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I disagree with assumption that year length has stayed constant the past 70 million years. The Earth experiences tidal friction from the Sun just like the Moon

I disagree with assumption that year length has stayed constant the past 70 million years. The Earth experiences tidal friction from the Sun just like the Moon and Earth affect each other. I am guessing the year lengthening effect slower than month & day lengthening because Suns tidal force is a third of Moons. In addition Earth year may have changed during the Great Solar System Reconfiguration Event when Jupiter and the other gaseous planets hypothesized to have migrated outwards from orbits closed to the Sun. This may have happened 3.8 billion years ago causing increase of craters on the terrestrial planets at that time. https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html https://www.nasa.gov/topics/solarsystem/features/young-jupit...

pfdietz 7y ago
The energy required to change the length of the year is very large. Solar tides could transfer some energy from the Earth's rotation to the Earth's revolution, but even tapping all that energy (leaving the Earth tidally locked to the Sun) would not change the year length very much,
- raxxorrax 7y ago
  It is basically defined by distance to the sun since it has ~99.8 of all mass of the solar system, so the change of Jupiters orbit would have a large effect (edit: for Jupiter).
- pdonis 7y ago
  > Solar tides could transfer some energy from the Earth's rotation to the Earth's revolution No, they can't. See my other response just upthread.
  - pfdietz 7y ago
    I have responded to that response and pointed out it cannot be correct.
    - pdonis 7y ago
      See my response in that other subthread.
      - pfdietz 7y ago
        It was a cloud of obfuscation where you never admitted your statement was wrong and violates conservation of angular momentum.
raxxorrax 7y ago
Interesting link. I wonder how that actually went down, since Jupiter and the other gas giants have relatively circular orbits. Is it just the gravity exchange of all the planets together? Quite difficult maneuver to just adjust your orbit height I would think.
- saagarjha 7y ago
  Interaction with gas in the protoplanetary disk, apparently.
- Balgair 7y ago
  It's called the Nice Model: https://en.wikipedia.org/wiki/Nice_model https://en.wikipedia.org/wiki/Nice_model Edit: Basically, the gas giants started really close into the sun but later moved outwards. We see a lot of other systems with gas giants close into their suns right now. In the Nice model, the larger gas giants had their orbits move slowly outwards, causing havoc in our system. This is possibly when the Moon was formed. It's still a lively debate, as we have not yet found Planet X yet. TLDR: Fund NASA more.
saagarjha 7y ago
You sure about the 3.8 billion number? That seems far too recent for any gradual, but drastic changes in orbits to have been possible.
- njarboe 7y ago
  There is evidence from the Moon that is was heavily cratered from about 4.1 to 3.8 billion years ago. What caused this is debated, but one leading theory is the Jupiter and Saturn got into a 2:1 resonance at that time and highly disturbed everything in the Solar System (well, except the Sun)[1]. It is even called the Late Heavy Bombardment, highlighting the unexpected recent age of the event. [1]https://en.wikipedia.org/wiki/Late_Heavy_Bombardment https://en.wikipedia.org/wiki/Late_Heavy_Bombardment
- Sharlin 7y ago
  Recent? It was only ~700 million years after the formation of the Solar system.
pdonis 7y ago
> I disagree with assumption that year length has stayed constant the past 70 million years. It's not an assumption, it's what our best current data tells us. We have abundant evidence of the length of the Earth's day changing--this article is certainly not news, we have known for decades that the Earth's rotation has been gradually slowing over the past few billion years. We have no evidence of the length of the Earth's year changing significantly, and calculations agree with that (see below). > The Earth experiences tidal friction from the Sun just like the Moon and Earth affect each other. I am guessing the year lengthening effect slower than month & day lengthening because Suns tidal force is a third of Moons. The size of the tidal bulge on the Earth due to the Sun is about a third of that due to the Moon. But that is not at all the same as the slowing of the Earth's year due to the Sun's tides being about a third of the slowing of the Earth's day due to the Moon's tides. The situations are very, very different. In the case of the Earth-Moon system, tidal friction causes angular momentum to be transferred from the Earth to the Moon. This slows the Earth's spin and increases the radius of the Moon's orbit. In the case of the Earth-Sun system, tidal friction can't transfer angular momentum from the Earth's spin to the angular momentum of the Earth's orbit about the Sun, because the Earth is not orbiting itself; the mechanism that transfers angular momentum from the Earth's spin to the Moon's orbit about the Earth simply does not apply to the Earth's orbit about the Sun. In fact, while the Sun's tidal friction does make the Earth's spin slow down a little more than it would due to the Moon alone, the result of this is to make the radius of the Moon's orbit increase a little more than it would if the Earth-Moon system were alone in space. In other words, the Sun's tidal friction simply augments the Moon's tidal friction in driving the same mechanism, transferring angular momentum from the Earth's spin to the Moon's orbit about the Earth. There is no transfer of angular momentum from the Earth's spin to the Earth's orbit about the Sun.
- pfdietz 7y ago
  "In the case of the Earth-Sun system, tidal friction can't transfer angular momentum from the Earth's spin to the angular momentum of the Earth's orbit about the Sun, because the Earth is not orbiting itself; the mechanism that transfers angular momentum from the Earth's spin to the Moon's orbit about the Earth simply does not apply to the Earth's orbit about the Sun." This argument cannot be correct. Suppose the sun were a point mass. It would still have tides at Earth, just like the real Sun does, but the interaction would not be able to cause any change to its spin. So, by conservation of angular momentum, if the Earth loses rotational angular momentum, that MUST be transferred to orbital angular momentum. The mechanism of course still exists. The Earth and Moon orbit each other; the Sun and Earth orbit each other. The bulge on the Earth induced by the Moon accelerates the Moon, and the bulge on the Earth induced by the Sun accelerates the Sun.

pfdietz 7y ago

The energy required to change the length of the year is very large. Solar tides could transfer some energy from the Earth's rotation to the Earth's revolution, but even tapping all that energy (leaving the Earth tidally locked to the Sun) would not change the year length very much,

raxxorrax 7y ago
It is basically defined by distance to the sun since it has ~99.8 of all mass of the solar system, so the change of Jupiters orbit would have a large effect (edit: for Jupiter).
pdonis 7y ago
> Solar tides could transfer some energy from the Earth's rotation to the Earth's revolution No, they can't. See my other response just upthread.
- pfdietz 7y ago
  I have responded to that response and pointed out it cannot be correct.
  - pdonis 7y ago
    See my response in that other subthread.
    - pfdietz 7y ago
      It was a cloud of obfuscation where you never admitted your statement was wrong and violates conservation of angular momentum.

raxxorrax 7y ago

Interesting link. I wonder how that actually went down, since Jupiter and the other gas giants have relatively circular orbits. Is it just the gravity exchange of all the planets together? Quite difficult maneuver to just adjust your orbit height I would think.

saagarjha 7y ago
Interaction with gas in the protoplanetary disk, apparently.
Balgair 7y ago
It's called the Nice Model: https://en.wikipedia.org/wiki/Nice_model https://en.wikipedia.org/wiki/Nice_model Edit: Basically, the gas giants started really close into the sun but later moved outwards. We see a lot of other systems with gas giants close into their suns right now. In the Nice model, the larger gas giants had their orbits move slowly outwards, causing havoc in our system. This is possibly when the Moon was formed. It's still a lively debate, as we have not yet found Planet X yet. TLDR: Fund NASA more.

saagarjha 7y ago

You sure about the 3.8 billion number? That seems far too recent for any gradual, but drastic changes in orbits to have been possible.

njarboe 7y ago
There is evidence from the Moon that is was heavily cratered from about 4.1 to 3.8 billion years ago. What caused this is debated, but one leading theory is the Jupiter and Saturn got into a 2:1 resonance at that time and highly disturbed everything in the Solar System (well, except the Sun)[1]. It is even called the Late Heavy Bombardment, highlighting the unexpected recent age of the event. [1]https://en.wikipedia.org/wiki/Late_Heavy_Bombardment https://en.wikipedia.org/wiki/Late_Heavy_Bombardment
Sharlin 7y ago
Recent? It was only ~700 million years after the formation of the Solar system.

pdonis 7y ago

> I disagree with assumption that year length has stayed constant the past 70 million years. It's not an assumption, it's what our best current data tells us. We have abundant evidence of the length of the Earth's day changing--this article is certainly not news, we have known for decades that the Earth's rotation has been gradually slowing over the past few billion years. We have no evidence of the length of the Earth's year changing significantly, and calculations agree with that (see below). > The Earth experiences tidal friction from the Sun just like the Moon and Earth affect each other. I am guessing the year lengthening effect slower than month & day lengthening because Suns tidal force is a third of Moons. The size of the tidal bulge on the Earth due to the Sun is about a third of that due to the Moon. But that is not at all the same as the slowing of the Earth's year due to the Sun's tides being about a third of the slowing of the Earth's day due to the Moon's tides. The situations are very, very different. In the case of the Earth-Moon system, tidal friction causes angular momentum to be transferred from the Earth to the Moon. This slows the Earth's spin and increases the radius of the Moon's orbit. In the case of the Earth-Sun system, tidal friction can't transfer angular momentum from the Earth's spin to the angular momentum of the Earth's orbit about the Sun, because the Earth is not orbiting itself; the mechanism that transfers angular momentum from the Earth's spin to the Moon's orbit about the Earth simply does not apply to the Earth's orbit about the Sun. In fact, while the Sun's tidal friction does make the Earth's spin slow down a little more than it would due to the Moon alone, the result of this is to make the radius of the Moon's orbit increase a little more than it would if the Earth-Moon system were alone in space. In other words, the Sun's tidal friction simply augments the Moon's tidal friction in driving the same mechanism, transferring angular momentum from the Earth's spin to the Moon's orbit about the Earth. There is no transfer of angular momentum from the Earth's spin to the Earth's orbit about the Sun.

pfdietz 7y ago
"In the case of the Earth-Sun system, tidal friction can't transfer angular momentum from the Earth's spin to the angular momentum of the Earth's orbit about the Sun, because the Earth is not orbiting itself; the mechanism that transfers angular momentum from the Earth's spin to the Moon's orbit about the Earth simply does not apply to the Earth's orbit about the Sun." This argument cannot be correct. Suppose the sun were a point mass. It would still have tides at Earth, just like the real Sun does, but the interaction would not be able to cause any change to its spin. So, by conservation of angular momentum, if the Earth loses rotational angular momentum, that MUST be transferred to orbital angular momentum. The mechanism of course still exists. The Earth and Moon orbit each other; the Sun and Earth orbit each other. The bulge on the Earth induced by the Moon accelerates the Moon, and the bulge on the Earth induced by the Sun accelerates the Sun.