7 ms·

Is Venus in some way tidally locked to Earth? (2020)

128 points by shmde 3y ago

deleted 3y ago
[deleted]
numlocked 3y ago
Interesting! Both the phenomenon itself, and the fact that there are two totally different explanations in the answers (“yes”, and “no - it’s a coincidence”), and it therefore seems the true answer is “we aren’t sure”.
t8sr 3y ago
tl;dr: Consider the birthday paradox. In astronomy we call these resonances. Sometimes, two seemingly unrelated periodic events will occur together, synchronized by a ratio between some small integers. I think the most typical example is the one they teach you in the first Solar System 101 class to wow you (it works): the 3:2 resonance between the orbits of Pluto and Neptune. Sometimes it might turn out to be a coincidence with more accurate measurements, or when you find evidence that this moment in time might be somehow unusual. For example, Earth and Venus also seem to be in 8:13 orbital resonance, but, in fact probably aren't. On closer inspection, it turns out that there is error of about 0.4% after 8 years and it compounds. It takes a while to compound, but effectively you can't use this "near resonance" to predict where the two will be in their orbits in a few thousand years. In fact, with enough bodies in the solar system and the birthday paradox, there are many compelling candidate resonances with small integer ratios, but the majority of them are probably just random coincidences.
- t8sr 3y ago
  Just to clarify the difference between "true" resonance and a coincidence: True resonance reinforces itself. For example, Pluto speeds up and slows down in its orbit as it passes Neptune and the exchange of energy between the two works out such that the lowest energy state is a 2:3 resonance, so that's where they would end up even if you "poked" the system a little. A coincidence is not self-reinforcing. If you "poked" the system, it would disrupt the ratio and it'd stay disrupted. Sometimes, the preconditions for resonance might disappear, and then you end up with a coincidence at a nearly perfect ratio that slowly drifts afterwards. The opposite also happens.
  - jgalt212 3y ago
    > A coincidence is not self-reinforcing. If you "poked" the system, it would disrupt the ratio and it'd stay disrupted. What would happen if you poked at object at one of the Lagrange points? e.g. the James Webb Space Telescope.
    - fhdkweig 3y ago
      Of the 5 Lagrange points, 2 are stable. If you poke an object at one of the 2 stable points, the object begins to orbit in a circle around that invisible point.
    - sp332 3y ago
      Most Lagrange points are unstable. Only L4 and L5 are stable. https://en.m.wikipedia.org/wiki/Lagrange_point#/media/File%3ALagrange_points2.svg https://en.m.wikipedia.org/wiki/Lagrange_point#/media/File%3...
  - sandworm101 3y ago
    But it is also possible, perhaps likely, that some coincidences are in fact higher-level resonances between groups of planets. These would be multi-body problems that may take thousand or millions of years to react to perturbations. The calculations for these may well be beyond our current capabilities to detect (3+ body problems).
  - deleted 3y ago
    [deleted]
- dr_dshiv 3y ago
  Hypothesis: near orbital resonances are more stable than perfect resonances.
  - t8sr 3y ago
    I mean… no? That makes no sense. You can’t just say “hypothesis: something random”, that’s not how anything works. :)
    - dr_dshiv 3y ago
      First of all— says who? Second of all, it’s not random. In music, near resonances are more consonant than perfect resonances. And, orbital resonances tend to disrupt stability (eg, if earth and Venus were in an orbital resonance, then they would often pull at mercury really hard, potentially pulling it out of orbit). Previously, I opted not to give my rationale for the hypothesis in case someone had any reason to refute it.
      - t8sr 3y ago
        How would anyone even refute a vague statement like that? Secondly, the word "consonant" has many different definitions, so again, your statement could mean almost anything. The concept of consonance has no obvious connection to whether or not a system is stable. "Orbital resonances tend to disrupt stability" - that's not true, especially not the thing about Mercury. The influence of the pair on each other would be great, and either cause the resonance to fall apart or, more rarely, to lock in. But mercury's orbital period is not in a simple ratio with the resonant pair, so nothing would be meaningfully different. Look, I can tell from your profile that you're a professor in some kind of social science. Is it possible that you're, like many people in academia, under the influence of a cognitive bias that makes you think your expertise in one field should somehow transfer into insights in a completely different field? And, again, showing up and just saying "hypothesis: whatever" is something people can either ignore or engage with, but if you really wanted to engage, you would try to say something concrete instead of just making yourself look clever.
- dabluecaboose 3y ago
  Another good example is when you're listening to music in the car and think your turn signal is perfectly in time with the song, only to have it slowly drift off once you notice.
- derefr 3y ago
  I can see how orbital mechanics would lead to these sorts of small-integer ratios being true for arbitrary periods and then disappearing, yet this fact still seems unintuitive/unsatisfying somehow. I think it's because we're so all familiar with quantum electrodynamics now, that it actually seems somewhat counterintuitive that the (stable) orbits of planets aren't quantized valence shells!
- deleted 3y ago
  [deleted]
DoreenMichele 3y ago
Prepare to openly and unabashedly hate on me and hit your downvote button: Some post here at some point did some analysis that concluded that Mercury was "the closest" or something for every planet for some analysis or other because Mercury is closest to the Sun. Both Mercury and Venus are closer to the Sun than Earth is and if you study astrology this means Mercury is never more than one sign away from your Sun sign and Venus is never more than two signs away and both very regularly appear to "run backwards" (called retrograde in astrology). Which is where you got those bizarre and complicated geocentric models of the solar system from before someone said "Oh, wait, if you assume the Sun is at the center of this, not the Earth, then it vastly simplifies everything and makes sense a la Occam's Razor/find the simplest explanation." Astrology and astronomy used to both be studied as one subject under the heading astrologia and astrology means "the study of the stars" and astronomy just means "the naming of the stars" presumably because when the two split it was sort of a pointless hobby for people rich enough to own a telescope and if you found a new one, you got to name it. Anyway, the point being, Venus and the Earth are -- shockingly -- both locked in orbit around the Sun, thus the phrase "solar system," and as a wild assed guess from some ignoramous who mostly is interested in astrology, not astronomy, that there is your so-called "tidal locking" mechanism.
- deleted 3y ago
  [deleted]
- d1sxeyes 3y ago
  It's a known fact that the point all bodies in the solar system orbit around is not actually the centre of the sun, but some point close to the sun, known as the barycentre of the solar system[0]. This moves around based on the exact configuration of the planets (where they are in their orbits).[1] By definition, this barycentre can only be considered 'locally'. For example, there is another 'barycentre' for the whole milky way, and presumably for the whole universe. Mercury is the 'closest' to all planets on average over time due to the fact it is closest to the sun (or more accurately, this barycentre), and due to an unintuitive but completely logical consequence of Mercury having a small orbit[2]. The last paragraph of your comment I was not able to properly understand. It is certainly true that the 'solar system' is made up of objects which rotate around the sun. But that's the definition of 'solar system'. Just as the 'milky way' is made up of objects which rotate together... including the solar system. It's just useful for us to have a term for our local corner of the universe. [0]: https://www.skymarvels.com/gallery/Vid%20-%20Solar%20System%20Barycenter.htm https://www.skymarvels.com/gallery/Vid%20-%20Solar%20System%... [1]: Satellites (both natural and artificial) also orbit this point when you map their path over the course of a full orbit of the body they primarily orbit: e.g. the moon orbits the Earth, but over the course of a year, the moon and Earth together orbit the barycentre of the solar system. [2]: This GIF shows it quite logically: https://engaging-data.com/pages/scripts/orbits/mercury-faster.gif https://engaging-data.com/pages/scripts/orbits/mercury-faste...
angiosperm 3y ago
I like that there was no way even to guess that this coincidence occurred until we became able to scan Venus with radar. Visually, all faces of Venus are indistinguishable. I wonder whether we have the moon to thank for Earth having retained a short day, and the short day for our magnetic field. Big moons of inner terrestrial planets must be vanishingly rare in the galaxy. If terrestrial planets with magnetic fields are uniquely suited to breed up complex life, that might by itself account for the Fermi paradox. But I don't know how to evaluate the notion that our gross moon has protected Earth from the near tidal locking Mercury and Venus suffer.
- chris_j 3y ago
  What is it that would make big moons of terrestrial inner planets vanishingly rare? And how likely is it that a planet without a large moon would fail to retain a short day? Mars has a day of similar length to that of Earth (though no magnetic field worth speaking of...).
- pyinstallwoes 3y ago
  That gets weird when you look up the ancient history of moon as a god and a time before when there was no moon and how it relates to chaos.
  - wildzzz 3y ago
    Ancients also thought solar eclipses were bad omens yet they happen on a predictable basis.
drojas 3y ago
If it is a coincidence then perhaps this case of "correlation is not causation" is explained by both planets having some magnetic interaction with the sun and perhaps the interaction with the sun determines rotational behavior of planets (speculation). I read sometime ago about "magnetic flux ropes" https://www.frontiersin.org/articles/10.3389/fspas.2020.605957/full https://www.frontiersin.org/articles/10.3389/fspas.2020.6059... Also I read time ago there is a "cometary" aspect to venus and it's "tail" touches the earth, which might also be in the same realm of physics (electromagnetic interactions leading to rotational behavior)
NeoTar 3y ago
If you are interested in patterns in the solar-system, then check out the Titus-Bode Law: https://en.m.wikipedia.org/wiki/Titius–Bode_law https://en.m.wikipedia.org/wiki/Titius–Bode_law Basically the inner planets seem to follow a pattern in their spacing from the Sun - and some of the outer-planets which were actually discovered after the law... ...but it's not a great correlation, and you need to have some hacks (e.g. including Ceres as a planet) to make it work... So, mainstream Astronomy has relegated it to the edges of the field, and into the realm of amateurs and crackpots. It's interesting though that apparently a similar pattern in the distances between planets seems to occur in those systems with multiple extrasolar planets that we have observed. But it still may be a mathematical artefact.
- deprecative 3y ago
  To be fair, Ceres was considered a planet at one point and it is now the closest dwarf planet to Earth. So, in that sense it is a planet but it is not a major planet.
  - dr_dshiv 3y ago
    Plus asteroid belt
- akomtu 3y ago
  One way to explain this curiously geometric composition of the solar system is to note the analogy with drum modes or even electron shells: suppose the sun's gravity produces a very slow oscillation that creates a stable pattern of nodes and antinodes, and planets naturally slide into those spots over billions of years.
musicale 3y ago
I knew astrology was real. ;-)

128 points by shmde 3y ago

deleted 3y ago

[deleted]

Interesting! Both the phenomenon itself, and the fact that there are two totally different explanations in the answers (“yes”, and “no - it’s a coincidence”), and it therefore seems the true answer is “we aren’t sure”.

t8sr 3y ago

tl;dr: Consider the birthday paradox. In astronomy we call these resonances. Sometimes, two seemingly unrelated periodic events will occur together, synchronized by a ratio between some small integers. I think the most typical example is the one they teach you in the first Solar System 101 class to wow you (it works): the 3:2 resonance between the orbits of Pluto and Neptune. Sometimes it might turn out to be a coincidence with more accurate measurements, or when you find evidence that this moment in time might be somehow unusual. For example, Earth and Venus also seem to be in 8:13 orbital resonance, but, in fact probably aren't. On closer inspection, it turns out that there is error of about 0.4% after 8 years and it compounds. It takes a while to compound, but effectively you can't use this "near resonance" to predict where the two will be in their orbits in a few thousand years. In fact, with enough bodies in the solar system and the birthday paradox, there are many compelling candidate resonances with small integer ratios, but the majority of them are probably just random coincidences.

t8sr 3y ago
Just to clarify the difference between "true" resonance and a coincidence: True resonance reinforces itself. For example, Pluto speeds up and slows down in its orbit as it passes Neptune and the exchange of energy between the two works out such that the lowest energy state is a 2:3 resonance, so that's where they would end up even if you "poked" the system a little. A coincidence is not self-reinforcing. If you "poked" the system, it would disrupt the ratio and it'd stay disrupted. Sometimes, the preconditions for resonance might disappear, and then you end up with a coincidence at a nearly perfect ratio that slowly drifts afterwards. The opposite also happens.
- jgalt212 3y ago
  > A coincidence is not self-reinforcing. If you "poked" the system, it would disrupt the ratio and it'd stay disrupted. What would happen if you poked at object at one of the Lagrange points? e.g. the James Webb Space Telescope.
  - fhdkweig 3y ago
    Of the 5 Lagrange points, 2 are stable. If you poke an object at one of the 2 stable points, the object begins to orbit in a circle around that invisible point.
  - sp332 3y ago
    Most Lagrange points are unstable. Only L4 and L5 are stable. https://en.m.wikipedia.org/wiki/Lagrange_point#/media/File%3ALagrange_points2.svg https://en.m.wikipedia.org/wiki/Lagrange_point#/media/File%3...
- sandworm101 3y ago
  But it is also possible, perhaps likely, that some coincidences are in fact higher-level resonances between groups of planets. These would be multi-body problems that may take thousand or millions of years to react to perturbations. The calculations for these may well be beyond our current capabilities to detect (3+ body problems).
- deleted 3y ago
  [deleted]
dr_dshiv 3y ago
Hypothesis: near orbital resonances are more stable than perfect resonances.
- t8sr 3y ago
  I mean… no? That makes no sense. You can’t just say “hypothesis: something random”, that’s not how anything works. :)
  - dr_dshiv 3y ago
    First of all— says who? Second of all, it’s not random. In music, near resonances are more consonant than perfect resonances. And, orbital resonances tend to disrupt stability (eg, if earth and Venus were in an orbital resonance, then they would often pull at mercury really hard, potentially pulling it out of orbit). Previously, I opted not to give my rationale for the hypothesis in case someone had any reason to refute it.
    - t8sr 3y ago
      How would anyone even refute a vague statement like that? Secondly, the word "consonant" has many different definitions, so again, your statement could mean almost anything. The concept of consonance has no obvious connection to whether or not a system is stable. "Orbital resonances tend to disrupt stability" - that's not true, especially not the thing about Mercury. The influence of the pair on each other would be great, and either cause the resonance to fall apart or, more rarely, to lock in. But mercury's orbital period is not in a simple ratio with the resonant pair, so nothing would be meaningfully different. Look, I can tell from your profile that you're a professor in some kind of social science. Is it possible that you're, like many people in academia, under the influence of a cognitive bias that makes you think your expertise in one field should somehow transfer into insights in a completely different field? And, again, showing up and just saying "hypothesis: whatever" is something people can either ignore or engage with, but if you really wanted to engage, you would try to say something concrete instead of just making yourself look clever.
dabluecaboose 3y ago
Another good example is when you're listening to music in the car and think your turn signal is perfectly in time with the song, only to have it slowly drift off once you notice.
derefr 3y ago
I can see how orbital mechanics would lead to these sorts of small-integer ratios being true for arbitrary periods and then disappearing, yet this fact still seems unintuitive/unsatisfying somehow. I think it's because we're so all familiar with quantum electrodynamics now, that it actually seems somewhat counterintuitive that the (stable) orbits of planets aren't quantized valence shells!
deleted 3y ago
[deleted]

DoreenMichele 3y ago

Prepare to openly and unabashedly hate on me and hit your downvote button: Some post here at some point did some analysis that concluded that Mercury was "the closest" or something for every planet for some analysis or other because Mercury is closest to the Sun. Both Mercury and Venus are closer to the Sun than Earth is and if you study astrology this means Mercury is never more than one sign away from your Sun sign and Venus is never more than two signs away and both very regularly appear to "run backwards" (called retrograde in astrology). Which is where you got those bizarre and complicated geocentric models of the solar system from before someone said "Oh, wait, if you assume the Sun is at the center of this, not the Earth, then it vastly simplifies everything and makes sense a la Occam's Razor/find the simplest explanation." Astrology and astronomy used to both be studied as one subject under the heading astrologia and astrology means "the study of the stars" and astronomy just means "the naming of the stars" presumably because when the two split it was sort of a pointless hobby for people rich enough to own a telescope and if you found a new one, you got to name it. Anyway, the point being, Venus and the Earth are -- shockingly -- both locked in orbit around the Sun, thus the phrase "solar system," and as a wild assed guess from some ignoramous who mostly is interested in astrology, not astronomy, that there is your so-called "tidal locking" mechanism.

