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Thread: Mass of the Kuiper Belt

  1. #1
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    Mass of the Kuiper Belt

    Has any one estimated the total mass of the Kuiper Belt? Based on the fact that two members (Pluto and Eris) are in the 1-2 * 1022 kg range, perhaps the mass is around 1023 kg. Would this be a good estimate or is it under/over?

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    I would think this would be well underestimated. If there are two members already having 1-2 1022 kg then you only need a few more objects and you are already at your limit.
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  3. #3
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    Actually this recent paper suggests you are either about right or low by just a factor of 2 depending on model chosen.

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    Wow, totally unexpected for me, I had thought there would be more mass.
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    Must admit I was somewhat surprised too given the amount of objects surmised in the Kuiper Belt. I suspect that Pluto and Eris must be rather large outliers on the mass distribution plot. You can get an awful lot of kilometre sized boulders from an Earth equivalent mass.

  6. #6
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    Thank you loglo!

    That is indeed a very interesting paper!

    Some caveats:
    * Iorio's determination/estimates are consistent with several others, but inconsistent with one (it's higher)
    * the scattered disk (component) is poorly understood - I expect there is quite a bit of scope for there to be more mass - and is, in any case, excluded from the Iorio estimate.

    [ETA: here's the arXiv preprint abstract; you can get the full paper (PDF) from here.]

  7. #7
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    I computed once how much mass the Kuiper Belt would need to explain the Pioneer anomoly. I believe I came up with about 10 Earth masses. But Kuiper Belt mass is never mentioned as a serious explanation for the Pioneer Anomoly, suggesting that the true figure is much less than 10 Earth masses. I'd say your figures are in the ballpark.

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    Does anyone understand the error numbers in Iorio's paper? He gives the total for the Classic Kuiper Belt as 0.033 +/- 0.115 (in Earth mass units) and 0.018 +/- 0.063 for the Plutinos. Why are the error bars larger than the numbers?

    There's a couple things I want to note here. First, the total mass of both groups is actually about 3 * 1023 kg (using 5.972 * 1024 kg for MEarth). Since he didn't calculate the mass of the Scattered KBOs, this figure is lower than the true total.

    Second, he says the Plutinos make up about 20% of the total number of TNOs (and 22% of the objects he computes the mass of), yet their mass is over 1/3 of the total. He doesn't discuss this in his paper. I can think of three reasons why this might be the case.

    1. Plutinos are significantly denser than CKBOs.

    2. Larger objects were more likely to end up in resonance with Neptune.

    3. Smaller Plutinos are more likely to be removed from this class.

    I can't think of a reason why either 1 or 2 would be the case, but perhaps there is some effect which preferentially causes small Plutinos to be perturbed out of their resonance and into Centaur orbits (or ejected). Don't ask me what this effect is, though.

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