# Beware the tidal bulges: We'll be devoured very soon

1. Feb 29, 2008

### arildno

According to this article, we'll be gobbled up by the Sun in the (approximately) imminent future, since the mutual bulging of the Sun and Earth from gravitational attraction will in effect slow Earth's motion around the Sun, causing us to die horribly as we spiral inwards.
That's it, folks, the end is near.
http://www.space.com/scienceastronomy/080226-vaporized-earth.html

2. Feb 29, 2008

### Staff: Mentor

I believe that is after the sun becomes a red giant in about 5 billion years or so. Hmmmm.

I'll probably be somewhere else by then.

3. Feb 29, 2008

### arildno

Don't count on it.

4. Feb 29, 2008

### Jimmy Snyder

Take it easy and never bet on disaster unless you are writing a book about it. I bet $1 million that the Earth will not be swallowed up by the sun in 7.6 billion years.$500,000 that it won't happen in 8.6 billion years.

5. Feb 29, 2008

### BobG

That seems counter-intuitive. The Sun's equator rotates about once every 27 days and the Earth takes 365 days to complete an orbit. Tidal forces should speed up the Earth, taking it further from the Sun - just the way the ocean tides speed up the Moon in its orbit.

The motion of the Sun's surface is a little more complicated and surface gases probably don't get pulled by the underlying gases quite the same way that the ocean bed pulls the tides out from under the Moon, but I wouldn't have expected the Sun's surface to slow the Earth.

6. Feb 29, 2008

### Staff: Mentor

Only if gravitational field can provide a shear force, as opposed to a direct (point to point) force.

7. Feb 29, 2008

### D H

Staff Emeritus
I agree. Did they simply get the effect backwards? This statement, "'Just as the Earth is pulling on the sun's bulge, it's pulling on the Earth, and that causes the Earth to slow in its orbit,' Smith said. 'It will spiral back and finally end up inside the sun.'" certainly makes it sound like they Smith and co. are talking about tidal locking.

This statement is also puzzling: "In addition, the gas that the sun expels will also drag Earth inward toward its demise." This can only mean that heliospheric drag overbalances the reduction in gravitational acceleration due to the reduced mass of the Sun. However, the article ends with "Smith's findings have been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society," which can only mean that the article passed peer review.

8. Feb 29, 2008

### Poop-Loops

Angular momentum has to be conserved. If the Earth speeds up around its own axis like they predict, it will have to orbit closer to the sun to compensate.

Same deal with the Moon slowing its own orbit, therefore moving further away from the Earth.

9. Feb 29, 2008

### D H

Staff Emeritus
Arxiv entry:

http://arxiv.org/abs/0801.4031
According to these solar evolution models, the closest encounter of planet Earth with the solar cool giant photosphere will occur during the tip-RGB phase. During this critical episode, for each time-step of the evolution model, we consider the loss of orbital angular momentum suffered by planet Earth from tidal interaction with the giant Sun, as well as dynamical drag in the lower chromosphere. We find that planet Earth will not be able to escape engulfment, despite the positive effect of solar mass-loss. In order to survive the solar tip-RGB phase, any hypothetical planet would require a present-day minimum orbital radius of about 1.15 AU.​

10. Mar 2, 2008

### BobG

They explain this almost right off the bat. As the Sun expands, its moment of inertia increases and it's rotation rate decreases - drastically, even if it takes a long time to get to these drastically reduced rates.

Eventually the rotation rate of the Sun is slower than the Earth's mean motion around the Sun and the Earth is having to drag the Sun's tidal bulge around behind it - hence the eventual decay of the Earth's orbit.

11. Mar 2, 2008

### Schrodinger's Dog

I'm betting we'll either be flung into the blackhole in the centre of the Galaxy or out into space when we collide with Andromeda in a few billion years.

Because of this I'm not making plans past about 4 billion years.

12. Mar 2, 2008

### wolram

I wonder how much my pension will be worth in four billion years.

13. Mar 2, 2008

### Staff: Mentor

I've made my reservation at Milliway's.

14. Mar 2, 2008

### Schrodinger's Dog

Alot, don't worry I obviously have looked into it. You'll be more than covered, although, it might be in dirt 86 feet under.

Me too, well it's never to soon or too late to book.

15. Mar 2, 2008

### Poop-Loops

Wouldn't Earth become uninhabitable way before we get sucked into the Sun? Like, even before we get to where Venus is now, we'd be toast (even not including the green house gases that Venus has).

16. Mar 2, 2008

### BobG

Has any species existed for even a million years? I don't think there's any chance humans will still be around. We might be smarter than other species, but I don't think we're the first immortal species in the history of Earth.

17. Mar 2, 2008

### Art

I think crocodiles hold the record at 200 million years.

18. Mar 3, 2008

### Math Jeans

You know, we will reach a point in technology where our advances have given the general population the ability to modify atoms and potentially make homemade atomic bombs.

I think at that point someone will destroy the earth, and I'm predicting that it will happen within another 1000 years.