From a Remote Observatory, He’s Defending Our Planet. Get a Glimpse Inside the Life of a Doomsday Asteroid Hunter

This article was originally published on Supercluster, a website dedicated to telling humanity’s greatest outer space stories.

David Rankin is the closest thing Earth has to a space superhero.

As an observer and operations engineer at the Catalina Sky Survey, a NASA-funded planetary defense program that utilizes the telescopes atop the Santa Catalina Mountains in Arizona, he spends hours looking for dangerous rocks that could cause catastrophic damage to Earth. Telescope operator, asteroid hunter, photographer, storm chaser and programmer are just some of his credentials—Rankin even has an ancient marine reptile named after him, a plesiosaur that he discovered at age 14.

At the mountain range’s highest point, Mt. Lemmon, we found the mild-mannered skywatcher nonchalantly protecting humans from extinction by space rock. Since 2019, Rankin has been trekking to the peak to look for solar system objects that might collide with our planet. The Catalina Sky Survey, based at the University of Arizona’s Lunar and Planetary Lab in Tucson, aims to catalog more than 90 percent of near-Earth objects larger than 140 meters across. According to Rankin, they’re about halfway there.

Supercluster dispatched photographer Levi Christiansen in July to capture this jack-of-all-trades at work and to peek inside the daily life of a planetary defender. After the photoshoot, Supercluster’s editorial team called Rankin, whose years of experience have coalesced into fascinating perspectives on doomsday, extraterrestrial life and the headline-grabbing interstellar object, 3I/ATLAS.

Here’s the conversation conducted in October, edited for clarity and brevity.

Supercluster: So, what is it like, on a human level, hunting asteroids up there on Mt. Lemmon? Are you typically alone while working overnight shifts?

David Rankin: Yeah, we work alone, and that was nice during the pandemic, because it didn’t really impact our safety. But, you know, it really is just you. You’ve got to be really passionate about this work. I’ve seen people come and go. It’s not easy being on a night shift schedule, responsible for 12 shifts between two full moons, sometimes with shifts of 12-plus hours, sundown to sunup.

But there’s a thrill with the job. We’re discovering minor planets that are in orbit around the sun that nobody’s ever seen before—on a nightly basis. I picked up two last night that are brand new. On a busy night, I’ve gotten 40.

And we find comets. There’s a lot of really neat stuff that you’re able to do while you’re sitting up in that telescope. And that’s a driving factor for me. I love that thrill of discovery.

On any given night, we could be working up there and pick up an asteroid that’s coming in past Mars, has never been seen before, and it’s gonna hit us. We could also pick up an asteroid that’s gonna hit us in 20 years.

So, it’s a high consequence job; it’s a high reward job. But yeah, the schedule is rough. You have to really live the lifestyle. Most of us stay on a night schedule, 24/7.

Supercluster: How many asteroids have you spotted on your watch?

Rankin: I quit counting—probably in the thousands at this point.

A lot of people don’t realize we live in a shooting gallery. On any given night, there are multiple, usually smaller, asteroids that are passing between us and the moon. And every now and then, a large one squeaks in and passes between us and the moon. Something in the 20-plus-meter class range.

We’re funded through Congress and NASA to find things that are 140 meters across. We’re not even digging down in the weeds on these 50-meter objects, and these are still very large. We’re just trying to focus on closing the catalog on those 140-meter class asteroids that come really close to the Earth. I think I found almost 30 of those so far. But there’s too many of the smaller ones.

So, for context, the giant hole outside Flagstaff in Arizona was made by a meteor that hit 50,000 years ago. That was a 30- to 60-meter-wide asteroid. 

There was one that hit in 2013 [and exploded over Chelyabinsk in Russia]. Everybody saw the videos online. Just stunning, terrifying. That was, like, a 20-meter rock. And we consider that pretty small in this business.

[The Chelyabinsk meteor] was made out of a stony material, so a lot of energy was discharged in the atmosphere. You get a solid nickel iron meteorite—it’s going to punch through the atmosphere like it’s not even there. And that’s kind of what happened outside Flagstaff. You had a rock that was made out of metal, [and] it blasted a mile-wide hole in the ground.

Supercluster: What is the largest object that you’ve discovered?

Rankin: I’ve discovered two that were over a kilometer wide. Those are very rare these days, and that’s a good thing.

This all was kicked off when [the comet] Shoemaker-Levy 9 impacted Jupiter. There were some small teams seriously looking for near-Earth asteroids back then. But when [Carolyn and Gene] Shoemaker and David Levy found Shoemaker-Levy 9 in the early ’90s, it had just passed Jupiter. It came so close to Jupiter that Jupiter’s gravity broke it apart in multiple fragments, like a string of pearls.

And then they realized it was gonna hit Jupiter the next year. It swung back around, because [the planet’s gravity] captured it, and it hit the southern hemisphere of Jupiter in multiple locations. The impact scars on the upper atmosphere of Jupiter were the size of our planet.

That’s what kicked off this planetary defense paradigm that we’re under right now. And the good news is this: We found you can’t hide a ten-kilometer-wide rock—the size of [the asteroid] that wiped out the dinosaurs—between us and Jupiter. It’s not easy. Those are big. You don’t need a big telescope to see those.

So, we found all of those. And down to one kilometer, we found over 99 percent of the hazardous ones, which is pretty impressive. That catalog was wrapping up completion around 2004.

It’s very rare to find a one-kilometer near-Earth object these days. I’ve only found two. There’s just very few of them left.

Now, we’re kind of pushing down into that half kilometer, down to 200 meters, down to 150-meter, 140-meter range, and we’ve still got about 50 percent of the 140-meter class rocks to find. And those are big rocks.

That’s regional devastation. Not the end of humanity, but the end of Arizona.

Supercluster: Tell me a little bit about your surroundings. What is this facility like? What’s the scientific infrastructure? Are your instruments up to date?

Rankin: A lot of what happened with the folks that founded Catalina Sky Survey happened on limited funds. A couple of students [at the University of Arizona] back in the ’90s realized that we had some telescopes sitting up on Mt. Lemmon that were put up during the Apollo era that could be repurposed for the search for hazardous asteroids. They put in their grants for NASA to repurpose these telescopes. And that’s where it all started.

Our telescopes are pretty old, but we keep them upgraded with the parts that matter. We reworked the optical systems on them to make them really fast and [have a] wide field of view. And then we have very high-end cameras that are 10K resolution. We develop a whole bunch of software in-house that kind of facilitates the hunt, like the tracking stuff.

Supercluster: Does the software automatically snap an image, or do you have to do it manually? 

Rankin: So, this is high-tech stuff. The telescopes look old, but don’t let that fool you. We have very talented software developers.

The whole thing is pretty much automated. So, I get up there, I tell it, ‘Hey, I want to look at this whole band of the night sky,’ and it will just run all night. I don’t even have to think about it. It will keep focused. It’ll take images. It does all that stuff and feeds those images into our data-reduction pipeline, and then it goes through that whole set of rings until it’s just ready to feed out to the person sitting in the chair who’s the observer. 

And, basically, it’s saying, ‘Hey, look, I removed all the non-moving sources from these four images, and then I identified all the known asteroids. So, here’s what I think are the new asteroids.’

And of course, 99 percent of those are just noise, because we’re digging really deep in these images. But every now and then, the software has identified a real asteroid, and it’s our job to weed that out and send that data off to the planetary defense community as quickly as possible.

Supercluster: What’s your take on the recent interstellar object 3I/ATLAS that has been dominating the news cycle and fueling conspiracy theories that the object is an alien spaceship?

Rankin: Extraordinary claims require extraordinary evidence, and there’s no evidence that this thing is anything other than a comet.

Everyone wants to find aliens. I have worked in this business for a long time. I know a lot of scientists. Nobody is saying: ‘Oh, I don’t want to find an alien.’ That would be the biggest discovery in the history of humanity. Everyone wants that. The idea that there’s some big astronomy community pushing back against that is ridiculous.

This is the third one of these [interstellar] objects. That’s why it’s called 3I/ATLAS. These objects were theorized for a very long time before the first one popped up in 2017, which was ‘Oumuamua. And basically, what it comes down to, is solar system formation is a very violent process. And as these planets and these large gas giants are migrating in and out of orbits, interacting with each other, forming, massive collisions are happening. It’s just not a very peaceful thing.

And they estimate that millions and millions of these objects get flung out of a solar system as it’s forming. So, you have to think about the billions of stars in our galaxy.

Even before we found the first one, the astronomers were telling us, ‘Hey, these things are between the stars. They have to be out there. There’s no way they’re not out there.’ Even today, we’ll watch Jupiter catch a comet that’s coming in and shoot it out of the solar system permanently—and that’s an interstellar comet. It just came from us. So why wouldn’t there be any that came from others?

Supercluster: That’s such a great point, because no one ever talks about ones that we would eject out of our solar system.

Rankin: Now, if 3I/ATLAS, as it was approaching the sun, if it started to slow down dramatically … that would raise eyebrows.

If this thing takes a 90-degree turn, it’s definitely artificial, right? But nothing has ever even come close to breaching that benchmark. It’s a beautiful object. It’s an amazing discovery, but it’s not aliens.

And that’s the problem with calling these things aliens—we don’t appreciate the actual astounding science that we’re seeing with the actual object and its actual classification.

I hope one day we have the technology to intercept these objects and study them more closely.

Supercluster: When you’re up there by yourself staring at the night sky, do you find yourself thinking about your place in the world? Do you think about your work on a philosophical level?

Rankin: I’m a fifth-generation Mormon, but I haven’t been associated with the church in many, many years. Science is not a religion. But if it were, it’s my religion.

I went from a point in my life where I had 100 percent certainty—because that’s what you get, usually, when you’re in these different Christian or other denominations—like, ‘You’ll die. You’ll go here. This will happen.’

What I’ve gained through my journey in life is a deep, deep, deep appreciation for uncertainty. I am perfectly fine not having all the answers. And I think that it would be boring to have them all. That’s how I feel about it. 

The wonderment that comes from staring out into the universe and making awesome discoveries is just fascinating, and it keeps me very happy. That’s where my joy comes from now, is being perfectly content with not having all the answers. I think it’s a 180 from the way I was raised.

Supercluster: You must have had this thought at some point: What if one day you’re sitting there and you look at the blip on the screen, and there’s a moment when you realize: ‘I’m the only person on Earth who knows that we’re doomed.’

What do you do at that moment?

Rankin: Luckily, the odds of that happening are very low. That moment would be unlikely to happen by itself, because it’s a team effort. When we find these objects, we usually don’t know where they’re going with high certainty. And that includes the orbits of these asteroids when they’re first found.

So, I might not have that realization at the moment that I find the object, but it could come hours or a day later—and how I would react to that, I don’t know. I don’t know that anybody in this business knows how they would react to it.

It would be terrifying. It would be exhilarating. The exhilaration comes from the fact that we’re not doomed.

If there’s enough lead time, there are things we can do about this, like the DART mission showed [when NASA smashed a spacecraft into an asteroid to alter its trajectory in 2022]. And at the very least, if we find a 50- or 100-meter-wide object that’s coming in, and it looks like it’s going to hit a populated area, we could have a week, maybe two weeks—that would be a very unlucky scenario. [But] that’s still plenty of time to get people out of harm’s way, to evacuate. 

Supercluster: So, you aren’t looking for doom, you’re looking for safety.

Rankin: Yeah, we’re funded for safety. What we’re doing here is we’re putting an investment into one of the only natural disasters we can actually do something about. You’re not going to stop a volcano eruption. You’re not going to stop a tsunami. You’re not going to stop a magnitude 9.2 earthquake. This is something we can stop. So that’s what we’re doing. 

We’re trying to find the asteroid that’s 500 meters wide that’s going to hit us in 100 years. So then our grandkids can go, ‘Hey, you know, we were able to deflect it. We’re good.’

And again, we’ve ruled out a dinosaur scenario. But there could easily be a half-kilometer-wide object that poses a threat in the future.

So, it’s an investment, it really is. And honestly, I hope that I’m not sitting at the telescope when we find a rock with short notice coming in. I hope that doesn’t happen. I hope that we find it a century early.