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Thread: Delay in New Information about Asteroid 1998 QE2

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    Delay in New Information about Asteroid 1998 QE2

    Phil Plait wrote on May 31st, in Slate, about asteroid 1998 QE2. He explained how the mass and density of the asteroid could be determined with straightforward mathematics, now that it was known to have a moon. He predicted that these figures would be coming in over the next few days.
    That was a bit over three weeks ago. Interesting that the delay should be so long. Perhaps the results were unusual, and had to be questioned, checked, rechecked, and independently vetted. One hopes to learn more of this asteroid soon.
    Last edited by Ross 54; 2013-Jun-22 at 04:27 PM.

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    A more recent article: http://cosmiclog.nbcnews.com/_news/2...est-radio-dish

    But it still just says that the moon will help determine the mass. Presumably, there are higher priority analyses to be done.

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    Have still heard nothing from any of various sources, about further information on asteroid 1998 QE2. I emailed an inquiry to a JPL representative, whose address was attached to an article on the asteroid, which was published some days ago. Will report back here, when I receive a reply.

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    Heard back on my inquiry in less than 24 hours. David Agle of JPL replied: "A very preliminary density estimate ~ 1g/cm^3. So a very high porosity object." An interesting reply. The density of the object seems to fall neatly between the average density of type C asteroids, which this one appears to be (1.4 g/cm^3), and that of comets (~ 0.4 g/cm^3). Type C asteroids typically have about 27 % porosity, or open spaces between rocky fragments. In order to account for such a low density, it appears that about half of this object would have to be taken up by such open spaces.
    Last edited by Ross 54; 2013-Jun-26 at 02:51 PM.

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    Quote Originally Posted by Ross 54 View Post
    Heard back on my inquiry in less than 24 hours. David Agle of JPL replied: "A very preliminary density estimate ~ 1g/cm^3. So a very high porosity object." An interesting reply. The density of the object seems to fall neatly between the average density of type C asteroids, which this one appears to be (1.4 g/cm^3), and that of comets (~ 0.4 g/cm^3). Type C asteroids typically have about 27 % porosity, or open spaces between rocky fragments. In order to account for such a low density, it appears that about half of this object would have to be taken up by such open spaces.
    If the density of the solid (non-open space) part of the comet is the same for both then:
    D * .73 + 0 * .27 = 1.4
    D * (1-x) + 0*x = 1

    1.4/.73 = 1/(1-x)

    Open space = .67 /1.4 = .478..., so I agree, about half

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    Quote Originally Posted by Ross 54 View Post
    Heard back on my inquiry in less than 24 hours. David Agle of JPL replied: "A very preliminary density estimate ~ 1g/cm^3. So a very high porosity object." An interesting reply. The density of the object seems to fall neatly between the average density of type C asteroids, which this one appears to be (1.4 g/cm^3), and that of comets (~ 0.4 g/cm^3). Type C asteroids typically have about 27 % porosity, or open spaces between rocky fragments. In order to account for such a low density, it appears that about half of this object would have to be taken up by such open spaces.
    I wonder if this also means there may be a lot of water ice, or frozen gases, incorporated in this object?
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    Dr. Stewart Ross Taylor has written that-- "Probably 40% of Apollos, Atens, and Amors are extinct comet Nuclei, in which the surface is coated with a thick, dark, nonvolatile lag deposit, which prevents solar heating from releasing any volatile ices left inside." That makes sense in this case, as we've been told the object is very dark. Also, a comet nucleus with much of its ice used up would tend to have a higher bulk density than active comets, but not as high as C class asteroids.
    Last edited by Ross 54; 2013-Jun-27 at 06:16 PM.

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    Looking further into the possibility that 1998 QE2 is a short period (extinct) comet, I see that it has a Tisserand Parameter of 3.24, with respect to Jupiter. This makes it unlikely that it is a Jupiter Family Comet, converted by Jupiter from a much longer orbit. I looked at a list of nearly 500 of these. None had a value this high. All but a dozen were less than 3. in a single case the value was 3.212; the highest of all.
    Last edited by Ross 54; 2013-Jun-28 at 07:21 PM.

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    I was wondering what progress they had made in getting spectrographic data on the asteroid, so as to get a line on what it's made of and how it would be classed, in relation to other asteroids. Had been assuming from the descriptions that it would be Class C, a dark, 'primitive' object, little disturbed since it's origin.
    Contacted Alessondra Springmann, an astrophysicist doing work on this asteroid. She responds that no definite classification has been assigned to the object yet. She added that it is probably somewhere between Class X and Class D. Class X asteroids are mostly metallic objects. Class D is more complex; mixed silicates, carbon compounds, and possibly water ice.
    An interesting mixture of two dissimilar types of objects.
    Last edited by Ross 54; 2013-Jun-30 at 02:58 PM.

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    Given the preliminary density estimate for 1998 QE2 (1 g/cm^3), it seem puzzling that it should appear spectroscopically to be of asteroidal class X or D. Class X has an average density of about 2.9 g/cm^3, and class D around 9.6. If this object is transitional between the two classes, one would expect a density of somewhere around 6. Very puzzling that the spectroscopic data should seem to be so at odds with the dynamically estimated density. I originally thought of a class C object because their average density is more in line with what is known about 1998 QE2.

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    Interesting that 1998 QE2 has been described as a 'primitive' object, little disturbed since its origin. If this is the case, why does its typology, a mixture of different asteroid classes, seem to suggest the complete mergence of two very dissimilar asteroids into one, essentially spherical object?

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    Erratum to my post, #11, July 1st. It should have read: Class X has an average density of about 9.6, and class D about 2.9, instead of the other way around.

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    There had seemed to be some sense that 1998 QE2 was, or would turn out to be a C class asteroid, essentially carbonaceous chondrite material, at least on its surface. I find that some spectra of the object were taken while it was still quite close, on June 5th, with the 5 meter Hale telescope at Palomar observatory. These produced a 'best fit' with class C asteroids.
    The source of data for this recent report, that the object is, instead, transitional between X and D classes is not clear. I have inquired of astrophysicist Alessondra Springmann again, in hopes that she can explain these seemingly contradictory findings.

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    Heard back from Ms. Springmann. In response to my follow-up question, she suggests that different sides of the object may be made up of different materials, thus explaining the seeming contradiction of one observation with the other. Is anyone familiar with a previous instance of an asteroid with one sort of mineral composition on one side, and a very different one on the other side? Does this make sense in a relatively small, loosely consolidated, apparently spherical object?
    Last edited by Ross 54; 2013-Jul-08 at 03:16 PM.

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    It's almost as if a Class C asteroid received debris on one side, from the nearby collision of a class D and a class X asteroid. Odd, though, that the debris didn't persist long enough to cover both sides. QE2 presents both its sides to any given direction, in only a few hours. Has anyone a better explanation for the odd mixing on mineral types on one side, and its difference from the composition of the other side of the object?

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    Now help me out with something. We've seen several objects caught by radars as they pass by. Yet I seem to remember the radar images all looking pretty much the same. The objects all present rather circular, rather than potato shaped. This must be some sort of artifact.

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    The radar beams 'illuminate' a circular area of an asteroid facing it. In any one still image, this would tend to produce the impression of a partially illuminated sphere, in objects of many, merely approximately rounded shapes, such as triaxial ellipsoids. In the case of QE2, an animated series of images showing its rotation seems to show that it presents a rounded shape of about the same radius, no matter which way it turns. This is presumably the basis of the astronomer's remarks, that the object is approximately round.

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    So that wasn't an artifact in that particular case after all.

    Is anyone writing a program to allow other more potato shaped objects to be displayed better? It always amazed me how radar operators in the cold war could distinguish one plane from another due to the shape of a blob.

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    10 gigahertz radar gives better resolution than a few gigahertz and infrared and visual telescopes are much better for asteroid shape than radar. Shape is inferred from changes in the brightness of the blob except when probes gather data from a few thousand kilometers instead of many millions of kilometers. This is especially true for asteroids with a large dimension less than 50 kilometers. Near spherical is likely rare for asteroids of any size. Neil
    Last edited by neilzero; 2013-Jul-15 at 01:54 AM.

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    QE 2 is generally considered to be a loosely consolidated group of pieces, weakly held together by gravity. If this is correct, it would help explain the object's very low density. It would also tend to explain its apparent largely rounded shape. The pieces would jostle about and grind against one another, and so, assume the nearest possible approximation of a sphere.

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    Seven weeks, now since QE2 passed nearest Earth, and about a month since a 'very preliminary' density figure of ~ 1 g/cm^3 was gotten. Even this figure had to be asked for. It had not, and has not since been published in any 'official' online source of which I am aware.
    I recently inquired of JPL about a better defined density figure, but that query went unanswered.
    I'm inclined to think that something about determining the density of this object, or perhaps the results of such work, present a large , and unexpected problem.

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