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The Numbers on NEOs

The Spaceguard program, originally mandated by Congress in the 1990s, is in the business of detecting, tracking and cataloging near-Earth objects (NEOs). Spaceguard’s goal has always been as ambitious as it is crucial: To locate ninety percent or more of the objects that approach the Earth and are more than one kilometer in diameter. So how is Spaceguard doing? According to Stephen M. Larson (University of Arizona), who manages the Catalina Sky Survey, “We’re about 85 percent there.”

But even when we reach 100 percent, the story is far from over. An object just a third of a kilometer in diameter would explode with an energy more than twenty times that of the largest thermonuclear bomb. NASA received another mandate in 2005 to identify near-Earth asteroids and comets down to 140 meters in diameter, still large enough to destroy a city. And even though impacts like these seem to occur only once every several thousand years, no one can say when the next potential strike could happen.

I’m looking at a University of Arizona news release that notes the Catalina Sky Survey’s score in 2008: 565 NEO discoveries, following 460 in 2007. A $3.16 million NASA grant has now been awarded to continue the search through 2012 using the CSS facilities, which include a new 1-meter telescope to be housed next to the existing 1.5-meter instrument on Mount Lemmon, north of Tucson. Used to follow up NEO discoveries, the telescope boosts CSS’ survey time on other instruments by 20 to 25 percent.

But CSS also includes a southern hemisphere presence in New South Wales using Australian National University’s 0.5-meter telescope, a reminder of the need for global search facilities. It was CSS that identified 2008 TC3, a six-foot object that disintegrated over Sudan last fall. Says Larson:

“There’s a bit of a misperception that what we do is find objects that are incoming, like the Sudan object. That’s not the case.

“We’re hoping to find objects that many orbits down the road might be hazardous, so that we have enough time to do something about them. We can calculate orbits quite accurately. We hope that we would have a few decades to study and characterize these things, and come up with the best plans to nudge them into another orbit so that it misses the Earth.”

The numbers here are stark. NASA’s Near Earth Object Program reports that we’ve found 5,955 NEOs, some 763 of which are at least one kilometer in diameter. 1008 NEOs larger than 140 meters across come within 4.5 million miles of Earth’s orbit, dangerous to us because perturbing influences could change their trajectories in the future. Centauri Dreams believes that the discovery of an object on a collision course with Earth would galvanize the space program as researchers looked for the best ways to deflect its path. The problem is time.

Would we find the object soon enough to be able to develop the needed technologies? Ponder this: 2008 TC3 was discovered when it was well outside the orbit of the Moon. Moving at 12 kilometers per second, it struck some nineteen hours later.

The more accurate our sky surveys, the more likely we are to find objects while we still have a chance to deflect them. The best insurance program for our planet involves not only observing programs to detect and characterize the potential trouble-makers, but a robust effort to study deflection strategies. Part of this must include a mission to a near-Earth asteroid, not only to learn more about the object itself, but to tune up the procedures for getting a payload on site quickly if the need arises.

Comments on this entry are closed.

  • ad koppen January 14, 2009, 2:33

    These are disturbing numbers of NEO`s, the normal told story that a big asteroid will hit Earth only once in so many thousand years is not valid anymore.
    It can happen tomorrow and next week again. It is waiting for the big hit and only then there will be action by governments.
    One thing is sure , the one that will hit Earth is on his way and has its eye already on that little blue dot.

  • John Hunt January 14, 2009, 4:02

    IF space budgets are a zero-sum game then I would prefer to put our money on accelerating the discovery of more and smaller NEOs. Part of the reason that the Sudan NEO was discovered so late was that it was so small. If one were 140 meters in diameter or larger we would likely get advanced warning and be able to evacuate a city if need be.

    We are getting to the point where nearly all of the civilization killing asteroids will be known. If any are headed our way, likely we’d have many years to develop a deflection strategy.

    It seems to me as though the risk from unknown NEOs is decreasing at a pretty rapid rate. I think that the development of self-replicating technology should, statistically, be considered a far greater concern than NEOs.

  • Adam January 14, 2009, 18:03

    Developing an accelerator capable of firing off small interstellar probes would also be a very effective anti-asteroid system, though rubble-pile asteroids might need towing via gravity tractors rather than blasting via impactors.

  • Administrator January 14, 2009, 19:09

    Nice idea, Adam. That’s a two-for-one technology I can live with!

  • ljk February 4, 2009, 8:08

    A team of French and Italian astronomers have devised a new method for measuring the size and shape of asteroids that are too small or too far away for traditional techniques, increasing the number of asteroids that can be measured by a factor of several hundred. This method takes advantage of the unique capabilities of ESO’s Very Large Telescope Interferometer (VLTI).

    Read more in ESO 04/09 at


  • ljk February 22, 2009, 10:01

    First tracked space rock recovered after impact

    22:31 19 February 2009 by David Shiga

    The discovery of meteorites from an asteroid that exploded over Sudan in October completes an astronomical trifecta. For the first time, scientists have detected a space rock ahead of a collision with Earth, watched it streak through the atmosphere, and then recovered pieces of it.

    Analysis of the meteorites could shed light on conditions in the early solar system more than 4 billion years ago.

    When the asteroid, called 2008 TC3, was discovered on 6 October last year, it was just 20 hours away from hitting Earth. Though the warning period was short, it was the first time a space rock had been found before it impacted the planet.

    Full article here:


  • ljk March 2, 2009, 10:09

    Space Rock 2009 DD45 Buzzes Earth

    Late word out of the IAU’s Minor Planet Center: a small asteroid will pass close to Earth tomorrow (March 2nd) at 13:44 Universal Time. How close? The MPC’s Timothy Spahr calculates that it’ll be 0.00047 astronomical unit from Earth’s center. That’s only about 40,000 miles (63,500 km) up — well inside the Moon’s orbit and roughly twice the altitude of most communications satellites!

    Full article here: