Summary: We have had several near-misses – asteroids passing close by with little warning from our sensors. This reminds us that asteroid and comet impacts have changed the course of life on Earth, and will again unless we stop them. Which we will, eventually, either when we go deeper into space – or after we are hit. This post discusses this risk and what steps we can take now to better prepare. Perhaps it is humanity’s role to defend the planet.
“The dinosaurs became extinct because they didn’t have a space program. And if we become extinct because we don’t have a space program, it’ll serve us right!”
— Science fiction author Larry Niven, as quoted by Arthur C. Clarke.
We can’t say that we weren’t warned
WaPo: “‘It snuck up on us.’ Scientists stunned by ‘city-killer’ asteroid that just missed Earth.”
How much would an asteroid impact hurt?
Even a small asteroid could devastate a city. What would impacts of different sizes do to your community? See the stunning results at Purdue U’s Impact Earth website. A presentation by NASA’s David Kring gives examples and consequences of impacts.
How likely is an impact? One could hit tomorrow.
The U.S. Government’s sensors recorded at least 556 meteors entering the atmosphere (fireballs, technically bolides) from 1994-2013. The largest in this record was a 20 meter asteroid near Chelyabins in central Russia on 15 February 2013 (details here), an explosion equivalent to 440- 500 kilotons of TNT.
The size of the dots on this NASA map represents the meteor’s optical radiant energy. The smallest dot on the map is 1 billion Joules (1 GJ), the equivalent of roughly 5 tons of TNT. The dots for 100, 10,000 and 1,000,000 GJ convert to 300 tons, 18,000 tons and one million tons of TNT. The Hiroshima blast was equivalent to 15,000 tons.
Scientists have accumulated enough data to estimate the odds of impacts from space.
“Every day Earth is bombarded with more than 100 tons of dust and sand-sized particles from space. About once a year, an automobile-sized asteroid hits Earth’s atmosphere, creating a spectacular fireball (bolide) event as the friction of the Earth’s atmosphere causes them to disintegrate – sometimes explosively.
“Studies of Earth’s history indicate that about once every 5,000 years or so on average an object the size of a football field hits Earth and causes significant damage. Once every few million years on average an object large enough to cause regional or global disaster impacts Earth. Impact craters on Earth, the Moon and other planetary bodies are evidence of these occurrences.
“Meteor Crater near Winslow, Arizona, is evidence of the impact with Earth’s surface of a 50-meter asteroid about 50,000 years ago. Impact of the metal-rich object released energy equivalent to a 10 megaton explosion and formed a 1.2 kilometer-diameter crater.” {Source: NASA.}
The National Research Council published a typically magisterial analysis of this threat: “Defending Planet Earth: Near-Earth Object Surveys & Hazard Mitigation Strategies“ (2010). Here are the numbers, comforting or terrifying, depending on your perspective. Thirty-five million years ago, a 5-8 km impactor blasted out the Popigai crater – at the time of the Eocene–Oligocene extinction event. The dinosaurs were killed by an object 11-81 km in diameter.
Books and films about how this happens and how we respond
Stories about collisions with space objects go back to the 19thC. Perhaps the best story about doom from the sky is When Worlds Collide
An example of an optimistic science-fiction story in this genre is Rendezvous with Rama
Lucifer’s Hammer
Hollywood has given the inspiring stories about defending the world against doom from space.
- When Worlds Collide
(1952). Trailer here. A faithful telling of the book.
- My favorite (for those who like big thinking): Gorath (1962)
. Trailer here. The object is too big to move. So they build giant fusion rockets in Antartica and move the Earth. See my review!
- Meteor (1979)
. Trailer here. Starring Sean Connery and Natalie Wood, it was inspired by the MIT report “Project Icarus” (1967). The Soviet Union and the US stop the Cold War and work together to save the world. It has a tragic scene in which the World Trade Center is destroyed.
- Armageddon (1998)
. Trailer here. Bruce Willis leads roughnecks into space to save the world. I enjoyed it!
- Deep Impact (1998)
. Trailer here. More scientifically accurate, but still a gripping story.
(1952). 
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. What can we do to prepare?
“Find all asteroid threats to human populations and know what to do about them.”
— NASA’s Grand Challenge, 18 June 2013.
The Apollo program burned billions of dollars but did little for America. Since then, the manned space program has done even less. The reason is simple: we lacked a good reason to put people in space. An asteroid or comet will eventually provide the motivation – either to prevent another impact or mitigate its effects. We have the technology and money to begin preparations.
Here are the four kinds of space threats, with warning times ranging from decades to days. Buying warning time is the key to preventing impacts or minimizing their damage, but it will take time to build the necessary sensor systems. As a first step, in 2016 NASA created the Planetary Defense Coordination Office. Its staff supervises NASA’s programs to detect and track potentially hazardous objects, issues notices of close passes and warnings of any detected potential impacts, and coordinates the US government’s efforts to prepare for impact threats. See their website, which has a wealth of information.
Other nations have similar programs. NASA is a member of the International Asteroid Warning Network.
What happens after we detect an object on a collision course with Earth? A presentation by NASA’s Dan Mazanek describes deflection strategies. This NASA video shows what a mission to intercept a threatening space object might look like.
The longer the warning time and the better the preparations, the higher the odds of success. Here are some ways to defend Earth: a Gravity Tractor, a Kinectic Impactor, and a Blast Deflection. This graphic shows which work best for various combinations of warning time and asteroid size. For short warning times, we can use only what we have ready to launch.
A last note about these threats
“Estimates of the frequency of space-rock strikes are just estimates, and may not tell us anything about when the next impact will occur – it could be an eon, it could be tomorrow. Floods, earthquakes, volcanoes, and tsunamis are sure to happen more frequently, but humanity will survive these events; we might not survive an impact from space. Meanwhile, nothing can be done to prevent earthquakes, volcanoes, and tsunamis. But space strikes appear to be entirely avoidable, and not necessarily with “massive repositioning of government funding.” A fraction of the money NASA wants to waste on a moon base would likely be sufficient.”
— By Gregg Easterbrook in The Atlantic, September 2008.
For More Information
As a great starting point, see The Asteroid Day website. Especially this six-article series by Rusty Scheweickart (astronaut, aeronautical engineer, and fighter pilot). To learn about asteroids and the defense against objects from space, see their education page. If you prefer videos, see them here.
Ideas! For shopping ideas, see my recommended books and films at Amazon.
If you liked this post, like us on Facebook and follow us on Twitter. See all posts about shockwave events, about NASA, about shockwaves, and especially these…
- Asteroid Day: reminding us of the threat, pushing us out into space.
- Three things to know about asteroids, certain death from the sky (eventually).
- Why we have not gone into space. Why we must.
Why do we keep getting hit by these things?
The solar system is not in equilibrium. To learn why I recommend the brief and clearly written Newton’s Clock: Chaos in the Solar System
“Peterson explains a mystery that has fascinated and tormented astronomers and mathematicians for centuries: are the orbits of planets and other bodies stable and predictable or are there elements affecting the dynamics of the solar system that defy calculation? It is one of the most perplexing, unsolved issues in astronomy, with each step toward its resolution-from Newton’s clocklike mathematical models to the astonishing work of super computers exposing additional uncertainties and deeper questions about the stability of the solar system.
“Newton’s Clock describes the development of celestial mechanics – from the star charts of ancient navigators to the great Renaissance scientists; from the crucial work of Poincare to the startling, sometimes controversial findings and theories made possible by modern mathematics and computer simulations. Equal parts science and history, the book shows how the exploration of the solar system has taken us from clocklike precision into chaos and complexity.”
Actually, most of proposed approaches to planetary defense are neither effective nor scalable even to asteroids capable of country-wide destruction. For example, it is unlikely that the kinetic impact will work because of the internal structure of near-Earth asteroids is crumbly: “We think they’re very loose aggregates. They’re not solid through and through” said Melissa Morris, OSIRIS-REx deputy program scientist at NASA Headquarters in Washington, D.C. The detailed photos and probe impacting of Bennu and Ryugu reveal rubble-pile natural properties of the NEOs, which will prevent shock wave propagation and proper impulse transfer.
The nuclear blast method is risky and can pose danger both on the ground and in the atmosphere. This type of explosion could potentially create a stream containing hundreds of “city-killing” radioactive pieces, e.g., in the case of disintegrating a sub-km asteroid. Moreover, as follows from computer simulations, shortly after explosion all of the pieces will tend to settle towards the center of mass, which would still be headed on a collision with the Earth.
The asteroid laser ablation method is not viable because of cooling concerns for powerful (over 100 W) lasers. In space, the laser source will not have a means to radiate heat quickly enough to avoid damage to itself.
As of now, it appears that asteroid ablation using highly concentrated sunlight is the only method that meets all of the following criteria: scalability up to global-threat sizes and any type of hazardous bodies owing to maximum thrusting power without huge volume of propellant, as well as low cost and environmental friendliness. This method creates thrust similar to the laser ablation method, creating a natural rocket out of the asteroid, without the power and heating concerns.
An improved concept for such solar-based deflection using an innovative solar collector was proposed and substantiated in 2013 – see https://link.springer.com/article/10.1007%2Fs11038-012-9410-2
and also a short demo-video
That’s a pretty tall order, considering the one they just missed. I don’t know, money better spent elsewhere.
Ron,
“That’s a pretty tall order”
What are you referring to, as a tall order?
“money better spent elsewhere.”
