What if Earth's day was only 85 minutes long?

[Mr Shifty]

In other words, what if the Earth spun fast enough that the velocity of objects on the Earth's surface at sea level was equal to the orbital velocity at that point? Could we all fly, or at least hover above the ground? Throwing a baseball would put it into orbit? I'm not sure about all the implications. Is this even possible? Has it been done in sci-fi?

[HarvesteR]

In real life, the centrifugal force would probably throw everything out, and the planet would disintegrate... but that's a pretty boring answer.

I tried this in KSP once, where such trivial matters aren't an issue, and sped up Kerbin's rotation to see the effects.

Assuming the planet is able to hold in one piece (as Kerbin did), yes, the rotating frame forces would effectively work to cancel out gravity. Throwing a baseball eastwards would send it on a slightly higher orbit than your own (you'd be orbiting too), and throwing it westward would send it on an impact course.

Of course, all that fun would only happen at the equator... As latitudes get higher, this effect becomes less pronounced, and at the pole you'd probably just get motion sickness from looking at the stars

Cheers

[ZedNova]

I don't think we'd fly, and i imagine it would look like the movie "2012" only alot worse.

[maltesh]

The planet would come apart. Gravity is the only thing holding the Earth together,and as it bulged at the equator from this tremendous spinning, large chunks of the planet would be sloughed off into elliptical orbits. The atmosphere would escape completely. You'd eventually reach an equilibrium point where enough of the angular momentum has been transferred that what remains of the Earth is spinning slowly enough that things at the surface aren't drifting off into space, but at that point, there is probably nobody left to throw baseballs.

[Jokurr]

I do not think that would be possible, the planet would be able to form. Though if you suspend your disbelief and we somehow had the earth as we know it rotating that fast, I believe you would have a zero g environment at the equator, with gravity increasing as you move towards the poles, where the gravity would be 1g. Assuming that the atmosphere had the same composition as it does now (it probably wouldn't), you would not be able to put a baseball in orbit, due to drag. Though once the baseball’s speed was reduced to zero from drag, it would just float where it stopped (assuming you hit it along the equator).

[WestAir]

So right now, in reality, we weigh more at the poles than we do at the equator because of the Earths spin?

[NovaSilisko]

In addition to Harv, I more recently ran a small experiment for a possible future planet or moon. There are a lot of issues to work out, but it's pretty weird and fun to play with. 70% of the planet is a continuous hill due to its oblateness. It rotates so fast (12 minutes I think) that at the equator, gravity is only 0.01g on the higher mountains. At the poles, it's 1.7g. I tried driving a rover from the equator to the pole, but because of the extreme centrifugal force, you begin rolling uphill as soon as you drive off the equator. If you can escape this, though, you'll then start accelerating downhill at an extreme velocity due to the ever increasing gravity and incredibly steep terrain. Needless to say my rover didn't last long.

On a related note, there's nothing stopping a planet from forming like this if it's made of malleable enough materials - ex. ice. As long as the equatorial rotation velocity is less than orbital velocity, it will retain material. If it's above orbital velocity, then that material is flung off into space, and the planet remains at a specific size. This sort of happens around two of Saturn's moons http://en.wikipedia.org/wiki/Atlas_(moon) http://en.wikipedia.org/wiki/Pan_(moon). Haumea, perhapts more aptly, is also squashed due to a rapid rotation http://en.wikipedia.org/wiki/Haumea_(dwarf_planet)

Bonus http://en.wikipedia.org/wiki/Mission_of_Gravity

Edited May 29, 2013 by NovaSilisko

[Jokurr]

So right now, in reality, we weigh more at the poles than we do at the equator because of the Earths spin?

Technically yes, though the difference is negligible.

[Mr Shifty]

Hey, thanks Nova! And now I have a new sci-fi novel in the to-be-read stack.

[Arrowstar]

In addition to Harv, I more recently ran a small experiment for a possible future planet or moon. There are a lot of issues to work out, but it's pretty weird and fun to play with. 70% of the planet is a continuous hill due to its oblateness. It rotates so fast (12 minutes I think) that at the equator, gravity is only 0.01g on the higher mountains. At the poles, it's 1.7g. I tried driving a rover from the equator to the pole, but because of the extreme centrifugal force, you begin rolling uphill as soon as you drive off the equator. If you can escape this, though, you'll then start accelerating downhill at an extreme velocity due to the ever increasing gravity and incredibly steep terrain. Needless to say my rover didn't last long.

On a related note, there's nothing stopping a planet from forming like this if it's made of malleable enough materials - ex. ice. As long as the equatorial rotation velocity is less than orbital velocity, it will retain material. If it's above orbital velocity, then that material is flung off into space, and the planet remains at a specific size. This sort of happens around two of Saturn's moons http://en.wikipedia.org/wiki/Atlas_(moon) http://en.wikipedia.org/wiki/Pan_(moon). Haumea, perhapts more aptly, is also squashed due to a rapid rotation http://en.wikipedia.org/wiki/Haumea_(dwarf_planet)

Bonus http://en.wikipedia.org/wiki/Mission_of_Gravity

Oh please, please, implement something like this in the future. That would be extremely awesome to play around with.

[AHO]

In addition to Harv, I more recently ran a small experiment for a possible future planet or moon. There are a lot of issues to work out, but it's pretty weird and fun to play with. 70% of the planet is a continuous hill due to its oblateness. It rotates so fast (12 minutes I think) that at the equator, gravity is only 0.01g on the higher mountains. At the poles, it's 1.7g. I tried driving a rover from the equator to the pole, but because of the extreme centrifugal force, you begin rolling uphill as soon as you drive off the equator. If you can escape this, though, you'll then start accelerating downhill at an extreme velocity due to the ever increasing gravity and incredibly steep terrain. Needless to say my rover didn't last long.

On a related note, there's nothing stopping a planet from forming like this if it's made of malleable enough materials - ex. ice. As long as the equatorial rotation velocity is less than orbital velocity, it will retain material. If it's above orbital velocity, then that material is flung off into space, and the planet remains at a specific size. This sort of happens around two of Saturn's moons http://en.wikipedia.org/wiki/Atlas_(moon) http://en.wikipedia.org/wiki/Pan_(moon). Haumea, perhapts more aptly, is also squashed due to a rapid rotation http://en.wikipedia.org/wiki/Haumea_(dwarf_planet)

Bonus http://en.wikipedia.org/wiki/Mission_of_Gravity

That's awesome! Do you think you could post a screenshot?

[AHO]

Crap, hope I didn't derail the thread...

[Brabbit1987]

If Earth's day was only 85 minutes long each year would have 6,183.5 days a year I believe. This would also mean everyone would have a much more unique birthday, only about 1,132,045 others would share the same day.

[Banbite]

Also the weather would be a lot more extreme, the atmosphere would be pulled around so fast that the windspeeds would be humongous and couple that with the insane coriolis forces we would have some pretty insane hurricanes occuring 24/7 (or should I say 1,4167/7 ). Unless, of course, the atmosphere gets flunged out into space that is.

But I think that this effects can occur on astroids, I remember reading somewhere that if we would start to do astroid mining we would have to tie ourself to the surface so we didn't get flung out into space by the centrifugal forces.

[Spaceisbeautifulul]

Its debatable what would happen. For a planet like Kerbin or Earth? Instant tearing apart.

HOWEVER there are some places, like gas giants and more commonly stars, where all that force from spinning would just make it bulge at the equator and make some weird egg shape. More like a fat pancakes though. We see a small example of this from our very own big brother, Jupiter. It spins very fast (a day is what, 10 hours?) so it bulges slightly at the equator.

Now, if you were a star, say a red dwarf, you would need to spin at RIDICULOUS rates to look flat. 85 minutes would show SIGNIFICANT flattening of the star or gas giant. Anyways, that aside, Earth would be ripped apart.

Edited May 31, 2013 by Spaceisbeautifulul

[RRoan]

85 minutes would show SIGNIFICANT flattening of the star or gas giant.

Achernar, the most non-spherical star known, has a rotation period almost three and a half times longer than that. I can't imagine an 85-minute period would be survivable for many stars, either.

[NovaSilisko]

"Ripped apart" implies a complete disintegration, which isn't the case really. At large scales, planets are surprisingly flexible, especially if they're made of things like ice. Most of the earth's interior is molten or at least partially molten, so what's mostly at risk is the hard, fragile crust and upper mantle. I think what would happen, assuming you magically increased earth's rotation speed without the force of doing so wrecking stuff in the first place...

First, the earth would begin stretching outward due to the newfound centrifugal force. As that happens, more matter is shoved above the roche limit (now at the former sea level), and goes into orbit. The atmosphere and oceans probably would be the first to go as they're much less dense than the rest of the planet. I envision a sort of... never-ending cycle of matter drifting away from the surface ALMOST at orbital velocities, going on a long trajectory, landing again, and then repeating the process. Eventually, it would reach an equilibrium after expelling quite a bit of mass out into orbits that don't intersect the surface (maybe forming a ring, or even a moon after longer timescales), while what's left of the planet would likely just be the mantle and core, probably glowing hot except at the poles. In fact, you might actually be able to survive the whole ordeal if you're at the pole.

Of course, I'm not an expert. What would be the best way to answer this is to mail something into what-if.xkcd.com. This seems like the sort of thing he'd love to answer

[Mr Shifty]

Of course, I'm not an expert. What would be the best way to answer this is to mail something into what-if.xkcd.com. This seems like the sort of thing he'd love to answer

Thanks for the speculation. I, in fact, e-mailed this question to Mr. Munroe simultaneously with posting on this forum when it occurred to me last week. It did seem like a perfect what-if for him.