Planetary Radio • Oct 19, 2022

Eyes on the Sky: Spacewatch and the Catalina Sky Survey

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Melissa Brucker

University of Arizona Research Scientist and Spacewatch Principal Investigator

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Eric Christensen

Catalina Sky Survey Principal Investigator at the University of Arizona’s Lunar and Planetary Lab

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

The University of Arizona in Tucson hosts two of the most successful asteroid searches on our planet. Together, they have discovered, tracked, and characterized tens of thousands of objects, many of which could pose a threat to Earth. Listen to back-to-back, in-person conversations with the leaders of both efforts. Then we’ll jump to the ever-watchful Bruce Betts for this week’s installment of What’s Up.

Catalina Sky Survey telescope
Catalina Sky Survey telescope Image: Catalina Sky Survey / Steward Observatory
Comet C/2021 A1 "Leonard"
Comet C/2021 A1 "Leonard" Comet Leonard photographed through a telescope on Dec. 3, 2021.Image: Adam Block /Steward Observatory/University of Arizona

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Venus is the solar system body that has valleys (valles) named after abandoned Earth cities.


Mat Kaplan: They are the hunters and trackers of thousands of potentially hazardous space rocks, and you'll meet them this week on Planetary Radio. Welcome. I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. There's something about the University of Arizona and asteroids. I suppose it's no accident. The great institution in Tucson is headquarters for several of our planet's most productive or promising projects designed to meet the challenge presented by near-Earth objects. I met the leaders of Spacewatch and the Catalina Sky Survey when I visited the campus in September. You'll hear my conversations with these defenders of Earth in minutes. Then we'll head out across the solar system with Bruce Betts. And what's up? Giving you another chance to win the coveted rubber asteroid. That's no comet. Or if it is, it was created by us when the double asteroid redirection test spacecraft slammed into asteroid and moonlet Dimorphos. You should see the striking image captured by the Hubble Space Telescope. You'll find it at the top of the October 14 edition of the Downlink, The Planetary Society's Free Weekly Newsletter. Okay, that long trail of debris does not mean we've made a comet, but it does tell us that we little humans now have the power to avoid the fate of the dinosaurs, which is a pretty good reason to light up the sky. Another great image of a subject much, much further away has been snapped by the JWST. It's a young star surrounded by a dense disk of gas and dust, a disk that is very likely to have baby worlds forming within it, much as scientists believe our own solar system was formed four and a half billion years ago. It's like looking at our own genesis. There's so much more waiting for you at Melissa Brucker is the University of Arizona research scientist who heads Spacewatch, the first of the two survey projects we'll learn about today. I was already in Tucson to host the NIAC symposium webcast that you may have heard excerpts of in last week's show. It was a warm walk across the campus to the headquarters of the Lunar and Planetary Lab where I met Melissa in the Spacewatch offices. Melissa, welcome to Planetary Radio. Thanks for joining us.

Melissa Brucker: Thank you so much for coming to visit.

Mat Kaplan: My plan was to get you and Eric Christensen together because I thought that'd be so cool to have the two leaders of two of the world's most successful, most prominent sky searches together in the same room. We couldn't quite make the schedules work, so I'm happy to talk to the two of you separately, but it would've been fun. Irony. You want to say hi to Eric?

Melissa Brucker: Hi Eric. We actually don't see each other in person very often.

Mat Kaplan: Even though his office is just upstairs, right?

Melissa Brucker: Yes. Yes. Well, we both do observing as well as managing the groups.

Mat Kaplan: Figures. So we are of course at the University of Arizona, which is not where either of you do your observing. You use those telescopes on that famous site known as Kitt Peak, which is still recovering from what was very close to a real observation ending disaster. How are you recovering from that fire?

Melissa Brucker: We were allowed to return to the summit in August and start cleaning up all of the dust and ash that had blown into all of the observatories. And then we tested our equipment. So we were able to start observing with our two main telescopes. We have a 1.8 meter or 72 inch that is a Lunar and Planetary Lab telescope built by Spacewatch. And we also use a Steward Observatory's 0.9 meter or 36 inch telescope. We tested all of our equipment there, made sure that we could open and close the domes and move the telescopes around and check that our instruments were still working. So we began observations again on September 11th.

Mat Kaplan: Congratulations. But you still don't have power or internet?

Melissa Brucker: Sort of. There are two or three generators that are providing energy for the power. Kitt Peak National Observatory has a Starlink dish that all of us together get a little bit of the data that goes through the Starlink dish.

Mat Kaplan: So thank you Elon Musk, I suppose.

Melissa Brucker: I suppose.

Mat Kaplan: Let's back up. Tell us about Spacewatch. I know it's been around for over four decades now.

Melissa Brucker: Yes. Yes. Spacewatch started in 1980 to find funds to build a telescope to do asteroid survey, sky surveys. We began taking images with a CCD in 1983. We were the first asteroid survey to use CCDs. Before that, there was photographic plates and other media, but this was the first survey using CCDs.

Mat Kaplan: For people who are too young to remember, and that may include you, what a change in capability CCDs brought about, right? Rather than... I mean, also a lot more convenient than dealing with big old glass plates.

Melissa Brucker: Yes. It was revolutionary.

Mat Kaplan: Yeah. Yeah.

Melissa Brucker: Really. So we began as a survey. We are not currently acting as a discovery survey right now. We do asymmetric follow up. So we look at objects that have just been discovered to get more measurements of them so that once we found them, they don't get lost.

Mat Kaplan: I'm going to follow up on your follow up work in a moment, but you're still making some discoveries, right?

Melissa Brucker: Yes.

Mat Kaplan: I saw a graph that showed a steadily rising line of newly discovered objects.

Melissa Brucker: Definitely. Yes.

Mat Kaplan: How do you quantify? How do you talk about the amount of work that's done overall? Because there are some specific types of follow ups, which I also want to get into because they're pretty exciting.

Melissa Brucker: So we have software that presents us with lots of near-Earth asteroid choices to look at and we tag them based on what lists they came from. So we focus primarily on virtual impactors, which are asteroids whose our knowledge of their orbits is uncertain enough that there is a possibility that it might hit the Earth within the next 100 years. So we focus on those. We focus on potentially hazardous asteroids, which are asteroids that are 140 meters in size or larger, and also whose orbit gets within 0.05 AU of Earth's orbit. So we try to look at PHAs that get really close to Earth within the next 40 years and also we try and look at them when their fainter than most other follow up telescopes can look at them.

Mat Kaplan: Who's making the bulk of the discoveries now if you guys are doing mostly follow up?

Melissa Brucker: Catalina Sky Survey here at University of Arizona. We're actually in the same department, the Lunar and Planetary Lab, and Pan-STARRS at the University of Hawaii. Between them, they discover most of the new near-Earth asteroids. There are several other discovery surveys as well that contribute to that.

Mat Kaplan: And of course we'll be talking as we sat there, Christensen. Well, just a few moments as people listen to this program, but Pan-STARRS, we've also talked about a little bit on them the show. There was another class of follow up that you do that I was fascinated to see, and it involves yet another effort that emanates now largely from the University of Arizona. And that's NEOWISE, under your colleague Amy Mainzer, who's an old friend of our show.

Melissa Brucker: Yes. In 2010, during the original WISE Mission, Spacewatch was the prominent follow up observatory of asteroids that WISE looked at and discovered. Bob McMillan, who was leading Spacewatch at the time, was part of the science team for the WISE Mission.

Mat Kaplan: You told me you don't run into Amy that often, but clearly this is an important part of this whole structure that now exists for finding, characterizing, tracking these objects which are so important.

Melissa Brucker: Yes. Professor Vishnu Reddy does a lot of near-Earth asteroid characterization. He is also in our department.

Mat Kaplan: It really seems to be a center for this kind of work, the University of Arizona.

Melissa Brucker: Yes. The department has built up a reputation for asteroid work. In fact, the OSIRIS-REx Mission was directed out of here, it actually still is, based in our department.

Mat Kaplan: A lot going on obviously. There is one more major thing that as we speak is only about a week away. We'll already have happened by the time people hear this program. You know what I'm leading up to. And again, Spacewatch got everything started.

Melissa Brucker: Yes. In April of 1996, one of our observers discovered the asteroid Didymos. Didymos moon will be the target of NASA's first planetary defense mission.

Mat Kaplan: You were telling me before we started recording that you folks are still very involved with the DART team at the Applied Physics Lab. What's the current status and what is your involvement at this point?

Melissa Brucker: Spacewatch's involvement is that we plan on taking light curve data of the Didymos system after the impact. So it will be visible from this latitude beginning in mid-October. And we'll probably start in November once it's rate across the sky slows down a bit. And we could observe it from November until March when it will be too faint to get extremely accurate data from it.

Mat Kaplan: What will be the goal of those observations? Will it be primarily to see if DART managed to nudge it a little bit?

Melissa Brucker: Yes. So the goal is to see if the orbit of the moon has changed after being impacted by the spacecraft. And how it changes depends also on what is the strength of the moon. When a spacecraft hits it, it will deform the moon but also it will change the orbit. So it depends on the angle of impact and the strength of the object. But over time, the orbit of the moon should change and that will change the pattern that we'll see of the change in brightness and darkness of the moon and the asteroid together as they individually rotate and as the moon orbits around the larger asteroid.

Mat Kaplan: What do we know about the nature of Dimorphos right now? I mean, I've heard people I think jokingly say, "What if it's just a big rubble pile and DART will just zoom right through it?" It's a little more massive probably than that, right?

Melissa Brucker: It's about 500 feet across. I think that people think that it is a rubble pile. I haven't done any studies of that, but we'll see.

Mat Kaplan: I imagine there must really be quite a bit of excitement around here knowing that this project that you folks discovered, that Spacewatch discovered, is now the subject of this very important test.

Melissa Brucker: Definitely. We are very excited to be able to look at Didymos and Dimorphos. It's really exciting. We can't wait. We've been working for the Planetary Defense Coordination Office before it was named that. And so to be part of the very first planetary defense physical test of hitting an astride is really exciting.

Mat Kaplan: I'll say. As is NEO Surveyor, you know?

Melissa Brucker: Yes.

Mat Kaplan: What Amy is doing up the hall here, I guess. I want to talk about something that The Planetary Society, it's been a major priority of ours, to see the study of near-Earth objects elevated by NASA and by other agencies around the world. We think that we've helped to contribute to that. And now of course it is centered in this group, the PDCO, Planetary Defense Coordination Office headed by Lindley Johnson, who's been our guest many times. I must assume that you think this is a really smart thing for NASA and other agencies to be doing.

Melissa Brucker: Definitely. The probability of any asteroids striking the Earth is extremely, extremely low, but it's not zero. So while we have not discovered a near-Earth asteroid that would be extremely dangerous to life on Earth, we want to be able to deal with that possibility even though it's a very low probability.

Mat Kaplan: Exactly how we put it as well. NASA of course provides a good part of your funding, right? The Spacewatch?

Melissa Brucker: Yes.

Mat Kaplan: Does that come through the PDCO?

Melissa Brucker: The grants are through the Near-Earth Object Observations Program. So it is part of the General ROSES call for funding that NASA puts out every year. The PDCO oversees that budget line, the NEO budget line.

Mat Kaplan: And there's a family foundation also that contributes?

Melissa Brucker: Yes. We have a program to observe near-Earth asteroids to collect light curves of them and determine the rotational periods of the asteroids, and that is funded by the Brinson Foundation of Chicago. In fact, that was the meeting that I was in just before this.

Mat Kaplan: Oh, okay.

Melissa Brucker: And it will be funding part of our work that we will be doing with Didymos.

Mat Kaplan: If people go to the Spacewatch website, there's a lot of great descriptive material there, but there is also this long list of firsts. I won't go through all of them, but a couple here. First astronomical group to develop automated real time software for moving object detection. We talked to a lot of amateur astronomers and they use, I'm sure, they're descendants of the software that was developed by Spacewatch. That seems like it was a pretty big advance.

Melissa Brucker: Yeah, that was in 1990.

Mat Kaplan: Wow. 32 years ago. That's amazing. And then another one, which I assume is similar except it was an actual discovery. First automatic discovery of a comet. How do you discover a comet automatically?

Melissa Brucker: The same way you discover an asteroid, but once you look at the images, you see it's fuzzy.

Mat Kaplan: I see. Okay. I mean, it's doing that old what used to be called I think the blink test?

Melissa Brucker: Yes. Yeah.

Mat Kaplan: Could you describe that?

Melissa Brucker: Well, we actually still use blinking. You take a series of images of one region of the sky and you blink the images back and forth when doing it by eye and see if anything is moving where it's not in the same place in the first image as compared to the second image. And then if it looks like in three images it's moving in a straight line, then you can assume it's probably the same object and you measure the positions in each of the three images and the specific times at which the image was taken. And that will give you not only three coordinates of where it was, but also two velocities.

Mat Kaplan: It worked for Clyde Tombaugh.

Melissa Brucker: It did. You can actually see copies of the Pluto discovery images at Lowell Observatory.

Mat Kaplan: Wow, that's great. Yeah, which of course is where he did that work. Amazing discovery of Pluto. It's one other thing. It said identify two new asteroid populations, small NEAs or near-Earth asteroids and distant centaurs, which have been mentioned now and then on the show, but not often. Could you talk about both of those?

Melissa Brucker: When you get better technology, you can see things that are fainter. So discovering small near-Earth objects required large enough telescopes, which at this time was the 36 inch telescope on Kitt Peak, we usually refer to it as a 0.9 meter now. And this dedicated survey. When you're doing an asteroid survey as opposed to an astrophysical survey, you're looking mainly in the ecliptic, so in the disk of the solar system because most small bodies in the solar system will be in that disk.

Mat Kaplan: They all flattened out into that disk just like their parents.

Melissa Brucker: Yes, they flattened out. Or if their orbits are inclined, they still have to pass through the disk twice.

Mat Kaplan: Sure. Yeah.

Melissa Brucker: The centaur population being further out, centaurs are usually considered to be icy objects. They're in unstable orbits between the giant planets. They have come inward from the Kuiper belt and are now orbiting around and they may end up coming in closer and becoming Jupiter family comets.

Mat Kaplan: Therefore would be pretty interesting objects to get up close to and study, right?

Melissa Brucker: Yes.

Mat Kaplan: Because if they came from the Kuiper belt, we've still only looked at a couple of things up close in the Kuiper belt If you count Pluto.

Melissa Brucker: Pluto, Charon and Arrokoth.

Mat Kaplan: Arrokoth. Yeah, right. We've made a lot of progress, but we obviously still have a long ways to go. I mean, we found the really big dudes, hopefully. Do you think we're on track for reaching the point where we really will know what rocks pose a major threat to Earth giving us the chance to do something about it?

Melissa Brucker: I think we are. In 2005, there was a congressional mandate to discover track and characterize 90% of the near-Earth asteroids that are 140 meters in size and larger. Unfortunately, it was unfunded mandate that was supposed to be completed by 2020. Right now it is about 59% complete. No, it's 59% incomplete. So it is-

Mat Kaplan: 41%. Yeah.... 41% complete as of last January. The NEO Surveyor mission, which you had mentioned is directed out of this department, will be able to make huge strides in accomplishing that goal as will the LSST once that comes online in October of 2024. Studies from a year or two ago, predicted that once both surveys are running, the mandate will be met within 10 years. Wow. That's a pretty good target that we're shooting for. And it sounds like we're on track. You mentioned the LSST, which is that big new southern hemisphere telescope?

Melissa Brucker: Yeah. So the telescope is the Vera C. Rubin Observatory, and it will be revolutionary in all aspects of astronomy, astrophysics, and planetary science.

Mat Kaplan: I mean, in addition to maybe saving the planet someday, these are just interesting objects to learn about, right?

Melissa Brucker: Yes. Every near-Earth asteroid that we've had up close images of has been different.

Mat Kaplan: One of my favorite things about talking to people like you across the 20 years of this show has been the surprises and the degree of diversity that we keep finding out there in our own backyard, our own solar system.

Melissa Brucker: Definitely. With the OSIRIS-REx TAG sampling of Bennu, they said that when the probe went in to collect the sample, the surface of Bennu did not slow the spacecraft down at all. What slowed it down was the thrusters, the engine thrusters,. So it just went right in. I heard someone say they described it as a ball pit.

Mat Kaplan: Wow.

Melissa Brucker: Like a children's ball pit.

Mat Kaplan: The kind my six year old grandson would have a great time in.

Melissa Brucker: Yes.

Mat Kaplan: Wow. So there's your rubble pile again.

Melissa Brucker: Mm-hmm.

Mat Kaplan: Just one more for you. I saw that before you came here, you were at Adler Planetarium, that famous facility next to the lake in Chicago, actually on the lake kind of.

Melissa Brucker: Yes.

Mat Kaplan: What were you doing there as a post grad?

Melissa Brucker: So I had a postdoc fellowship there working with Mark Hammergren to do near-Earth asteroid tracking. We had a share of the Apache Point 3.5 meter telescope in New Mexico. And so we would observe near-Earth asteroids for about two hours every other night in the middle of their night to follow up on track, some of those fainter objects, fainter near-Earth asteroids. And we also had time to use their spectrograph. So we would take spectra of some of the asteroids as well.

Mat Kaplan: Did you ever... I mean, were you actually based at the planetarium?

Melissa Brucker: Yes, we had offices in the planetarium. There actually is a full-time research staff there, and so I was part of that research staff.

Mat Kaplan: I've talked to some of those folks in the past. Did you have any interaction with the public as hundreds of thousands of people who come through there?

Melissa Brucker: Oh yes. All of the astronomers there spend time on the floor of the planetarium speaking with visitors. They have a special visualization room that we can talk with people in. And also just on the floor talking with people. After the New Horizons flyby of Pluto, I actually spent two or three full days up there talking with the public since my dissertation was on Kuiper belt objects.

Mat Kaplan: Oh, okay. I didn't know that. It sounds like you enjoy that interaction. It wasn't just a distraction from your observations?

Melissa Brucker: No, It's always great interacting with the public and sharing the things that we're excited about.

Mat Kaplan: I will note that the building we're in right now, the Kuiper Space Sciences Building, the headquarters for Lunar and Planetary Lab is right next to a planetarium here in Tucson. Kind of fun that you are still working, if not at, nor right next to another planetarium.

Melissa Brucker: Yes. Yes.

Mat Kaplan: Melissa, thank you very much. What's ahead for Spacewatch other than getting power back on from the grid and getting off of your must provided satellite dish?

Melissa Brucker: Yes, we're [inaudible 00:22:29] awaiting full internet so that we can actually transmit image data.

Mat Kaplan: I bet.

Melissa Brucker: So we are working on coming up with a plan to interact with the LSST data. Because it will be orders of magnitude, more discoveries of asteroids the community will still need asteroid follow up like what we are doing now, but it will have a different face in the future.

Mat Kaplan: A flood of data just ahead.

Melissa Brucker: Yes.

Mat Kaplan: Very exciting stuff. Thank you for welcoming us to your office. Well, we'll talk with Eric Christensen next about the Catalina Sky Survey. Your neighbor here. And I'll make sure that he knows you said hello.

Melissa Brucker: That sounds great.

Mat Kaplan: University of Arizona astronomer Melissa Brucker is principal investigator for Spacewatch. As promised, we'll meet her colleague Eric Christensen in a minute.

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Mat Kaplan: 25 or so comets are likely to forever bear the name of our next guest. In addition to discovering those comets and working for five years at an observatory in Chile, Eric Christensen now directs the fantastically successful Catalina Sky Survey as principal investigator. I made that walk across the University of Arizona campus once again on my last day in Tucson so that I could sit down with Eric in his office. Eric, thank you for welcoming me to your office here in the Lunar and Planetary Lab offices at the University of Arizona. Thanks very much.

Eric Christensen: Thank you for joining me. It's my pleasure.

Mat Kaplan: As you know, I've already talked to your colleague, Melissa Brucker, who had Spacewatch. And by the way, she says hello. That's interesting. As I said to her that these two extremely well known, I mean internationally renowned searches, sky searches, are both based on this campus actually just a few floors apart in this building. It's an interesting relationship.

Eric Christensen: That's right. We've evolved along similar but parallel tracks. We occupy the fifth floor, they occupy the second floor. We occupy Mount Lemmon, they occupy Kitt Peak. We've both done a number of discovery efforts and also follow up.

Mat Kaplan: Very, very successfully. Now, while Spacewatch now, I guess, is mostly all about follow up, you guys are still very, very much in the discovery business and very successful at it. We're most of the way through 2022. How many near-Earth objects have you guys come up with this year?

Eric Christensen: I don't have an exact count. The number changes pretty much every day, but if we can produce roughly what we've produced the last few years, we'll find maybe 1,500 near-Earth asteroids, new near-Earth asteroids this year.

Mat Kaplan: Absolutely amazing. I read that of the roughly 30,000 or so that have been found so far, CSS, Catalina Sky Survey's responsible for about almost half of those.

Eric Christensen: Nearly half. Yes, certainly when combined with Spacewatch, the University of Arizona has discovered over half of the near-Earth asteroid population.

Mat Kaplan: Really the only survey that I saw that is kind of neck and neck with you is Pan-STARRS in Hawaii. Is there any sense of competition there of-

Eric Christensen: Inevitably there is some. However, we're all on team NASA, team Planet Earth, team near-Earth asteroid, and so it's also a collaborative relationship. We root for them. I hope they root for us. Hey, Richard. Hey, Rob.

Mat Kaplan: I'm sure it's a balance of collaboration and competition.

Eric Christensen: It is.

Mat Kaplan: You've mentioned the NASA relationship. Is that now partly at least through the Planetary Defense Coordination Office?

Eric Christensen: It is. The Planetary Defense Coordination Office runs the near-Earth Object Observation Program at which we apply to every few years for our funding. But most of the near-Earth asteroids that have been discovered in the last 25 years have been discovered by NASA-funded projects. Currently, Catalina Sky Survey, Pan-STARRS, the Atlas Project are the main ground based NEO discovery projects. But historically, there have been several that have come and gone and some of which like Catalina are still going.

Mat Kaplan: Lindley Johnson, the head of the PDCO, Planetary Defense Officer for NASA, he's been on the show many times, a good friend of the show. It's so interesting to see how the United States and really across the world in just the last few years seem to have much greater recognition of how important these searches are. Have you seen that as well, this transition?

Eric Christensen: I think I have. It's maybe a little difficult because I am deeply embedded in the near-Earth asteroid observations.

Mat Kaplan: You've been doing it for years. Sure.

Eric Christensen: Yeah. But yeah, I think there is a greater public consciousness today than there was 10 years ago, and certainly greater today than 20 or 25 years ago when the initial efforts to detect near-Earth asteroids at scale began.

Mat Kaplan: You know that I walked over here across campus from the Mural lab where I was spending time with a director there, the chair and director Buell Jannuzi, and that's an interview and tour that we'll be sharing before too long. He mentioned LPL, Lunar and Planetary Lab, as as a sister department on campus. I mean, there's more evidence of how much effort is underway across everything space at the University of Arizona. I mean, what's your relationship with the Steward Observatory?

Eric Christensen: Well, the Catalina Sky Survey operates several telescopes, some of which we operate full time, some of which we apply for time on and use part-time. But all of these telescopes are owned by the Steward Observatory. We have partnered with them to put these telescopes to use, but we work very closely with their Mountain Operations team who keeps keep the telescopes up and running, and also with the directorship to explore new possible ways forward, possible future directions for Catalina Sky Survey.

Mat Kaplan: Tell me about the telescopes, the instruments that you use to get these great results.

Eric Christensen: Well, I'm glad we're doing a radio show because the telescopes, I have to admit are not that attractive.

Mat Kaplan: I don't know. I've never seen a telescope I didn't like.

Eric Christensen: Well, I love these telescopes, but what I mean by that is these are older telescopes. People might have the impression that automated sky surveys are performed by shiny robots in sleek, futuristic buildings perched on top of mountains. These telescopes that we use date from the 1960s and '70s, that's when they were originally constructed and put to use. And Catalina Sky Survey has been using them for over 20 years now, about 20 years for some of them. So they're older telescopes. We've done our best to keep them modified and modernized, again, in collaboration with Steward Observatory and through funding from NASA. These telescopes are available to us in part because they were underutilized at the time. So there was an opportunity, telescopes that were available, a newly formed Near-Earth Object Observations program that was supplying funding. And so this dates back to the late '90s, but that was sort the opportunity, the seed from which Catalina Sky Survey grew.

Mat Kaplan: And of course, even if you're depending on the same lenses or mirrors, there's a lot you can do particularly with cameras, right? I mean, the advances have been amazing.

Eric Christensen: That's right. There have been a series of cameras on a few of the Catalina Sky Survey telescopes and a series of telescope control systems as well. So the TCS is what drives the telescope and how we can interact with that.

Mat Kaplan: TCS?

Eric Christensen: Telescope control system.

Mat Kaplan: Right.

Eric Christensen: Sort of the generic term for a system of electronics and software that will control the telescope. But yes, we've been able to upgrade the sensors for the survey telescopes a few years ago. And with that, we've widened our field of view on each of the survey telescopes. So that allows us to cover more sky. More sky coverage equals more NEO discoveries.

Mat Kaplan: I got to note that the one of your telescopes, so 1.5 meter, actually built in 1967 under the direction of someone whose name will be familiar to pretty much everybody who listens to this show, Gerard Kuiper of the famous Kuiper Belt. I mean, that's quite a legacy.

Eric Christensen: It is, yes. And you can draw fairly straight line between the founding of the Lunar and Planetary Lab under Kuiper's direction. Kuiper was a mentor of the founder of Catalina Sky Survey, Steve Larson. They worked very closely for a number of years. So yes, we're still using the tools that were built for the decades when lunar exploration was in its heyday. We're happy to be able to continue to put these telescopes to good use.

Mat Kaplan: What are the other secrets of your success? I hate to call them secrets. I mean, it's not just great, even if there's somewhat old telescopes and terrific sensors at one end of it. There's other stuff that's happened. I mean, you talked about the fact that these searches now are largely automated.

Eric Christensen: Sure. There's a number of secrets which I will divulge here. One of them is simply having full-time access to these telescopes. So the fact that we can use these telescopes in a way that we see fit, we can optimize their operation for the task of near-Earth asteroid survey. So full-time access to these telescopes is one. I did mention that these telescopes are highly automated. However, another secret to our success is that we have expert observers running these telescopes in real time at the telescopes. So they're staying up all night. They're executing the plans. They are monitoring the systems, making sure that everything is in good focus and watching for weather. But one of the main roles for our astronomers is that they will validate. And that they will view, shortly after the data are taken and process, they will view these near-Earth asteroid candidates. And the fact that we can within a few minutes put together a sequence of images to display to the observers, they can very quickly determine whether something is real or not. Since we can do that, we can really dig deep into the noise of our systems. So we could further automate things and remove that human validation step, but it would come at a cost of sensitivity to real objects.

Mat Kaplan: So humans and machines, it sounds like.

Eric Christensen: Humans and machines. Yes.

Mat Kaplan: Are your observers at the telescopes or are they working remotely or is it a combination?

Eric Christensen: It's a combination. Our survey telescopes are usually operated on site. So somebody is in a climate controlled room in the dome itself or adjacent to the dome. We operate a follow up telescope that does not have a control room. So that is always operated remotely. Usually from Tucson here at the University of Arizona, during the pandemic, we set things up so people could operate from home. Generally, we have one or two people on Mount Lemmon every clear night or most every clear night of the year.

Mat Kaplan: Have you largely developed the software behind these automatic automated searches here? As part of the CSS?

Eric Christensen: A lot of the software has been developed in house, and that's another sort of key to our success. We can identify areas in the software that can be improved and work to fix those. If you make a 1% improvement in a piece of software and then you do that a few times a year over a few decades, you're really sort of sharpening your instruments for finding near-Earth asteroids. We also use freely available software. I mean, we don't build what is already out there for use. So we use common open source packages that are in wide use by astronomy. The detection software of course is homegrown and very highly attuned to our specific telescopes and sensors and observing cadence.

Mat Kaplan: Are there any standout discoveries that you'd want to call attention to? I mean, I'm sure we could go for an hour just going through some of the things that the CSS has found across the solar system. But I have one in mind in particular, actually, something that happened in 2008 that you're Richard Kowalski discovered. I bet you know the one I'm talking about.

Eric Christensen: That's right. Yeah. Most asteroid names just sound like license plates. They're a bunch of numbers and letters. But this is 2008 TC3 that you're referring to.

Mat Kaplan: Yeah. Yeah, that's it.

Eric Christensen: That was the first asteroid that was detected prior to Earth impact. So Richard Kowalski was at the telescope operating the survey as he often did along with other observers. But on this night, he detected something that was later shown to be on a very near term impact course with the Earth. It was a surprise. It was a surprise to all of us. I mean, we had been searching the skies for the better part of a decade looking for near-Earth asteroids. But I don't think we really thought that we would actually find something immediately before it hit. The common wisdom at the time, and really to this day, is that we need to find large objects well in advance of any possible close approaches or impacts. Our mandate is to find objects that are 140 meters and larger, but in order to do that, we have to cast a pretty wide net for things that are moving. And that net can sweep up 140 meter objects, but also three or four meter objects, which is about the size of 2008 TC3.

Mat Kaplan: And I remember those photos of people in the desert in Sudan actually finding fragments. I mean, if I was Richard Kowalski, I'd be pretty proud of this discovery.

Eric Christensen: Yes, and deservedly so. I mean, it was a nice confluence of this sort of human automation interaction where we had a highly automated system and an expert observer at the telescope able to correctly identify near-Earth asteroid candidates and even get follow up observations. So going back to your earlier question about what are the secrets of the CSS success, real time validation and reporting and the ability to schedule follow up observations even the same night makes it a lot easier to keep those objects or to make sure that those objects are re-observed and their orbits determined and published.

Mat Kaplan: Are there any others? Maybe a couple that you'd want to call attention to that are standouts?

Eric Christensen: Well, there's a few more impactors. So after the 2008 TC3 in 2008, there were two others that we detected prior to impact. I say we as the Catalina Sky Survey, but as it happens, Richard Kowalski was in the chair that night. I'm not sure what his magic secret is, but we hope to find more. We've also detected a few so-called mini moons. Again, very small near-Earth asteroids, very close to the Earth that were temporarily captured by the Earth's gravity and maybe did a few erratic loops around the Earth before leaving the Earth-moon system. That was another surprise. I guess something that we were not specifically looking for, but again, we had a system that was attuned to finding fast moving objects near the Earth.

Mat Kaplan: There are some descriptions of some of these as well, as well as pretty much everything else that we're talking about on the Catalina Sky Survey website, which we will link to from this week's show at, including these little temporary moons of Earth that just a fascinating find. Remind us, we've talked about this on the show before, once a discovery is made confirmed by one of your human observers, what's the process? What happens then with that data, that discovery?

Eric Christensen: Well, when we detect near-Earth asteroids, we distill that data into what's called astrometry, which is just a text listing of position and time in the sky and encodes the observatory from where we're observing, so the place on planet Earth. And those are sort of the building blocks of orbits. And we send those building blocks to the Minor Planet Center. And the Minor Planet Center is charged with consolidating all these observations, identifying which observations belong to which object, identifying if there are new objects that need to be published, and then publishing those not only the astrometry, but the orbits as well. So they are the clearinghouse of all near-Earth object observations, as well as all minor planet observations in the solar system.

Mat Kaplan: And then that database that the MPC maintains, that's looked at by astronomers all over the world, right? Including amateur astronomers who we have talked about many times on this show. You may know The Planetary Society has a grant program, our Shoemaker NEO Grant Program that actually helps these amateurs improve their systems. But most of them now doing follow up. I mean, lots of them following up on discoveries made by the CSS.

Eric Christensen: That's right. Amateurs play a very important role. Occasionally in discovery, there are still room for amateurs to make new discoveries of near-Earth asteroids, but also particularly in follow up. So sky surveys like Catalina, like Pan-STARRS, like Atlas, we would love to just survey the sky all night and not have to break our cadences and steer our survey telescopes toward single objects where that's not the best use of these survey telescopes. That's why dedicated follow up stations, NASA funds many of them. We operate one telescope that is dedicated to follow up. But the act of follow up is important to help build our understanding of the orbit at least to the point where the orbit is well enough known that we can say, "This is a real object. We know it's a near-Earth object. It is unique, it hasn't been seen before. So it gets entered into the catalog." Even after that, follow up is still important because these objects have uncertainties associated with their orbital elements. We don't know exactly where they're going so just checking in on them periodically will help beat down that uncertainty and improve the orbit so they don't get misplaced.

Mat Kaplan: Yeah. We don't want to misplace them because you never know which one has our name on it as we say around here.

Eric Christensen: Sure.

Mat Kaplan: Let's look to the future. I want to start with another colleague of yours in the Lunar and Planetary Lab, Amy Mainzer from JPL, now a professor here on campus, as you know developing the NEO Surveyor infrared space telescope that were very supportive of it at The Planetary Society. How is that going to change things when NEO Surveyors up there scanning the skies from above Earth's atmosphere?

Eric Christensen: We're all looking forward to the launch and healthy operation of the NEO Surveyor. NEO Surveyor is going to be a very powerful survey instrument. It has the advantage of working above the Earth's atmosphere, working in infrared light where asteroids are relatively brighter, being able to operate day and night. There are no day night cycles at L1. However, round based NEO surveys, optical NEO surveys and space-based IR surveys, we expect they'll work in very complimentary ways. So ground based optical surveys look outward from the Earth into the night sky and a little bit toward the twilight sky as well. But NEO Surveyor will look more in the twilight sky and not be able to look directly outward from the Earth. There's likely to be differences in the kinds of objects that NEO survey will be sensitive to. NEO Surveyor is designed to essentially fulfill the original mandate to find 140 meter near-Earth asteroids or potentially hazardous asteroids. We expect that it will be able to do that very efficiently and much more quickly than we could from the ground. But things like 2008 TC3, those are likely to be the purview of ground-based surveys. I think there's a future for ground-based follow up, ground-based survey, space-based survey, space-based follow up. Let's throw that in there too. But yeah, there's plenty of work to be done for everybody.

Mat Kaplan: Lots more rocks out there to discover.

Eric Christensen: That's right.

Mat Kaplan: And we should mention L1, of course, Lagrangian point 1, one of those relatively stable spots out there in space where a spacecraft like NEO Surveyor can just kind of sit and not have to do a lot of work to stay in that one spot. What else is ahead? What's in the future for the Catalina Sky Survey?

Eric Christensen: It's always the perennial question for me. I mean, we expect that we'll be continuing to survey and discover new asteroids for as long as NASA is interested in funding us. In the last few years and looking toward the future, we've shifted some of our focus and our attention toward the problem of follow up. We've built some tools to help us do that. And the community, we have a tool called NEOfixer now, which is available to the public. And this is a way for anybody with a telescope to get a customized list of objects that they can observe and that need observations.

Mat Kaplan: Huh.

Eric Christensen: There's a lot of near-Earth objects that are observable, and many of them don't need to be observed. They're numbered, they're well known, they've been observed for decades. So this NEOfixer is a way for us to schedule our own follow up telescopes and hopefully help coordinate the global follow up effort as well.

Mat Kaplan: That's very cool. And that's exactly where I was hoping to go next because of the outreach activities of the CSS and also the citizen science angle of what you do. Say something about the Catalina Sky Survey Orbit View, which I had some fun playing with a couple of days ago.

Eric Christensen: Yeah. The CSS Orbit View is linked on our website. It was developed by one of our astronomers, David Rankin. It's a way of visualizing the orbit of an asteroid, a near-Earth asteroid in the context of the solar system. So you can pan and zoom and reorient the view. You can center your view on the sun or the Earth or the asteroid and run it backward and forward in time so you can visualize close approaches. It's one of those tools that we find useful and we have made it available to the public and hope that other people like you might find them.

Mat Kaplan: Yeah, it's pretty fun. It's a lot of fun. I encourage people to take a look at this little interactive tool. You told me that you've got another citizen science project. I get maybe still in the works, something that'll happen through Zooniverse?

Eric Christensen: Right. Another of our astronomer/engineers, Carson Fuls, is working on a citizen science effort that will essentially ask the public for help identifying moving objects much as we do at the telescope on a nightly basis. This platform will enable us to put more of our data in front of the public in a way that's hopefully easy to understand and easy to interact with and not only give people the flavor of what it's like to actually work at a project like Catalina Sky Survey, at least one aspect of it, but also to make meaningful contributions. We expect that we will be sending data onto the Zooniverse platform through this citizen science project that has been reprocessed. We're currently reprocessing decades of our older data. Every night we scan through most of the data, but there's always always additional data that didn't quite make the cut that we know has real objects there. And so maybe this might be an opportunity to have people help find new near-Earth asteroids as well.

Mat Kaplan: There's one more thing that might be fun even for other folks out there, lay people like myself or maybe people who own a telescope like myself, but I don't call myself much of an astronomer. it's something else I found on the website called Ask an Asteroid Hunter, where you can throw a question at you and your staff.

Eric Christensen: That's right. That is managed by yet another of our multitude of talented team members, Greg Leonard. It's basically just what it says. If you have a question about asteroids or a question for Catalina Sky Survey, you can go to Ask an Asteroid Hunter and type that in and expect a reply.

Mat Kaplan: That's very cool. You're an observer. I'm just wondering, do you have a telescope someplace with 20 little notches or maybe little comet silhouettes inscribed on the side, because you've got... Or is it more than that now? 20 comets.

Eric Christensen: It's 25, I think.

Mat Kaplan: Wow.

Eric Christensen: Yeah.

Mat Kaplan: Okay. Yeah. Well, the page I saw must be out of date.

Eric Christensen: Okay. Yeah, so when I started with the Catalina Sky Survey in 2003, it was sort of the earlier days of CSS, there had just been some major upgrades and improvements and we were just trying to figure out how to efficiently use these systems. And so I did spend a lot of time observing for the first four years or so when I was at Catalina. One of the perks of looking at the sky night after night is that sometimes you find something that nobody else has seen before. Guidelines dictate, that object, if it's confirmed as a new comet, can bear your name. So yes, I've had the good fortune to find a number of comets.

Mat Kaplan: Amazing.

Eric Christensen: As have most of the people who have done any observing with Catalina Sky Survey.

Mat Kaplan: Yeah, there was a little scorecard going through your staff. I think maybe the others are out of date as well. But pretty impressive to combine the fact that you are learning about these objects, which is valuable in itself, but that you may also, with the work of Catalina Sky Survey, be helping some place on Earth or maybe all of Earth avoid a whole bunch of trouble someday, but you are also getting this opportunity to see things that no human has ever seen before.

Eric Christensen: We do always have in the back of our mind the main reason why we're here and why we're funded by NASA, is to find potentially hazardous near-Earth asteroids. But in addition to that, it's just an interesting project. It's an interesting technical challenge. It's an interesting sociological area to work in. I've been fascinated by near-Earth asteroids essentially since I started working with Catalina Sky Survey and I'm glad to be able to still contribute to the effort.

Mat Kaplan: I'm glad that you and your great team are doing all this work on our behalf, Eric. Keep up the great work. Clear skies. And thanks for taking a few minutes with us on Planetary Radio.

Eric Christensen: Thank you very much, Mat.

Mat Kaplan: It's time for What's Up on Planetary Radio. We are going to have some fun today. Boy, we got some really fun responses, Bruce, to the question that you asked a couple of weeks ago for the contest. Welcome the Chief scientist of The Planetary Society, everybody.

Bruce Betts: Hey everybody, how're you doing?

Mat Kaplan: I keep getting these wonderful messages that make me feel great and I'm going to share this one because it's from Chris Midden in Illinois, who I actually met when I was going down there for the big solar eclipse a few years ago and hope to go back in 2024. "Mat, your influence of sharing the PB and J of space will never be gone. When I teach my middle school science class, I often reflect on all you have shared over the years. And that excitement and passion you shared stays with me and I pass it on." Thank you, Chris.

Bruce Betts: Yeah, yeah. You're great.

Mat Kaplan: I really am getting so many of these. It's just-

Bruce Betts: No, it's really wonderful. And you truly deserve it.

Mat Kaplan: I got it out of him. Hey, you don't have to go on. It's okay. You can tell us about the night sky.

Bruce Betts: Thank you. All right, so we've got planets in the evening sky. It's just a wonderful time to look at planets in the evening sky. I saw Mars the other night, it added. It made me joyful. It's getting so very bright. Just after sunset, we've got Jupiter looking very bright over in the east, east-southeast. And to its upper right quite a ways is yellowish Saturn looking kind of bright. If you wait another hour, a couple hours, you'll see this freely bright, not Jupiter bright, but we're getting there reddish planet thing, which is Mars. It looks like a red star, but it's bright. And way over to it's... Where I was in the early evening, over to its right is Aldebaran, which is a now much dimmer reddish star, which used to be similar in brightness. So Earth and Mars are closing in on each other and it'll be a December 8th, they'll be at opposition and it'll keep brightening until then when it's on the opposite side of the Earth from the sun. On the evening of the 20th and 21st of October and for a few nights afterwards, there's still increased meteor activity from the Orionids, which is it's kind of an average shower produces, maybe 20 meters per hour from a dark site left by debris from comet Halley. So go stare at the sky if you're patient, you'll see some meteors. And then if you live in most of Europe... Do you live in most of Europe, Mat? No, you don't.

Mat Kaplan: I don't even live in a small portion of Europe.

Bruce Betts: In most of Europe, Southwestern Asia and northeastern Africa, on October 25th the moon will cover part of the sun. Ah. It's normal, everyone. Don't worry. It is a partial solar eclipse. However, do not stare at the sun because it still will burn your eyes out. So find an indirect way. You can find plenty of tips on the web for watching it if that's where you are. You can get times and dates, just search on the web.

Mat Kaplan: Jupiter really is bright. You don't need to wear glasses or protection or anything like that. Have you been pointing Jupiter out to strangers? Doesn't everybody? I do.

Bruce Betts: I have in my time pointed it out to strangers. I'm pointing it out right now to strangers that are listening. They're so strange because they're listening. I'm just kidding. We appreciate you, just like you all appreciate Mat. Onto this week in space history, Mars Odyssey working since 2001.

Mat Kaplan: Wow.

Bruce Betts: Amazing. And four years ago, BepiColombo launched and is headed on its way. We're winding its way to Mercury with a couple of spacecraft with ESA and JAXA, the Japanese space agency involved. I move on to Random Space Fact.

Mat Kaplan: I think you made it to fifth gear there.

Bruce Betts: Yeah. I was trying for eighth. So you may ask yourself, Mat, I know I've heard you ask, who was the first ESA astronaut to command the International Space Station? So there were a bunch of Americans and Russians. And you know who that was, Mat?

Mat Kaplan: I have heard the name. I forget. Who was it?

Bruce Betts: He'd from most of Europe, but most specifically Belgium. Frank Viscount De Winne.

Mat Kaplan: Yes. That is the name that I remember. Little nobility in space.

Bruce Betts: Onto the trivia contest. I asked you to name the solar system body and the category of geologic feature that are officially named after abandoned cities of antiquity. How'd we do, Mat?

Mat Kaplan: Just a moderate response, but some really good stuff in here. We have a poem and a song. I'm going to start with a poem from our poet Laureate Day Fairchild in Kansas. Apologies to anyone who may have once lived in one of these ancient cities [inaudible 00:56:21]. "I traveled to Timgad and also to Angkor. Cahokia marked off my list, to Paestum I journeyed, Caral then I hurried before they would cease to exist. These cities of ancients abandon on Earth our histories try to explain. And all of them named as a lengthening vallis engraved out on Mercury's plane.

Bruce Betts: Ooh.

Mat Kaplan: Very dramatic.

Bruce Betts: Yeah, I feel a... What is that? A sense of awe.

Mat Kaplan: Ah, yes, you should. So these are vallis, right? Otherwise in Latin, vallis on Mercury.

Bruce Betts: Yes, that is exactly right. That is what is named after the abandoned cities or technically towns or settlements of antiquity that you've nicely listed off. Most, if not all of them. Who is our winner?

Mat Kaplan: Lisa Warner. She's a first time winner out of Wisconsin. She said valeries. Valeries. vallis on Mercury. And so congratulations, Lisa. We have a terrific prize for you. It's the CD, the just released album of the Moon Symphony from Signum Classics with liner notes partially prepared by yours truly.

Bruce Betts: What?

Mat Kaplan: Seriously. It's that marvelous performance by the London Symphony Orchestra under the baton of Marin Alsop, composed by Amanda Lee Falkenberg who of course we have had on the show and we covered that recording session. So congratulations, Lisa. We'll put that in the mail. I think it's a signed copy of the CD signed by Marin Alsop. I got more.

Bruce Betts: Really? Cool.

Mat Kaplan: A bunch of people, including Scott Borgsmiller in Maryland, longtime listener mentioned that Vallis Cahokia, that's in Illinois, his home state of Illinois, even though he is in Maryland now. It's the Cahokia Mounds left by the indigenous peoples who lived there many, many years ago.

Bruce Betts: Yes. And in fact I learned more about them and dug into Google Images and like when I saw that. I was not familiar with the mounds in Illinois. Pretty cool. Maybe you can see it when you go for the next eclipse.

Mat Kaplan: That'd be fun. I wonder if they're in southern Illinois. Yeah. I hadn't heard of them either. From Laura Dodd in California, another longtime listener. "Dang, Bruce. I started out thinking that the name of the solar system body you were thinking of was also named for an abandoned city. What a long search through asteroids that was."

Bruce Betts: Oh gosh, I'm sorry.

Mat Kaplan: Mel Powell in California, another regular. Funny guy. "But Dr. Betts, how do we know that there are no abandoned cities on other solar system bodies? How do we really know? Huh? Huh?"

Bruce Betts: Let's just say I'm not at liberty to tell you.

Mat Kaplan: I knew it. I knew it. And finally, this from Gene Lewin in the lovely state of Washington. "Down in the vallis, the vallis so low, we'll soon see a space craft, BepiColombo. The sun's closest planet, it is Mercury. The vallis are named for abandoned cities. There's plenty of sunshine and bright as can be, a temperature span of 900 degrees. I'd name all the cities, but the names don't quite rhyme. But all have been empty for quite a long time." [inaudible 00:59:52]. Please take us to another contest.

Bruce Betts: Put your thinking caps and research fingers on ready. Although it did as possible. You will know this. In which case, I salute you. What popular... Let me rephrase. What video game popular particularly in the 1980s owes its name to William Herschel? Huh. So to narrow it down, because that Herschel guy got around popular in the 1980s and other times, but that was it's heyday. Go to

Mat Kaplan: That is very interesting. And you have until the 26th, October 26th at 8:00 AM Pacific time to get us this one. We have to stick with this theme after talking to two of the great discoverers of asteroids, discoverers and trackers in our solar system. What else but a Planetary Society Kick Asteroid, rubber asteroid for the one who gets this one. That's it.

Bruce Betts: How very appropriate. All right, everybody go out there, look up the night sky and think about a video game where the main character is Mat. Thank you and good night. Oh, that's a... Oh, oh, Mat, watch out. Look out! Look out!

Mat Kaplan: Apparently, you have played Donkey Kong. That's Bruce. He's the chief scientist of The Planetary Society who joins me, Mario, every week for What's Up.

Bruce Betts: Oh, I did. I was debating between Donkey Kong and the Princess.

Mat Kaplan: Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by its watchful members. There may be no better way for us non astronomers to defend Earth than to become part of The Planetary Society at Mark Hilverda and Rae Paoletta are our associate producers. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Ad asteroid.