How much do you believe a better detection system would cost? Probably 1% of the cost of the F-35 program (which doesn’t work well), or less than 1% of the B-21 program (which is a total waste of money).
Larry,
“How much do you believe a better detection system would cost?”
A detection system is one thing, knocking them out of the sky is another.
My money would go to the war on drugs, the hard stuff. It kills more people and ruins more lives than asteroids ever would, in present time.
Ron,
Who is proposing building a system to “knock them out of the sky”? Nobody that I know of. The proposals now are for better detection systems.
That’s for the future, when we have better tech, more wealth, and (perhaps) a larger presence in space.
An effective detection system is not that easy to build, even conceptually.
There are asteroid orbits at crazy angles, way off the ecliptic, some with very long periods. They are essentially invisible until the sun heats them up. Radars don’t cut it, the distances are too great and the reflectivity too low.
To really do the job would require a surveillance system that monitors all bodies larger than 50 feet within the solar system sphere inside the orbit of Jupiter. We don’t have that kind of capability and we’re not likely to have it any time this century. So surprises will remain possible, no matter what the program managers/advocates would claim.
etudeian,
“An effective detection system is not that easy to build, even conceptually.”
There are two problems with that statement. First, the word “effective” does not mean what you appear to think it means. It does NOT mean “perfect” – as in “detects every potential impactor with lots and lots of warning time.” It means “effective” at detecting them. As in cost-effective, catching as many as possible within our current budget. Objects are detected with operating parameters: time until impact and size of object. As better systems are built, we find smaller objects, get longer warning times, and have greater ability to respond.
Second, you don’t appear to have carefully read the post.
Building these systems will happen in steps, as sensors and defensive systems improve over time. It will certainly take many decades, perhaps a century or two, to have systems capable of handling city-killing objects.
This is virtue signaling rather than addressing the issue.
Yes there is decent ability to detect in plane asteroids, we see them with telescopes and they drift in and out of our orbit fairly predictably.
The trouble is that the object that just missed us was well out of plane and fairly small.
No way to pick it up before it is too close to change its trajectory. Nor would it be found on the existing proposed surveillance.
The sensible way to deflect celestial threats is to nudge them very early, when a very small change produces a miss.
NASA understands that and has focused on trying to use the small mass of a station keeping probe to deflect the trajectory of a potentially threatening object.
That only works if there is good knowledge of what is actually out there. That mandates a much larger surveillance task, which no one is currently ready to address.
etudiant,
Good to know that you are right and so many experts are wrong. QED.
Baltimore?
Gute,
Yes, Baltimore is a city. What’s your point?
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Probably already we are lucky. There have been some massive hits in the last billion years. Astronomers recognise the importance of Jupiter in protecting us. We’ll basically just have to hope It still works.
We need to concentrate on Bolides large enough to see with telescopes and try to combat them. We just have to hope for the best for the small ones. If Tungusta in 1908 was earlier[?] by 4 hours, instead of Siberia it would have landed in the middle of Europe.
John,
“We’ll basically just have to hope it {Jupiter} still works.”
Are you kidding?
I think you have the descritions reversed of Armageddon and Deep Impact. Armageddon had Bruce Willis. I agree with your opinion of both movies. Armageddon was a very enjoyable popcorn movie. Technical errors there were in plenty, but it was fun from start to finish.
Deep Impact was more scientifically accurate, not give away spoilers, I thought the scene aboard the spcecraft at the climax of he movie was a lot more realistic in a dramatic sense, than the comparable moment in Armageddon. Pretty close to how a scene like that might play out in real life.
My only comment on the subject matter of the post is that asteroid defense is to our home planet what homeowner’s insurance is to your house. Smart people keep theirs paid up. The only real difference is that you may never have an actual house fire in your lifetime, but if you wait long enough, sooner or later you will end up filing a claim on your asteroid defense. Remember that business in Tunguska? Insurance is about preparing for known past events. So is this.
The Man,
Thanks! Great catch. Fixed!
Think the problem is complicated, as usual.
In plane threats are the most numerous, but also the easiest to track and monitor. They probably cover most of the cases.
The problem is out of plane bodies. they massively expand the threat space, but there is nothing practical to monitor
that huge volume.
A system that is in plane will catch most threats, but will be caught flat footed by anything out of plane.
I’d not want to be the NASA person defending the ‘space surveillance net’ if something deadly came out of left field.
etudiant,
“Think the problem is complicated, as usual.”
Nope, not at all. Defenses are built incrementally, step by step over time. Things that are difficult now will be less so in the future. That is the process described by the experts who have written about this subject. I don’t know why you ignore that, and appear to believe you are so much smarter than they are.
I’ve said this several times, and you keep ignoring it. No more, please.
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That looks like a lava rock from my gas grill.
370,
It is. Just a million times larger.
Larry,
Not to mention coming at you ~50,000mph.