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Defending the Planet from Asteroids

Season 5Episode 1Feb 21, 2023

Our solar system contains millions of asteroids, orbiting our sun and rocketing through the night sky! Join scientists Kelly Fast, Tom Statler, and Davide Farnocchia as we discover what we can learn from these building blocks of the universe, and how NASA would respond if one were ever headed our way.

The cover art display for the NASA's Curious Universe podcast.

NASA's Curious Universe

Introducing NASA’s Curious Universe

Our universe is a wild and wonderful place. Join NASA astronauts, scientists, and engineers on a new adventure each episode — all you need is your curiosity. Explore the lifesaving systems of space suits, break through the sound barrier, and search for life among the stars. First-time space explorers welcome.

Episode Description: Our solar system contains millions of asteroids, orbiting our sun and rocketing through the night sky! Join scientists Kelly Fast, Tom Statler, and Davide Farnocchia as we discover what we can learn from these building blocks of the universe, and how NASA would respond if one were ever headed our way.


[Song: Backward Mirror Instrumental by Niska Wahl]

Kelly Fast

It’s important to try to monitor the asteroids that are in Earth’s neighborhood because if one were to impact Earth, we would want to know.

[[Sound effect of ticking clock begins]]

Kelly Fast

There was a time when we didn’t have weather satellites, and you didn’t know that a hurricane was approaching, except maybe the way the sky started behaving, the weather started behaving. But you didn’t have the type of notice that we have now, the ability to know that, okay, this particular region of the coastline is likely to be affected.

Kelly Fast

If you have the capability to do that for asteroids, it would be the responsible thing to use that capability. Because if you had notice, if you knew years or decades in advance that an asteroid was going to impact Earth, you could actually do something about it.

[[Sound effect of ticking clock ends]]

[Theme Song: Curiosity Theme by SYSTEM Sounds]

HOST PADI BOYD: This is NASA’s Curious Universe. Our universe is a wild and wonderful place. I’m your host Padi Boyd and in this podcast, NASA is your tour guide.

HOST PADI BOYD: Welcome back to another season exploring our incredible universe! We’ve got a lot in store over the next eight weeks, and we’re so glad you’re along for the ride!

HOST PADI BOYD: While we were on a break, NASA’s DART mission successfully collided a spacecraft head-on with an asteroid named Dimorphos, over 7 million miles from Earth.

[Song: ]

[[Sound of control room during DART launch, applause after collision]]

[[Oh wow. 10, 9… Oh my goodness. 8, 7, 6… Oh wow… 5, 4, 3, 2, 1. Oh my gosh. We’re waiting to hear ground confirmation. Alright]]

HOST PADI BOYD: This mission made history. It was the first time we have ever made a noticeable change to the orbit of a celestial object.

HOST PADI BOYD: And there’s a lot of more information coming our way about asteroids soon. In the next few years, we’ll learn so much more from DART, plus two other missions called OSIRIS-REx and Lucy.

HOST PADI BOYD: So we’ve decided to kick off season five with an exploration of asteroids.

HOST PADI BOYD: What exactly are these tiny planetary bodies in our solar system, and if one of them were hurtling toward Earth, how would we know?

[Song: Fish Can Fly Instrumental by Donje Elliott]

Tom Statler

I’m Tom Statler. I’m a program scientist. I get to send robotic spacecraft to explore the solar system. I work on our asteroid missions, the Lucy mission to the Trojan asteroids, the DART mission that successfully moved an asteroid.

Tom Statler

An asteroid is basically something that’s orbiting the sun that’s smaller than a planet or a dwarf planet.

Tom Statler

It’s a rock. It’s a hunk of rock. It might have some icy stuff mixed into it, it might be a solid rock, it might be a pile of rocks loosely held together by gravity. It might be a piece leftover literally from the formation of the planets. It might be a fragment of a collision between two other asteroids in the distant past. It might be a reaccumulation of fragments from one of those collisions in the past.

Tom Statler

There are millions of them. They are orbiting the sun. Most of them never come close to the Earth, but some of them do. And some of them can and have impacted the Earth. We want to make sure that we can do whatever we can to prevent that from happening in a bad way in the future.

HOST PADI BOYD: There are so many things out in the universe! A look through a telescope on a clear night sky could reveal lots of different space rocks! So let’s do a quick term review of different celestial bodies.

[Song: Quantum Networks Underscore by Burrows]

HOST PADI BOYD: Asteroids are rocky bodies larger than a meter in size that don’t have enough mass to qualify as a planet. Like a planet, they each have their own orbit around our sun, traveling at different speeds and trajectories.

[[Zooming sound effect from left to right]]

HOST PADI BOYD: Moons are celestial bodies that circle a different planetary object. To make things even more confusing, some asteroids havemoons, additional asteroids orbiting around them!

[[Two tones echoing each other sound]]

HOST PADI BOYD: Meteoroids are rocky bodies smaller than an asteroid, even down to a grain of sand.

[[Ping sound]]

HOST PADI BOYD: A meteor is what we call the visible light phenomenon as an asteroid or meteoroid enters a planet’s atmosphere.

[[Zooming/falling star sound]]

HOST PADI BOYD: And if pieces survive the trip and land on the ground, then we call them meteorites.

[[Echoing bouncing tone sound]]

HOST PADI BOYD: But what about comets vs asteroids? Those two traveling bodies might be more similar to each other than scientists once thought!

Tom Statler

Asteroids and comets used to be considered totally different things. A comet was this thing that appeared in the sky with this great big tail, sometimes even visible in the daylight. Such a strange change to the sky that they were considered harbingers of doom or signs from the gods, or things like that.

Tom Statler

Asteroids are rocks. They’re small, they’re mostly dark. So it was thousands of years after people knew about comets that the first asteroid was even discovered.

Tom Statler

Is there a hard division between things that are definitely asteroids and not comets and things that are definitely comets, not asteroids? Well, not quite as much as we once thought. It’s one of the things we’re trying to better understand about our solar system.

HOST PADI BOYD: Asteroids can be hard to see in the night sky. Dark rock reflecting sunlight may not stand out strongly against the dark expanse of space. So scientists use all the tools we have to study them! Asteroids are found using telescopes here on Earth and sometimes out in space. Astronomers look for points of light moving relative to the stars and follow them night after night to see what they are and where they’re going.

HOST PADI BOYD: This has been a really successful method of discovery! The current known asteroid count is over 1.1 million objects, of all different shapes and sizes. They can even reach hundreds of miles across!

[Song: Gadget Theory Instrumental by Burrows]

HOST PADI BOYD: With that many pinpoints of light to keep track of, we’ve found different ways to classify and describe them in order to learn more about where they came from, where they’re headed, and what they’re made of.

Tom Statler

Asteroids get classified in different ways because they are in different places in the solar system. They’re in different kinds of orbits. Probably just about everybody has heard of the asteroid belt between the orbits of Mars and Jupiter, those asteroids are orbiting around the Sun spending most of their time in that zone. But it doesn’t mean they stay there all the time.

HOST PADI BOYD: The asteroid belt is an area of our solar system between Mars and Jupiter containing asteroids on their orbits around the sun. There are lots of these planetary bodies out there, but it isn’t as crowded as you might be imagining. In our solar system, if you were standing on an asteroid in the asteroid belt, unless you were lucky, you would still need a telescope to see the next nearest one.

HOST PADI BOYD: But that doesn’t mean there aren’t a lot of them. We have already discovered over a million main belt asteroids and there is still so much more to discover!

Tom Statler

Another way of classifying them is by their colors. It’s almost like butterfly collecting. Looking at what is out there and where are the ones that are similar and where are the ones that are different, and how many different kinds of color types, spectral types are there.

Tom Statler

There’s a classification scheme with, oh, around a dozen or 20 different types. But we still only have a partial understanding of which what each of those types really means in terms of what is the asteroid made of.

HOST PADI BOYD: The most common type of asteroid is C-type, which are rich in carbon compounds. These are thought to be some of the oldest objects in our solar system!