deleted 3y ago
[deleted]
d1sxeyes 3y ago
It's a known fact that the point all bodies in the solar system orbit around is not actually the centre of the sun, but some point close to the sun, known as the barycentre of the solar system[0]. This moves around based on the exact configuration of the planets (where they are in their orbits).[1] By definition, this barycentre can only be considered 'locally'. For example, there is another 'barycentre' for the whole milky way, and presumably for the whole universe. Mercury is the 'closest' to all planets on average over time due to the fact it is closest to the sun (or more accurately, this barycentre), and due to an unintuitive but completely logical consequence of Mercury having a small orbit[2]. The last paragraph of your comment I was not able to properly understand. It is certainly true that the 'solar system' is made up of objects which rotate around the sun. But that's the definition of 'solar system'. Just as the 'milky way' is made up of objects which rotate together... including the solar system. It's just useful for us to have a term for our local corner of the universe. [0]: https://www.skymarvels.com/gallery/Vid%20-%20Solar%20System%20Barycenter.htm https://www.skymarvels.com/gallery/Vid%20-%20Solar%20System%... [1]: Satellites (both natural and artificial) also orbit this point when you map their path over the course of a full orbit of the body they primarily orbit: e.g. the moon orbits the Earth, but over the course of a year, the moon and Earth together orbit the barycentre of the solar system. [2]: This GIF shows it quite logically: https://engaging-data.com/pages/scripts/orbits/mercury-faster.gif https://engaging-data.com/pages/scripts/orbits/mercury-faste...

angiosperm 3y ago

I like that there was no way even to guess that this coincidence occurred until we became able to scan Venus with radar. Visually, all faces of Venus are indistinguishable. I wonder whether we have the moon to thank for Earth having retained a short day, and the short day for our magnetic field. Big moons of inner terrestrial planets must be vanishingly rare in the galaxy. If terrestrial planets with magnetic fields are uniquely suited to breed up complex life, that might by itself account for the Fermi paradox. But I don't know how to evaluate the notion that our gross moon has protected Earth from the near tidal locking Mercury and Venus suffer.

chris_j 3y ago
What is it that would make big moons of terrestrial inner planets vanishingly rare? And how likely is it that a planet without a large moon would fail to retain a short day? Mars has a day of similar length to that of Earth (though no magnetic field worth speaking of...).
pyinstallwoes 3y ago
That gets weird when you look up the ancient history of moon as a god and a time before when there was no moon and how it relates to chaos.
- wildzzz 3y ago
  Ancients also thought solar eclipses were bad omens yet they happen on a predictable basis.

drojas 3y ago

If it is a coincidence then perhaps this case of "correlation is not causation" is explained by both planets having some magnetic interaction with the sun and perhaps the interaction with the sun determines rotational behavior of planets (speculation). I read sometime ago about "magnetic flux ropes" https://www.frontiersin.org/articles/10.3389/fspas.2020.605957/full https://www.frontiersin.org/articles/10.3389/fspas.2020.6059... Also I read time ago there is a "cometary" aspect to venus and it's "tail" touches the earth, which might also be in the same realm of physics (electromagnetic interactions leading to rotational behavior)

NeoTar 3y ago

If you are interested in patterns in the solar-system, then check out the Titus-Bode Law: https://en.m.wikipedia.org/wiki/Titius–Bode_law https://en.m.wikipedia.org/wiki/Titius–Bode_law Basically the inner planets seem to follow a pattern in their spacing from the Sun - and some of the outer-planets which were actually discovered after the law... ...but it's not a great correlation, and you need to have some hacks (e.g. including Ceres as a planet) to make it work... So, mainstream Astronomy has relegated it to the edges of the field, and into the realm of amateurs and crackpots. It's interesting though that apparently a similar pattern in the distances between planets seems to occur in those systems with multiple extrasolar planets that we have observed. But it still may be a mathematical artefact.

deprecative 3y ago
To be fair, Ceres was considered a planet at one point and it is now the closest dwarf planet to Earth. So, in that sense it is a planet but it is not a major planet.
- dr_dshiv 3y ago
  Plus asteroid belt
akomtu 3y ago
One way to explain this curiously geometric composition of the solar system is to note the analogy with drum modes or even electron shells: suppose the sun's gravity produces a very slow oscillation that creates a stable pattern of nodes and antinodes, and planets naturally slide into those spots over billions of years.

musicale 3y ago

I knew astrology was real. ;-)