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The Daily Need

Faraway, so close: the Earth’s most loyal stalker

Astronomers at the Armagh Observatory in Northern Ireland believe that an asteroid that’s been trailing the Earth for a quarter of a million years may share some of our planet’s DNA.

In a paper published in the Monthly Notices of the Royal Astronomical Society, Apostolos Christou and David Asher reveal the unusual orbit of 2010 SO16, an asteroid discovered in 2009 by the WISE satellite. 2010 SO16 orbits the sun at about the same distance as the Earth, almost sharing our planet’s orbit. But when it reaches the Earth, it does an abrupt about-face and goes back around the sun in the opposite direction, moving in a horseshoe pattern.

Source: Armagh Observatory

On the Observatory’s website, Christou described the asteroid as “terraphobic”: “It keeps well away from the Earth. So well, in fact, that it has likely been in this orbit for several hundred thousand years, never coming closer to our planet than 50 times the distance to the moon.”

The asteroid takes 175 years to move from one end of the horseshoe to the other, and is currently at one of the ends, trailing closely behind the earth.

At least three other known asteroids have a horseshoe-shaped orbital, but these are much younger and much smaller than 2010 SO16, and are expected to soon move off through the solar system to other orbits. 2010 SO16, however, has been in the same orbit for at least the last 250,000 years.

Christou and Asher are hoping to learn more about the asteroid while it is still nearby. They postulate that it may be leftover material from the formation of the Earth, moon and other inner planets 4.5 billion years ago. Continued study could reveal some clues about our own planet’s past.

Meanwhile, those wanting to get a glimpse of 2010 SO16 only need a medium-sized professional telescope to spot it. The astronomers say that the asteroid will remain as visible in the evening skies for years to come.

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  • Wavyhead

    I find it hard to believe that it can maintain a ‘horseshoe’ orbit.

  • Hormel

    From The name “horseshoe” is derived from the shape of the object’s orbit as seen from Earth–that is, it doesn’t stop mid-orbit, turn around, and travel in the other direction. It has everything to do with shifts in the object’s orbital path and our perspective of the object as it gets closer, shifts orbit, and then gets further away without ever passing Earth.

  • Xyz

    Why? Have you an astronomy background?

  • Xyz
  • Mac463

    I find it hard to believe that people 250,000 years ago were concerned about an asteroid. Must have been the first astronomer.

  • Tomelehman

    Yes, I agree with Xyz and Hormel: Think about perceptions that the planets (esp. Mars!) made ‘loop-de-loops’ around Earth, until Copernicus, Galileo and Kepler and others grasped they were elipses w/in a heliocentric strucure. “Horseshoe” is just nomenclature that makes sense from a terra-centric perspective– I think the authors used it because SO16 will be ‘visible’ with a moderately low-powered scope, and people can’find; it if they ‘know’ its orbit ‘reverses’ in a ‘horseshoe’.

  • Rian Mueller

    Note the date on the research paper.

  • Kurtis Morin

    Yes the orbit only appears “horse shoe” from out vantage point, it is actually elliptical and the asteroid does not stop or turn around in its orbit imagine a circle turned edge on but bent inward at the top and bottom to form a horse shoe shape when viewed for this edge on view point.

  • Invisible Eye

    As written, I think this story is terribly misleading. A little less mystification and a little more explanation please. Science is not some carny sideshow meant to amaze the rubes — it’s the why behind the things we observe appearing the way they do. The other commenters provide better explanations than the journo who wrote the post.

  • Steven Earl Salmony

    Stalking science leading to the restoration of balance and sustainability……

    Would professionals with appropriate expertise please examine the extant science regarding human population dynamics and human overpopulation of Earth? How can this knowledge be used to move the human community from the dangerous and patently unsustainable ‘trajectory’ it is on now to sustainable lifestyles and right-sized corporate enterprises?

    —–Original Message—–
    Sir John Sulston, Chair
    People and the Planet Working Group
    UK Royal Society
    March 31, 2011

    Dear Sir John Sulston:

    Your recent comments regarding the review of research on the human population and its impact on the planet we inhabit by a high level panel of experts give rise to hope for the future of children everywhere. Thanks for all you, the Planet and the People Working Group and the UK Royal Society are doing to protect biodiversity from massive extirpation, the environment from irreversible degradation and the Earth from wanton dissipation of its finite resources by the human species. I am especially appreciative for two quotes from you,

    …… “we’ve got to make sure that population is recognized… as a multiplier of many others. We’ve got to make sure that population really does peak out when we hope it will.”

    …….”what we want to do is to see the issue of population in the open, dispassionately discussed…. and then we’ll see where it goes.”

    Inasmuch as you and an esteemed group of professionals with appropriate expertise are examining scientific evidence regarding the unbridled increase of absolute global human population numbers, please note there is research that has been summarily dismissed by many too many of our colleagues regarding human population dynamics and human overpopulation which I would like to bring to your attention. For the past ten years I have been unsuccessfully attempting to draw attention to certain evidence that to date remains both unchallenged and ignored by virtually every top-rank professional. They appear unable to refute the evidence and simultaneously unwilling to believe it. Their unexpected conspiracy of silence has served to conceal certain research by David Pimentel and Russell Hopfenberg. How else can it be that so many established professionals with adequate expertise act as if they are willfully blind, hysterically deaf and electively mute in the face of scientific evidence of human population dynamics and human overpopulation? The conscious denial of what could somehow be real about the growth of the human population in our time is not doing anything that can be construed as somehow right and good for future human wellbeing and environmental health, I suppose. It appears as if we could be witnesses to the most colossal failure of intellectual honesty, moral courage and nerve in human history.

    Peer-reviewed professional publications, letters to the editor, slideshow presentations et cetera can be found at the following link,

    Thank you for attending to this request for careful, skillful and rigorous scrutiny of research from two outstanding scientists. Please know I am holding onto a ray of hope that the research of Hopfenberg and Pimentel is fundamentally flawed; that human population dynamics is different from, not essentially similar to, the population dynamics of other species; and that human population numbers are not primarily a function of an available supply of food necessary for human existence. That would be the best news.

    Sometime soon, I trust, many scientists will speak up with regard to apparently unforeseen and unfortunately unwelcome science of human population dynamics and human overpopulation the way people in huge numbers in the Mid-East are calling out for democracy now.

    Respectfully yours,

    Steve Salmony

    Steven Earl Salmony
    AWAREness Campaign on The Human Population,
    Established 2001