HOST PADI BOYD: S-type asteroids are stony and M-type asteroids are high in metals, suggesting planetary iron cores and volcanic lava!

Tom Statler

Yet another way to classify asteroids that we’re just scratching the surface of is literally what happens if you scratch the surface. What does the surface look like? Is it a smooth surface, is it a cratered surface? Is it a rubble-y surface?

[Song: Ideas like Bonfires Instrumental by Gleissner]

Tom Statler

One of the things we’ve come to understand so far about asteroids is that there’s no such thing as just another asteroid. There are asteroids that superficially look the same, and yet we know they’re compositionally different.

Tom Statler

Every asteroid is telling us a different part of the story of our solar system.

HOST PADI BOYD: At the time of this recording, in spring 2023, there are two missions in flight right now that will teach us so much more about these orbiting objects!

HOST PADI BOYD: The OSIRIS-REx mission made contact with the dark, carbon-rich asteroid Bennu in 2018, collecting samples from the surface. It is expected to deliver the samples back to Earth and yield so much more information about asteroids on September 24, 2023.

Tom Statler

One place where we’re gonna get a lot better understanding this is with the OSIRIS-REx mission, bringing samples back from the asteroid Bennu. Bennu is a B-type asteroid, it’s very, very dark. It almost certainly is made of materials that has a lot of carbon. As anybody who has a barbecue knows, carbon is very, very dark.

HOST PADI BOYD: Another mission, Lucy, is traveling out into the solar system to study an exciting population of asteroids!

Tom Statler

The Lucy spacecraft is going to a family of asteroids that is not in the main asteroid belt. This is a different family of asteroids called the Jupiter Trojan asteroids. They’re orbiting the sun at the distance of Jupiter. They’re not orbiting around Jupiter, they’re not close to Jupiter at all.

Tom Statler

Our current understanding suggests that these are totally different from the main belt asteroids because where the main belt asteroids are the leftover raw materials from the formation of Mercury, Venus, Earth and Mars, probably broken up and ground up through four billion years’ worth of collisions.

Tom Statler

The Jupiter Trojan asteroids are probably the leftover raw materials from the formation of Jupiter, Saturn, Uranus, and Neptune. They look different from the main belt asteroids, they’re redder, and yet they’re not all the same. There are color differences, there are orbital differences. And so the Lucy spacecraft is going to do a tour past several different asteroids.

Tom Statler

The science value coming from that isn’t the number of asteroids we go to. It is the number of comparisons between asteroids that we can make. This one is red, this one is not so red. Why?

[Song: Ascension Underscore by Lyons]

HOST PADI BOYD: There’s a third asteroid mission right around the corner: Psyche. This spacecraft will head out to an asteroid in that main belt past Mars and is preparing for launch in 2023.

HOST PADI BOYD: When you’re studying these fascinating, unique objects, scientists not only learn from each new and exciting trait but by comparing asteroids to each other.

HOST PADI BOYD: Figuring out where they are, what they’re made of, how they act and orbit, can teach us about the building blocks of our solar system!

HOST PADI BOYD: But there’s another great reason to keep our eyes on these objects in the sky.

[Song: Human Quietus Instrumental by Babelian Falco]

HOST PADI BOYD: As any science fiction writer or doomsday blockbuster will tell you, some of these asteroids might have an orbit that brings them really close to Earth…too close to Earth.

[[Low tone whoosh sound falling, passing]]

HOST PADI BOYD: Asteroids have collided with the Earth and they will again! So it’s important to know what’s coming, especially ones that are big enough to cause damage.

Tom Statler

We also talk about the near-Earth asteroids. And sometimes we talk about the potentially hazardous asteroids. This is the small minority of asteroids that are on orbits that bring them close to the orbit of the Earth. That doesn’t mean that they’re always close to the orbit the Earth, sometimes they’re clear across the solar system from where the Earth is.

Tom Statler

But it opens the possibility that you could have an intersection. And that’s the only time that an asteroid ever becomes dangerous. If the two objects happen to arrive at that intersection point at the same time, that’s when you have a collision, you have an asteroid impact. Those are the circumstances that in the Planetary Defense Coordination Office we’re working to avoid.

Kelly Fast

My name is Kelly Fast. I am the Near-Earth Object Observations Program Manager in the Planetary Defense Coordination Office.

[Song: Hands of Time Underscore by Wittaker Gilbey]

Kelly Fast

So, NASA has been studying near-Earth objects for many years, since 1998, that’s when it’s Near-Earth Object Observations Program started. But in 2016, NASA formally stood up this Planetary Defense Coordination Office. The Planetary Defense Coordination Office builds off of this long history NASA already has, but really formalized it and structured it to kind of keep it moving forward into the future as the whole field has progressed.

HOST PADI BOYD: The Planetary Defense Coordination Office’s four goals are to find, warn, mitigate, and coordinate about near-Earth objects that could hit our home planet. Kelly works on the first goal, finding what’s out there.

Kelly Fast

I manage the part of the program that finds the asteroids, calculating the orbits, discovering their physical properties.

[Song: Future in the Making Underscore by Burrows]

Kelly Fast

So, near-Earth objects are natural objects, asteroids, or comets, whose orbits bring them into the inner solar system. And the formal definition is anything that comes within 1.3 astronomical units, which means one and a third times the distance from the Sun to the Earth. Extending from the Sun out to beyond Earth towards Mars, that region, so any objects whose orbits bring them within that region are called near-Earth objects.

Kelly Fast

But many near-Earth objects never actually come close to Earth, thankfully. In particular, there’s another class of objects that we really want to keep an eye on, which are referred to as potentially hazardous objects. These are objects that are large, or that should they impact Earth, they could really do damage. That population is something we really want to keep an eye on, should their orbits ever change and intersect Earth in the future.

HOST PADI BOYD: Most of the objects out in the solar system are so small that they would disintegrate in our atmosphere if one were to impact, causing nothing more than a pretty meteor light show in the sky.

HOST PADI BOYD: However once you reach a certain size of asteroid, there can be cause for concern. Larger asteroids could do damage. The potentially hazardous objects are any celestial bodies over 140 meters across that come within about 5 million miles of Earth’s orbit. Scientists searching for these objects utilize information about the night sky every night, from around the world, to find and track these potentially hazardous bodies!

Kelly Fast

NASA’s Planetary Defense Coordination Office funds institutions that have telescopes to go look for near-Earth asteroids. And they’re a little different in that, you think of telescopes that zero in on a particular object, the James Webb Space Telescope, for instance, or Hubble Space Telescope.

Kelly Fast

These telescopes that look for near-Earth asteroids or that otherwise survey the skies, they have wide fields of view.

[Song: Scientific Theories Instrumental by Gregory]

Kelly Fast

So these telescopes, look at wide swaths of the sky. They’re looking for moving objects relative to the stars. When they find those, they get the positions of those objects relative to the stars.

HOST PADI BOYD: Once a new object has been located, the information collaboration begins! Those positions are reported by astronomers to the Minor Planet Center which is the international database for tracking these orbiting bodies.

HOST PADI BOYD: We haven’t yet found all the near-Earth asteroids we predict are out there, but we have found most of the big ones. Those are easier to spot! And they are the ones that would cause the most trouble if we had an impact. Luckily, there’s currently nothing on those lists that are cause for concern.

Kelly Fast

And the nice thing is right now, we don’t know of anything that poses a significant impact threat in the future. Anything on the list, is like, way, way down in its probability. It’s what we don’t know about that we want to find out, is there something we haven’t found yet that could pose an impact threat?

HOST PADI BOYD: Tracking these Near Earth Objects is a team effort… a collaboration of professionals and amateurs around the world! Here at NASA, a lot of that effort comes from JPL – the Jet Propulsion Laboratory – and its Center for Near-Earth Object Studies.

[Song: Enemy Instrumental by Stevenson Zero]

Davide Farnocchia

My name is Davide Farnocchia. I’m a navigation engineer at JPL. And my job is computing trajectories for small bodies in the solar system, so asteroids and comets.

Davide Farnocchia

My job can be fascinating to a lot of people, because I say, ‘Oh I deal with possible asteroid impacts’. And so people start thinking about movies like Armageddon and the End of the World, these kind of things. But really what I do is spend most of my time at a computer and crunch numbers.

HOST PADI BOYD: Davide is one of the scientists analyzing these near-Earth objects for the Planetary Defense Coordination Office! He uses all the data submitted by professional and amateur astronomers to the Minor Planet Center to determine an asteroid’s orbit and predict where it is going to end up in the future.

Davide Farnocchia

We essentially take observational data from astronomers all over the world. They observe the night sky, and sometimes they see small objects that move compared to background stars, and they report that information to us.

Davide Farnocchia

Those are asteroids or comets that move in the solar system. And we take these data and compute the trajectories and see where they are now, where they were in the past and where they’re going.

HOST PADI BOYD: But how exactly do we know where these objects are going to end up? We are, after all, talking about specks of light in outer space. Well, Davide and his team start with a known position in the solar system and then they make a hypothesis. Or rather, a lot of different hypotheses, and use the process of elimination.

[Song: Eagle Eye Underscore by Goble O’Brien]

Davide Farnocchia

Now, when you discover an object in the sky, you have information of where the object is precisely in the sky. And you also see how it’s moving in the sky. And so you have the rate of motion. You don’t know how far it is. And you don’t know if it’s coming toward you, or if it’s receding from you.

Davide Farnocchia

So what you can do is to make hypothesis on how far the object is and which way it’s going. And as you get new data, you can see which one of those assumptions survive. Every time you get additional data, some of the previously considered solutions are going to be ruled out until you remain with just one. And that’s going to be the trajectory.

HOST PADI BOYD: A large asteroid impact could be a disaster for our planet, which is why we have our eyes on it.

[Song: High Frequency Underscore by Minucci Williams]

So what would happen if the Planetary Defense Coordination Office noticed an object that posed an impact concern? Word would probably spread pretty quickly.

Kelly Fast

The data are public. The Minor Planet Center data are public. There are amateur orbit calculators out there. It’s gonna be all over social media.

Kelly Fast

And this has happened before because we’ve had very small asteroids impact Earth and there’s already chatter about it ahead of time. The movies always talk about like the government cover up or whatever, you can’t cover the sky.

Kelly Fast

But if there was one that was going to impact Earth that was of a size that NASA was required to notify about, not one of these tiny objects that would just make a pretty fireball. There is a National Near-Earth Object Preparedness Strategy and Action Plan, a White House plan that’s defined for the roles of different government agencies when it comes to the asteroid hazard.

Kelly Fash

NASA does have a notification policy through the agency and over to the White House and to other government agencies. If there was going to be an impact outside of the US, working through the State Department.

Kelly Fast

And just like for a hurricane approaching the coastline, you notify people, you do evacuations. FEMA and other government agencies, they’re very well trained in that, making all of that happen. And what do they need? Information, to do that sort of thing. That’s what NASA’s role is here. We’re scientists and engineers. We study the skies, look for asteroids, and provide that information.

HOST PADI BOYD: The scientists tracking and analyzing asteroids haven’t found any heading our way in the next 100 years that would cause any real damage. But there are asteroids out there we don’t yet know about, so we’re constantly on the lookout. And even for small asteroids that will disintegrate in our atmosphere, people notice and keep track.

[Song: ]Mechanical Muse Instrumental by Whittaker Gibley

David Farnocchia

It has happened that objects very small, just a few meters in size, have been discovered prior to reaching the Earth. When that happens, we get notified. We get text messages. And so we get really excited because we want to see what’s going on, we want to see whether the possibility is real. And whether we can pinpoint the impact location.

David Farnocchia

I guess one of the rules is that this always happens at a bad time. I was home spending some quality time with my daughters, and my wife was having lunch with some friends. And at some point, I got a text message and I look and it said, ‘Oh, possible impact within two hours’. I had to juggle between children and computer, but I put a movie on TV, set the children on the couch. And then went to my computer just to double check that the results were actually correct, the positional measurements were really indicating a possible impact. The brightness of the object was increasing at the rate you would expect for something coming toward Earth. We were able to confirm that the object was about to reach the Earth and pinpoint the impact location in the Norwegian Sea. All that within two hours from first detection.

HOST PADI BOYD: Finding and warning are only two of the goals of the Planetary Defense Coordination Office. They’re also working to mitigate and coordinate, working with other agencies to plan for any sort of “what if” scenario. And with 2022’s successful DART mission, they figured out a big win for mitigating a potential impact. All you have to do is give the asteroid a little nudge at the right place and time.

[Song: Future in the Ma king Underscore by Burrows]

Kelly Fast

There are techniques for deflecting an asteroid, and the kinetic impactor technique was just tested with the DART mission. If you had years or decades’ notice, you wouldn’t have to deflect an asteroid very much for it to miss Earth down the road in the future. An asteroid impact is, it’s the only natural disaster that you could actually avoid; you could actually do something about it.

Kelly Fast

There is no reason to be afraid of any of the asteroids that we know about, there is no known impact threat. There is a risk list of objects to keep an eye on because maybe they have a very, very low probability in the future. But that’s the nice thing, there’s nothing that has a significant probability of impacting Earth, even the thing with the most significant probability, it’s way, way, way down, very low.

Kelly Fast

It’s the objects that we don’t know about that we’re concerned about. But at the same time, it’s not something that any of us working on this lose sleep over.

HOST PADI BOYD: The great news from the Planetary Defense Coordination Office is that nothing we’ve found so far is on track to hurt Earth. But that doesn’t quite mean there’s no hazard from asteroids. Kelly and her team continue to keep an eye out for any bodies potentially in our path. And it’s always better to be prepared.

Kelly Fast

It needs to be at the level that’s appropriate. We’ve got the capability to look for these objects, to look for asteroids and comets, to see if any could pose a threat, we need to do that. But at the same time, we might not even ever have to deal with this in our lifetimes, in our children’s lifetimes. But it’s a service to our descendants to do this type of a survey, and to fill up that catalog, just so we know.

HOST PADI BOYD: With millions of space rocks out in the solar system, the job of locating these asteroids is still underway! And as we find them, there is a lot of science to be uncovered. With new information from OSIRIS-REx and Lucy just around the corner, we are about to learn so much more about these fascinating space rocks. What they’re made of, where they’re going, and even, how our solar system was formed.

[Song: Curiosity Outro by SYSTEM Sounds]

HOST PADI BOYD: This is NASA’s Curious Universe. This episode was written and produced by Christina Dana. Our executive producer is Katie Konans. The Curious Universe team includes Maddie Arnold and Micheala Sosby, with support from Christian Elliott.

HOST PADI BOYD: Our theme song was composed by Matt Russo and Andrew Santaguida of SYSTEM Sounds.

HOST PADI BOYD: Special thanks to Alana Johnson, Erin Morton, and Josh Handal.

HOST PADI BOYD: We named a lot of cool asteroid missions in this episode, including DART, Lucy, and OSIRIS-REx. If you’d like to learn more about their groundbreaking discoveries, check out the asteroids page of

HOST PADI BOYD: Plus, if you’d like to hear about DART in Spanish, check out our companion podcast, Universo Curioso de la NASA. Host Noelia Gonzalez explores the exciting world of asteroids with NASA experts in their own language! Check it out anywhere you find our show!

Producer Christina Dana

So asteroids orbit our sun in our solar system. Is there anything we know about asteroids that orbit a different star in a different solar system?

Tom Statler

Orbiting another star? There are exoplanets and there are exomoons and I presume there are exo-asteroids although I don’t think I’ve seen that term in print, but I bet it is. There’s also of course, well, OK, we didn’t even talk about the exo-objects, the interstellar objects, right? Because we’ve had a couple of identified, not quite sure how asteroid-y or how comet-y they are. But a couple of things that have flown through the solar system that came from beyond our solar system, went back out again. Not a surprise, we’ve known pretty much forever that those things would be there, it was just interesting to finally discover them.