A conversation about NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Echelon-Cross-Echelle Spectrograph (EXES) science instrument with Matthew Richter, Principle Investigator, and Edward Montiel, Postdoctoral Scholar.

Transcript

Matthew C. Buffington (Host):Welcome to NASA in Silicon Valley, episode 29. NASA’s airborne telescope, called SOFIA, has many powerful instruments to study the solar system and beyond while flying at 43,000 feet. One of these instruments, called EXES, can study water around young stars, on planets like Mars and Venus, and coming soon it will look for evidence of water on Jupiter’s moon Europa, as a follow up on possible water plumes spotted by the Hubble Space Telescope. Today we are chatting with Matthew Richter and Edward Montiel as they discuss their work on SOFIA and what their observations may reveal. Without further delay, here is Matt and Edward.

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Matthew C. Buffington (Host): We have Matt on the phone and Ed sitting here in the studio with me. But we love starting it off with just people explaining, “How did you join NASA?” “How did you get to Silicon Valley?” So, Ed, I’ll shoot over to you just real quick. How did you get into this room?

Edward Montiel: Sure. It was by Matt hiring me last February or March officially.

Host: Nice.

Matt Richter: Something like that. Yeah.

Edward Montiel: So that’s how I guess I would have wound up at NASA since I was finishing up roughly at Louisiana State University, my PhD. Matt had posted looking for a new postdoc and I applied and he hired me.

Host: Pretty straight forward. Was it always like, “I’m going to work for NASA one day”?

Edward Montiel: No, not even that. I guess the idea is to try to stay at least one foot in the door with academia and I kind of still have that since I’m officially a UC Davis employee and a federal contractor here at NASA. I guess if I can work at somehow a full time job at NASA in the future, then that would be great.

Host: How fortuitous that you have Matt right here who brought you in. So Matt, how about you, man? How did you end up joining NASA? How did you end up over here?

Matt Richter: I’m also officially UC Davis, a researcher here. I don’t have a tenured track position. I survive on the grants that I’m able to bring in. But I went to grad school in Berkeley. I actually grew up in the bay area, so I knew about NASA Ames way back when. And when I was at Berkeley in grad school, we had meetings down there once a month for a few years, I think it was. Then I went away to the University of Texas, got involved with the instrument EXES and our ground-based instrument TEXES that we’ll talk about later. I moved to UC Davis when my wife got a job here back in 2002. I continued on working on the instrument and I took over the instrument about 2010 as a collaboration between NASA Ames and UC Davis. And it’s worked pretty well. We’ve been — the hardware lives at NASA Ames and I come down there periodically. And then we fly on SOFIA, which is run out of NASA Ames.

Host: Cool. Yeah, this is the interesting thing about being here. The different paths and the different ways that people work at NASA – whether it’s civil service, contractor, postdocs, students, interns — there’s all these various ways to get in. When people ask, “So how do I join NASA?” It’s like, there’re so many different paths. But there’s a lot of different ways and — even the scientific community, as Ed was saying, keeping your hands in that community is crucial to eventually taking advantage of something later on.

Matt Richter: Yeah. It’s important for us as academics, we’ve got to keep publishing articles and establishing our reputation that way.

Host: Cool. So, for folks who are listening, we’ve done a podcast before talking about SOFIA, kind of getting to the nuts and bolts about what it is. But I’ll throw this to either of you guys. The short version of “What is SOFIA?”

Matt Richter: SOFIA is a 747 with a hole cut in the side so a telescope can look out. What I call the basic version. And the advantage it brings that telescope up into the stratosphere where you’re above most of the water vapor so you can look at wave lengths that you can’t look at from even the best ground-based sites. The highest telescopes on the ground are, I think, around 17,000-18,000 feet down in Chile. There are certain wavelengths that are hopeless from the ground. But from SOFIA become quite clean.

Host: Yeah, it’s interesting when you think of the telescopes, you think of the large telescopes that are on a mountain or on the ground. Or these space telescopes like Kepler or Hubble. You guys are kind of in the middle of those.

Matt Richter: Right, and they’re definitely some advantages to that.

Host: Yeah, so talk a little bit — yeah, Ed, what are some of those advantages, some of the differences?

Edward Montiel: Right. I got to fly this previous flight so it’s my first time being on SOFIA and seeing it in action and it’s an impressive feat that you have the telescope flying at about 40,000 feet roughly all the time and you go to observe in the mid-infrared window between roughly 4 or 4 and a half microns to even longer out to hundreds of microns depending on which instrument is involved. In EXES we go out to at least 28.3 microns.

Host: And that’s mainly infrared.

Edward Montiel: Right. And just seeing that suddenly, if you were looking at the ground, you would just see noth– it’s just the sky and our own atmosphere. Suddenly it’s a window at 40,000 feet that you can start seeing sources, planets, other stars.

Host: Talk a little bit about that difference of — you guys mentioned the water vapor and being able to see through that and SOFIA primarily looks at the infrared spectrum. So why is that so important? How does the water vapor mess things up?

Edward Montiel: Yeah, water vapor is an infrared emitter itself. It has a lot of glow in the infrared from its rotations and vibrations. It’s a molecule. It’s two hydrogen and one oxygen. It can spin. It can vibrate. And that energy that’s released is light that we also observe from other sources.

Matt Richter:And when we get to the stratosphere, two things really happen. The amount of water above the airplane, above our telescope, is dramatically lower. It’s like compared to a good night on Mauna Kea, it can easily be a hundred times lower. But then also, because we’re in such a high altitude, the pressure is so much lower. And so these lines, these molecular features that Ed mentioned, they’re a lot narrower. The molecules are not bumping into each other so they’re not broadened because of that. And so even if there is a strong feature, particularly say of water vapor, we are able to look just at a slight shift. Earth’s motion about the sun can shift the wavelength of light from water vapor and some source enough that we can see it.

Host: Oh, wow. Talk a little bit about — you’re on this plane. I’d imagine that you’re in a cabin, people are working. With being a 747, normally a space telescope has all these restrictions about its weight and getting things just picture perfectly going there. But fortunately for you guys it’s just going up and down. How does the weight of the instruments play in or can you even switch out different instruments and have a little bit more flexibility?

Edward Montiel: Right. From what I can see SOFIA has about seven instruments that swap out depending on what science wants to be done that night. And you have blocks. So you have a week of EXES observations back to back to back. And then they’ll switch in another one, such as GREAT, which is a German instrument. Or HAWC, which is a NASA Ames facility instrument. And in terms of weight, Matt, since you started with SOFIA and putting it on the plane, I don’t know what types of limits you guys had or what the instructions were.

Matt Richter: Yeah, so if I remember right – and there’s no guarantee to that – I think about 1,200 pounds is the weight limit. EXES is definitely lighter than that. But there are some instruments that come up close to the limit. HAWC+ is particularly a big instrument. I think it’s closer to the weight limit. EXES is a long instrument. The heart of it is one optic that’s about a meter long, as a diffraction grading that’s very carefully built and that single piece of aluminum weighs 32 pounds. Putting something a meter long that weighs 32 pounds up on a satellite would be really challenging especially when you consider all the rest of the optics and the mechanical support that has to go around it.

Host: Talk a little bit about EXES because this is one of seven instruments that SOFIA potentially has. So what exactly – I’m just getting down to it, what is EXES and what makes it different from the other instruments?

Matt Richter: Ed, I want you to do this first. That way I can see how much you’ve learned.

Edward Montiel: Sure, sure. EXES stands for the Echelon-Cross-Echelle Spectrograph or I always forget the two because it has an echelle and an echelon. What that allows for is that we can do what is considered very high resolution. We can take the light that come from these astronomical objects and look at it in a very fine tooth with the, by wavelength of light. So, we can get up to parts and one in a hundred thousand of resolving the individual wavelengths of light from an object. It primarily, of course, resolving molecular features in the atmospheres of planets in our solar system and young stellar objects around evolved stars. It allows much better sensitivity than you would from the ground being out on SOFIA.

Host: So this is a spectrometer not infrared.

Edward Montiel: It is an infrared spectrometer.

Host: Okay. All of the above.

Edward Montiel: It’s different than being a camera where you would take a photo and get an image of what you’re looking at. We take the light and — think about in the optical, what we see when you pass light through a prism, you get the rainbow. We’re just doing that effect in the infrared. So taking that light and spreading it out into its individual components.

Host: Does that sound right to you, Matt?

Matt Richter: Yeah, that sounds pretty good.

Host: Ed still has a job.

Matt Richter: Yeah and the one thing Ed had mentioned earlier that for EXES, we’re a mid-infrared instrument. So we go from about five to 28 microns or so. That’s limited by the detector and some of the optics that we chose to use. And getting back to your question about what’s different us compared to other instruments. Some of the other instruments on SOFIA go out to a couple hundred microns. So they’re observing at much longer wavelengths. And then there are a couple that are even shorter wavelengths. There’s another SOFIA instrument for the mid-infrared, but it’s a camera. So it’s not separating the light much. It does have that type of mode, a spectroscopic mode. But mostly it’s taking pictures in different filters, whereas, we are putting a slit up on the sky and spreading the light out to get the wave to get source emission as a function of wavelength. What light is coming from the object as a function of wavelength?

Host: So if I understand, basically, we’re thinking of a spectrometer that is bringing in light in like a prism, dividing it in so you can see what those subcomponents are. And why is that important?

Edward Montiel: When each individual element has – or in any atom you have transitions, let’s say, initially in electrons. They go up and down energy levels. And when they move, mainly when they move either if they go from a lower energy state to a higher energy state they take in energy or light. And so in a spectrum if you’re looking at it and you see, let’s say, something’s flat and a dip and then comes back, then that’s light of a particular wavelength being taken away. And that can tell you maybe that you see oxygen there, if it’s at a certain wavelength. Or if you see light were if some were to have a bright spot that being emitted, that’s the atom itself, the electron moving down in energy and emitting the photon that we can see at that wavelength.

Host: It brings back memories of a college chemistry class where they burn different chemicals and you can see the different colors. If it’s blue, you know it’s oxygen or if — I’m probably mixing up these wrong colors.

Matt Richter: That’s exactly the right idea. You’ve got the physics lab or chemistry lab where up in front there the gas discharge tube and you’ve got some little spectrometer or something that lets you try and identify what gasses are in the tube. I know it’s something we do with undergraduates here at Davis.

Host: Excellent. And then that plays in really well because then if you guys are looking at stars or even looking at Mars for that matter, you’re looking at different objects in space by looking at it with these instruments you can tell what they’re made of.

Edward Montiel: Right.

Host: Go into a little bit of that. What are some of the cool things that you guys have looked at?

Matt Richter: One thing I want to go back on a little bit, we were talking about atoms. I remember when I was a grad student and maybe this was late, I don’t know Ed, you might have learned this earlier – the idea that molecules can do this emission just by how they’re rotating. And they can’t rotate at whatever speed they want. Quantum mechanics says exactly how fast different molecules can rotate and in order to change that rotation frequency, they have to give out a photon. It’s going to be a really low energy photon, but still it’s not at any frequency. It’s set by the quantum mechanics. I remember the class where I learned about that and it was kind of, “Wow, that’s pretty cool.” It was something new for me.

In general, with EXES in particular, I like to think about it as how we’re using molecules both to study the chemistry that’s going on in objects. How many molecules are there? What type are they? Just to learn about how the molecules in space are getting built up or getting changed over time. Or the other way we can use them is as diagnostics of what the gas in general is doing or what temperature it is. We can use this emission to say, “Oh, well that gas is coming towards us” or “That gas is moving away from us” or maybe if it’s in a disk it’s doing both. The molecular features can be used to study the chemistry, study the molecules themselves, or as a proxy for what the broader gas is doing.

One of the cool things that we’ve done, at least cool for me, is looking at water vapor. Water is a really simple molecule. It’s common in space. But it’s really hard to study from Earth.

Host: I was going to say, we had a podcast — sometimes we’ll do a conversational podcast where we also have done reads of web features that show up on NASA.gov. There was one relatively recently where we talked about water vapor around a protostar. So yeah, Matt, talk about that.

Matt Richter: That’s one thing that we did on our very first flight when we took some observations. It was this star about 10 times more massive than the sun, but it’s still in the gas and dust that it was formed out of, so you can’t see it visibly at all. All the light from that massive star is getting intercepted by dust and eating up the dust. Because the dust is getting warmer, it’s giving off a lot of infrared radiation, so it’s really a pretty bright source in the infrared. And what we can do is use it as a background lamp and look and ask about what’s the gas in between us and that star? What do we see taking photons out, like Ed was describing – absorption lights? The other thing about when the star heats up the surrounding dust, is any molecules that have coated on the dust or maybe that had formed from smaller atoms or molecules that been coated onto the dust, they get released again into the gas. And EXES, because of our high spectral resolution, how finely we separate the light, we’re really good at studying gas features. So on this flight we were able to look and ask about how much water vapor there was towards this protostar and what temperature it was and what velocity it was moving. It turns out it was moving away from the star at about 10 kilometers a second, if I remember right. Actually, that sounds a little low. It might have been a little faster than that.

And it was a temperature of several hundred Kelvin and this was just something new that people hadn’t really been able to study in the same way. We were following up on a satellite that went up in the 90s where they could look at a lot more wavelengths but not spread the light out so finely. So, they were just saying, “Well, overall, it looks like we have a temperature in an abundance that fit all these different wavelengths.” But in some cases they had lots of lines that got smashed together because they weren’t spreading the features out. We were able to do a little bit better job than that.

Host: Cool. So stepping back, even away from some of the stars, you guys have been able to look at some cool things in our own solar system. Maybe we can do a little tour and talk about some of the cool stuff that you guys have found closer in our neighborhood.

Edward Montiel: From the most recent flight series that I was on, we did some observations. We were able to map across the disk of Venus where we got to try to help a guest observer track the ratio of deuterium, which is an isotope. Just like hydrogen is one proton, one electron, if you add one neutron to the nucleus, then it’s still hydrogen. It’s just called heavy hydrogen so it’s called deuterium. And the ratio of deuterium to regular hydrogen, that ratio then through looking at heavy water to water, HDO to H2O, and that will allow the observers to track the water loss history on Venus, since it’s believed that Venus early in the solar system had an ocean, much like Earth did and over time lost that ocean.

Host: That’s kind of in that greenhouse effect that went crazy.

Edward Montiel: Right. That was on this past series and we also looked at Mars.

Matt Richter: Doing almost the same thing. Looking at H2O to HDO to look at Mars’ water history was one of the projects on Mars.

Host: Then looking at Mars was also something to do with methane, or are you looking at different…?

Edward Montiel: Right, so there’s been throughout the last, I don’t know, 10 or 20 years – Matt can correct me on that – there’s been various detections of whether or not there’s methane in the Martian atmosphere, which methane is typically an organic. On Earth, it’s created – I believe – mainly through organic processes and can be used as a proxy for whether or not there’s some type of bacterial life maybe or microbes under the surface on Mars. It’s been seen that sometimes there is this big metha – and big I mean a few parts per billion — but methane abundance and then sometimes it’s gone. What is that cycle doing? These observations help follow up an observer who has some earlier detections or measurements looking for the methane and also NASA’s Curiosity has its own limits. It’s on the surface and can track this and so just following up and helping put limits on whether or not the methane is there in the Martian atmosphere.

Matt Richter: So far, the initial results from observations we did last March where the investigator has done some careful analysis and modeling, is that we’re not seeing any methane from those observations. But one of the things about this is that’s it’s appearing to be quite time-variable and our understanding of Martian atmosphere says that if you have a release of methane it should get destroyed on fairly short time scales. I can’t remember the exact number of how long it’s expected to live, but some of these detections over the last 15 years – I think is a good number – It’s puzzling how it can be there and then not. I’m not sure that that’s really well understood if we take the detections at face value.

Host: One of the big things that that NASA’s looking forward to of, not only Jupiter, but looking at the moons like Europa and understanding whether it’s proposals to put a rover or to do more studying of Europa. What is in the works for EXES and some of the work you guys are doing looking at the ice moon?

Edward Montiel: Matt did you want to answer that?

Matt Richter: Yeah, I want to take this one. There have been Hubble Space Telescope observations of water coming off Europa. Hubble is able to use ultraviolet light. And the molecular transitions there are stronger. Hubble’s a fantastic tool and so these are pretty sensitive observations. While EXES will be able to look at these vibration transitions of water, I guess I put this in the high risk, high reward category. And that my real expectation is that most likely, we’re not going to see anything. And that doesn’t necessarily mean that it won’t contradict Hubble, in my opinion. It’s just that we may not have the – well, one thing there could be time variability, and in fact, Hubble has seen that. So maybe we’re unlucky. But also just the amount of water and how the gas gets excited and how it fills the EXES beam from SOFIA, all that makes it a tough observation. So, my guess is we’re probably not going to see anything, but I really hope I’m wrong and you wouldn’t know unless you look. We’re going to do our best. This is a three and a half hour observation each time. We’re going to make sure that even if we don’t see anything, we are able to say, “Well, the fact that we didn’t see anything we can really say, ‘There couldn’t have been this much water vapor emitting.’” Hopefully we’ll be able to get some good science in the limits that we put, even if we don’t detect any emission.

This would be really cool to see things, the high reward. We’d be detecting water vapor that’s coming in between the cracks on the moon from that ocean. It would be great if EXES could cover more wavelengths at one time because then, not only would we be able to see more water vapor lines, but maybe there’s some other molecules that happen to be caught up with the water vapor. We can set limits on those too. But truth be told, especially for the first observations, we’ve got to look at where we think we’ve got the best chance of detecting the water vapor itself. And we’ll see if we can do that. The chance for serendipity of other molecules is pretty negligible at that wavelength setting.

Host: The quest will continue and I’m sure it’ll be a hot topic from NASA. And even as more results, as more things come up, we’ll have you guys come on over and talk a little bit more about that.

Matt Richter: Yeah, I mean we’re going to try this we’ll see. The two cases each time, we’re looking at a different side of Europa. And the Hubble observations seem to suggest that on one side it’s actually much more likely that you’re going to see something.

Host: For folks who are listening who have more burning questions, anything to ask you guys, I’m guessing the best place to go is over to NASA.gov/SOFIA. Probably the most sense to find your information.

Matt Richter: Yeah, I think that could be right or there’s a SOFIA website whenever I put into Google rather than a direct link. You have to make sure you say “astronomy” as well because otherwise you get some actress or you get the capital of Bulgaria.

Host: Or the actress from “The Golden Girls.” This is great, but also for anybody who is listening who has questions, we are on Twitter @NASAAmes but also the SOFIA telescope is @SOFIAtelescope. And we are using the #NASASiliconValley so any questions, feel free to go ahead and tweet us at any of those handles and we’ll loop back to Matt and Ed and get all the information out of them. But thanks for coming on over guys.

Edward Montiel: Thanks for having us.

Matt Richter: Yeah, it’s our pleasure. Thank you.

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