A conversation with Kimberly Ennico Smith, the project scientist for the SOFIA mission at NASA’s Ames Research Center in Silicon Valley, and Michael Person, a research scientist at the Massachusetts Institute of Technology, discussing the science behind using an occultation to learn more about objects in space, such as Neptune’s moon Triton.

Transcript

Frank Tavares: You are listening to NASA in Silicon Valley, episode 72. This is Frank Tavares, trying to do an even better Matthew Buffington impression than Abby Tabor from last week, which was a hard act to follow. So, Abby Tabor is here with me again, and Abby, tell us who our guest is this week!

Abby Tabor (Host):Okay, well, today we actually have two guests. We have Kimberly Ennico Smith, who is the project scientist for SOFIA

Frank Tavares: And I think she’s been on the podcast before, right?

Host:Yeah, yeah, yeah! Exactly, Kimberly has talked about SOFIA before. SOFIA is, actually, a modified airplane that carries a telescope in the back, and this is very cool because it can fly above most of the Earth’s atmosphere and it’s also completely mobile. So this makes a lot of cool science possible.

Frank Tavares: So you can take it wherever in the world you want.

Host:Yeah, yeah, exactly, and they do! And that’s something we talk about on the episode today. But to give you a better idea, Kimberly is the boss of all the science basically that SOFIA does. But then SOFIA also takes on guest observers, like our second guest today, who is Michael Person from MIT. So he observes stellar occultations, now that’ something like an eclipse. It’s when an object passes in front of a very distant star.

Frank Tavares: Kind of like the one we had earlier this year, but with our Sun and our moon?

Host:Yeah, yeah! It’s the same kind of phenomenon, but using a very distant star. The object passes in front of it and then looking at the light from the star that passes around it, they can learn a lot about that object.

Frank Tavares: Neat!

Host:So SOFIA has used this technique to study Pluto, and also MU69, which is the next target for the New Horizons spacecraft. And that’s a small rocky object way out in the solar system. And thirdly, Triton, which is a moon of Neptune. So that’s something we talk about in the episode today.

Frank Tavares: Awesome. So it sounds like this is academia working with NASA to learn a bunch of cool things about the universe.

Host:Oh, definitely. Yup!

Frank Tavares: Awesome! Well, as Matt likes to always remind everyone, we are a NASA podcast, but we are not the only NASA podcast. We want to give a shout out to our friends at the Johnson Space Center that have a podcast called “Houston, We Have a Podcast.” We actually did a joint episode with them two episodes ago.

Host:I remember.

Frank Tavares: So, if you haven’t checked that out yet, that’s definitely worth a listen. NASA Headquarters has a new podcast called Gravity Assist. It’s basically a virtual tour of the solar system. And yeah, before we jump into our episode, just a reminder that we actually have a phone number, you can call in with any questions, comments, concerns, leave us a message, and we’ll figure out how we can integrate that into a future episode. That number is (650) 604-1400. And as always, you can always send us a message on social media using the hashtag #NASASiliconValley on the social media platform of your choice. But for today…

Host:… Let’s listen to Kimberly Ennico Smith and Michael Person.

[Music]

Host: Today I’m joined by two different people who will be talking to us about SOFIA, the Stratospheric Observatory for Infrared Astronomy. So my two guests today are Dr. Kimberly Ennico Smith from NASA Ames and Dr. Michael Person from MIT. Kimberly, could you start us off by reminding us what exactly SOFIA is?

Kimberly Smith: SOFIA, S-O-F-I-A, Stratospheric Observatory for Infrared Astronomy is a 747 aircraft that we’ve cut a hole in the side of it and placed a Hubble sized telescope, a two and a half meter telescope. Being an airplane, we fly not above the clouds, but we can go up to about 12.5 kilometers, or about 45,000 feet, in altitude. That gets us above 99% of the Earth’s water vapor. This reveals the infrared universe. We can see things that you cannot see when you’re stuck on the ground. That’s why we’re an infrared observatory, but we are a mobile observatory as well. We can move the plane. This is one of the key aspects of how SOFIA does occultation science.

Host: Okay, occultations. I remember occultations from last summer when everyone was abuzz about the solar eclipse, the total solar eclipse. Occultations are somehow similar to an eclipse right? Michael, could you remind us?

Kimberly Smith: Certainly.

Host: You study occultations right?

Michael Person Yes. An occultation fairly simply is when something passes in front of something else. For the solar eclipse, we had our moon passing in front of the sun. What we’re observing here from SOFIA are what we call stellar occultations, where a body in the solar system passes directly in front of a star. When we do that, we can watch the light from the star disappear behind the body, and measure how long that takes, so how big the body is. But if the body has an atmosphere, like Triton does or like Pluto does, then we can watch the light slowly disappear as it goes deeper into the atmosphere, and we can learn about the atmosphere, measure its temperature, its pressure, its density, and basically get measurements in the atmosphere of a body that we can’t get any other way from Earth.

Host: Right. That’s incredible how much you can know about a body that is so far away.

Michael Person Yeah it’s the only way we can make these detailed measurements from Earth. If you look at the object directly with a telescope, it often is just five or six pixels across, five or six little dots on your screen. But with the occultation method as we watch the starlight go away slowly and come back slowly, we can measure at kilometer resolution all throughout the atmosphere and learn about the structure of the atmosphere, what’s in it, et cetera.

Host: That’s incredible. Now I heard that you have an interesting history with occultations and Uranus’ rings. Is that true? Did you work with someone who worked on that?

Michael Person Yes. I’ve been doing occultations for most of my career. When I started I was, as a student, I had the privilege of working with the great Professor James Elliott of MIT. He did a lot of the pioneering work in occultations for studying solar system bodies, especially those with atmospheres. He, in 1977, used the previous flying observatory, the Kuiper Airborne Observatory, to discover the rings of Uranus. He and his team were actually studying the atmosphere of Uranus and perhaps fortuitously, or accidentally, discovered the rings while they were doing that. But ever since I joined his team, we started doing occultations of small bodies like Triton and Pluto, et cetera. I’ve been keeping up the work since he passed away in 2011.

Host: Wow.

Kimberly Ennico Smith: To point out about the discovery of the Uranus’ rings in 1977, I mean that was prior to the Voyager 2 flyby of the planet, which was in 1982 I believe. So setting the stage, of course we got wonderful images from a spacecraft that actually can travel to the other world, but you can certainly learn a lot about the object, even just here from armchair Earth just looking at the occultations.

Host: Right, completely. Yeah, that shows us that the kinds of discoveries you can make are not insignificant, and the amount of information you can gather also is significant. Interesting.

Michael Person And that was very similar to what happened in Pluto’s case where in 2000, or I’m sorry back in 1988-

Kimberly Ennico Smith: 1988, yes.

Michael Person -the atmosphere was discovered by stellar occultation. Then in 2015, New Horizons got there to take actual pictures that we hadn’t had before.

Host: Wow.

Kimberly Ennico Smith: We had a series of occultations of Pluto passing in front of a star from 1988 all the way up to the early 2000s, which showed that the atmosphere was changing.

Host: Ah, you’re right.

Kimberly Ennico Smith: Which led to a building need to build the New Horizon spacecraft to send it to Pluto to find out what actually might be going on.

Host: Right okay. Yeah, so it lays the groundwork for much future work that gets established later, yeah.

Kimberly Ennico Smith: To be, the poetry of it all is after that wonderful flyby from July 2015, Pluto has returned to back to being an astronomical object again. And how we are going to study and monitor Pluto’s atmosphere, until another space mission is brought forth, is through occultations. We can use this technique to continue to monitor Pluto’s atmosphere, monitor Triton’s atmosphere that Michael has been studying. You have an ability to revisit the problem.

Host: Right, right. That’s also going to be interesting to the public I think who has seen Pluto rise and fall in its status. People are going to like following that. So listening to you two talk about the way this work has evolved, and hearing you go back and forth, can you explain a little bit about how you work together because Michael is a SOFIA Guest Observer I think? What does that mean? Scientists at different institutions will use SOFIA?

Michael Person Basically I write proposals to use SOFIA, and I put forth a science case saying that the aircraft would be the perfect platform to do this particular science. Those proposals are reviewed by NASA and experts in various fields. Then when time is awarded, I get to fly aboard the aircraft to gather the data I’m looking for, but I’m not actually a member of the SOFIA staff, or a NASA employee. I work for MIT, and we just take the data that we get from SOFIA, and then move on and try and understand the science that we can figure out.

Host: Okay.

Kimberly Ennico Smith: On the project side, Michael’s proposal that was successfully selected to go forth, plus several dozens others to be fit within our cycle, for an occultation what needs to be looked at is where does the plane need to be, on what day, at what latitude longitude, and at what time, and to do a feasibility study on can the plane actually get there. We had an occultation event of MU69, which is another Kuiper Belt Object that we observed in July of this past summer, its trajectory was over the South Pacific. In fact, it flew over, we had to fly really north from Christchurch up to the Fiji islands to catch it.

Host: Oh wow.

Kimberly Ennico Smith: We had to do a feasibility study on can we take the plane to be in the right place at the right time. Michael’s study of Triton, Neptune’s moon, in October of this year was off of the South Atlantic Ocean. The plane was positioned to Florida, and then flew over the Atlantic to catch that event. For the non-occultation science, the infrared science, you have to look at where the object that’s been selected to observe is in the sky. There are summertime objects, wintertime objects, Northern and Southern Hemisphere objects, and we move the plane to maximize that. That’s things that we are doing on the project side.

Host: Right, so SOFIA is all over the place. That of course is the point and the great advantage of an airborne observatory, right?

Michael Person Yeah that’s one of the main things that we like about it in the occultation business. A lot of observers are interested in SOFIA for its infrared capabilities, the fact that it flies high above most of the water. That’s certainly useful for us. We use infrared data in our occultation research, but the most important part for us is that SOFIA can be positioned to where the shadow is because the shadow of these small objects are not actually any bigger than the objects themselves. Often they’re just over the ocean, or in the middle of the desert where we don’t have any telescopes. Having SOFIA be able to be put in the shadow is what makes all of this possible.

Host: Right. How on earth do you make that happen? How do you calculate where this tiny shadow from across the solar system is going to land?

Michael Person That’s actually the majority of our work. It’s always surprising to people that the most difficult part of the occultation observations are not observing the event, but figuring out where it’s going to be.

Host: Yeah I bet.

Michael Person We spend months measuring the position of the star to accuracies far greater than they are in the catalogs. We spend months measuring the position of Triton as it moves through the sky and carefully extrapolating when the two are going to intersect. Then plotting where Triton will cast a shadow in starlight on the Earth. That shadow is the only place where you can see it, and ideally you want to get right into the center of the shadow so you can get the best data.

Host: Okay.

Kimberly Ennico Smith: The MU69 one, I was on that flight in July, but this Kuiper belt object 7 billion kilometers away, the second NISA target that New Horizons will flyby in January 1st on 2019. This will be, there was a series of three occultations this past summer. One on June 3rd, one on July 10th, and one on July 17th. The June 3rd occultation Marc Buie and his colleagues from Southwest Research Institute in Boulder, Colorado, they were the Michael Person’s. They were the Guest Observers who got their proposals selected. They did a ground based campaign with a picket fence. They arrayed 25 telescopes, half a meter, relatively larger for an amateur astronomer, but so they could be mobile, and laid them out over South Africa and Patagonia.

Host: Oh I see.

Kimberly Ennico Smith: And missed the object.

Host: Oh gosh.

Kimberly Ennico Smith: But-

Michael Person Yeah it was very disappointing.

Kimberly Ennico Smith: Yeah, but it was an interesting detective game because it turns out in the time between June 3rd, when they got a null result, and then planning for the July 10th SOFIA flight to intercept it, they had realized that they could improve the prediction of where the object would be by a refined technique. With MU69, it had only been discovered by Hubble space telescope in 2014, and they didn’t actually know its orbit that well, so they had a new prediction in place. When we went to go look for it, or catch the shadow, we went with the best knowledge of the time.

Then seven days later there would be a third occultation over South America again, for which 25 telescopes were laid out and only five of them caught it. But we were now using the same predicted position, so a change in our knowledge of where that object was. Yeah, it was an initial disappoint, but it made you scratch your heads and you realized that you know what, we were off by several hundred of kilometers because we didn’t quite know where it was. But then we knew where, they redid the calculations, they had a new prediction, and the two events caught the occultation, July 10th and July 17th.

Host: Wow. Okay, so it’s a business of constantly refining and getting closer.

Kimberly Ennico Smith: Yeah, it’s as Michael had said, a lot of the work is done in trying to predict where the event will occur, the timing and the location, and understanding the star because each occultation, the object is passing in front of a different star so you have to study that star. If that star is a binary, you want to know that because then you could help tease out what you might see.

Host: Yeah, definitely.

Michael Person The prediction updates happen right up until the last minute. I was on one of the ground teams that Marc Buie’s team deployed to South Africa and we were getting daily phone calls with slight updates, and moving our position around in South Africa trying to get to the best point. That one missed, but the same thing happened again, as Kimberly said in July, and they managed to get it that time.

Host: Wow, my gosh. You’re hot on its tail, you’re chasing after it.

Kimberly Ennico Smith: I mean they’re called KBO chasers for a reason. That is an object that we didn’t know much about and it’s got an intriguing story. With Michael’s Triton occultation, I mean that object’s been studied for a while. Michael could tell you more about what we know about that, but they were still doing last minute changes as well.

Host: Amazing.

Michael Person Yeah with SOFIA we have the opportunity to put the telescope directly in the center. Usually I do occultation observations from the ground, and the telescope is where it is and you can’t do much about that, although we’ve had small telescopes in the field. When you get a bright star you can move the small telescopes around.

Host: Right.

Michael Person But with SOFIA, you can put it precisely where you want it, so that makes the stakes on the prediction all the higher. Rather than just saying is it going to happen or not, we’re trying to say can we get to the exact center? We have to bring the accuracy on the predictions down to kilometers and seconds, and get the plane in the right place at the right time. For that sort of thing SOFIA is ideal, but it certainly means there’s a lot more work that needs to be done during the prediction phase. That phase lasts right up until the night of the event. Like an hour before we took off for the Triton event, we were changing the prediction.

Host: Oh my gosh.

Kimberly Ennico Smith: Then once the plane takes off, if it takes off on time, because those who travel by airplane, even just for business or pleasure, sometimes you don’t take off on time. The project often has contingencies on designing the flight path to make up time, or in a case for an airplane, it’s often easier to slow yourself down rather than to speed up to intercept a particular location. So they’ll be some, if you look at the flight paths for the occultations, they’ll put in things called trombone legs. These are sort of delay lines such that we can make sure that we can get to the right place at the right time. The predictions are still going on the day before, or even sometimes on the flight, but even on the flight itself… Plus the plane itself is moving with the winds.

Host: Oh, of course.

Kimberly Ennico Smith: If you’re going to into a headwind or a tailwind, you know as much as you could, but once you’re in flight you’re actually making a lot of calls on the fly, but in the right approach to get the plane to where it needs to be. It has a very different flavor to it.

Host: All this action, yeah it does bring a new flavor to the image of doing astronomy I think. It’s not all just telescope time booked in advance and sitting there doing your calculations. It’s exciting.

Michael Person It’s always impressed me how well-oiled the flight team, and the flight planning team, and the aircraft crew are on the SOFIA flights because there’s so much happening while you’re in the air, especially when I’m receiving phone calls from our ground team saying that the prediction has shifted slightly as they get new data. I pass that along to the flight planners, they pass it to the flight crew, the plane moves. It’s just a really amazing example of teamwork, of so many people getting this done in order to get an event that lasts three minutes long.

Host: Oh wait, that’s true too. It’s a fleeting event, but all the more reason to be a well- oiled machine.

Kimberly Ennico Smith: And the duration of the event depends upon the size of the object. It’s a three minute event for Pluto and Triton, for MU69 it was less than a two second event.

Host: No, two seconds?

Kimberly Ennico Smith: Because the object was 100 times smaller than Pluto and Triton, so if you’re chasing the smaller guys, that leads to an interesting timing problem.

Host: Wow. That puts a new spin on it.

Kimberly Ennico Smith: Time domain astronomy in a new light, but time domain astronomy with a moving telescope.

Host: Right.

Kimberly Ennico Smith: While your object is moving as well, and the Earth is turning.

Host: Is that all? Let’s talk a little more about the MU69 occultation. What are you looking for exactly? Why are we studying this small object out there?

Kimberly Ennico Smith: Marc Buie, the guest observer who put in the proposal, and Elliott Young and his team, their team, they’re members of the New Horizons team. The purpose was this will be our first chance to perhaps get a size of the object. It had been observed, discovered by Hubble space telescope when the New Horizons team was trying to find another target to fly by after Pluto within its trajectory range. To leap forward on that, once this object had been discovered and we knew where it would be and the spacecraft is on its way to move there, we didn’t know much about it, nor about its environment.

To do the occultations, sort of like what Michael had said about discovering Uranus’ rings, you’re curious whether there’s rings around this object as well. We’re interested in the size, the shape, and whether the environment around there. The environment around the object is important to New Horizons spacecraft because they need to give a heads up, this would have been about a year and a half before the flyby, and it gives them time to adjust how close they want to predict to get to fly by the object. Probing the area around the object was of equal interest to the New Horizons team.

Host: Okay, so SOFIA is going to learn many things about the object MU69 itself plus allow New Horizons to make the best decisions about how it’s going to observe up close.

Kimberly Ennico Smith: Exactly right. Then when the detection was made clearly in five of the 25 telescopes in July, that was no longer a disappointment but a great success because it actually pinpointed our knowledge of the position of this object, which had been known to certain errors because it allowed you a different viewpoint. But then it was a surprising result because the five out of the 25 telescopes did not detect the event at the exact same time, which implied something very interesting about the object.

Such that it most likely is not spherical, and it might even be a binary object, which is a high possibility. I mean there’s a lot of binary KBO objects out there in the outer solar system. But that’s one interpretation of the data. Our SOFIA data, which also detected it, but we must have grazed not the center of the object, but maybe went down the neck, because the duration of our detection, which was much smaller than anticipated. So again, I think we got a cord across the object, but we have two datasets separated by seven days which feed into understanding the size of the object and where it is. There was no indication of any other sort of debris.

Host: I see.

Kimberly Ennico Smith: Yeah, we’re very excited about the role that SOFIA played in this field of occultations, and to help out New Horizons and other NASA missions.

Host: Yeah cool, so you’re still digging through the data to figure out what exactly you can deduce from that occultation?

Kimberly Ennico Smith: Mm-hmm.

Host: Neat. Could I ask a little more about the shadow and how you find it, and what you’re able to see? I’m amazed that a shadow can travel that far, be cast that far across the solar system and still be something suitable on Earth. I’m not sure what to ask, but is it truly a shadow? Is it very, very, very faint by the time it reaches Earth?

Michael Person It’s essentially, I mean it is a shadow. The stars that are doing the occulting are very, very far away, so all the light from them is coming to us effectively all of it from the same direction. So that makes the shadow, the light lines at the edge of the shadow, very straight. They’re very parallel. The shadow just gets cast across the solar system, and it moves very quickly. Mostly because the things in the solar system are moving, primarily us here on the Earth, so the shadows tend to move something like 20 kilometers a second and you have to predict exactly where they’re going to be when in order to get your telescope in the right place. But it really is a shadow.

When there’s an atmosphere, it’s a little more interesting because the atmosphere around the body acts kind of like a lens. Not only do you get a shadow, but you get a focusing, and that makes it, momentarily in the center of the occultation when it should be the darkest, it makes it momentarily bright. That’s called the central flash, which is what we’re looking for when we try to travel to the middle of the shadow with SOFIA.

Host: I see. Wow, so that’s why it’s important to get the shadow’s location exactly right, so you can be exactly in the center?

Kimberly Ennico Smith: In the center.

Host: I see because you’re going to get more information there than you would on the sides?

Kimberly Ennico Smith: Mm-hmm, if the object has an atmosphere and has that lensing effect.

Host: Gives you the central flash, is that what it was called?

Michael Person Yeah.

Host: Cool. All right. Nice.

Kimberly Ennico Smith: When Pluto occulted a star back in 2011, and then also again in 2015, in 2015 it was two weeks before the New Horizons flyby, SOFIA was called to action. Michael Person was also the Guest Observer running the show, and obtained measurements of Pluto’s atmosphere and the central flash.

Host: And what did we learn from that? What kind of information do you glean from the central flash?

Michael Person The central flash lets you look lower in Pluto’s atmosphere than the rest of the occultation because it’s focused around the entire planet. You can see light levels far deeper into the atmosphere than you can without the focusing, so we get to look in the lower atmosphere. But what we learned from the 2015 event was there had been a debate for decades as to whether or not there was a strong dust layer in Pluto’s atmosphere. We detected it with SOFIA by measuring the light levels and the various infrared channels, invisible channels, available to the telescope. The differences between those led us to conclude that there definitely was a haze layer, very small particle dust throughout the atmosphere. This was confirmed just a few weeks later when New Horizons managed to get pictures of the haze during its flyby.

Host: That must have been gratifying.

Michael Person Oh yes.

Kimberly Ennico Smith: Finally you’re calibrating the two different techniques.

Host: Okay, right.

Michael Person We had been using the occultation technique to monitor Pluto’s atmosphere for decades, but we are always comparing occultation data to other occultation data. So it was wonderful during the New Horizon’s flyby to have some other source of data we could compare all of our occultations to. And as Kimberly said, that basically allowed us to calibrate decades worth of data and really solidify our understanding of how Pluto’s atmosphere has been growing and changing, et cetera.

Host: That’s right. So you take all your occultation data and now you know this relates to this, that we can see up close with New Horizons?

Michael Person Exactly.

Host: Tells you?

Kimberly Ennico Smith: And Michael is doing the same thing with Triton, Neptune’s moon.

Host: Right, tell us more about that.

Michael Person Well throughout the 90s we were observing Triton’s atmosphere through occultations from the ground here. We had various ground campaigns, and observed it several times. Over the course of the 1990s we noticed that Triton’s atmosphere was growing. There was global warming on Triton.

Host: Wow.

Michael Person We were really hoping to follow up on this, but around the turn of the century Neptune, the body Triton is orbiting around, passed into a fairly sparse star field. There just aren’t that many stars. Since our last successful observation in 2001, we hadn’t had any chances to check out the atmosphere until just this year. This October, on October 5th, we got our first good star that Triton passed in front of.

Host: Finally.

Michael Person Yes, finally. I have been looking for stars for the last decade or so, and finally found one. During the occultation we got our first measurements of Triton’s atmosphere in over 15 years. Even now, back in my lab, we are going over that data we got a month ago and hope to have results for what’s happening in Triton’s atmosphere shortly.

Host: That is so cool. SOFIA makes this possible.

Michael Person Yeah, without SOFIA we couldn’t put the telescope where we need it. Especially with Triton, the occultations are so infrequent you can’t wait for an occultation to not only happen, but just happen to pass over a good telescope. So with SOFIA we can move the good telescope where we need it.

Host: That’s right, but then that puts all the more pressure on getting that flight path just right to end up just in the center. What if you had missed your one star in a decade?

Michael Person Oh that would be disappointing, but luckily we didn’t. Actually, beyond luck, we have an excellent prediction team back at MIT led by Dr. Amanda Bosh and our Research Assistant Carlos Zuluaga. They spend countless hours going over the data, refining the prediction, making updates as we go, and call those prediction changes up to me on the plane where I inform the flight planners. As they say, it takes a lot of people to get these data, but we’ve spent years perfecting how to work as a team, and the SOFIA flight people are always on top of their jobs, so everything tends to work out.

Host: Yeah I imagine.

Kimberly Ennico Smith: In the case of Triton, the universe finally behaved and sent us, had an arrangement so that a star was available for an occultation that we could observe. We just had to wait.

Host: It finally cooperated. Are there upcoming occultations that you’re excited about that you could talk about already?

Michael Person Yup. We have a successful SOFIA proposal, it was accepted, to observe an occultation by Triton, the giant moon of Saturn that everyone is interested in with the deep methane atmosphere. We’ll be observing that in July of next year.

Host: Very cool.

Michael Person We are of course always on the lookout for more Triton occultations. We have another one coming up in a couple of years that we’ll put in proposals to see once we’ve nailed down where we think it’s going to be.

Host: Well that’s good, you won’t have to wait as long this time. I know a lot of people are excited about Titan, so they’ll be looking forward to that.

Kimberly Ennico Smith: Then with all other large, dwarf planets out in the outer solar system, so like Haumea or Makemake, whenever an occultation prediction comes, a proposal will be put in to the SOFIA observatory and we can make a measurement.

Host: Could you tell us about which objects you –

Kimberly Ennico Smith: I don’t know, Michael I don’t think there’s any occultations coming up until about 2019. We were looking at, we have a program to do targets of opportunity. One of them is for any trans-Neptunian object, if it does occur with a stellar occultation. A Trans-Neptunian object is any object beyond sort of Neptune. It includes Pluto. It would include some of the larger Kuiper belt objects like Makemake or Haumea, or Eris, which when James Webb the James Webb Space Telescope is launched in a few years time, they could look at those objects too. A couple pixels across, still frontier territory there, but combining those type of measurements with the occultations, perhaps we’ll find about the atmospheres of these objects if they do have any atmospheres. It’s a new world out there.

Host: Right.

Kimberly Ennico Smith: The outer solar system we know so very little about. What we’ve learned about Pluto is beyond anyone’s expectations, and a world in itself. We’re continuing to learn about the moons of the giant planets, so Triton and Titan, and using those with stellar occultations too.

Host: That’s exciting. Does SOFIA always look at the outer solar system? Is there any reason to use that kind of astronomy to look at close by objects?

Kimberly Ennico Smith: Well we are studying other objects in the solar system as well. We have the ability actually to observe Venus because we can observe objects near sunrise and sunset more so than a ground based telescope or a space to space telescope because we can maneuver the telescope to be pointed closer to the sun. Last year we looked at Venus, but this year we’re also looking at some comets. Comets are also, when they become more vibrant is when they’re closer to the sun. In the past, SOFIA has studied Mars, studying its atmosphere. We also searched for plumes on Europa, Jupiter’s moon, because those were sporadic. Although we had a null detection, it just meant that we didn’t catch it at the right time. So we are studying other objects as well in the solar system.

We’ve studied the infrared properties of asteroids. You can measure the thermal properties of a dark asteroid by measuring it in the infrared. Actually on the science flight coming back from Florida, Andy Rivkin from APL, was studying some asteroids for a PhD thesis for a student. That was pretty exciting. I don’t know what data he got, but we do study a lot of solar system objects as well.

Host: That’s so exciting. You guys are all over the Earth and looking all over the solar system with SOFIA.

Kimberly Ennico Smith: Within constraints.

Host: Yes.

Kimberly Ennico Smith: There are certain air spaces we can’t fly over.

Host: Oh sure.

Kimberly Ennico Smith: There’s a lot of restrictions over even the continental U.S.

Host: Yeah, but where you can fly you’re able to go.

Kimberly Ennico Smith: But where we can fly, and how high we fly, can help with not just the occultations that particular latitude longitude at a certain time, but with the infrared astronomy the higher you go or the where you can get into the stratosphere above the water vapor makes the longer wavelength science much more impactful. You get a… because if you’re studying water in an object, you want to get away from water in Earth’s atmosphere.

Host: Yeah, naturally. All right, well is there anything either of you would like to add to this story?

Michael Person Well one of the main reasons we keep doing these occultations, as we mentioned before, is that they’re pretty much the only way that we can monitor these objects on an ongoing basis. New Horizons provided fabulous data on Pluto, but that data was all constrained to those few days around the flyby. If we want to monitor that and see how Pluto’s atmosphere changes or evolves in the years to come, we have to keep looking at it from here. Stellar occultations are the only way to actually get resolvable data on Pluto’s atmosphere. We’re just going to have to keep doing it for as long as we can.

Host: Right, so they’re two kinds of missions that are complimentary right?

Kimberly Ennico Smith: Mm-hmm.

Host: I see. Great. Any final thoughts from Kimberly?

Kimberly Ennico Smith: Well you know we’re just delighted that the observatory has this agile ability.

Host: That’s a good word.

Kimberly Ennico Smith: And recognition within the community to be able to use it as a tool. I mean we have a big telescope, a two and a half meter telescope. It’s much larger than the mobile telescopes that can be maneuvered, so we can do occultations when the star is slightly fainter and also move to over the ocean where the mobile telescopes can’t move, or the large glass ground-based telescopes, the eight meters and 10 meters, are fixed.

Host: Of course.

Kimberly Ennico Smith: It’s a delight to see this unique aspect of astronomy being used by a unique platform, the flying observatory.

Host: It certainly is unique, very cool.

Michael Person Yeah. One of the big challenges in occultation science is that you can’t put the stars or the shadows where you want them. You just have to take them where they are.

Host: Exactly.

Michael Person For many years when you make predictions, two-thirds of them you throw out immediately because they’re over the ocean. Now onboard observatories such as SOFIA give us an opportunity to fly out there and actually get all of this data that we were losing.

Host: How cool.

Kimberly Ennico Smith: For those who had seen the great American eclipse, or the eclipse in August this year, there were several people who chartered airplanes to go fly to the path of totality for the same thing. If they weren’t… It’s not coming to them, we’ll go to you.

Host: Yeah, exactly.

Kimberly Ennico Smith: The same approach we’ll do it for the stellar occultation as several people did with getting on a plane and flying through the path of totality of the solar eclipse that we had a couple months ago.

Host: Right, it’s pretty much the same. It’s just as fleeting and probably just as exciting for the scientists. Very good. All right, well thank you both for joining me today. This has been super interesting.

Michael Person Thank you, Abby.

Kimberly Ennico Smith: And there will be more to come when we have an occultation of Titan this coming year.

Host: That’s right.

Michael Person Yes, I’m looking forward to that next year.

Host: Stay tuned, maybe we can get you both back in here for another conversation.