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Tightening the Focus on Near Earth Asteroids

The impact at Tunguska, Siberia on June 30,1908, evidently a small asteroid, devastated 1300 square kilometers, which works out to be the equivalent of a large metropolitan area. June 30, 2015 is thus an appropriate date to launch Asteroid Day, a global awareness campaign to put the issue of dangerous impacts in front of as many people as possible. An early December press conference at the London Science Museum, hosted by Lord Martin Rees, UK Royal Astronomer, announced the campaign and released a declaration of needed action:

  • Employ the available technology to detect and track near-Earth asteroids that threaten human populations
  • A rapid hundred-fold (100x) acceleration of the discovery and tracking of NEOs
  • Global adoption of Asteroid Day on June 30, 2015, to heighten awareness of the asteroid hazard and our efforts to prevent future impacts

The list of scientists, business leaders and artists behind the 100x Declaration, as it’s being called, is an impressive one that includes Jill Tarter, Kip Thorne, Stewart Brand, Richard Dawkins, Google’s Peter Norvig, astrophysicist and guitarist Brian May, Alexei Leonov, Jim Lovell and Rusty Schweickart, a group numerous and diverse enough that I’ll send you to the list of signatories available on the Asteroid Day website for more. Founding partners of the event include The Planetary Society, Astronomy Magazine, the Association of Space Explorers (ASE), and the California Academy of Sciences. ASE chairman Tom Jones explains:

“Finding hazardous asteroids early through an accelerated search program is the key to preventing future destructive impacts. The 100x Declaration will focus space policymakers on that important goal. ASE called last year for a stepped-up, global search effort; this can lead within a decade to an international deflection demonstration mission to show we know how to nudge an asteroid. Once we know what’s coming, we can design an effective space deflection campaign against dangerous objects we find.”

Visualizing Asteroid Data

In November, NASA’s Near Earth Object Program released a map showing a visualization of data gathered between 1994 and 2013. Atmospheric impacts large enough to produce a fireball occurred on 556 occasions during this period, with almost all the small asteroids disintegrating before they reached the ground. The most prominent exception is the Chelyabinsk event in 2013, the largest asteroid to cause surface damage during this period. We learn that asteroids no larger than a meter in diameter hit the atmosphere and break apart about every other week. The Chelyabinsk event was caused by the explosion in the atmosphere of an asteroid thought to be about 20 meters in size.


Image: This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth’s atmosphere to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”. Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size. Credit: Planetary Science.

The good news is that the Earth’s atmosphere screens small asteroids from the surface quite effectively, but Lindley Johnson (NASA NEO Observations Program) says that data like these will help us figure out how often asteroids large enough to cause ground damage do get through. According to this JPL news release, the NEO Observations Program has identified 96 percent of the estimated population of one-kilometer or larger asteroids, with a goal of finding 90 percent of NEO’s larger than 140 meters in diameter. These are estimated to be as much as 25 times more numerous than the one kilometer asteroids. The NEO Observations Program finds and tracks asteroids whose orbits bring them within 50 million kilometers of Earth’s orbit.

Two other notes: A 2013 paper from Peter Brown and team reports that existing telescopic surveys have discovered about 500 near-Earth asteroids that are 10-20 meters in diameter — that’s Chelyabinsk size — out of an estimated near-Earth asteroid population of roughly 20 million, “… implying that a significant impactor population at these sizes could be present but not yet cataloged in the discovered near-Earth asteroid population.” All of which gives the 100x Declaration some punch and underscores how much we still have to do.

And in a paper just released on the arXiv site, Clemens Rumpf (University of Southampton, UK) unveils ARMOR, the Asteroid Risk Mitigation Optimization and Research tool currently being developed at the university. The tool calculates the impact location and probability distribution on Earth’s surface (the so-called ‘risk corridor’), using (in this paper) a sample size of ten asteroids. Future iterations of ARMOR may prove useful in assessing the risk of individual asteroids.

The Brown paper is “The flux of small near-Earth objects colliding with the Earth,” Nature, Vol. 420 (21 Nov. 2002), pp. 294-296 (abstract). The Rumpf paper (thanks to Ashley Baldwin for the tip) is “Global Asteroid Risk Analysis” (abstract).





Comments on this entry are closed.

  • Alex Tolley December 15, 2014, 16:02

    Astronomy Notes has a nice equation for the height of a tsunami wave based on the energy of the impact and the distance from the impact.

    The tidal wave height in meters =10.9 × (distance from impact in kilometers)^-0.717 × (energy of impact in megatons TNT)^0.495

    So while a land impact would be devastating to a city, an impact offshore could have serious repercussions over a wider area, much like the Tsunami that hit Japan and took out the nuclear reactors.

    A 100m asteroid hitting 100 km offshore would generate a wave 2.4m high. If that happened at high tide in Florida, the effect would be large scale flooding. It is comparable to the 1953 North Sea flood that devastated southern England. Even a 1000km offshore impact would create 1/2 meter wave that could cause flooding, especially if it was concentrated in a river estuary and overflowed the banks.

    Fortunately such a large impactor is only expected every ~5000 years.

  • Ashley Baldwin December 15, 2014, 16:23

    Thanks Paul… I think. Glad it’s only a small sample size as the strip runs right over my house! Seriously though, great piece. Scary but stimulating. The sooner that B612 Foundation’s “Sentinel” telescope is up and working near Venus in 2018 the better. With the Earth based scheme described , the WISE telescope plus the giant LSST in Chile we will have pretty comprehensive coverage in a decade. Sentinel will see 90% of all 140m asteroids and a big portion of those down to 40m, hopefully decades before any impact.
    I think it’s very coincidental that the first manned mission with the Orion/SLS combination is an asteroid capture. Perhaps it wasn’t just because it is cheaper than returning to the moon…. . Good to know the option of deflection is there after discovery though. Asteroid capture is just fine from my point of view. NASA’s new ion thruster system will be needed to avoid lugging large chemical rockets into orbit . A low specific impulse but works over years and builds up. The NEXT system is ready to go. The main obstacle to bigger versions ( which would be ideal for fast interplanetary missions, or even interstellar- 90,000mph plus to start) is power. As always. These systems use a ton of it (tens to hundreds of kilowatts anyway). NEXT uses solar power but anything more powerful will need a nuclear reactor with all the baggage that brings. Readers may be aware of NASA’s under development VASIMR drive which will need just that . Russia have orbited two reactors so far with 6 KW power ( a whole lot more didn’t make it and ended up in high decaying orbits or on the bottom of the ocean) and the U.S. began “Project Prometheus” ( great name ) looking at 2-300KW reactor design a few years back but pulled the plug when recession hit. Watch that space though.

  • Andrew Palfreyman December 15, 2014, 18:56

    The problem is of course that if a dangerously sized one of the as-yet-undiscovered asteroids augurs in unexpectedly, we have nothing sitting ready on the ground to launch at it. It could be argued that this should be a 4th action item in this declaration.

  • LocalFluff December 16, 2014, 9:12

    It seems as if light pollution makes detection less likely in Europe. Ships at sea have a field day in this respect.

  • Al Jackson December 16, 2014, 11:03

    Anyone who would like to practice doing big augering on the Earth’s surface can go to Impact Earth!


    Jay Melosh told me when they first put this site up they had to redo it because people were using the speed of light as an impact velocity!

  • Mike Helton December 16, 2014, 11:38

    It seems the only thing we humans could do at this time if it was discovered that an asteroid would be impacting the Earth in say 4 or 5 months would be to put in place an evacuation plan for any population areas that would be affected. What can be done now (before any such discovery) is to do some pre-planning for doing and execution such a plan.

  • Brandy Samoa December 17, 2014, 15:05

    The abstract for “Global Asteroid Risk Analysis” is here: http://arxiv.org/abs/1410.4471