Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A New Explanation for Venus' Retrograde Rotation

  1. Jan 12, 2006 #1
    Consider this scenario: a Mars-size object strikes a glancing blow at Venus's backside that's facing toward the Sun. The resultant debris cloud would then coalesce into a large moon having a retrograde orbit. Tidal friction would then slow down Venus' rotation until it was tidally locked to its moon. Meanwhile Venus' angular momentum would transfer to the moon pushing it into a higher orbit.

    Now, a rough calculation based on Kepler's third law and Earth's geostationary orbit suggests that the geostationary orbit for an Earth-sized planet with a rotation of 243 days (Venus's current sidereal rotation period) would have a radius of about 1.4 million kilometers. However, the L1 point for Venus is only about 1.0 million kilometers. Thus, at some point before true tidal locking occurred, Venus's moon would be captured by the Sun, thus becoming the "planet" known to us as Mercury. Eventually, Mercury settled into its present orbit because of Bode's Law.

    The proposed scenario would account for a number of features:

    1. the eccentricity of Mercury's orbit;
    2. the continental highlands of Venus;
    3. the retrograde rotation of Venus;
    4. that the Earth/Venus resonance is too fast by a factor of 5 (there being five Venusian solar days per Earth/Venus conjunction).

    I know this probably sounds crazy, but is it plausible? Has anyone else heard of such a scenario? (There's nothing in Wikipedia that I can find.)
    Last edited: Jan 12, 2006
  2. jcsd
  3. Jan 13, 2006 #2
    Velichovski's Venus

    There is probably a number of explainations for the retrograde rotion you are observing one of which may involve what I googled on a Dr. Velichovski.

    What actually happened was that there was only one entry on google about Velichovski and it happened to be my post in the archives of the physicsforum!

    Velichovski was a physicist who associated with Einstein and who Einstein listened to with great interest, repeatedly inviting him for coffee, dinner, pipe tobacco and drinks.

    Here is what i posted in the archives about what I read in a biography about Velichovski. Dont' expect to get any info off the net about him since his theories were never included in astro physics or with much regard in physics.

    If you request it I can find the book at some point and transpose some of the many points he makes about why he is satisfied that his theory explains the relative newness of Venus and its odd behaviour when compared to the other planets in the solar system.

    Last edited by a moderator: May 2, 2017
  4. Jan 13, 2006 #3


    User Avatar
    Gold Member

    This is not true. Velikovsky's theories are not accepted amongst people who believe that the scientific method - as opposed to fanciful but sloppy speculation - is the best compass to truth.
  5. Jan 13, 2006 #4
    "And Velikovsky is neither crank nor charlatan—although to state my opinion and to quote one of my colleagues, he is at least gloriously wrong." - Stephen J. Gould

    QuantumCarl, this Velikovsky was quite a character. No doubt if he was still alive to post here in PF he would have been sent to the IR dungeon! :yuck:

    I think you didn't get more results from your search because you misspelled his name. There's a long article on him in Wikipedia.

    And Dave, give the man a break--he's dead. A planet sized collision with Earth is now the orthdox explanation for the origin of the Moon--it just didn't happen in historical times. And Velikovsky died before extraterrestrial impacts from comets and asteroids became widely acknowledged sources of catastrophy on Earth (perhaps in part due to Velikovsky's popularization if the idea that extraterrestrially caused catastrophes are possible). Besides, if he was a buddy of Einstein's, he couldn't have been all bad.

    As for Mercury being an escaped moon of Venus, the biggest hurdle for this hypothesis is the relatively high iron content of Mercury compared to Venus. But this could be explained by scorching from the Sun when Mercury was first captured. After all, scorching has been invoked to explain the high iron content in theories that take it for granted that Mercury formed on its own.
    Last edited: Jan 13, 2006
  6. Jan 13, 2006 #5
    Thanks for the reply. When I find time to find Velikovski's autobiography I'll give exerpts of the astrophysical data he's gathered about Venus, tempurature, rotation, elemental composition and so forth and how he uses these measurements to support his ideas.

    I hope his reliance on historical accounts like those of catastrophic "fire from the sky" and "a scorge of frogs by the river running red" are just a little emotional back-up for some sound astro-physics. If he's Russian, that might explain his passion for this sort of thing.

    Your idea about mercury once being a part of venus is just as plausible as Velikovski's Jupiter-Venus expulsion. Although, in his model, Velikovski sees Venus being ejected as a reaction that helped maintain Jupiter's orbit around the sun.

    What would cause something the size of Mercury to separate from Venus? Would a collision with Mars be sufficent?
  7. Jan 13, 2006 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, I'd say that the biggest hurdle is how Mercury got to its present orbit. You mentioned Bode's Law, but this is not a true law in the scientific sense, it is just an empirical relationship.(one, by the way, that Neptune does not fit into.)

    There is nothing about it that suggests that it has the power to shift existing bodies into prefered positions. If there is anything else to Bode's law, It would be that it predicts the spacing of planets when a system is first formed. In that case Mercury's present fit to the Law would be evidence that points to it having formed close to the orbit it now has. (Neptune's non-fit would then be an indicator that it has been disturbed and moved from its original orbit.)
  8. Jan 15, 2006 #7
    God, this posting here can be a pain in the ass. There's no way that I have been the only one to lose several paragraphes of writing because a wrong button--or even the right button--was pushed. Because it's happened to me many times. .. . . .

    Let's try again:>

    I tested the idea using GravitySimulator. The first time, a highly eccentric orbit inside of the Venus orbit resulted which looked promising. However, the moon wasn't in a retrograde orbit, and the SMA was at 1.4 million km from Venus. So tryed again, this time with a retrograde orbit with the SMA set exactly at the L1 point that I had calculated (1,004,630 Km). I let it run and "Mercury" actually did a few orbits before it was left behind. The planets chased each other and I let it run while I went to the bar to watch the Broncos kick ass. When I came back, the two had collided and fused into one.

    So, anyway, I must be a great scientist since I falsified my own hypothesis.
    :tongue2: :tongue2: :tongue2:
  9. Jan 15, 2006 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    How long did you run it for (in simulation time)? The solar system is chaotic on timescales of millions of years, so if it were longer than that, your result could be different with slightly different initial conditions. Also, did you include only Venus and Mercury? The other planets (out to Jupiter or Saturn, at least) should have a non-negligible impact as well.

    That's why scientists usually wait for quantitative results before they present their work. :tongue2:

    Theories of solar system formation and history are tricky business, partially because of the chaotic behavior of the many-body problem. Even if you were to confirm that your theory could work, you'd likely only be able to give a probability that Mercury would end up where it is.
  10. Jan 16, 2006 #9
    Hey ST, long time, hope your holidays went well. The simulations I've run so far have only been on the order of several thousands to perhaps a few 10s of thousands of years of simulated time. The highest time step I used was 8192. The data for Venus and the Sun was copied from Wikipedia. For the moon I entered a mass about twice the size of Mercury (as the scorching hypothesis conjectures), viz. 0.1 Earth masses. The orbital data for the moon: reference object Venus, inclination 180 (for a retrograde orbit), eccentricity 0, SMA 1004630 Km (L1 distance for Venus), diameter 6223km (based on Venus-like density). Like I said earlier the first run resulted in collision (the new Venus mass was .915 Earth masses). I haven't included any other planets yet--just trying to see what this simple system does before complicating things.

    I let it run last night all night long and seemed to have settled into a fairly stable Pluto-Neptune looking pattern where the moon's orbit almost looked like it was on a transfer orbit between Earth and Venus, and I restarted it this morning and the moon has settled into a stable interior orbit but that looks like its about to change. I never changed the initial conditions: mathematical errors induced by switching the time step are enough to produce different results

    In every case, as the moon is lost it first gets boosted into a slightly higher orbit, then a close encounter with Venus will either send it to the inside, or to a higher orbit, often trading places. Always though, part of the moon's orbit either crosses or comes very close to the Venus orbit. That is the moon never settles into a stable mostly circular orbit anywhere near where present day Mercury is. So I suspect collision might be the most probable outcome. I'll need to really crank up the time step to get into the millions of years though, and I'm not sure if this will reduce the accuracy of the simulation too much. I have attached the simulation file, but I changed file extension to .txt to get the PF brouser to accept it, so anyone who wants to fiddle around with it will need to change the extension back to .gsim .

    But I have already achieved a serendiptous result that I shall now share with the world. Venus might have had a moon in a retrograde orbit that induced the retrograde rotation of Venus, but in the process of transferring angular momentum to the moon, the moon was spun out past the L1 distance, and became lost. For a while the two bodies pursued their separate paths, but pretty much in the same zone, so that at about 500 million years ago, Venus's old moon crashed into Venus causing the massive resurfacing event that we know about. Debris from this catastrophe eventually made its way to Earth and caused the mass extinction at the end of the Cambrian. Also, just by looking at their orbits, I predict that Pluto will be shown to be an escaped moon of Neptune.

    :!!) :!!) :!!)

    Attached Files:

  11. Jan 16, 2006 #10


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I'm a little uncomfortable continuing an open exploration of these ideas of yours Warren, as they seem to me to be close to what we here at PF set up the Independent Research section to cater for.

    (Not to mention that, AFAIK, there is no evidence in the geological record of any impact - or impacts - around the time of the Cambrian mass extinction; no Ir spikes, no shocked quartz, no crater, no ....)
  12. Jan 16, 2006 #11
    OK, I retract the part about the Cambrian mass extinction. The early results of the Magellan probe by Schaber and his colleages suggested that the resurfacing event ended about 500 mypb, which corresponds well with the Cambrian-Ordovician boundary. But more rigorous estimates now place the timing of the resurfacing event closer to 700-800 mybp.
    :grumpy: :mad: :devil:

    Still, I think I have shown that the following are not outside the realm of possibility without recourse to Velikovskyian ideas:

    1. A moon in a retrograde orbit to which Venus was tidally locked would have been well past the L1 point based on Venus's current rotation rate;

    2. Such a moon would then escape from Venus orbit.

    3. The escaped moon could then be free to collide with Venus, perhaps accounting for the resurfacing event, if the catastrophic model of Schaber et al. turns out to be true.
    :cool: :cool: :cool:
    Last edited: Jan 16, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook