Astronomy/cosmology questions...

[Buster's Uncle]

Well the science has gone back and forth -and I hate to go into this much detail because Lori will, very correctly, correct me- in just the last few years on where all the water on this planet came from, judging from the (frequently bullcrap-ish, mostly through ineptitude) mainstream science articles I've seen.  It might be worth it to you to search, I dunno, "Comet water" in both the science subforums.  I'm trying to think of a good search term to turn up the at least one article that talks about a study that indicates the water molecules were just there with the rest of the matter cloud that Earth formed from, but --- "Earth's Water" maybe?  The search engine sucks, in true forum tradition, but a lot of those articles reference -even link; I always bother to do the link if there's one to a journal article- actual science and don't set off my bullcrap/the-writer-didn't-understand detector.

I believe the issue has more to do with steam being not-dense, the ice form being whitish/reflective, so either way, water molecules would tend not to stay around this distance from the sun in free orbits because light pressure - and the water form of water is a narrow temperature range unlikely to last long outside current earth conditions, not least in vacuum.  Science articles tend to frame it as molten early earth was too hot so it steamed off, but that's nonsense and bad reporting, surely...  Because it's steam it flies out of the atmosphere into space at escape velocity?  Surely more the same reason there's so much more ice and gas in the outer system than inner, which they tend to assume was light pressure pushing away the lighter atoms in the primordial cloud faster than the heaver ones. - and moreso close in where the light's spread out less.

Lori will still be more help...

[Valka]

Of course - it's been over 20 years since I last took any formal astronomy courses, and while I've tried to keep up, too many of those 20 years were spent in a mental fog because I was really sick, housebound, and unable to concentrate on much of anything. So I've missed a lot.

[Buster's Uncle]

I wish I recalled more about what the Dawn probe found at Vesta -but that never got as much coverage as it rates, not unlike Ceres now, and I'm not sure it's still there, it gets so little attention...

Vesta, IIRC, is indeed pretty icy - but they've been fairly confident about that for a very long time; high albedo and I don't know what-all.  The last I recall about Ceres, they were thinking the shiny spots were more like crysaline salt buildups left behind from ice sublimation in vacuum or something of the sort...

[Valka]

Should be interesting to see just how dated Ben Bova's Asteroid Wars series becomes when they find out more about Ceres. A significant amount of the action in those novels take place in a mining outpost in Ceres (they live underground) and in orbit.

[Buster's Uncle]

[shrugs]  Larry Niven likes to girldog that his first published story The Coldest Place, was rendered obsolete about a week before the magazine it appeared in hit the stands - the point of the tale hinges on Mercury being orbitally locked, and it was 1964 and Mariner happened...

[Valka]

Progress happens. 

Pretty much everything Heinlein and Bradbury have written about places in the Solar System became dated decades ago. And every time I hear someone talking about some "Rigel colony" or civilization on a planet orbiting Vega, I'm just taken right out of the story because what we know now means those colonies are impossible.

I realize that we can't hold writers from 50-80 years ago responsible for not knowing what new knowledge would come along; they worked with what they knew at the time, but it does take a mental toggleswitch to enjoy the stories now (at least for me).

[Buster's Uncle]

Bradbury doesn't count - his stuff is Norman Rockwell fantasy, not SF, with spaceships and/or the boogerman, never had anything to do for a second with the scientific state of the art, ever.  I don't get the appeal of Bradbury, for that matter.

[Lorizael]

Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model, according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?

[Buster's Uncle]

...I wonder how the Theia impact may have informed all that.  It had to be a somewhat low-energy event as two planets colliding goes, but it can't have not affected the orbit...


I left out something about that paper last year that posited the water was just there all along - 1.) It's not that much water in the first place, proportionately, and 2.) there was much about evidence/calculations the researcher(s) claimed to have found that the tendency of water in all its states to bond with and/or plate on the surface of denser particles tends to account for the proportions found on Earth's surface even with light pressure in the primordial cloud, so no icy late bombardment need apply.

It is the nature of how science works -slowly, sometimes, as a community- that this has not taken over the dominant thinking, as far as I know, and no idea if other solar system formation scientists aware of it find it to have merit.  There's certainly still references to Earth's comet water coming up in popular reporting still, very notably the Rosetta team mentioning it, not that they wouldn't be a bit married to it by the nature of what they were researching...

[Lorizael]

...I wonder how the Theia impact may have informed all that.  It had to be a somewhat low-energy event as two planets colliding goes, but it can't have not affected the orbit...

Really all depends. Currently, thinking is that Theia was about Mars-sized, having ~1/10 the mass of the Earth. So you have a relatively slow collision between the Earth and a much lighter object. Momentum gets transferred, but the change in momentum might not have been very large. That's because the Earth has a lot of momentum, both from its orbit around the Sun and its own spinning. If some of the momentum goes into changing the Earth's orbit, and some into changing it spin (which depends on how off-center the impact was), then maybe the orbit doesn't get changed much at all.

[Buster's Uncle]

It had to have ended in a pretty fast spin by our current standards, with the nascent molten moon freaky close -which must have been a SIGHT, not that there would a place to stand nor weather for good seeing- and tidal drag effects and all and over four billion years dragging to make a 24 hour period.

-ISTR something on the Discovery channel claiming 15 hours, but cable documentary channels are pretty much the National Enquirer of science these days, and I know not to have enormous respect for that figure...

[Valka]

Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model, according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?

THANK YOU!!!

Would it be permissible to post a link to this post over at CFC? In any case, I will post the link you provided to the Nice model.

(and it's nice - no pun intended - to see references to the Oort Cloud; this guy thinks it's not real and accuses me of "believing" in it as though it's some kind of religious thing or fairy tale, even though I've posted links about it)

[E_T]

One method that I can think of that helped to shape the planetary rotational planes would be tidal forces and effects on orbiting debris that are in the process of stellar and planetary formations...

[Lorizael]

Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model, according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?

THANK YOU!!!

Would it be permissible to post a link to this post over at CFC? In any case, I will post the link you provided to the Nice model.

(and it's nice - no pun intended - to see references to the Oort Cloud; this guy thinks it's not real and accuses me of "believing" in it as though it's some kind of religious thing or fairy tale, even though I've posted links about it)

Sure, you can link to it. I should note that we haven't seen the Oort Cloud, but we have every reason to believe it exists based on (a) the nebular hypothesis and (b) the frequency and trajectories of long period comets. Jan Oort's original paper from 1950 about his eponymous cloud is a great read, btw.

[Valka]

Thank you, Lorizael. It's nice to hear reason instead of "but it can't exist, because it it did, we should see comets every night and we don't."

Well, maybe because when you consider the average human life span and the incredibly long orbits of some of these comets... it'll be thousands of years before Hale-Bopp or Hyakutake come this way again, so I consider myself extremely fortunate to have seen them with my own eyes.

Actually, I started writing a filk about comets, 20-odd years ago. Never finished it, though. I got bogged down in the last verse and still haven't figured out the last two lines.