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How Earth Avoided a Fiery Premature Death

kdawson posted more than 4 years ago | from the flood-next-time dept.

Earth 114

Hugh Pickens writes "Space.com has a piece about changing theories of planet migration. The classic picture suggests that planets like Earth should have plummeted into the sun while they were still planetesimals, asteroid-sized building blocks that eventually collide to form full-fledged planets. 'Well, this contradicts basic observational evidence, like We. Are. Here,' says astronomer Moredecai-Mark Mac Low. Researchers investigating this discrepancy came up with a new model that explains how planets can migrate as they're forming and still avoid a fiery premature death. One problem with the classic view of planet formation and migration is that it assumes that the temperature of the protoplanetary disk around a star is constant across its whole span. It turns out that portions of the disk are opaque and so cannot cool quickly by radiating heat out to space. So in the new model, temperature differences in the space around the sun, 4.6 billion years ago, caused Earth to migrate outward as much as gravity was trying to pull it inward, and so the fledgling world found equilibrium in its current, habitable, orbit. 'We are trying to understand how planets interact with the gas disks from which they form as the disk evolves over its lifetime,' adds Mac Low. 'We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun.'"

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First post! (-1, Offtopic)

toastar (573882) | more than 4 years ago | (#30718936)

Wouldn't the drag of the gas slow it down?

Re:First post! (3, Funny)

zippthorne (748122) | more than 4 years ago | (#30719010)

Morbo: Orbital mechanics do not work that way.

Re:First post! (1)

icebike (68054) | more than 4 years ago | (#30719096)

Well then what part of orbital dynamics suggest the inner planets would have crashed into the sun?

After all, accretion would happen mostly from the "back" side (hemisphere opposite the orbital direction). The planetoid wouldn't "catch" anything in its orbit, but would be over taken by things on more elliptic orbits.

Therefore the impacts would be accellerative, and puhs the planetoid to a higher orbit.

So where did the original assumption that they would spiral into the sun come from?

Re:First post! (4, Informative)

wizardforce (1005805) | more than 4 years ago | (#30719246)

A transfer of angular momentum from one region of the disk to another would cause some section of the disk to migrate toward the sun while another set migrated outward. However, it probably isn't caused by a drag force through the residual gas in the disk as most of it is orbiting the same direction as the debris its self. As for accretion, it depends on the distribution of close encounters with objects in a more elliptical orbit. It's fairly easy for an object in orbit to catch up to an elliptically orbiting body.

Re:First post! (1)

icebike (68054) | more than 4 years ago | (#30719284)

> It's fairly easy for an object in orbit to catch up to an elliptically orbiting body.

Well, not really.

Elliptical orbiters are going much faster as the approach the orbits of the inner planets, and they exit faster too. Most of these are crossing paths.

Re:First post! (2, Informative)

wizardforce (1005805) | more than 4 years ago | (#30719342)

Take a look at the velocity vectors; not all of that velocity is effectively directed in the same direction as the object it's colliding with that has a lower eccentricity.

Re:First post! (1)

icebike (68054) | more than 4 years ago | (#30719696)

Well, yeah, I've wasted some youth at the pool table...

But of many thousands of hits by smaller objects one would expect it to sort of average out...

Re:First post! (2, Interesting)

wizardforce (1005805) | more than 4 years ago | (#30719920)

Indeed, it should largely cancel; the momentum transfer should be a bell-like curve centered near zero depending on where the material is in the nebula.

Migration effects (1, Informative)

Anonymous Coward | more than 4 years ago | (#30719320)

So, the writer of the space.com article got a wee bit confused, understandably so given that it's quite a tricky topic.

The orbital migration is driven by three effects, one of which was neglected in the original calculations showing inspiral. The main one that was treated was the *imbalance* in the shapes of the spiral arms produced in the disk gas by the orbiting planet. Each spiral arm exerts a gravitational torque on the planet, and the negative torque (removing angular momentum, causing inward migration) turns out to be consistently larger than the positive torque -- in the locally isothermal case. Similar calculations show a lesser contribution from gas in the same orbit as the planet.

However, including 1) the effect of gas on "horseshoe orbits" that overtake the planet, get slingshotted outward (to a slower orbit) then are overtaken by the planet and slingshotted back to the inner, faster orbit, and 2) the actual, local compressibility of gas in the opaque midplane of the disk, reveals that if there is a negative temperature gradient outward, migration will also be outward (positive torques outweigh negative torques).

Hard to capture all that in a soundbite to be sure. The paper should be out in a few weeks, and meanwhile, if you want more, Paardekooper's papers on arXiv.org are the technical foundation for this work.

Re:First post! (1)

OrangeCatholic (1495411) | more than 4 years ago | (#30720204)

>Well then what part of orbital dynamics suggest the inner planets would have crashed into the sun?

Nothing. According to that theory, everything always gets sucked into everything else, and the universe would be one giant star. Obviously that's not the case, so anyone operating under that theory has a screw loose.

>Therefore the impacts would be accellerative, and puhs the planetoid to a higher orbit.

They don't need to. We could have started from a higher orbit and fallen inward to where we are now. Of course this contradicts the accepted theory that God created humans 6,000 years ago along with the dinosaurs.

Re:First post! (2, Interesting)

CheshireCatCO (185193) | more than 4 years ago | (#30721708)

After all, accretion would happen mostly from the "back" side (hemisphere opposite the orbital direction).

Not really. Simulations show that the accretion happens pretty much symmetrically from both sides.

The planetoid wouldn't "catch" anything in its orbit, but would be over taken by things on more elliptic orbits.

In its precise orbit, no. But from nearby circular orbits? Yes. And the planets tend to feed on stuff from nearby like that. (They definitely have access, where is chance strikes from elliptical orbits are harder to engineer.)

Re:First post! (1)

CheshireCatCO (185193) | more than 4 years ago | (#30719590)

Actually, no. Original poster is right, the gas in the disk orbits slightly slower than the solids do. So there is drag. However, the gas is pretty tenuous, so the drag only really affects things that are small, say less than a meter or so. (Or so classical theory has argued.)

Re:First post! (1)

zippthorne (748122) | more than 4 years ago | (#30720492)

Yes, but going slower... makes you go faster. From a certain point of view.

Re:First post! (1)

CheshireCatCO (185193) | more than 4 years ago | (#30721692)

True, but I think what the OP meant was that it'd lose energy and move toward the Sun.

Neptune - Uranus shuffle (4, Interesting)

sznupi (719324) | more than 4 years ago | (#30718938)

For me the most amazing aspect of planetary migration is the probable exchange of order for Neptune and Uranus, with Neptune being thrown out to the position of outer planet; without it being ejected from the system, plunging into the Sun or colliding with other big body. Though who knows, perhaps some planet was doomed that way; certainly wild axial tilt of Uranus isn't a testament of calm times.

http://en.wikipedia.org/wiki/Nice_model [wikipedia.org]

PS. There's some joke here, with Uranus ending up closer to the Sun, about total asses always ending the race in better place...

Re:Neptune - Uranus shuffle (1)

toastar (573882) | more than 4 years ago | (#30718998)

ok neat, But how did the main asteroid belt form again,

Re:Neptune - Uranus shuffle (2, Informative)

Nefarious Wheel (628136) | more than 4 years ago | (#30719086)

ok neat, But how did the main asteroid belt form again,

Roche Limit [wikipedia.org] fail? Jupiter was nearby, relatively speaking, could have been a disruptive influence.

Re:Neptune - Uranus shuffle (1)

sznupi (719324) | more than 4 years ago | (#30722836)

Gravitational influence of Jupiter; Roche limit - NO!!! That's a very specific term, dealing with tidal forces when bodies get very near. In case of Jupiter & asteroid belt it was more about orbital resonances & energy transfer.

Re:Neptune - Uranus shuffle (2, Funny)

Anonymous Coward | more than 4 years ago | (#30719260)

ok neat, But how did the main asteroid belt form again,

According to Heinlein, the inhabitants of the original 5th planet annoyed the Martians.

Re:Neptune - Uranus shuffle (5, Funny)

Cryacin (657549) | more than 4 years ago | (#30719328)

Where's the kaboom! There's *supposed* to be an *earth* shattering kaboom!

Re:Neptune - Uranus shuffle (1)

bdcrazy (817679) | more than 4 years ago | (#30719796)

You may want to contact the manufacturer of your targeting system. It appears the target selection queue order has been accidentally reversed. Hopefully they have an update and you can finally get your kaboom.

Re:Neptune - Uranus shuffle (1)

mcgrew (92797) | more than 4 years ago | (#30722364)

Though who knows, perhaps some planet was doomed that way

One was -- Earth. They think the moon formed when a Mars-sized object collided with Earth, and the molten rock that splashed condensed and coalesced into what is now our moon.

What I wonder is how the collision affected its orbit?

Re:Neptune - Uranus shuffle (2, Informative)

sznupi (719324) | more than 4 years ago | (#30722630)

Not exactly. The body that caused formation of the Moon likely formed in Earth L4 or L5 point; technically making it not a planet. Coming from there also gives less chance for axial tilt such wild as in the case of Uranus...

Since it was already gravitationally bound with Earth, I don't think it changed its orbit in significant way.

Re:Neptune - Uranus shuffle (0)

Anonymous Coward | more than 4 years ago | (#30723374)

Does this all mean Velikovsky was right?

If it didn't happen, it wouldn't have happened. (0)

LostCluster (625375) | more than 4 years ago | (#30718940)

I think this is just another case of if the Earth wasn't destined to exist, it wouldn't exist.

Re:If it didn't happen, it wouldn't have happened. (3, Insightful)

MichaelSmith (789609) | more than 4 years ago | (#30718954)

I suppose so but this article is about why it didn't happen.

Re:If it didn't happen, it wouldn't have happened. (1)

Hatta (162192) | more than 4 years ago | (#30725662)

I think it's more about how it didn't happen. Why is left up to philosophers, theologians and the like.

Re:If it didn't happen, it wouldn't have happened. (0)

Anonymous Coward | more than 4 years ago | (#30719106)

Much like 'if Chickens weren't meant to be eaten, they wouldn't taste so good.'

Re:If it didn't happen, it wouldn't have happened. (1)

Hardtrance (55355) | more than 4 years ago | (#30719272)

I first read that as "designed to exist." Was gonna mod you funny.

Re:If it didn't happen, it wouldn't have happened. (4, Interesting)

MBGMorden (803437) | more than 4 years ago | (#30720198)

Destiny doesn't really factor into it. What we're learning is that essentially our planet is rare. Rocky planet of about the right size, at about the right distance, where our planet didn't fall into the sun, nor did a gas giant falling inwards destroy us, and with a very large moon serving to stabilize the planet's wobble.

All those things coming together for our perfect scenario seem like being very, very against the odds, but the reality is that there's an effing huge number of stars in the universe, and repeat their formation process enough times and you're bound to get our scenario play out from time to time (it obviously happened here or we wouldn't be here).

Only downside is that with all these specific things we're learning that make Earth like planets so rare, it may just be the case that such planets are rare enough that we might as well be the only one. The reality is that if they were rare enough that there were only say, 1 such planet per galaxy, then while the universe itself would be pretty much swimming in Earth-like planets (billions of them), but we'd never be able to detect them, much less contact any possible civilizations on them.

Re:If it didn't happen, it wouldn't have happened. (4, Insightful)

bronney (638318) | more than 4 years ago | (#30721256)

I just want to point out 1 more important factor in contacting, or meeting other civilizations in the universe: Time.

The age of our sun is a blink of an eye in the cosmological time scale. It's like tiny little lightbulbs going on and off and on and off. We might not reach an "on" one before ours turns "off", the destination is simply not turned on yet. It's a very lonely picture, but highly probable.

Re:If it didn't happen, it wouldn't have happened. (0)

Anonymous Coward | more than 4 years ago | (#30723212)

you should be modded up +5 insightful

If not, slashdot mods dont know maths, forget astronomy.
That's the big point when you consider badastronomy blog's phil plait's discussion of the mega-magnetar explosion 50 thousand light years away, naturally 50k years ago that sent a massive pulse of radiation that reached us and screwed satellite antennae 5 years ago. That blog post is mighty awesome.

Re:If it didn't happen, it wouldn't have happened. (2, Interesting)

Chris Burke (6130) | more than 4 years ago | (#30725904)

Destiny doesn't really factor into it. What we're learning is that essentially our planet is rare. Rocky planet of about the right size, at about the right distance, where our planet didn't fall into the sun, nor did a gas giant falling inwards destroy us, and with a very large moon serving to stabilize the planet's wobble.

Are we learning that?

I thought things were heading in the opposite direction. Considering that we've been finding exoplanets basically as fast as our capability allows, and every time we enhance our ability to find smaller planets farther from their star, we almost immediately find such a planet. We've found quite a few planets that are earth-like in mass already, closer to their parent star, not to mention tons of other things we didn't even think possible (like gas giants orbiting in earth-like orbits). So the evidence seems to be pointing at a ubiquity of planets, and a wider variety than we imagined.

Even this story is covering an improved model that seems to make earth-like planets in earth-like orbits more likely, not less. At least, if we figure that accretion disks of non-uniform temperature is more likely than uniform.

So I think the jury is still out on earth being a "perfect" scenario of extremely unlikely happenstance. But it wasn't that long ago that it was possible that planetary systems of any kind were a rarity, so at least the current trend is clear.

Lottery analogy (3, Interesting)

Rhaban (987410) | more than 4 years ago | (#30721038)

From the viewpoint of the lottery winner, it always look like destiny: "if my birthdate is the winning numbers, I must be special in some way".

From an outside viewpoint, some random guy won lottery because when millions of tickets are bought, there's a high probability that someone checked the winning numbers.

Difference is, in the case of a planet not forming, there's no exterior viewpoint: losers and non-players simply don't exist.

It wasn't like that! (0, Troll)

postmortem (906676) | more than 4 years ago | (#30718944)

Read the Holy Bible.

Re:It wasn't like that! (1, Funny)

Anonymous Coward | more than 4 years ago | (#30718956)

Don't. It's a work of fiction and a pretty boring one at that.

All that begatting and not a bare breast in sight.

Re:It wasn't like that! (0)

Anonymous Coward | more than 4 years ago | (#30719048)

The sequel is kinda mainstream. All the hard core action is in the first part.

Re:It wasn't like that! (1, Funny)

Anonymous Coward | more than 4 years ago | (#30719054)

Surely the mindless violence [biblegateway.com] makes up for that.

Re:It wasn't like that! (1)

eleuthero (812560) | more than 4 years ago | (#30719940)

Mindless violence? To a modern reader, it may seem like that - but if you live in a society where blood vengeance is sworn by any survivors, you kind of have to wipe out any people group you attack. ... and from a purely human perspective (which would appear to be your own perspective), you kind of have to attack someone if you are fleeing THE aggressive super-power of the era and have to go through antagonistic locals to escape the super-power. Compare it to the infighting in Africa within countries... people flee the larger powers and sometimes have to fight through lesser powers to ensure they have safe distance from the main aggressor. It isn't pretty, but it is understandable. You again see this even today in less developed countries (though I recall we recently had a discussion over whether we can actually say 'less developed' given all the stuff the 'developed' world does to others).

Re:It wasn't like that! (0)

Anonymous Coward | more than 4 years ago | (#30720190)

Wait, are you putting the Bible in historical context? Heathen!

Re:It wasn't like that! (1)

Hognoxious (631665) | more than 4 years ago | (#30721426)

Whatever next - suggesting that the kosher/halal rules for food make sense for avoiding food poisoning in a hot climate with no refrigeration? That's crazy talk!

Re:It wasn't like that! (1)

M. Baranczak (726671) | more than 4 years ago | (#30719164)

All that begatting and not a bare breast in sight.

You should check out R. Crumb's "Book of Genesis".

Re:It wasn't like that! (1)

gyrogeerloose (849181) | more than 4 years ago | (#30719300)

All that begatting and not a bare breast in sight.

Plenty of sex (check out the Psalms sometime) and violence, though. Especially violence.

Re:It wasn't like that! (1)

daniel.b.douglas (1654503) | more than 4 years ago | (#30719666)

I wasn't aware of sex playing any major role in the Psalms, which are holy liturgical songs, though admittedly I've only read about half of them. I believe you are thinking of the erotic Song of Solomon, various sexual imagery in the prophesies of Ezekiel and Hosea, and historical/mythological narrative in Genesis, 2 Samuel, etc.

Re:It wasn't like that! (1)

gyrogeerloose (849181) | more than 4 years ago | (#30720610)

I believe you are thinking of the erotic Song of Solomon

Yes, you're right. What little I know about the Bible was learned many years ago (and against my will) so it's sometimes a little sketchy.

The violence part still stands, though. Plenty of that all through the Old Testament.

Re:It wasn't like that! (0)

Anonymous Coward | more than 4 years ago | (#30719098)

Here's a simple haiku for you ...

In the Beginning
Sounds like a big bang to me
Yet we cannot agree

Re:It wasn't like that! (0, Offtopic)

Nefarious Wheel (628136) | more than 4 years ago | (#30719110)

Your haiku is poor Next line has five syllables! (Facepalm)

Re:It wasn't like that! (3, Funny)

Nefarious Wheel (628136) | more than 4 years ago | (#30719116)

My haiku is poor!

Each line must end with p-tags!

I am mortified.

Re:It wasn't like that! (0, Offtopic)

postmortem (906676) | more than 4 years ago | (#30719656)

Wonderful mods on Slashdot, can't recognize humor unless it explicit says so. My post was meant to be funny. Thanks.

Re:It wasn't like that! (1)

Greg Hullender (621024) | more than 4 years ago | (#30719738)

Yeah, I guess we really need a way to let people mark their own stuff as funny or not. Then the mods can give ratings like "not very funny" "didn't get the joke" etc. In this case, lacking a smiley, it's hard to see how most people would guess it was a joke.

--Greg (No, I'm not one of the folks who moderated it!)

not this shit again (-1, Troll)

Anonymous Coward | more than 4 years ago | (#30718984)

another ridiculous explanation that makes no sense. Meanwhile, all the facts fit perfectly into the electric universe model.

Re:not this shit again (2, Insightful)

Loomismeister (1589505) | more than 4 years ago | (#30719672)

No, the facts don't fit that bogus model.

Soft on outside Crunchy on inside (4, Interesting)

icebike (68054) | more than 4 years ago | (#30719060)

This would seem to suggest the inner planets formed first and swept the disk of hard derbies, leaving nothing but the gas, which was ultimately blown outward by the pressure of the sun as the disk was swept clear of big chunks.

The gas giants would accumulate at a much slower rate, and almost by definition must be far younger than the rocky planets.

Then there are the oddball moons of the outer planets. Captured planetoids forming late, almost falling into the sun because the disk was pretty much cleared by that time, but being slung outward and captured by chance?

Re:Soft on outside Crunchy on inside (2, Funny)

Anonymous Coward | more than 4 years ago | (#30719314)

This would seem to suggest the inner planets formed first and swept the disk of hard derbies...

Then the disk sang to the Sun: "I'd tip my hat to you, but I haven't got a hat".

Re:Soft on outside Crunchy on inside (1)

icebike (68054) | more than 4 years ago | (#30719706)

Say now...
I save my best spellink for peopl whu pay me...

Re:Soft on outside Crunchy on inside (1)

John Hasler (414242) | more than 4 years ago | (#30719336)

> This would seem to suggest the inner planets formed first and swept the disk
> of hard *derbies*...

So the Earth's crust is old hat?

Re:Soft on outside Crunchy on inside (1)

nirriajaika (1718026) | more than 4 years ago | (#30719624)

NICE topic this is and i like this , and he work really hard, about this, Paraslime Force [ezinearticles.com]

Who knows (1, Insightful)

BhaKi (1316335) | more than 4 years ago | (#30719074)

Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

Re:Who knows (3, Informative)

Sulphur (1548251) | more than 4 years ago | (#30719186)

Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

Al is that you?

Re:Who knows (0)

Anonymous Coward | more than 4 years ago | (#30719280)

hey your village called the want their idiot back

Re:Who knows (2, Insightful)

gyrogeerloose (849181) | more than 4 years ago | (#30719346)

Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable.

Except for the fact that if something is falling slowly, it ain't a plummet. From the Oxford American Dictionary:

plummet [verb]

1 fall or drop straight down at high speed
2 decrease rapidly in value or amount

[noun]

1 a steep and rapid fall or drop.

Re:Who knows (1)

BhaKi (1316335) | more than 4 years ago | (#30720068)

I admit I didn't know the exact meaning of plummet when I posted it. Thanks for the info.

Now there's another interesting idea. It's possible that the fall is quick in comparison to the sun's or earth's age, while still being many orders of magnitude longer than human lifetime.

Re:Who knows (1)

someone1234 (830754) | more than 4 years ago | (#30721784)

Earth is plummeting towards the Sun, just always misses it.

Re:Who knows (1)

M8e (1008767) | more than 4 years ago | (#30721792)

We are plummeting at a speed of 107,218 km/h, it's just that we are falling toward a diffrent 'down'.

Re:Who knows (1)

turbidostato (878842) | more than 4 years ago | (#30719598)

"Or maybe we ARE plummeting into sun, but at a rate that is too slow to be observable."

Well, we ARE plummeting into Sun at a very observable rate. It's only that such rate is exactly the same we move to the side to avoid the mark.

How did we avoid firey, premature death? (4, Funny)

darkpixel2k (623900) | more than 4 years ago | (#30719184)

How Earth Avoided a Fiery Premature Death

The dinosaurs were smart (especially the Velociraptors). They stopped driving SUVs. That's why we're here.

Re:How did we avoid firey, premature death? (1)

mjwx (966435) | more than 4 years ago | (#30719966)

The dinosaurs were smart (especially the Velociraptors). They stopped driving SUVs. That's why we're here.

I had to check [google.com.au] .

Re:How did we avoid firey, premature death? (1)

Atriqus (826899) | more than 4 years ago | (#30720252)

They solved their energy crisis and are now in process of cleaning up our goto problem [xkcd.com] .

The article isn't great for the lay-person (4, Interesting)

Cedric Tsui (890887) | more than 4 years ago | (#30719286)

If I'm reading the article right, it says that the gravity of a gas/rock disk around a star will cause the whole thing to migrate inward until it is consumed by the sun. However, account for temperature differences due to varying cooling rates across the disk, then this causes a different force which can be shown to balance out the inward migration.

My question is. Why does the gravitational effects of a gas disk around a star cause inward migration? The only thing I would expect to cause inward migration would be friction resulting in the loss of kinetic energy. I haven't the foggiest idea how a temperature gradient can cause matter to climb out of a gravity well. Maybe I should go looking for the original paper.

Re:The article isn't great for the lay-person (2, Informative)

MosesJones (55544) | more than 4 years ago | (#30719702)

Why does the gravitational effects of a gas disk around a star cause inward migration?

Throw a ball up... it comes down. This is gravity. The "base state" for gravity is everything sticking in the centre. Now when something has the right velocity this acceleration towards the centre just causes it to form an orbit around the body.

However given that gasses expand to fill up available space its very hard to have a stable orbit of gas moving at a constant velocity and thus obtaining an orbit. Gasses just don't behave like solids so it doesn't work like that. The expectation would be that as a gas spreads some of it will get pulled in and over time this "some" would become "all".

Re:The article isn't great for the lay-person (1)

Cedric Tsui (890887) | more than 4 years ago | (#30720008)

"Throw a ball up... it comes down. This is gravity. The "base state" for gravity is everything sticking in the centre."

Nope. Your ball analogy doesn't work here. Things in orbit STAY in orbit unless they somehow lose all of their kinetic energy. A ball behaves differently because it NEVER gains enough energy for an orbit. The article says it is the interaction between the cloud and the proto-planet that causes the proto-planets to migrate towards the sun.

"We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun."

I can understand this part. But the article also says that a gas disk with varying temperatures would cause certain orbits to migrate outwards instead of inwards and THIS is why proto-planets can survive. But it doesn't say how a temperature gradient can cause migration.

Re:The article isn't great for the lay-person (1)

MosesJones (55544) | more than 4 years ago | (#30720304)

Things in orbit STAY in orbit unless they somehow lose all of their kinetic energy.

Nope, they have to have ENOUGH velocity (Kinetic energy is about the energy required to get it to a given speed) at the right angle in order to counteract the acceleration of the object towards the planet. If the velocity (a vector) isn't right then it will either move out of the orbit into a further orbit (or even escape) if it is too fast or it will fall towards the planet if too slow (as inner orbits require faster velocities). Things do not stay in orbit if they aren't moving fast enough. If an object was stationary (not geo-stationary) with respect to the earth then it would fall back to earth in the same way as a ball when thrown up comes back down.

If you through a ball hard enough STRAIGHT UP then it could escape the Earth's gravity well, if you through it at the right angle (lets say 45 degrees for arguements sake) and at the right speed then you could indeed put that ball into orbit.

Gravity is an acceleration towards.

Temperature gradients indicate the amount of energy in a given area and various pieces of physics talk about how things will shift from high to low energy areas over time, I assume that this is what they are getting at. I just understood the old stuff (while knowing it was clearly wrong), I don't understand the new stuff yet!

Re:The article isn't great for the lay-person (0)

XSpud (801834) | more than 4 years ago | (#30721440)

If you through a ball hard enough STRAIGHT UP then it could escape the Earth's gravity well, if you through it at the right angle (lets say 45 degrees for arguements sake) and at the right speed then you could indeed put that ball into orbit.

Actually you cannot launch a projectile into orbit from the earth's surface without some additional sideways force after release. Throwing any ball will send it into an elliptical orbit around the earth's centre but the length of the minor axis will always be less than the earth's diameter. So the ball released at 45 degrees will at some point hit the earth again, also at an angle of 45 degrees. This of course ignores air friction etc.

Re:The article isn't great for the lay-person (1)

khallow (566160) | more than 4 years ago | (#30720514)

I can understand this part. But the article also says that a gas disk with varying temperatures would cause certain orbits to migrate outwards instead of inwards and THIS is why proto-planets can survive. But it doesn't say how a temperature gradient can cause migration.

My guess is that there's some sort of considerable net light pressure away from the star. Not acting directly on the planet, but on the gas cloud. What's probably different is that in old models, the light pressure acted only on the surface of the gas cloud, while in this model, due to the temperature gradient, you have light pressure much deeper in the cloud. This means the gas cloud is experiencing net force away from the star throughout a considerable portion of the cloud. That'll help keep planetoids from spiraling in, especially if the planetoid continually runs into gas that is slowly moving away from the star.

Re:The article isn't great for the lay-person (1)

jstults (1406161) | more than 4 years ago | (#30722816)

I haven't the foggiest idea how a temperature gradient can cause matter to climb out of a gravity well.

Thermophoresis [wikipedia.org] causes particles in a fluid to move because of a temperature gradient. The similarity parameters (Reynolds / Mach / Knudsen) for a planetesimal in an accretion disk are probably similar to the aerosal particles in air that the wiki article talks about.

Worst. Semantic. Structure. Ever. (2, Insightful)

Anonymous Coward | more than 4 years ago | (#30719468)

The incorrect use of periods to indicate emphasis is not linguistic evolution. It is just semantic stupidity. I wish it didn't catch on.

Re:Worst. Semantic. Structure. Ever. (1)

eleuthero (812560) | more than 4 years ago | (#30719964)

Yet, it would appear to have caught on. As such... it's linguistic. evolution. As an adult native speaker of English, what I say that effectively communicates my intended point to my intended audience... is English, particularly so if I am emulated by others. One could even argue that I don't have to be a native speaker, though in this case, it is unlikely that emulation by large audiences would occur, limiting the evolution to a temporary mutation. Yes, I am a fan of descriptive grammars.

Re:Worst. Semantic. Structure. Ever. (1)

Hognoxious (631665) | more than 4 years ago | (#30721478)

Isn't it meant to emulate the delivery of one W. Shatner esquire, who pronounces each word as if it's a separate sentence?

Here's some more info (3, Informative)

Greg Hullender (621024) | more than 4 years ago | (#30719498)

According to Science Daily [sciencedaily.com] this was the result of a computer simulation which was designed based on a paper, published last year http://arxiv.org/abs/0909.4552 [arxiv.org] . The simulation was "one-dimensional," which seems curious, and they could only afford to simulate 1,000 years out of the estimated 1,000,000 such a disk is expected to last.

So look for more reports of this sort over the next few years. Still, it looks like a big jump forward for our early-solar-system models.

--Greg

Re:Here's some more info (5, Informative)

enilnomi (797821) | more than 4 years ago | (#30719548)

You misread. The relevant paragraph is, "We used a one-dimensional model for this project," says co-author Wladimir Lyra, a postdoctoral researcher in the Department of Astrophysics at the Museum. "Three dimensional models are so computationally expensive that we could only follow the evolution of disks for about 100 orbits -- about 1,000 years. We want to see what happens over the entire multimillion year lifetime of a disk."

Re:Here's some more info (1)

Greg Hullender (621024) | more than 4 years ago | (#30719690)

You're right. Oops. That still leaves us wondering what a one-dimensional model of the solar system is like, though. Likewise, one could expect better results over time as people do work out how to do three-dimensional models for longer periods.

Good catch. Thanks.

--Greg

Re:Here's some more info (1, Informative)

Anonymous Coward | more than 4 years ago | (#30720388)

Presumably, you'd do your modeling as a slice through the disk. Basically, what you're interested in is the effects at different distances from the sun. Hopefully, you can ignore the part about distance above/below the ecliptic and the actual whizzing around the sun, and just focus on a single radial.

And they said religion has no part in science (0, Troll)

Zxeses (236430) | more than 4 years ago | (#30719764)

Wow, thank you for that faith inspiring rhetoric; I can't think of how I could further prove that modern day theory is not much better then religion for the people who can't yet invent a new "God" or Genesis story.

I could come up with a much better theory, about how the sun's rotation speed caused all the slower particles to form planets much faster as a result of the suns unequal gravitational balance, however I fear that would be lost in the argument about why such circumstance would come to be when no evidence of such things suggest a theory even close to mine, much less this one...

The next time I pick a random thought out of my head, I'll be sure to post it on slashdot however... oh wait..

Re:And they said religion has no part in science (0, Offtopic)

The End Of Days (1243248) | more than 4 years ago | (#30719960)

Come up with a model that supports your theory and doesn't contradict other things we've observed and you've made it as far as this story. Skip the part about not contradicting observations and you've made your new Genesis.

The difference isn't even subtle.

I probably *am* the only one. (3, Funny)

thePowerOfGrayskull (905905) | more than 4 years ago | (#30720118)

I probably am the only one who misread the title as "How to avoid a fiery premature death."

Re:I probably *am* the only one. (1)

Post-O-Matron (1273882) | more than 4 years ago | (#30721192)

The question is, how many slahsdot readers would it take for the probability of you not being alone becoming non-negligent. Given that, and the rate at which we find new slashdot readers all the time. It only follows that one day someone just like you will be found. but they might have tentacles.

Premature? (1)

KharmaWidow (1504025) | more than 4 years ago | (#30720224)

How do we know if the death of Earth is premature? We have absolutely no relative data to compare an M-class planet's typical life.

0.3 billion years old (3, Funny)

Hal_Porter (817932) | more than 4 years ago | (#30720234)

> 4.6 billion years ago

I like the way it's just a bit bigger than 2^32 to stop you using 32 bit variables for the year.

Premature death (1)

dushkin (965522) | more than 4 years ago | (#30720442)

Premature? More like "long overdue" amirite.

Re:Premature death (1)

operagost (62405) | more than 4 years ago | (#30724966)

noyourenot

gravity as a side effect (1)

gringer (252588) | more than 4 years ago | (#30721410)

So in the new model, temperature differences in the space around the sun, 4.6 billion years ago, caused Earth to migrate outward as much as gravity was trying to pull it inward

Or, perhaps, gravity could be a consequence of temperature differences [scientificblogging.com] , so the "pull" and the "push" don't really happen.

Model != reality (0)

Anonymous Coward | more than 4 years ago | (#30721798)

Who knew?

Somebody better not tell global warming "scientists" lest the journal such "denial" is published in gets removed from the realm of "reputable".

Something about this seems wrong to me... (1)

Dinatius (731383) | more than 4 years ago | (#30722040)

"It turns out that portions of the disk are opaque " Maybe I'm off my rocker but the way this is stated, it sounds like a fact they observed rather than a model that they created. While this "fact" makes logical sense it is far too often that I see the statement "It turns out..."

Very informative article (1)

ascari (1400977) | more than 4 years ago | (#30722326)

And here I was all along believing it had something to do with Bruce Willis!

half the stars may have planets (1)

peter303 (12292) | more than 4 years ago | (#30723794)

Astronomers have announced over 500 extra-solar planets and they have barely begun looking. So there are a lot of processes out there creating planets in spite of hypothetical process which may destroy them.

Epic Fail (0)

Anonymous Coward | more than 4 years ago | (#30724392)

Excluding Copernicus and that chap the pope arrested etc. every one knows the earth stayed still and the sun moved.

inference by nostalgia (1)

epine (68316) | more than 4 years ago | (#30724922)

Any statistic significantly skewed by adding or subtracting 1 to either your numerator or denominator is a statistic too fragile to support a conclusion.

The "we are here" argument is a functional celebration of innumeracy, which reminds me of Operation HUMBUG when Canada first introduced Metric: inference by nostalgia.

Contradicts basic observational evidence (1)

Hurricane78 (562437) | more than 4 years ago | (#30725004)

'Well, this contradicts basic observational evidence, like We. Are. Here,' says astronomer Moredecai-Mark Mac Low.

Well, this didn’t stop dark matter supporters, did it? ;)

Didn't read (0)

Anonymous Coward | more than 4 years ago | (#30725052)

I didn't read the article but I can only assume if Earth avoided a fiery premature death that Chuck Norris was certainly involved.

Best. Quote. Ever. (1)

sirwired (27582) | more than 4 years ago | (#30725918)

There is no better way to sum up some of the gaps between theoretical and applied science other than: "This contradicts basic observational evidence, like We. Are. Here." Did the proponents of the "classic" model not notice this minor flaw in their reasoning?

SirWired

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