Three things to know about asteroids, certain death from the sky (eventually)

Summary: Asteroid Day approaches (mark June 30 on your calendar), reminding us about the risk of death from the sky from asteroids and comets — one of the largest of the many shockwaves looming in our future. Here are the three things to know about this danger. This is a follow-up to Asteroid Day: reminding us of the threat, pushing us out into space.

“Find all asteroid threats to human populations and know what to do about them.”
— NASA’s Grand Challenge Statement, 18 June 2013.

Deep Impact

(1)  Earth is a target for objects from space

U.S. Government sensors recorded at least 556 meteors entering the atmosphere (fireballs, technically bolides) from 1994-2013. See the map below; the dots represent the meteor’s optical radiant energy measured by the sensor. As a rough conversion between that and the total energy: the smallest dot on the map represents 1 billion Joules (1 GJ) of optical radiant energy, the equivalent of ~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. The Hiroshima blast was equivalent to 15,000 tons.

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 NASA note puts these in a long-term context …

NASA map of bolide events

The dots’ size shows optical energy radiated in billion Joules (GJ). Yellow are day; blue are night.

“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.”

Unless we prepare, eventually an object will fall to destroy a city, by direct impact or the resulting tsunami. Eventually one will destroy a nation. Eventually one will will destroy civilized life on Earth. Fortunately we can build the necessary defenses slowly.

(2) NASA is preparing (slowly) for this inevitable threat

This year NASA created the Planetary Defense Coordination Office (PDCO). 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  US governmental efforts to prepare for impact threats. See their website, which has a wealth of information. NASA is a member of the International Asteroid Warning Network.

What are we doing? The first step is finding potential impactors. Warning time is the key to preventing impacts of NEOs. The National Academy of Sciences gave a status report: “Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies” (2010).

“The United States spends about $4 million annually searching for near-Earth objects (NEOs), according to NASA. The goal is to detect those that may collide with Earth. The funding helps to operate several observatories that scan the sky searching for NEOs, but, as explained below, it is insufficient to detect the majority of NEOs that may present a tangible threat to humanity. A smaller amount of funding (significantly less than $1 million per year) supports the study of ways to protect Earth from such a potential collision (“mitigation”).

“Congress established two mandates for the search for NEOs by NASA. The first, in 1998 and now referred to as the Spaceguard Survey, called for the agency to discover 90% of NEOs with a diameter of 1 kilometer or greater within 10 years. An object of this limiting size is considered by many experts to be the minimum that could produce global devastation if it struck Earth. NASA is close to achieving this goal and should reach it within a few years. However, as the recent (2009) discovery of an approximately 2- to 3-kilometer-diameter NEO demonstrates, there are still large objects to be detected.

“The second mandate, established in 2005, known as the George E. Brown, Jr. Near-Earth Object Survey Act, called for NASA to detect 90% of NEOs 140 meters in diameter or greater by 2020. … The current near-Earth object surveys cannot meet {this} goal …”

By 2014 scientists had found less than 1% of NEOs under 140 meters in diameter and 25-30% of those 140+ meters objects, per a report for NASA by Hap McSween (Prof Planetary Geoscience, U TN-Knoxville).

NEA Survey Status: April 2016

Scientists find NEOs using optical and infrared telescopes in a complex process described by by Lindley Johnson of NASA in “Finding Near Earth Objects“. The search will move faster once the Large Synoptic Survey Telescope is completed, now under construction in Chilé.

What should we do after discovering an asteroid on an collision course with Earth? There are no easy answers, as discussed in this paper by Benny Peiser (Senior Lecturer, Liverpool John Moores U).

See for yourself what a meteor impact will affect you

Impact Earth!

Describe an impact and see its effects, a website by Purdue U (London).

(3)  Can we defend against an asteroid or comet?

Today? Not very well. Defenses could be built with time and money, such as a Gravity Tractor, a Kinectic Impactor, or a Blast Deflection. The key is how much warning we have, days or decades. See this graphic by Dan Mazanek of NASA.

The four kinds of Near Earth Objects

For more information see these two presentations (video and slides): David Kring with examples and consequences of NEO impacts and Dan Mazanek about NEO deflection strategies. A mission to intercept a threatening NEO might look like this…

About shockwaves

Shockwaves are low probability, high-impact events. What is the cost of minimum prevention or mitigation of the “plausible worst case” for all these risks? Probably a lot more than we will spend. Perhaps more than we can afford to spend.

The precautionary principle provides analysis of individual threats, such as climate change, but it does not work well for full the universe of risks. The finance industry copes with this problem every day. Each security in a portfolio has its own range of risk exposures, but risk can be meaningfully assessed only at the portfolio level — compared to a risk budget. This is different than the risks a nation (or world) faces, but offers some useful ideas.

To provide Congress and the public with recommendations, the government could create a Commission (with staff, amply funded) to assess individual risk, with a brief analysis of each, applying a common analytical framework to rate each risk in terms of probability and impact. The results would provide a basis for discussion and further analysis, liberating us from the narrow perspectives of special interest activists.

Asteroid approaching Earth

For More Information

If you liked this post, like us on Facebook and follow us on Twitter. See all posts about shockwave events, about NASA, and especially Men in space: an expensive trip to nowhere, Why we have not gone into space, & why we will, and Asteroid Day: reminding us of the threat, pushing us out into space.

To understand why these objects keep coming to Earth

Newton's Clock
Available at Amazon.

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 by Ivars Peterson. From the publisher…

“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.”

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7 thoughts on “Three things to know about asteroids, certain death from the sky (eventually)

    1. Frederick,

      I don’t know about their exaggerated alarms, but more puzzleing is why we have two NOAAs. We should move NASA’s climate research to NOAA, allowing NASA to concentrate on space exploration and building our space infrastructure.

      I asked Gavin Schmidt this question, and his typically dishonestly defensive answer showed that it hit a nerve (the prospect of supervision by an agency that understands weather and climate): he pretended to be horrified at the prospect of abandoning all our weather satellites (as if the responsibilities and staffs could not be moved to NOAA, with NASA’s role being like that of communication and research satellites).

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  1. It’s quite a bit of a stretch to say we can defend ourselves against NEOs isn’t it? Our military barely has the capability to hit and destroy man-made objects – much less an irregular object hurtling at high speed toward the planet. People should understand that we’ve just scratched the surface when it comes to detecting NEOs.

    With adequate funding, we may speed detection, but it could take decades (and billion$) to develop technology (and skills) to defend. It might be better – at least in the near term – to build adequate shelters to preserve as much of the population as possible.

    Just a thought. Enjoyed your article!

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    1. Heavypen,

      “It’s quite a bit of a stretch to say we can defend ourselves against NEOs isn’t it?”

      Let’s replay the tape to see what I actually said.

      “Can we defend against an asteroid or comet? Today? Not very well. Defenses could be built with time and money, such as a Gravity Tractor, a Kinectic Impactor, or a Blast Deflection. The key is how much warning we have, days or decades.”

      So I pretty much said the opposite of what you assert that I said.

      “People should understand that we’ve just scratched the surface when it comes to detecting NEOs”

      I gave NASA’s specific estimates of the status of their tracking NEOs. It’s quite the exaggeration to call that just “scratch the surface.” They’ve found 90%+ of “planet killers” (1km+). By 2014 scientists had found 25-30% of those 140 – 1,000 meters. What remains are surveys to find new NEOs and smaller (but still dangerous) ones.

      “it could take decades (and billion$) to develop technology (and skills) to defend”

      The goal is to have the orbits plotted so that we have decades of warning, time to use our current tech to build deep-space vessels to intercept a dangerous NEO. Getting that detection capability for 99% or 99.99% will take a long time, but the risk of impacts is low during the next few decades — which justifies that slow pace of work. There are many shockwaves, and resources have to be rationally allocated among them.

      “to build adequate shelters to preserve as much of the population as possible.”

      I doubt that vast cost of building shelters for the world’s population is sensible over any likely time horizon, given the low risk of an unexpected (i.e., too short warning time) event during the next few decades. There are many more pressing needs: higher probability shockwaves — and high probability threats (i.e., we’re killing the oceans right now).

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  2. I wonder what exotic defenses future civilizations might use. Maybe adding some more mass to the giant outer planets to help them catch more asteroids?

    Here and now, that map of Bolide events freaks me out, both because of what it tells us (there were how many nuke-level explosions from space in the last twenty years?) and because I was entirely ignorant of it. And I’m not normally ignorant of anything related to space science. Hell, I used to intern for an actual astrophysicist, working on a NASA-funded project, and I’ve never stopped following the relevant news or keeping in touch with informed people.

    And yet here I was, utterly blind to the fiery death being barely held at bay by our wispy atmosphere. I’m getting worried about what else I’m ignorant of.

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    1. Matthijs,

      Welcome to the FM website! We try to bring you information from the edge of the known, including revealing things that we know aren’t so.

      “I wonder what exotic defenses future civilizations might use.”

      That’s an interesting thought! Fortunately our existing technology — ramped up a bit — will suffice. As described in yesterday’s post, Arthur C. Clarke’s Rendezvous with Rama describes how it might work. Giant radars plus survey ships map the solar system to provide ample warning, two large prepositioned ships stand ready to move anything dangerous.

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