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Venus Spinning Slower Than Thought

  1. Jul 4, 2012 #1
    Apparantly this one was missed, at least nothing turned up on a search.

    Obviously you can speculate all you want about atmosphere and winds but you can't explain away the loss of angular momentum.

    But then again, a long time ago, when thinking out the box was still allowed, there was a thread speculating about how Venus could have lost its spinning and what happened to the related energy. For those who are familiar with that, there is no reason at all to be 'stumped'.
     
    Last edited: Jul 4, 2012
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  3. Jul 4, 2012 #2
    It's more likely the outer crust has been migrating over the molten interior.

    I've read something in that article about the features on the surface being 20 km from where they should be. A 20 km migration of the crust doesn't seem that much to me, considering Venus' volcanic past, with a lot of its surface covered with lava.
     
  4. Jul 4, 2012 #3
    Oh but before thinking out of the box, one should be thorougly familiar with the box first, to paraphrase Lisab.

    Here is some study material:

    http://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus1.2002.pdf
    http://www.gps.caltech.edu/classes/ge151/references/phillips_and_hansen_1998.pdf [Broken]
     
    Last edited by a moderator: May 6, 2017
  5. Jul 4, 2012 #4
    The best theory I can remember for the rotation of Venus is that the planet was hit by another proto-planet in the distant past, close to the time the solar system was created.
    Such impacts are also attributed for the the creation of Earth's Moon, for an extremely large crater on Mars which covers most of Mars' north side, for the peculiar inclination of Uranus, and maybe other examples.

    As for the current observed slowing down, I don't believe it is possible to slow down an entire planet. You can however slow down the movement of it's outer crust. Whether it's the atmosphere doing this, or some other phenomenon, that's a matter for research.
     
  6. Jul 4, 2012 #5

    DaveC426913

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    It's all those gravity-assists by those Earthers and their probes!

    First air pollution, light pollution and noise pollution - now they've invented celestial mechanical pollution!
     
  7. Jul 4, 2012 #6

    Hurkyl

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    If you believe Wikipedia, the moon lengthens an Earth day by 15 microseconds per year, and the 2004 Indian Ocean earthquake shortened the Earth day by over 2 microseconds.
     
  8. Jul 4, 2012 #7

    Hurkyl

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    Do you have a reference that isn't science entertainment?
     
  9. Jul 5, 2012 #8
  10. Jul 5, 2012 #9
    If Venus has a rather thin crust over a molten layer, that crust can shift under the influence of the atmosphere.
    The thinner the crust, the bigger this effect can be.

    Atmospheric weather and earthquakes only affect the movement of the crust, not of the entire planet.
    Tidal forces slow down the entire planet, but this effect is very very slow.
     
  11. Jul 5, 2012 #10
    Wouldn't the viscosity of the magma also be higher in the areas near the crust because more heat is trapped there than on Earth? Or least the magma might be more completely molten throughout the border areas. The very frequent intrusion of magma onto the planet's surface, not just from volcano tops, is very much evident from the Magellan imaging.
     
  12. Jul 5, 2012 #11

    D H

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    Venus' atmosphere is very weird. Venus as a planet rotates very slowly, once per 243 days, and retrograde with respect to the solar system's angular momentum. Venus' upper atmosphere rotates very quickly, once every four days, and posigrade with respect to the solar system's angular momentum (so retrograde with respect to Venus).

    One obvious (and probably the most obvious) explanation is that there must be some unexplained decades-long variations in Venus' atmosphere that result in transfer of angular momentum between Venus proper and it's atmosphere. The problem is the mechanism. Scientists do not know, and this site is not the place to be making speculations.

    We do see this transfer of angular momentum between planet and atmosphere right here on the Earth. The Earth's rotational rate varies with the seasons (the Earth slows down a tiny bit in January and February, then speeds up again), and it turns out that the atmosphere is the key cause.

    We also see decadal variations in the Earth's rotation rate. Those variations remain an unexplained mystery, at least to some extent. There are too many possible culprits, too little data to narrow down the cause. We have millions and millions of measurements for the Earth and yet the Earth's rotation is not a fully solved problem. We have orders of magnitude fewer measurements of Venus. Is it any surprise that Venus' rotation is not a fully solved problem?
     
  13. Jul 5, 2012 #12

    Hurkyl

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    So grain of salt, and all of that. You indicate there has been no further news, so I'm forced to conclude that there really wasn't anything noteworthy.


    I must say, I'm rather befuddled that claims of the day having slowed down were made by observing a 0.00186% error in an extrapolation from 20 year old data rather than, y'know, re-measuring the rotation of Venus.

    Amusingly, the error in the length of the Venusian day between the two articles is nearly as large as the reported error of 6.5 minutes.

    IMO the fact we haven't heard anything again is far more likely to be publication bias than anything else: that the announcement was made prematurely, and nobody thought it was worth publishing a retraction.

    Or, it is true but uninteresting, and the fact it was even mentioned in the first place is an anomaly.
     
  14. Jul 5, 2012 #13

    D H

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    Venus has a thick crust over a solid mantle. Planetary mantles are solid, not liquid.
     
  15. Jul 5, 2012 #14
    Parts of the Earth's mantle are made of "plastic flowing rock".
    I've seen no evidence for "Venus has a thick crust over a solid mantle". Do you have a reference for that ?

    You're obviously not an expert on this subject, but as you're a moderator you give infractions and your words on a subject your knowledge seems limited on, are supposed to carry weight.
     
  16. Jul 5, 2012 #15
    About the data, the article states:

    I learned on school that if no further details are given, one has to assume that the error margin is equal to the last digit: 243.01865 +/- 0.00001, that's almost 9 seconds.

    However

    That's well over an order of magnitude compared to the error margin

    Furthermore it's interesting to understand how the accuracy in astronomy and space exploration can decay over time, when far before Magellan, success or failure depended on many more digits accuracy.
     
    Last edited: Jul 5, 2012
  17. Jul 5, 2012 #16

    Hurkyl

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    But how confident can one really be in that assumption?

    But it's interesting to note that web searching for the figure already shows much greater error than that. The two articles you linked show 243.015 and 243.0185. Wikipedia reports the latter. NASA's page on Venus says 243.018, and also reports the figure in hours: 5832.4 -- a figure with listed precision three digits less than yours!

    I could not find any references that have error bounds on this figure.

    Incidentally, your post is the only Google hit for "243.01865 venus".
     
  18. Jul 5, 2012 #17

    D H

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    I'll give you the benefit of the doubt here and assume you meant 243.0185 ± 0.0001 days. The ESA article said 243.0185 days, not 243.01865, and your 9 seconds is just about 0.0001 days.

    That said, that's a bad assumption. You need to look deeper if you aren't given further details and you need those details. You might have just gotten lucky with that assumption of a 9 second error. The scientific literature is always a good place to look deeper.


    The latter figure is correct. The NatGeo article linked in the OP made the opposite mistake that Andre did. They omitted a digit.

    That site is for kids!

    From Davies et al., The Rotation Period, Direction of the North Pole, and Geodetic Control Network of Venus, Journal of Geophysical Research, 97:E8 (1992) DOI:10.1029/92JE01166 http://www.agu.org/pubs/crossref/1992.../92JE01166.shtml

    "A rotation period estimate of 243.0185 ± 0.0001 days was determined via the ephemeris improvement technique applied simultaneously to two overlapping orbit blocks with many common points and separated by two full Venus rotations."
     
  19. Jul 6, 2012 #18
    Sorry about the typo. Obviously I hit two keys with that figure and overlooked it.

    And indeed that was a too hasty publication of ESA. They should have investigated first and then they would have quickly found this.

    That's consistent with the 6.5 minutes, but if that would have been the average decay in spinning since Magellan, then the last measurements would have to be much slower. Obviously Magellan was not accurate.

    Sorry about the fuss.
     
  20. Jul 6, 2012 #19

    D H

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    Andre, ESA didn't miss your "this". Your this is a conference paper on some preliminary results from the VIRTIS, one of the scientific instruments aboard the Venus Express. Your this is not just consistent with that reported 6.5 minute change in Venus' rotation period, it is the source of that reported change.

    The problem is that your this was just a conference paper, the finding was but one part of that paper, and the finding was preliminary. I suspect that there's a journal paper somewhere in the pipeline, particularly since this change has now been confirmed independently. Problem: We don't know if there is such a paper. The best thing to do at this point is to wait. If a paper comes out, great. We can continue the discussion then.
     
  21. Jul 6, 2012 #20
    I'm confused. Maybe I should have quoted this sentence:

    .

    I wonder if somebody at ESA had picked up the phone and did the same, wouldn't they have brought out another story?

    Also (oh please don't ley me make such a horrible typo again...) the difference between 234.023 and 234.0185 days, 0.0045 days is 6 min and 29 sec. So if Margot sees that 'now' too (2007 - 2009) - and the difference in real and assumed position of the geography -as per Magellan- is consistent with an average slowdown of 6:30 min per evolution, then, expecting a gradual decay, the first revolution after Magellan would not have been so much less, hence the last revolutions would have been much slower ie some 13 minutes less - to meet that average. But obviously that's not what Margot appears to have observed. So things seems only consistent if Magellan was just off by that bit.
     
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