The Sky is Falling
Earth is in a cosmic shooting gallery. With so many asteroids zipping around, how can we find them all before they find us?
[Russian speaker, Chelyabinsk explosion]
[0:09] Narrator: On February 15, 2003, the sky exploded in Russia.
[news report montage]
[0:47] Narrator: When the meteor over Chelyabinsk tore through the atmosphere and exploded, it produced a flash brighter than the Sun and gave many witnesses an instant sunburn. The flash caused people for miles around to run to their windows to see what was going on. Unfortunately for them, the shockwave then hit, blasting those windows into millions of flying glass shards. The shockwave also knocked some right off their feet. More than 1500 people were injured that day.
This wasn’t the first time a massive meteor blew up over Russia. Over a hundred years ago, in 1908, a rock from space exploded near the Podkamennaya Tunguska river in Siberia. Over 800 square miles of forest – 80 million trees -- were immediately flattened. The energy released is estimated to have been a thousand times greater than from an atomic bomb.
Forty miles away from the epicenter of the Tunguska air burst, a man sitting on a porch was thrown clear out of his chair, and briefly lost consciousness. He awoke to an apocalypse.
Male reader with Russian accent: “Suddenly the sky was split in two, and high above the forest, the whole northern part of the sky appeared to be covered with fire. I felt a great heat, as though my shirt had caught fire. At that moment, there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The Earth trembled.”
[2:52] Narrator: Welcome to “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory in Pasadena California. I’m Leslie Mullen, a science journalist based at JPL. In the first season of this podcast, I shared the stories and science behind the InSight mission to Mars. In this second season, instead of focusing on a single mission, we’re going to look at space rocks, also known as asteroids, from the view of many missions.
This is season two, episode one: The Sky is Falling.
[3:27] Narrator: Asteroids go by many names: Near-Earth object. Planetesimal, planetoid, minor planet. Meteoroid. Quasi-moon. When they hit Earth’s atmosphere, they become meteors or bolides. When they smash into the ground, they’re called meteorites. There are Trojans, Greeks, and Centaurs: asteroids as actors in an ancient play. Comets are basically icy asteroids that release water vapor and dust as they’re warmed by the Sun. What an asteroid is called largely depends on where it is, and what it’s doing.
[Movie clip: Armageddon]
“It’s a meteor shower.”
“This new one you’re tracking: how big?”
“It’s what we call a global killer. Nothing would survive, not even bacteria.” (fade)
[4:11] Narrator: Movies like ‘Armageddon’ depict a massive asteroid hitting Earth, causing widespread destruction and chaos. Huge rocks falling from the sky could take out a city, a nation, or even lay waste to the whole planet, and that can feel like the universe is out to get us. Daily news headlines that scream about asteroids coming too close to Earth encourage this paranoia.
The truth is, our planet IS in the middle of a cosmic shooting gallery. Asteroids often fly by, and the Earth is hit every day with hundreds of tons of dust grains and small rocks. Most of them burn up in the atmosphere, and sometimes we see them as meteor showers or shooting stars.
[music: When you wish upon a star: Cliff Edwards/Disney]
[4:59] Narrator: The small rocks from space do little to no damage. It’s the big ones we worry about. And there are big asteroids out there, monsters lurking in the dark, large enough to take us out. Currently, none of the really big asteroids are headed for us. But we haven’t found them all.
JPL maintains a list of all the known potentially hazardous asteroids. You can find them on the Center for Near-Earth Object Studies website. The list is updated all the time, thanks to telescopes dedicated to hunting down new asteroids.
And that’s where this season’s journey begins.
[sound of driving]
[5:42] Narrator: I’m in Tucson, home of the Lunar and Planetary Laboratory at the University of Arizona, a major center for asteroid studies. I’m driving up to nearby Mount Lemmon, the site of the Catalina Sky Survey. This survey is one of several that scan the skies every night in search of asteroids that come close to Earth.
As I drive near the base of the mountain, I see legions of saguaro cactus populating the red rocks. They’re the kind of cactus I think of as cartoonish, because I first saw them in Bugs Bunny-Roadrunner cartoons. The cacti are like green fingers pointing the way. “Up,” they all seem to gesture, encouraging this journey up the long and winding mountain road to look up at the stars.
And up I go, all the way to the top. Even though it was about 95 degrees Fahrenheit in Tucson, there’s ice on the road as I reach the summit.
Greg Leonard, the astronomer working this night, greets me at the observatory gate. As we drive in, I see several large domes standing starkly white against the rocky landscape. There’s something vaguely alien about them in this natural setting, reminding me of the black monolith in Stanley Kubrick’s movie, “2001: A Space Odyssey”.
[music: Gyory Legiti’s “Requiem”]
[7:04] Narrator: Like the monolith in that movie, these sentinels are tied to the stars. The observatory domes are painted bright white to deflect heat. Heat is the enemy of stargazing, because it messes with the sensors in the telescopes inside the domes. Heat also can disturb the atmosphere, blurring our view of the cosmos.
Greg takes me inside the observation dome, and opens a portion of the roof to the sky just as the Sun sinks below the horizon. The observatory is a big echo-y, mostly empty space, except for some mechanical equipment and a large telescope in the middle of it.
Greg Leonard: So we're opening up the Mount Lemmon Station 60-inch, 1.5-meter Cassegrain reflecting telescope. This is one of my favorite times of night when we open up and we can see the Sun has set. There's few to no clouds up above us, and it's kind of a promise of the night to come. Maybe we're going to discover some near-Earth asteroids if the skies are clear.
[8:03] Narrator: The telescope is about ten feet long, and has a mirror in the bottom.
Greg Leonard: The light from stars or the night sky comes down, hits the big mirror. The mirror’s just like a big pupil. It's a big eye. It collects just that much more data than your eye will collect. Then it bounces that light back up to the top. And that's where our sensor is. And that collects the images and the data that get piped into the warm room where our computer rack is.
[8:29] Narrator: The top of the mountain is cold, which is good for telescopes, but not so good for people. In the past, astronomers would have to suffer all night long, hunched over telescopes in temperatures so cold, their photographic plates would crack. Thanks to computers, those hardships are over. Catalina Sky Survey observers do their work in a warm and comfortable room right next to the telescope. The room has a kitchenette, chairs, a big computer rack, many computer monitors…. and a red phone. But Greg claims the phone isn’t a hot line to the White House to report an oncoming asteroid.
Greg sits at the computer to focus the telescope, and then the observing run begins. One of the computer monitors shows the night sky overlaid with a grid of rectangles. Each rectangle in the grid is called a field, and the telescope takes a series of images from each one.
Greg Leonard: We're going to start tonight here at set number one. It's gonna take a thirty second picture at this field. When it's done that it moves to the next field over and takes a thirty second image there. It'll march through the entire set of twelve fields. When it's finished with the twelfth one, it's gonna go back to the first one and it's gonna do the same thing. This happens four times and a set takes roughly forty minutes or so and then it's gonna move on to set two.
[9:54] Narrator: The asteroids and stars all look like bright dots. The word “asteroid” actually comes from the Greek word for “star-like.” The big difference here is the stars appear eternally fixed, while asteroids zip around like fireflies. By taking several photos of the same patch of sky over time, the computer can compare the images and see if any dots of light are moving against the background stars. The speed the asteroids move can indicate how close they are – faster ones generally are nearer to Earth than the points of light that barely crawl from one image to the next.
The computer also figures a rough size based on how bright they are. Asteroids are typically dark rocks, but sunlight reflecting off their surfaces make them look, from our vantage point, like tiny stars. So the bigger the asteroid, the brighter the asteroid.
But this brightness rule of thumb only works if they’re all the same distance from us. Combining their brightness with their speed provides a better estimate of how big and far away they really are.
Greg Leonard: All of this work is being done in the computer here and after several minutes upon completing set one, it will start presenting me, the observer, with potential candidates for near-Earth asteroids. But first, coffee.
[11:11] Narrator: Fueled with caffeine, Greg tackles the first list of asteroid candidates the computer has identified.
Greg Leonard: The computers are not quite good enough yet to be able to pick out a false positive from a real asteroid. It picks out the asteroids that are already known in databases and catalogs. But for new candidates, it still can’t tell the difference between some noisy pixels, or background stars and what could be real. And that is the reason why we have full-time observers in real-time, validating the images. Here you see it’s like a linear streak of light. And it’s probably from a bright star that is down lower in the image that is just producing a little bit of reflection. The software is saying, "Hey, Greg. Do you think this is a real asteroid or not?" And right away I say, "No, of course that’s not."
[12:02] Narrator: Greg quickly scans through all the images of the candidates, assessing which could be an asteroid and which are merely light aberrations or some other noise in the data. He figures that for every several hundred detections the computer sends him, he finds maybe one promising candidate. Kind of like Tinder for asteroids. It takes a lot of “no” swipes before he finds one that could be the real deal.
When that happens, he’ll immediately send it to the Minor Planet Center in Cambridge, Massachusetts.
Greg Leonard: That is the clearing house for all astronomical observations. They will do another deep dive into their databases. And [if] it didn't come up with any known objects, that becomes a new Near-Earth Object candidate. That is how a discovery is made. That is only really the beginning of the story.
The Minor Planet Center maintains what is known as the NEOCP, the Near-Earth Object Confirmation Page. This is a public database. And other professional institutions, even advanced amateurs around the world that have capabilities to track this object, they will say, "Great. Catalina discovered a new object. It is within the grasp of my telescope. It is bright enough. I am going to try to get follow-up positions for this."
And then, at JPL there is a program called Scout, and it is fairly automated. They get all the data from the Minor Planet Center, and they put it through their algorithms. And if any of their orbital solutions say this could be an Earth-grazer, or maybe even an impactor, then it goes basically onto an alert system. And it says, "We still need more data. However, the data that we do have indicated that it is going to come maybe very close to Earth, or maybe there is even collision solutions too." And that alerts the community. Say, "This is an extra special object that requires immediate follow-up and attention." And then, all the telescopes that can or able will turn to that.
[13:58] Narrator: That’s why their red phone is just a joke: a lot of calculations and follow-up observations have to happen before they can say where an asteroid is heading.
Richard Kowalski, another Catalina Sky Survey observer, holds the world record for discovering asteroids right before they hit Earth.
Richard Kowalski: The first one occurred in 2008. One night in October I came across one of several new discoveries. And the next day I woke up to find many hundreds of e-mails in my inbox talking about this object that I had discovered the night before, and that it was going to impact that evening.
[14:34] Narrator: After Richard had finished his work for the night, while he slept, his discovery of the asteroid known as “2008 TC3” had made the rounds at the Minor Planet Center, JPL, and the general astronomical observing community. By the time Richard woke up to begin another observing run, NASA had already issued a press release about the incoming asteroid.
Richard Kowalski: I was literally the last person in the community to know that this object was going to impact.
[15:07] Narrator: The SUV-sized asteroid came down in the Nubian Desert in northern Sudan. Because astronomers could pinpoint where and when it would hit, they were able to send out a warning.
Richard Kowalski: It was the first time in history that that sort of thing could be predicted. And then we just waited to find out if anyone witnessed it. And it turns out that a number of people did. There were people in the area with cellphones, and there was some video and still photos made of the smoke trail from this object.
It was also witnessed by a KLM flight over Africa. And they had been alerted to take a look for this impact by their dispatcher. It was quite a distance -- it was I believe several hundred miles -- they were in no danger. When a rock enters the Earth's atmosphere, it's moving so fast that the friction makes it glow. It's actually burning some of the rock off, because it's so hot. So they didn't see the actual object. They saw the glow of the meteorite being burned by the atmosphere.
[16:10] Narrator: Although the Earth’s atmosphere seems like an insubstantial barrier, it actually protects us from small asteroids. The air is densest at sea level and then thins the higher you go. For asteroids, that means the closer they get to the ground, the more air resistance they face. The friction of the fast-moving asteroid pushing its way through an increasing amount of air molecules not only creates heat, it can even cause the rock to break apart.
The asteroid in Sudan exploded in the air, but because the region is relatively unpopulated, no one was harmed. Richard’s next incoming asteroid discovery was on New Year’s Day, 2014. That asteroid hit before a warning could be issued.
Richard Kowalski: By the time that the news had gotten out that it was going to impact, other observatories could not get additional observations of it. So I was the only observer to see this object before it hit. And the calculations did show that it probably hit the Earth. They could triangulate where the object came down: in the Atlantic, just northeast of Venezuela. So unfortunately no one witnessed this one coming in, and there's no meteorites to be able to retrieve. They're all at the bottom of the ocean.
[17:24] Narrator: Richard’s most recent incoming-asteroid discovery came down in Botswana in June 2018. Like the one in Sudan in 2008, this asteroid exploded in the air but didn’t cause any harm. And as with his previous two discoveries, the turn-around time between detection and impact wasn’t very long.
Richard Kowalski: Between my first observations and the time of impact was about 20 hours. Part of what happens with these objects is that they're so small that they don't reflect a lot of light. We can't detect them until they're relatively close to the Earth. And that has been what's happened with these objects, is that we detect them a little bit further out than the Moon is from the Earth.
[18:06] Narrator: Despite the difficulty, Richard seems to have a knack for spotting incoming asteroids.
Richard Kowalski: I never thought that I would discover one, much less three of them. Especially considering I'm not the only observer at Catalina, and we're not the only survey looking for these objects. And yet I'm the only person in history who has discovered any, and I've got three now.
[18:28] Narrator: After we recorded this interview, astronomers with the PanSTARRS survey in Hawaii discovered an asteroid right before it hit. But Richard’s discovery record is still extraordinary – and all the more so given the roundabout path that led him to the Catalina Sky Survey.
Richard Kowalski: I was, for much of my life, an amateur astronomer. But my employment was working for an airline, loading and unloading aircraft.
You know, everyone has their own paths in life, and you never know where you're going to end up. The path that I took didn't bring me to college. I went right to work with the airlines after high school. Back in the '80s, airline jobs were very good with really good benefits and good pay. So I stuck with that.
My hands are quite arthritic now. But I got out in time that I didn't have knee replacements like many of the people that I used to work with have had. Because you do spend a lot of time on your knees. There's only so much room inside the cargo hold of an aircraft. So the only way you can really maneuver and lift the bags and stack them up is to be on your knees. So you're lifting lots of weight while you're kneeling down. So there's a lot of knee problems in the industry.
It was a tough job, and became even harder after 9/11. Security was much greater, and not as many people were flying, and the airlines were in quite a bit of trouble. So there are a number of reasons that I decided to leave the airlines. And I was actually driving a tractor trailer in Florida for about six months.
All this time I had been applying for positions at professional observatories. I had a small telescope; I was making observations very similar to what I'm doing with our professional telescopes. So, measuring the positions of these objects in the sky. That's called astrometry. And I was also using my telescope to measure the light coming from asteroids so we could get light curves. And that's called photometry. So I was doing both measuring the positions and the brightness of asteroids with my backyard telescope. And I created the Minor Planet mailing list in 1998, primarily because I knew there were people working with asteroids and doing what I wanted to do with my backyard telescope. And I figured if I could get a few of them to join my list, I would be able to ask them questions. And very quickly I had many professional astronomers, and amateurs that were working with asteroids already, on the mailing list, so I had a plethora of people that I could communicate with. And I started attending conferences. I had my research published as well.
I kept applying for positions and kept getting turned down. And when Catalina brought our 60-inch telescope online after we had refurbished it, there was another opening for an observer. And at first I decided, well, I keep applying and I keep getting turned down. I'm not going to apply for this. I said, "Well, what do I have to lose?" And that was the one that did it.
My life didn't take me in the path to get me here the normal way, quote, unquote. And yet here I am. I've added to the history of this illustrious institution in my own way.
[music: When you wish upon a star, Louie Armstrong]
[22:29] Narrator: Back up at the top of Mount Lemmon, Greg Leonard is looking at a vast field of stars in the hopes of finding new asteroids flying through Earth’s neighborhood.
He says a lot of the asteroids they see end up being “main belt asteroids” – asteroids that orbit between the planets Mars and Jupiter. There are millions of asteroids in the asteroid belt, but as long as they stay there, they aren’t a threat to Earth.
Greg Leonard: We are constantly discovering new worlds, even if it’s not the target of interest, a near-Earth asteroid. It‘s kind of neat to think that we are discovering lots of new Main Belt asteroids too.
[23:02] Narrator: Catalina Sky Survey is part of a larger Near-Earth object professional search community that includes the previously mentioned Hawaiian-based PAN-STARRS, the ATLAS project also in Hawaii, and LINEAR in New Mexico. This community lately has been finding more than two thousand near-Earth asteroids each year.
Greg Leonard: This is just a recent development because of the great new software, new detection algorithms, new sensors that we have, we really improved our ability to discover these things. The era of really high-speed computers, great CCDs, these electro-optical sensors. We’re really just starting to hit our stride I think with the technology, we’re constantly improving the systems. So that is the reason for our increase in discovery rates. But, we really need to do a lot more. We need more hands on deck, I think. We really need a number of efforts across the planet.
[23:56] Narrator: Part of Greg’s urgency comes from a Congressional mandate directing NASA to find most of the asteroids that are 140 meters in size or greater by the year 2020. Observers helping NASA work towards that goal take note of everything they can find, but as Richard said earlier, the smaller asteroids can only be seen when they get close to Earth. And the really small ones can take us entirely by surprise, like the one that exploded over Chelyabinsk.
Greg Leonard: The reason we missed it, (A), it was very small. And so it needs to be pretty much on our Earth doorstep for us to detect it. And (B), it came out of the direction of the Sun. Just like in a car when you are driving down the freeway, the Earth has a blind spot. And the blind spot is looking into the Sun. In our daytime sky we don’t have a capability yet to be able to do detections or to survey in the day sky. But, the saving grace here was that it came in at a very shallow angle, meaning that it traveled through a lot of thick atmosphere. And that thick atmosphere did its job in slowing down that asteroid, so it burnt up in the atmosphere and fragmented.
Chelyabinsk was 20 meters. That is small compared to what we are looking for. And that produced a large shock wave in the upper atmosphere. It was a pretty serious event. But, we see now that these relatively smaller asteroids can be quite dangerous. So, we are wanting to up our game and find asteroids of all sizes.
[25:29] Narrator: The night I went up to the Catalina Sky Survey, Greg found three new asteroids. One of them, estimated to be about 500 meters in size, occasionally crosses Earth’s path around the Sun. If Earth and that asteroid ever happen to be in the same place at the same time, it would be a very bad day. But orbital calculations show that won’t happen in the foreseeable future, so for now, the asteroid is of little concern.
Greg Leonard: The great thing about the work we do here is that we discover almost every night, and there's very few scientific endeavors where one can make discoveries really on a nightly or daily basis.
And because there's so few surveys looking for near-Earth asteroids, I am tonight one of the few people on the planet looking out for potentially incoming asteroids, or ones that could be incoming in the near future. Or in the distant future too.
So in a way we are sort of the eyes of the planet. Right here, the eyes of the planet for the evening.
[26:32] Narrator: Before we go, I’d like thank Igor Uchenik. I briefly pulled him away from his regular job as flight software engineer for NASA’s upcoming Mars 2020 mission, to have him read the Tunguska eyewitness account. Thanks for your help, Igor.
In this episode, we heard about a few small asteroids that hit us recently. Next time, what happens when the asteroid is really big?
Excerpt from Episode 2: Impact! Sean Gulick: So it's obviously a bad day in the Gulf of Mexico. I mean you're hitting with something that's the equivalent of 10 billion Hiroshimas worth of energy.
[27:04] Narrator: If you like this podcast, please subscribe, rate us on your favorite podcast platform, and share us on social media. We’re “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory.