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A Crowded Inner System

A small asteroid hitting the Earth’s atmosphere is a spectacular phenomenon, but one likely to go unseen if the object has not been previously tracked. But that may be changing as we continue to install automated cameras across the planet. Take a look at this video of the object that exploded over Scandinavia on January 17. A Swedish camera recorded the event, which now goes worldwide over the Net thanks to the camera’s owner, one Roger Svensson, and spaceweather.com.

The January 17 incident was little more than a lightshow, startling for local wildlife but unnoticed by the sleeping nation beneath the brief glare. It does, however, remind us of the 1017 potentially hazardous asteroids (PHAs) now known to scientists. A PHA is an asteroid larger than 100 meters that may come closer than 0.05 AU to Earth. Prowling around the spaceweather.com site, I find twelve Earth-asteroid encounters this January alone, the closest being the 1.8 lunar distance passage of 2009 BD on January 25. Only one of these is a PHA, a 120-meter rock called 2002 AO11.

A list of close approaches to the Earth by potentially hazardous asteroids can be found here, as assembled by the Minor Planet Center. Necessarily, such lists do not include recently discovered objects whose orbits have yet to be firmed up, and the site points out that the distances involved can be quite uncertain. We’re learning more all the time, prizing out the more unusual of these nearby objects. Below is the MPC’s plot of the inner Solar System. Seen at this scale, the environment the planets move through is a crowded place!


Image (click to enlarge and update): The orbits of the major planets are shown in light blue: the current location of the major planets is indicated by large colored dots. The locations of the minor planets, including numbered and multiple-apparition/long-arc unnumbered objects, are indicated by green circles. Objects with perihelia within 1.3 AU are shown by red circles. Objects observed at more than one opposition are indicated by filled circles, objects seen at only one opposition are indicated by outline circles. The two “clouds” of objects 60° ahead and behind Jupiter (and at or near Jupiter’s distance from the sun) are the Jupiter Trojans, here colored deep blue. Numbered periodic comets are shown as filled light-blue squares. Other comets are shown as unfilled light-blue squares. Credit: Minor Planet Center.

2009 BD is itself a rather interesting object. When it passed by the Earth on Sunday, it was about 645,000 kilometers away, a 10-meter rock whose orbit seems remarkably close to that of the Earth. What this means is that the asteroid will stay around for some months, never wandering further than 0.1 AU until late next year. You may be reminded of asteroid 2003 YN107, which took on a corkscrew motion around the Earth after arriving in our vicinity in 1999. Says Paul Chodas of NASA’s Near Earth Object Program at JPL:

“It’s a very curious object… We believe 2003 YN107 is one of a whole population of near-Earth asteroids that don’t just fly by Earth. They pause and corkscrew in our vicinity for years before moving along.”

The term for these objects is Earth Co-orbital Asteroids, whose population may be augmented by 2009 BD if further study confirms the addition. With an orbit of almost precisely one year, they can catch up with our planet, becoming in effect a small, new moon for the duration of their visit. The co-orbital 2004 GU9, about 200 meters across, has evidently been looping around the Earth for five hundred years. 2003 YN107, on the other hand, has already departed, although it is due for another visit in about sixty years. Needless to say, such objects are interesting targets for robotic or manned exploration.

Comments on this entry are closed.

  • tacitus January 27, 2009, 17:03

    That asteroid chart is quite impressive when you first see it, but it can leave the uninformed a little more startled than they really need to be since it really doesn’t do justice to the ginormous (a technical term) amount of space these objects have to fly around in.

  • Adam January 27, 2009, 21:04

    Nice point tacitus. A thousand ‘roids distributed through a cubic AU would be about 15 million km apart on average. Even the 1E+34 bits of 0.1 micron interplanetary dust are more than a metre apart on average. Yet our System is relatively dust-free compared to some other systems out there – Epsilon Eridani and Tau Ceti are two nearby dust-ridden systems, and a bit further out we have Fomalhaut and Vega. They’d all be fantastic sites for in-space living – asteroids for city-making aplenty.

    A step further out from Sol and we’re in the Oort Cloud – the Outer part of which sees cometoids 10 AU or so apart, increasing in density to form the Inner Disk, the ragged inner edge of which merges into the Kuiper Belt and Scattered Disk. So many bodies in all of them and it makes me laugh when ETI skeptics claim there’s no signs of ETIs in our Solar System. Imagine the gigantic task required to visit the trillion plus bodies that are out there.

    How long would such a gargantuan effort take?

    A thousand robotic survey vehicles might take a billion years to visit them all. Of course if we let loose a self-replicating Explorer then it’d only take a few doublings to do the job – assuming a 1 year trip to new destinations and a doubling time of once per year, then the survey of two trillion bodies takes 41 generations and 82 years… but then we’d have a couple of trillion very capable and hardy self-replicators to contend with.

  • kurt9 January 28, 2009, 0:19

    Lots of NEOs simply means lots of resources to build O’neill style space colonies.

  • Adam January 29, 2009, 19:22

    Hi kurt9

    Why build CylCits at all? Just dig holes in the ‘roids. Centrifuges don’t need to be as gigantic as O’Neill assumed and the gargantuan CylCits were supposedly landscaped to be Earth-like – but who could afford that??? As much as I loved the artwork there won’t be CylCits as envisaged by O’Neill – too much dead volume and dead mass to be affordable.

    I think the NEOs will be tapped for volatiles before we go turn them into habitats.

  • James M. Essig February 1, 2009, 14:42

    Hi Paul;

    The presense of so many NEOs, some of which closely match Earth’s orbital period could be great resources for solar powered mining ships or bases which could harvest the materials within these asteriods. Since some asteriods are heavy in iron and nickel, the raw materials could be fabricated into iron/nickel alloys some of which are extremely tough.

    Manufacturing these materials in the vaccuum of space might permit various alloy grain patterns or alloy crystalline structures not producable on Earth to be made in bulk as well as be made far stronger, harder, and/or tougher then Earth based alloys.

    Manned missions to these asteriods are one of several good first steps in our journey outward and ultimately to the stars.


    Interesting points. A few trillion comets adds of to a great supply of fusion fuel, and other resources for manned interstellar space faring crafts. We have much to explore in the planetary solar system, the Kuiper Belt, and especially the Oort cloud. The fascinating analogues around other stars will permit even more objects of study and resource utilization. Perhaps we will find the hulks of disabled ETI space craft out there among the trillions of comets orbiting the Sun.



  • ljk February 9, 2009, 12:14

    February 7, 2009

    New Potentially Hazardous Asteroid Discovered

    Written by Nancy Atkinson

    While observing a known asteroid on January 31, 2009, astronomer Robert Holmes from the Astronomical Research Institute near Charleston, Illinois found another high speed object moving nearby through the same field of view.

    The object has now been confirmed to be a previously undiscovered Potentially Hazardous Asteroid (PHA), with several possible Earth impact risks after 2042.

    This relatively small near-Earth asteroid, named 2009 BD81, will make its closest approach to Earth in 2009 on February 27, passing a comfortable 7 million kilometers away.

    In 2042, current projections have it passing within 5.5 Earth radii, (approximately 31,800 km or 19,800 miles) with an even closer approach in 2044. Data from the NASA/JPL Risk web page show 2009 BD81 to be fairly small, with a diameter of 0.314 km (about 1000 ft.).

    Holmes, one of the world’s most prolific near Earth object (NEO) observers, said currently, the chance of this asteroid hitting Earth in 33 years or so is quite small; the odds are about 1 in 2 million, but follow-up observations are needed to provide precise calculations of the asteroid’s potential future orbital path.

    Full article here: