if you’re required to have a

21 Jupiter it may be a 10% number at best. And then some of the extreme large diversity we see in biocomposition of similar mass planets in a given tight impact system may be due to some late impacts that occur after the gas has gone away. And we think this may be a good explanation especially for some of these model plant systems that you’ll hear about like Kepler-1120, and 36, and so on and so forth. So with that let me finish here and I’ll be happy to take any questions.

Dr. Emma Marcucci: All right thank you very much. Thank you both Farisa and Hilke. So we now have lots of time for questions. As a reminder please restrict yourself to one question so everyone has a chance to ask their question. I know I have a few myself but I will throw it out to the audience before I take over, if you have a question please unmute and speak up.

Adrienne Provenzano: Yes hi. This is Adrienne Provenzano, a Solar System Ambassador. And I had a question for the first speaker about what is the significance of determining the iciness rather than the rockiness? I’m going to mute my phone. Thanks.

Dr. Farisa Morales: Hi. Well to me establishing the presence of ice in exo-debris disks brings us closer to understanding our own formation, how the solar system got here, how you and I are here. To me that’s a triumph of this type of data and this type of work that we are getting closer to seeing the same conditions replicating elsewhere.

Dr. Emma Marcucci: Great. Other questions that are out in the audience? All right well I’ll throw one out there myself. Hilke, you mentioned on Slide 41 that empty space of planets is probably because we aren’t able to detect them yet and it looks like that’s where a lot of our solar system planets live. Is there a thinking or is there a common thought among the community that solar system exoplanetary

22 system do look like our solar system or are we kind of the odd one out in terms of filling in that hole?

Dr. Hilke Schlichting: Yes, I guess it depends a little bit on how exactly you pose that question, how you define our solar system. We already know that at least 50% of systems are different from us in the sense that they do have these close in planets and we have none. We don’t yet know - if you wanted to find a solar system up here is just interested in how common are terrestrial type planets say like Earth and Venus. We actually do not truly know the answer to that yet because we don’t have the method to test that observationally. There is no answer to that question yet. We can estimate it very roughly but those estimates vary widely between 1% to a few tenths of a percent answer. What I think the data has demonstrated really strongly is that there are many planetary systems out there that are very different from us. Dr. Emma Marcucci: Great, thank you. Are there other questions from the audience?

Kevin: Hi. This is Kevin, Solar System Ambassador. I’ve got a question about the giant impacts that can strip the atmosphere. In relationship to our own solar system, we’ve all been paying attention to Mars lately because of the close approach and studying the moon Phobos and Deimos. And one of the theories was that it might be captured asteroids but then another one was that it could have been a planetoid that rammed into it that split into a couple of pieces. I’m wondering if that latter was the case and that had a giant impact could that have something to do as well as the solar wind effect of taking away that Martian atmosphere and if that would have any effect on why it doesn’t have a significant magnetic field?

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Dr. Hilke Schlichting: Yes these are all very good questions. So maybe I’ll start by saying that, we generally believe that the terrestrial planets including Mars were assembled in a phase of giant impact. So the Earth is thought to have been assembled by sort of a dozen or so of those large scale impacts; the same is true for Venus. With Mars, we argue a little bit because in theory it could have been an embryo that didn’t have any major impact but it for sure had smaller impacts that could have stripped its atmosphere and it could have formed Phobos and Deimos - that’s definitely a possibility we can’t really rule out.

And some of the compositional constraints would sort of at least be consistent with that thought. They actually probably were quite common. In our solar system and even around other stars, we actually see some of those warmer belts, within 1AU that could also be traces of such giant impacts where you could use a lot of dust and debris that we can see.

Dr. Emma Marcucci: Thank you. Kurtz Miller: I have a question.

Dr. Emma Marcucci: Yes, please go ahead.

Kurtz Miller: This is Solar System Ambassador Kurtz Miller from Ohio. I’m just curious to know if there seems to be any type of relationship between the spectral type of star and types of planets or the numbers or the distribution?

Dr. Farisa Morales: I saw -- this is Farisa -- I saw some results a couple years ago from Crepp et al. And they have a soft correlation between early spectral type stars and larger planets. So the later the star or the smaller the less mass of the star is, the less mass the planets tend to be. It was still a soft correlation not, you know, limited by - and these weren’t all directly imaged planets and it looks

24 like it’s similar for other techniques. I’m not sure where this will end up but it’s looking like the bigger the star the bigger the planets.

Dr. Hilke Schlichting: Yes, and I guess maybe I can add to that. I think the strongest correlation we found is if you look at the metallicity, so basically the abundance of elements in a star that are not hydrogen and helium, the more of those they have the more likely it is that they have giant planets. So if you care about Jupiters and Saturns those seem to be more abundant around stars that basically have more things other than hydrogen and helium. That seemed to only hold for the more massive planets. If you go down to terrestrial type masses, that correlation seems to go away or there doesn’t seem to be a strong preference.

Dr. Emma Marcucci: Thank you. Other questions...

((Crosstalk)) Dr. Emma Marcucci: Go ahead please.

Dr. Farisa Morales: Yes we need more data.

Dr. Emma Marcucci: Data always good.

