Hypothetical Question about Earth's Distant Future

by scifi5
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scifi5 is offline
Oct19-10, 10:06 AM
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I am not a physicist and I am writing a fictious story about earth's distant future so I would like to base it as possibly close to a plausible scenario. Therefore I ask for your help.

Assume that the moon is blown up. Would that cause the earth's rotation to slowly fade away? And if yes how long would that take?

When will the sun be a white dwarf and what would the earth's state be by then? Would earth have been swallowed during the giant phase or not? Would it's rotation change by the sun's transformation?

If the sun turns to a white dwarf will the habitable zone shrink in diameter and will earth be left outside it?

If one side is constantly facing the white dwarf how will that affect the climate? Will one side be inflamed or more like a dessert? Would the oceans evaporate?

In the twilight zone ring between the two sides could vegetation exist without a day/night cycle?

Thank you in advance and I apologise if hypothetical and uninformed questions are off topic.
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Andre is offline
Oct19-10, 12:10 PM
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Well, It is the mark of an educated mind to be able to entertain a thought without accepting it according to Aristotle.

How would one "blow up" the moon? There will be plenty of gravitational interactions possible, if you scatter it to pieces in all directions, a lot will land on earth, most debris could form a saturnus like ring, but maybe mutual gravity might have it cluster together eventually maybe forming a new moon again. I don't know. Modellers will likely love that kind of exercise.

However a moonless earth may have a distinct resonance problem between the precession cycle and the obliquity cycle. The gravity of the moon is causing the precession cycle to be much faster (26 Ka) than the obliquity cycle (41 ka). Without that moon the precession would slow down and could get to resonate with the obliquity cycle, leading to a chaotic spin with extreme inclinations of the spin axis, as explained here.

It is hypothized that this has happened to Venus, ultimately making it lose its spin

that's it for now
scifi5 is offline
Oct19-10, 12:49 PM
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Thank you for the links and the insight.

Is there a way to estimate roughly how long would a moonless earth's chaotic to finally no spin scenario would take? Or at least make up a timeframe that is believable?

Evo is offline
Oct19-10, 01:04 PM
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Hypothetical Question about Earth's Distant Future

Here's an article for you. You know that the moon drifts farther away from us every day?

What If the Moon Didn't Exist? http://www.astrosociety.org/educatio...tnl/33/33.html

To answer your question about the sun. http://curious.astro.cornell.edu/question.php?number=48
scifi5 is offline
Oct19-10, 01:27 PM
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Thank you Evo, very helpful reads both of them!

The sun has about 4.5 billion years before it starts the giant phase. I wonder how long the moon has til it breaks free from the earth.
Evo is offline
Oct19-10, 01:41 PM
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Quote Quote by scifi5 View Post
Thank you Evo, very helpful reads both of them!

The sun has about 4.5 billion years before it starts the giant phase. I wonder how long the moon has til it breaks free from the earth.
The moon won't break free. Here are two slightly different views on the subject.

Because the Earth-Moon system shares angular momentum, which always is conserved, the Moon receives the energy Earth loses. This boosts the Moon to a higher orbit, currently pushing it 1.25 inches farther away each year. The higher orbit also makes it move slower. Eventually, Earth's rotation and the Moon's revolution will match — both will be 40 days long.
Then, for millions of years, one side of Earth will face the Moon. Half the world will watch the Moon hover above for what seems like forever, while the other half will never see it. Who gets the Moon: China or us? No way to know — the continents will have drifted into new patterns by then.
This stable situation is where the story might end, except the Sun has something to say about it, too. Today, the Sun's tidal pull on Earth is only half as strong as the Moon's. But as the Moon departs, the Sun grows relatively more influential.

Ultimately, it makes Earth spin even slower than its new once-a-month rotation. Angular momentum then harasses the Moon again, this time by robbing it of energy. Thus begins the era when the Moon starts falling toward us.

Fortunately for humanity's fate, the Moon will break apart before it reaches 10,000 miles (16,000 kilometers) away because its silicate rocks are only half as dense as Earth's heavier materials.
Voilà! Earth gets a ring even more glorious than Saturn's. Pencil it in around 3 billion years from now.

And then NASA.

Moon Leaves Earth's Gravity?
Will the Moon leave the Earth's gravity?
The Moon will not leave the Earth's gravity, even though the orbit of the Moon is increasing slightly. The Earth's rotation is slowing down (due to "tidal braking"), and to conserve angular momentum the Moon is accelerating. The Moon's orbit increases by about 3 cm/year.

The Earth and the Moon eventually will be "locked" together with each only having one side constantly facing the other. (Right now the same side of the Moon faces the Earth, but all sides of the Earth see the Moon. In the future this will not be true!) Life on Earth will be quite different then, but this won't occur for billions of years yet. When it does occur, the Moon's orbit will be 50% larger than it is now, and a month will be about 50 days.

Dr. Louis Barbier


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