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Thread: Finding asteroids

  1. #1
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    Question Finding asteroids

    I posted this a few days ago on the podcast section but it seems to have gotten overlooked, so I'll ask here. I am referring to the Podcast "Asteroids Make Bad Neighbors". I have a question I hope someone can answer:
    I don't have the greatest understanding of astronomy, so hopefully someone has a simplified answer for me. I thought this article really explained many aspects of asteroid studies quite well and understandably too. My questions concerns whether all >1km asteroids will be found if they are outside the plane of the ecliptic. From the article she says:
    "Nowadays there are multiple telescopes set up around the planet that scan each part of the sky along the ecliptic five times in a given night. They're constantly going through processing, looking for things and discovering new things on a regular basis and calculating the orbits in rapid fire"
    and:
    "There's a bunch of different programs that go out and take picture after picture after picture of areas specifically along the ecliptic in the sky. This is the area in the sky that the sun travels through and where we see all the planets. More or less, the majority of the asteroids and comets confine themselves to the ecliptic. There are some exceptions, things get thrown around through gravitational interactions and to find asteroids and comets, they look for things that move in their pictures"
    So what about the other areas of the sky not on the ecliptic (and "deep space")-Are systems in place that cover those others areas too? Thanks...

  2. #2
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    Yes there are. I can tell you of automated telescopes that are sweeping the skies nightly. Like a blink comparator they take repeated images and compare them so as to find any object that is moving against the background. Sweeping the sky looking for things has become a science of its own and the computers that register all this information are impressive in that the speed there results reach us. Objects as small as half a metre can be detected. There are lots that size. The larger fast moving object are easy to spot. Not just along the ecliptic line. For example there are two such automated observatories on the Antarctic ice.

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    Quote Originally Posted by astromark View Post
    Yes there are. I can tell you of automated telescopes that are sweeping the skies nightly.
    How efficient are we at this point? I wanted to do some figr'in.
    (I did this quickly, so corrections may be a natural outcome)
    I found a Keck image is 10 arcsec wide (true?)
    A sphere is 1296000 arcsec circum...or 534,638,377,792 surface area
    Divided by the 10x10 image, it would take 5 billion pictures to scan the skys with one scope.
    How long of an exposure would be needed?

    And you still might miss it...

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    I'm pretty sure that the 'scopes being use specifcally to search for NEOs are going to be designed to have a wider field of view than the standard astronomical ones.

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    Quote Originally Posted by Grashtel View Post
    I'm pretty sure that the 'scopes being use specifcally to search for NEOs are going to be designed to have a wider field of view than the standard astronomical ones.
    That would be my guess, plus we are talking about multiple scopes.

    I was giving my own line of thinking to hopefully spark a line of conversation that can put it into a better perspective.

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    Quote Originally Posted by 2001Intrepid View Post
    So what about the other areas of the sky not on the ecliptic (and "deep space")-Are systems in place that cover those others areas too? Thanks...
    All asteroids pass through the ecliptic, so watching the ecliptic should be enough for now. Later we will need some missions that observe from an orbit closer to the Sun to see asteroids that never get further out than Earth's orbit.
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    All asteroids pass through the ecliptic, so watching the ecliptic should be enough for now. Later we will need some missions that observe from an orbit closer to the Sun to see asteroids that never get further out than Earth's orbit.
    What about highly eccentric ones? Or those in some kind of resonance orbit?

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    Quote Originally Posted by NEOWatcher View Post
    What about highly eccentric ones? Or those in some kind of resonance orbit?
    Yes, I wondered about the highly eccentric ones also. I heard that NEAT has a limited area for scanning but LINEAR does better. Then I read something about the Pan/Starrs system which is yet to implemented. Does anyone have a good link that summarizes just how throughly the skies are being watched? Thanks.

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    Quote Originally Posted by NEOWatcher View Post
    I found a Keck image is 10 arcsec wide (true?)
    Perhaps that is true for the Adaptive Optics modes of Keck, but not for the general field of view of the telescope, which is probably in the 1/4 of a degree range - I'd have to check for sure.

    You wouldn't use a telescope like Keck for wide field surveys.

  10. #10
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    Forget the Keck telescope. It is used for deep space observation not near Earth asteroid hunting. The Earth crosser search is done by much smaller faster purpose designed telescopes. Note that I used the term automated. The only things that seem to get missed are objects that have had there trajectory changed by soler gravity encounters. We have spotted them as little as hours out., or as they go. could be a problem.

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    It would be good to use thousands of Keck class telescopes as they would occasionally find asteroids with dimentions of about one millimeter. Asteroids smaller than one centimeter are typically too dim to be found in the present search method.
    I think the telescopes pan slowly and continously so exposure can be minutes, in most favorable senarios. Typicaly the the asteroid moves across the field of view, so effective exposure is only about one second = A line of exposed CCD cells, I think. If the line is tilted with respect to the lines made by the distant stars, an asteroid, comet, GEO, LEO satellite or airplane is likely.
    We could collect data from world class telescopes, whenever they pan to the next experiment. Even with perfect sychronization with Earth's rotation, asteroids etc occasionally, pass though the field of view and could provide valuable data with a suitable computer program. Also there is at least an hour each day when the sky is too bright and or partly cloudy for most experiments, but these world class telescopes could still out perform the typical one meter telescopes being used for asteroid hunting.
    Something like 5 billion pictures are needed to cover the sky once, but every little bit helps. Neil
    Last edited by neilzero; 2007-Apr-26 at 09:10 PM.

  12. #12
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    Quote Originally Posted by NEOWatcher View Post
    How efficient are we at this point? I wanted to do some figr'in.
    (I did this quickly, so corrections may be a natural outcome)
    I found a Keck image is 10 arcsec wide (true?)
    A sphere is 1296000 arcsec circum...or 534,638,377,792 surface area
    Divided by the 10x10 image, it would take 5 billion pictures to scan the skys with one scope.
    How long of an exposure would be needed?

    And you still might miss it...
    Hi,

    That's associated with some of the slightly more misunderstood notions of telescopes. Bigger doesn't mean better for a particular application. For stars and objects with no apparent size, bigger telescopes yield more light coming in by size. For extended sized objects - those that can be actually seen (like planets and nebulae and galaxies) the exposure depends upon the F/d (f-number) of the telescope which is the focal length divided by the diameter. The larger this value, the long the exposure required. One typically finds this value between F/2 and F/14 with relatively few exceptions (in the amateur world) and most of these exceptions are on upper end. The practicality of going lower gets pretty rough and the usefulness of going higher tends to be minimal.

    For imaging, the area of sky you capture at prime focus depends upon the focal length of the telescope and the size of the film or sensor. Due to the benefits of CCD imaging over film, most scientific imaging now is done with CCDs which tend to get rather costly as the size increases. Because the F/d value depends on the diameter and since this F/d value doesn't vary much, one finds that by necessity, the focal length for larger telescopes must be greater than smaller telescopes. That means the field of view must be less for larger telescopes.

    Even though one can collect more light with a larger telescope, the advent of the CCD astronomy camera can make up for that benefit when using a smaller telescope which will cover a larger area of sky. Most amateurs have smaller CCD sizes in their cameras which makes things even out a bit but for instance my low cost camera can cover about 1/4 of a degree in one image with a moderate sized amateur imaging telescope.

    As such, there are amateurs and groups of amateurs (in many cases - amateur because they do it for the love of astronomy and do not get paid for it as a full time occupation) who regularly image looking for near earth asteroids. An example I'm a little bit familar with is the Ft Bend Astronomy Club asteroid search group. They have discovered many near earth asteroids and are based just south of Houston TX. They use an 18 1/2 " telescope and now use a fairly expensive camera provided them in a grant for doing this sort of research. They were quite successful originally using a homebrew CCD camera referred to as the cookbook camera.

    Although I don't know how many groups out there are doing this, there are definitely some doing so successfully as well as individuals doing so. This same equipment is also being used for supernovae searches and for GRB afterglow searches by other club members. Despite the shared equipment and part time nature of the members, their asteroid discoveries are beyond the dozens, perhaps even into the hundreds - although I don't recall offhand just what the FBAC group count is nowadays but I'd guess somewhere in the 30-300 range.

    Despite all this work there are problems. If we find every last one of the near earth asteroids at one point in time, after a few years, there's likely to be a new set of them to be discovered. One has the asteroid belt, the kuiper belt and the oort cloud for places where lots of bodies varying in size from dust to pluto planet size. Objects with over say 500 year orbits are likely to be totally unknown and likely to remain unknown at least until they come whizzing through the inner solar system again.

    Ten years ago we witnessed the levy schoemaker comet come into the solar system's inner areas and less than 2 years after discover, it smacked into jupiter, creating plumes and 'damage' spots on jupiter's atmosphere that were the size of the earth and easily imaged by professionals and amateurs alike. Were that to have been earth rather than jupiter, it's possible it could have been an extinction level event and would have probably ended any semblance of current modern civilization.

    There's no way man could deal with such a pending disaster in that time frame. Ten years warning might have a possibility.

    Even worse, a long orbit time object could come from the other side of the solar system - out of the sun's direction. Back in 2002 or 2003 there was a newly discovered asteroid supposed to come through about 3 months later - about time and a half the distance of earth to moon and about the size of a sports stadium.

    In the weeks preceeding this event as I was planning on imaging the close approach with a video imaging camera, I learned of another unknown asteroid came whizzing through evidently as close as about 75000 miles or so. It was thought to be about 1km in diameter. It was discovered about 3 days after nearest approach having come from the direction of the sun.

    As david levy has stated in a televised interview, the liklihood (at that time) was that time a killer asteroid would be discovered probably be discovered was 10 seconds after it hit the atmosphere. While that might have tipped some towards knowning about many of these objects with none due for any potential damaging approaches within our potential life times (or at most maybe one or two that are questionable), This possibility will never be reduced to zero as it won't matter if we know 10 seconds after it starts to happen or even 10 months before it happens. It takes time to influence the orbit of a massive body.

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    LIke Antoniseb said, they have to pass through the ecliptic, so there's no reason we can't ambush them there. And unless they spend all their time interior to the Earth (in which case they are not an immediate threat), they must have an Earth opposition from time to time. At opposition, they are at their brightest, and they move fastest against the background sky.

    I'm not sure how the asteroid surveys are conducted, but it wouldn't surprise me to find out that they concentrated heavily in the sky 180 degrees away from the Sun.

    Resonant asteroids can be a problem if their resonance keeps them from coming close enough to Earth to detect. But in that case we are protected by the resonance. At other times, a resonant asteroid can spend a great deal of time near Earth. Cruithne makes a close pass to Earth once a year. But year after year, the close pass distance gets greater. In a few centuries from now, Cruithne will spend many decades on the opposite side of the Sun, leaving it undetectable.

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    There are two superlative programmes in the works that will do wonders for asteroid finding: Pan-STARRS and the LSST.

    While neither is optimised for finding PHAs (potentially hazardous asteroids), I think either would run rings around any existing programme (some caveats apply).

    After they've been working for a few years, my guess is that attention will turn to the small regions of PHA parameter space which neither is good in, and to the rarer, but more troubling, wild things - comets making their first appearance in the inner solar system (or those with extremely long periods).
    Last edited by Nereid; 2007-Apr-27 at 06:51 PM. Reason: Added links

  15. #15
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    Well, It appears that my method of trying to get it explained the way my mind works isn't going the direction that I had hoped.

    Ok; Ok; I know Keck was a bad example...all I wanted was a starting point.

    Anyway;
    It sounds like a common amateur sighter would about 1/4 degree with a 1sec exposure. I'm also getting the impression that the timing is of such great importance that the size of the scope/image is almost meaningless.
    Am I close?

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    Let's send some flashbulbs out there to help illuminate our neighborhood. A few well-placed nukes would do wonders.

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    Quote Originally Posted by tony873004 View Post
    LIke Antoniseb said, they have to pass through the ecliptic, so there's no reason we can't ambush them there. And unless they spend all their time interior to the Earth (in which case they are not an immediate threat), they must have an Earth opposition from time to time. At opposition, they are at their brightest, and they move fastest against the background sky.

    I'm not sure how the asteroid surveys are conducted, but it wouldn't surprise me to find out that they concentrated heavily in the sky 180 degrees away from the Sun.

    Resonant asteroids can be a problem if their resonance keeps them from coming close enough to Earth to detect. But in that case we are protected by the resonance. At other times, a resonant asteroid can spend a great deal of time near Earth. Cruithne makes a close pass to Earth once a year. But year after year, the close pass distance gets greater. In a few centuries from now, Cruithne will spend many decades on the opposite side of the Sun, leaving it undetectable.
    Sorry but when you stare at the sun these days, you'll find well beyond it all that space that was 180 degrees from the sun about 6 months ago. Ambushing an asteroid 2 months out from impact only works in the movies. It's sorta like handing someone a shovel and tell them to go make a mountain out of a mole hill (mound created at the entrance to a tunnel entrance made by a small furry rodent).

    Having a highly eccentric orbit that brings an object to the inner solar system only every few thousand years isn't likely to be one we've seen. Having a resonance with some other planet - like jupiter makes no assurances it won't splat into us on the very next pass even if it's assured not to crash into jupiter.

    The odds may tip in the favor of the next splatt happening with an object we detected as being a probable threat years before the actual event. Even if we developed full proof technology to deflect asteroids given a 10 year warning, there are still the 'newbies' on the block which we discover at or just before impact when it's too late to act successfully that can get through and do severe damage. We don't know what the case was with the dinos 60 million years ago (other than they had no technology for asteroid defense) so we don't know if had we been there with technology we could develop in the near future, whether or not we'd detect the event in time to act successfully.

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    Cool

    [QUOTE=cbacba;976615]Sorry but when you stare at the sun these days, you'll find well beyond it all that space that was 180 degrees from the sun about 6 months ago. Ambushing an asteroid 2 months out from impact only works in the movies.
    Having a highly eccentric orbit that brings an object to the inner solar system only every few thousand years isn't likely to be one we've seen. Having a resonance with some other planet - like Jupiter makes no assurances it won't splat into us on the very next pass even if it's assured not to crash into Jupiter. Thanks, cbacba.


    This has almost happened. At least twice in the last few years we have been told of asteroid passes at near lunar distances to Earth after the event. One of these was a four km., lump of rock.
    After, is I suspect, too late.
    The fact that these objects approached Earth from the behind the sun is not uncommon.
    A close look at this side of the moon reveals a splattering of impact creators. Most of those object would have come mighty close to this planet as they zeroed in to the lunar surface. We know of many impact events on planet Earth. Just because we have built a civilization with all its venerability does not exempt us from the dangers of impacting object. Just as building cities on top of volcanic fields is a good idea- NOT. Time and the inevitable are the enemy. Advanced technology might be our only salvation.

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    Quote Originally Posted by cbacba View Post
    Sorry but when you stare at the sun these days, you'll find well beyond it all that space that was 180 degrees from the sun about 6 months ago. Ambushing an asteroid 2 months out from impact only works in the movies...

    ...Having a resonance with some other planet - like jupiter makes no assurances it won't splat into us on the very next pass even if it's assured not to crash into jupiter.
    I never mentioned anything about ambushing it 2 months prior to impact. The plan is to take inventory of all hazardous asteroids in the hopes that we can discover any possible impactors decades or centuries in advance. All asteroids whose aphelions are greater than 1 AU will make oppositions to Earth from time to time, usually every couple of years. The exceptions are ones that are locked in trojan resonances with Earth. To date we have not discovered any Earth trojans, but there are probably many. Horeshoe orbits can keep a potentially hazardous asteroid from coming close to Earth for centuries. Additionally, objects in near resonances can prevent them from having close oppositions for many decades, but ultimately they will come around to have a close Earth opposition.

    Asteroids locked in resonance with Jupiter can strike Earth. But since they're not locked in resonance with Earth, they will pass through opposition every few years. Toutatis is one example. Opposition is the easiest time to spot them as their proper motion is at its greatest, and their brightness is at its greatest.

    Quote Originally Posted by cbacba View Post
    Having a highly eccentric orbit that brings an object to the inner solar system only every few thousand years isn't likely to be one we've seen.
    Those are comets, not asteroids. And yes, they're a big danger. Many that we witness are passing through the inner solar system for the first time.

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