Woman 1: Yes. I had two questions, one was I’ve heard about Jupiter possibly being in a different location than it’s most around. I’m wondering if there’s been any evidence of that for any of the other exoplanet systems? I had another one but

25 I’ve now forgotten so if you can answer that maybe I’ll think of my other question. Thanks.

Dr. Hilke Schlichting: Yes, I’d be happy to answer this. The very first exoplanets we found or that were found were planets that are as big as Jupiter but that orbit their star on a three day orbit. So they’re very, very close to their host stars. The best explanation we have for those planets in terms of their formation is that they formed much further away and that they then moved together, probably with the gases but there are other ways, but they basically move close to the star during or after their formation. So there is evidence in other systems that planets do move around.

Woman 1: Okay. Oh and my other question was since we said that Earth could not be detected or our planets couldn’t be detected using the system we’re using to detect exoplanets how could we detect planets like that?

Dr. Hilke Schlichting: Yes we will find them. If we could have had Kepler for longer we would have found them but unfortunately as you probably know the reaction wheels Kepler didn’t - I mean they lasted as long as it should have but we would have loved to have them last for much longer. Then we could have probed the longer period planets that are also small in size because in the transiting exoplanet game, the longer you wait the more transits you can collect and hence the smaller of the planets you can find. And so eventually we would have been able to push out in that period space to find true Earth analogs. So now there’s a new mission called TESS and although right now it’s focusing on slightly shorter orbital periods than the Earth, I heard that things are going so well they’re going to have fuel to continue operating until 2038. And if this is true I’m 100% sure we’re going to fill in all those spaces.

Woman 1: Thank you. Okay that’s good news. All right thank you.

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Dr. Emma Marcucci: So along those lines I’m going to - this is Emma - I’m going to throw out one last question and then in the interest of time to be respectful of our time we’ll wrap up. But could each of you maybe say a little bit about the future missions and how those are going to inform these aspects. I know Hilke you just kind of talked a little bit about TESS. Are there other things looking forward in the future, either space or ground based missions?

Dr. Hilke Schlichting: I’m happy to start but I’m also happy to go second so…

Dr. Farisa Morales: Well I’ll be brief. I’m looking forward to the launch of JWST [James Webb Space Telescope]. I think that JWST is going to be revolutionary in terms of how much we’re going to learn from the dust that is forming these planetary systems, and inform the dynamics of planets in those systems and how they affect each other. I made some calculations about what JWST is going to be able to do it is going to be able to tell me a lot more about the inner warm dust in the habitable zone around these stars that we’ve been studying. So we know a lot about the outer region. We know that it’s icy material. We know how big the rings are. But the inner one we need a higher resolution for that and JWST will provide that. So getting into the terrestrial planet zone and probing that is very exciting to me.

Dr. Emma Marcucci: Thanks.

Dr. Hilke Schlichting: Yes and I think in terms of the exoplanets yes I think TESS is great and it’s going to sort of continue what Kepler has started, focusing on nearby

27 bright stars. The great thing about this is that those we can actually then follow-up and characterize the planets very well by James Webb will be very important and other ground-based facilities and Spitzer.

We learned so much about exoplanets from Spitzer in terms of the thermal properties, the cloud patterns. So I think that has been - between HST [Hubble Space Telescope], Spitzer and then James Webb, we’ll be in this amazing situation that we can really characterize those newly discovered worlds well and we can say something about the direct atmospheric composition and sort of probe deeper and deeper into the question of are any of those worlds habitable and how did they become to be the way we see them?

Dr. Emma Marcucci: Great. Well thank you very much. Thank you again for everyone who joined us today. If you had a question you didn’t - we didn’t get to or if you think of a question in the future please reach out and we will work with our speakers or answer them for you. Thank you Farisa and Hilke, for joining us today and for that great presentation on the origins and diversity of planetary systems.

We’ll go to Slide 50 and I’ll do our standard wrap up. These briefings that we do in conjunction with the Museum Alliance are done through our program NASA’s Universe of Learning which is a STEM Learning and Literacy program funded through NASA. And we want to ensure that we are meeting your needs, the community’s needs. So we have regular evaluations. For those of you who had been with us last year you may have received an email from our evaluator this summer. We appreciate your time and filling that out. If you would prefer not to participate in the evaluation process please opt out by contacting Kay. And with that I will pass it back over to Kay for any final words.

28 Kay Ferrari: Thank you very much Emma and thanks to our speakers as well. This was absolutely wonderful. I want to thank everybody who attended today and to let you know that our next telecon will be next Tuesday, August 7. It’s an informal chat with Dr. Ota Lutz regarding Next Generation Science Standards. We hope you again join us at that time. So thanks very much everybody and we are going to sign off now. So have a good evening.

Carolyn: All right but first before you go I just wanted to say -- this is Carolyn -- I will get those axis fixed up on those four or so slides that Hilke had, that had lost their labeling. So I will get those fixed up and reposted. So if you check back in maybe a week or so we’ll try to get an updated slide set up there for you that looks proper.

Kay Ferrari: Thank you.

Dr. Hilke Schlichting: Thank you.

Kay Ferrari: Thanks everybody. Have a good evening.

END

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