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TheGodless
2016-Feb-22, 08:06 PM
From Space.com:

"Astronomers have discovered the largest and oldest mass of water ever detected in the universe a gigantic, 12-billion-year-old cloud harboring 140 trillion times more water than all of Earth's oceans combined."

--------

What are the chances that when the Earth and other water rich planets were being formed, they had a giant space cloud of water to form from? Wouldn't ice particles and liquid water also be able to clump together and clump with dust particles and other forms of matter to give us the amount of water we have today? I'm a big ignorant of the science behind planetary formation, so I could easily be missing an important aspect that makes this an impossibility, but if we know that planets form from the matter created by dying stars and we know that water is created in a certain manner and have observed giant clouds of water in space, it seems like the only reasonable explanation for how all of our water rich planets got their water. If it is a viable explanation, I'm guessing that it would be fairly easy to prove since there should be remnants of the cloud of water floating around somewhere near our solar system.

Hornblower
2016-Feb-23, 03:48 AM
It has been billions of years since the formation of our solar system. I would expect any portion of the original nebula that was not accreted to be dispersed beyond recognition all over the galactic disk.

The proto-Earth could have started with a lot of water, lost it from the heating during the early contraction along with heat from the Sun, and then be replenished by comets that formed in colder regions and were deflected to the inner solar system after the Earth had cooled enough to retain water.

ToSeek
2016-Feb-23, 03:41 PM
Moved from ATM to Q&A as a more appropriate location.

Amber Robot
2016-Feb-23, 05:54 PM
There may be clouds in space that have more water than other ones, due to the local conditions driving the astrochemistry, but it is highly doubtful that there are actually "clouds of water" in space, i.e., clouds with only water or with more water than can be explained by chemistry.

Jeff Root
2016-Feb-23, 06:21 PM
I haven't seen a convincing argument to make me think that Earth's
water isn't almost entirely primordial.

-- Jeff, in Minneapolis

efanton
2016-Feb-23, 06:37 PM
I haven't seen a convincing argument to make me think that Earth's
water isn't almost entirely primordial.

-- Jeff, in Minneapolis

I would tend to agree.

The idea that Earth's water was delivered later by asteroids and comets, the very stuff the primordial Earth was made of, seems to me to be completely contradictory.

We also hear, what I consider to be nonsensical, that all that primordial water was boiled off; This appears to ignore the fact that water and volcanoes are closely linked. Water plays significant roles if not crucial roles throughout the "life cycle" of magma: from its production deep within the Earth, to its escape at a volcano, to its final cooling. From experiments it is known that water decreases the melting point of rock. Without this water it would be very hard for magma to form.

So it appears to me much of Earth water has been here since the very beginning of the formation of the Earth. That doesnt mean that additional water was added by later meteoroids and comets.

schlaugh
2016-Feb-23, 07:15 PM
As reference, here's the source story from space.com.

http://www.space.com/12400-universe-biggest-oldest-cloud-water.html

The "cloud" is apparently 300 trillion times less dense than the earth's atmosphere and hundreds of light years in size.

I think we're talking apples and oranges here. The original discovery seems to have nothing to do with how planets accrete water from external sources, be they comets or clouds.

Swift
2016-Feb-23, 10:01 PM
<snip>
We also hear, what I consider to be nonsensical, that all that primordial water was boiled off; This appears to ignore the fact that water and volcanoes are closely linked. Water plays significant roles if not crucial roles throughout the "life cycle" of magma: from its production deep within the Earth, to its escape at a volcano, to its final cooling. From experiments it is known that water decreases the melting point of rock. Without this water it would be very hard for magma to form.

I think such comments come from the idea that the event that created the Moon (a collision with a Mars-sized object) would have removed all/most/much of the water from the surface and mantle of the Earth, and thus the majority of water on Earth would have come here after that event.

I think the details of that event, its consequences, and the origins of Earth's water, are still hotly debated topics. I believe the Universe Today blog has had posts about all of this.

Reality Check
2016-Feb-23, 11:36 PM
I haven't seen a convincing argument to make me think that Earth's
water isn't almost entirely primordial.
The "convincing" argument is simple enough - a planet with a molten surface being heated by impacts should not retain water. There is also the possible creation of the Moon from a massive impact that would also eject water from the Earth. That lead to the theory that the water came from external sources such as comets (now implausible) and asteroids. However there has always been the theory that some or even a majority of the water came from internal sources, e.g. water vapor from volcanic eruptions.

efanton
2016-Feb-23, 11:46 PM
I think such comments come from the idea that the event that created the Moon (a collision with a Mars-sized object) would have removed all/most/much of the water from the surface and mantle of the Earth, and thus the majority of water on Earth would have come here after that event.

Removed to where?

I would assume that this vapour would still be within the gravitational bounds of the Earth. Most of it would return to earth although some would be trapped during the formation of the moon. Also with such a huge impact, it is very unlikely that the Theia Impact created nothing but vapour. Much of the ejected material would have been solid or in the form of molten magma which is constituted partly of water and the majority of this returned to the planet Earth.

For any liquid water or water vapour that escaped Earth's or the forming Moons immediate gravity it is likely that it remained in orbit around the sun and later gravitationally drawn back to Earth. Where else could it go?

Also worth bearing in mind is that it is reasonable to assume Theia almost certainly contained considerable water deposits being that it was formed in similar circumstance to the Earth. It would be reasonable to assume that much of the water lost by the Earth, if not all, would have been replaced by water brought by Theia.

As you have said a lot of this is hotly debated but it seems reasonable to assume much of what I have written if you adopt the principals of Occum's razor, Also, to my knowledge there doesnt appear to be many statistics available for the Theia planet apart from its estimated size of 6,000 km which leaves the question open as to how much water came with the planet Theia

Noclevername
2016-Feb-24, 12:19 AM
For any liquid water or water vapour that escaped Earth's or the forming Moons immediate gravity it is likely that it remained in orbit around the sun and later gravitationally drawn back to Earth. Where else could it go?


Water in space can be disassociated into H and O by sunlight. Hydrogen, being so light, gets pushed away by Solar Wind and moves to the outer Solar system. Oxygen is left behind and returns to the planet, bonding to the surface materials. It's partially by this method that Venus and Mars are thought to have been rendered into their current desiccated states.

efanton
2016-Feb-24, 12:51 AM
Water in space can be disassociated into H and O by sunlight. Hydrogen, being so light, gets pushed away by Solar Wind and moves to the outer Solar system. Oxygen is left behind and returns to the planet, bonding to the surface materials. It's partially by this method that Venus and Mars are thought to have been rendered into their current desiccated states.

good point. I wonder if that mechanism is partially responsible for the Gas Giants being futher out that the rocky planets.

efanton
2016-Feb-24, 01:15 AM
The "convincing" argument is simple enough - a planet with a molten surface being heated by impacts should not retain water. There is also the possible creation of the Moon from a massive impact that would also eject water from the Earth. That lead to the theory that the water came from external sources such as comets (now implausible) and asteroids. However there has always been the theory that some or even a majority of the water came from internal sources, e.g. water vapor from volcanic eruptions.

this simply is not the case. It has been proven that volcanos, and magma and water are all dependent on each other. The US geological survey have done a lot of research regarding this and apparently if there is no water there is no magma vent or volcano. As I understand it its the water in the Earth's crust that lowers the temperatures required for it to become molten and the subsequent depth of material that becomes molten. When magma is formed a lot of the water is still trapped within the magma and will remain in the magma for a considerable time. Water can account for up to to 10% of magma's weight

Here's an interesting article that shows how long water can remain trapped by magma even after a truly massive event such as the one that created the moon. The magma that partly formed the moon although solidified still contains considerable water deposits.

http://www.usgs.gov/newsroom/article.asp?ID=3669#.Vs0ANLFnzcs

Cougar
2016-Feb-24, 02:17 AM
This is sort of related :)



"Twenty five years ago, astronomers thought the interstellar medium within our galaxy consisted of single atoms. But using radio telescopes and detectors sensitive to radiation emitted by molecules, "they found that 10 to 50 percent of the gas in our galaxy is molecular -- atoms stuck together -- and that it tends to cluster in giant clouds. About 99 percent of this gas is molecular hydrogen... but at least 53 other molecules have been detected, including ethyl alcohol, or vodka. The clouds of gas near the center of our galaxy contain enough vodka to fill more than 10,000 goblets the size of earth." [Heinz Pagels, Perfect Symmetry]

schlaugh
2016-Feb-24, 02:43 AM
This is sort of related :)


"Twenty five years ago, astronomers thought the interstellar medium within our galaxy consisted of single atoms. But using radio telescopes and detectors sensitive to radiation emitted by molecules, "they found that 10 to 50 percent of the gas in our galaxy is molecular -- atoms stuck together -- and that it tends to cluster in giant clouds. About 99 percent of this gas is molecular hydrogen... but at least 53 other molecules have been detected, including ethyl alcohol, or vodka. The clouds of gas near the center of our galaxy contain enough vodka to fill more than 10,000 goblets the size of earth." [Heinz Pagels, Perfect Symmetry]


Shaken, not stirred please. And a lemon the size of Jupiter or three Neptune olives.

kzb
2016-Feb-24, 12:41 PM
It's my understanding that water and other volatiles would've been lost from the inner portion of the protoplanetary disk.

Planets that formed there (the terrestrial planets) would already be very dry. Even if the cloud from which the solar system formed was very rich in water to begin with. The small bodies which form in the initial stages of planetary formation have almost no gravity to hold onto water vapour, so if water is volatilised by warmth, it's gone and driven outwards beyond the snow line.

Also, it doesn't matter whether you believe the impact that formed the moon or other events would have driven off water or not. The Earth was already dry.

The volatiles (including water) would be re-delivered later, after Earth had the gravity to hold onto it. It's a good point about the alcohol though; we hear a lot about water, ammonia, methane and cyanide, but I wonder if the first oceans were actually about 13 degrees proof like wine?

efanton
2016-Feb-24, 05:10 PM
It's my understanding that water and other volatiles would've been lost from the inner portion of the protoplanetary disk.

That's an interesting comment, So what you are saying is that even before planets started forming, the water and water vapour had already migrated outwards from the Sun.

Its not that I dont believe you but all the documentaries seem to claim the interest in outer solar system objects is because they represent the materials that planets and early solar system were made of. There's an obvious contradiction there.

Can anyone elaborate on this?

korjik
2016-Feb-24, 05:46 PM
That's an interesting comment, So what you are saying is that even before planets started forming, the water and water vapour had already migrated outwards from the Sun.

Its not that I dont believe you but all the documentaries seem to claim the interest in outer solar system objects is because they represent the materials that planets and early solar system were made of. There's an obvious contradiction there.

Can anyone elaborate on this?

Big sun. Hot. Makes water go away. Outer planets. Not hot. Water doesnt go away.

Not very contradictory.

Once the sun started emitting light and heat, the light pressure and radiation started pushing the volatiles out of the inner solar system. The outer solar system is where the radiation intensity got low enough that the volatiles could hang around long enough to be incorporated into protoplanets. Heck, that is one of the definitions of the difference between inner and outer solar system

korjik
2016-Feb-24, 05:49 PM
this simply is not the case. It has been proven that volcanos, and magma and water are all dependent on each other. The US geological survey have done a lot of research regarding this and apparently if there is no water there is no magma vent or volcano. As I understand it its the water in the Earth's crust that lowers the temperatures required for it to become molten and the subsequent depth of material that becomes molten. When magma is formed a lot of the water is still trapped within the magma and will remain in the magma for a considerable time. Water can account for up to to 10% of magma's weight

Here's an interesting article that shows how long water can remain trapped by magma even after a truly massive event such as the one that created the moon. The magma that partly formed the moon although solidified still contains considerable water deposits.

http://www.usgs.gov/newsroom/article.asp?ID=3669#.Vs0ANLFnzcs

Todays volcanism is going to be quite different than that of the primordial Earth. The Earth had alot more internal heat, alot more radioactive decay heat and big asteroids impacting frequently. We arent talking about volcanoes, we are talking about the whole Earth being hot enough to melt rock

efanton
2016-Feb-24, 06:04 PM
Big sun. Hot. Makes water go away. Outer planets. Not hot. Water doesnt go away.

Not very contradictory.

Once the sun started emitting light and heat, the light pressure and radiation started pushing the volatiles out of the inner solar system. The outer solar system is where the radiation intensity got low enough that the volatiles could hang around long enough to be incorporated into protoplanets. Heck, that is one of the definitions of the difference between inner and outer solar system

Thanks for that.

So the documentaries are being slightly misleading when they say the interest in outer solar system objects is because they represent the materials that planets and early solar system were made of. The fact would be that no this is not the case for the inner rocky planets at all.

Swift
2016-Feb-24, 06:16 PM
That's an interesting comment, So what you are saying is that even before planets started forming, the water and water vapour had already migrated outwards from the Sun.

Its not that I dont believe you but all the documentaries seem to claim the interest in outer solar system objects is because they represent the materials that planets and early solar system were made of. There's an obvious contradiction there.

Can anyone elaborate on this?
Not a contradiction. These are the materials the solar system was made from, it is just the "construction" didn't happen in one step. The water came later, from asteroids and comets, that were formed in the early solar system.

You might want to check out "frost line" (wikipedia link (https://en.wikipedia.org/wiki/Frost_line_(astrophysics)))


In astronomy or planetary science, the frost line, also known as the snow line or ice line, is the particular distance in the solar nebula from the central protostar where it is cold enough for volatile compounds such as water, ammonia, methane, carbon dioxide, carbon monoxide to condense into solid ice grains. This condensation temperature depends on the volatile substance and the partial pressure of vapor in the protostar nebula. The actual temperature and distance for the snow line of water ice depend on the physical model used to calculate it:

I don't think this is settled science. The origin of Earth's water seems to be on-going topic of discovery, particularly as to whether comets or asteroids (or some mixture) were the source.

kzb
2016-Feb-24, 06:17 PM
TV science documentaries are often very poor indeed. I wouldn't take any notice of them as a source of educational material.

korjik
2016-Feb-24, 06:49 PM
Thanks for that.

So the documentaries are being slightly misleading when they say the interest in outer solar system objects is because they represent the materials that planets and early solar system were made of. The fact would be that no this is not the case for the inner rocky planets at all.

All documentaries are flat out lies. As a matter of fact, no physicist has ever told you the truth. We always take shortcuts and make assumptions, because the universe is really complex.

efanton
2016-Feb-24, 07:10 PM
Thanks Swift, kzb and korjik. something new I have learned today,

It baffles me sometimes when scientist criticise the scientific ignorance of the masses, the lowering standards in our schools and then go on television and compound the problem by deliberately misleading them.

I was always under the impression that earth was formed by similar material as we know to exist in the asteroid belt and Oort cloud.Obviously this presupposes the existence of substantial amounts of water during Earth's formation. I see no reason why it was so difficult for these scientists / presenters to explain that water and water vapour had migrated outwards first before the rocky planets were formed as you have just done in a few short lines, literally a second or two of TV time.

Its easy to see why so many distrust what is said by scientists, and instead accept religious dogma when it can be proven some of what is said on tv and in documentaries is false. If some is false then its easier to believe all is false.

Amber Robot
2016-Feb-24, 07:37 PM
Don't always blame the scientists. They probably rarely, if ever, have any control over the editing of a documentary and how much of what they say in an interview is used in the documentary and in what context.

Often times, an attempt to describe a scientific finding without use of the technical jargon associated with that finding will result in something that is not an ideal representation of that finding. Combine that with snippets of interviews without full context and you're bound to have things be/sound misleading even if that's not the intent of either the filmmaker or the scientist.

Jeff Root
2016-Feb-24, 07:41 PM
I see no reason to think that the inner Solar System was swept
clear of water and other volatiles before the inner planets formed.
I believe the formation of the inner planets began before the Sun
became bright enough to do any sweeping at all, and came to a
nearly complete halt when the Sun did become that bright.

-- Jeff, in Minneapolis

Swift
2016-Feb-24, 09:16 PM
Don't always blame the scientists. They probably rarely, if ever, have any control over the editing of a documentary and how much of what they say in an interview is used in the documentary and in what context.

Often times, an attempt to describe a scientific finding without use of the technical jargon associated with that finding will result in something that is not an ideal representation of that finding. Combine that with snippets of interviews without full context and you're bound to have things be/sound misleading even if that's not the intent of either the filmmaker or the scientist.
Yes and yes.

You also have to consider the audience for a particular documentary. Some Discovery channel TV program may not go into a great level of detail, and the stuff you (efanton) are talking about is details for a broad audience. Learning that the solar system formed from a cloud of material and some of that material is still out in the solar system, and that's why we are spending your tax dollars to send a space probe to some asteroid, is probably the limit of most people's interest.

Amber Robot
2016-Feb-24, 09:25 PM
Yes and yes.

You also have to consider the audience for a particular documentary. Some Discovery channel TV program may not go into a great level of detail, and the stuff you (efanton) are talking about is details for a broad audience. Learning that the solar system formed from a cloud of material and some of that material is still out in the solar system, and that's why we are spending your tax dollars to send a space probe to some asteroid, is probably the limit of most people's interest.

It makes me wonder whether people have a similar intolerance to jargon in the reporting of other activities in which they might be interested. Is it really wrong to expect that the consumer of scientific information have some level of science literacy in order to adequately ingest the information? Do people listening to sports expect the reporting to be dumbed down and avoid using jargon? Would you expect the reporting on the Super Bowl to not use terms like "touchdown", "interception", and "fumble"?

When I was a kid I never really played baseball or watched it much. When I did watch it, it seemed painfully boring to watch. It wasn't until I was in grad school, when I played inter-departmental softball that I learned enough about what was going on in a baseball match to enjoy watching the sport.

Making new scientific discoveries isn't easy and it takes a lot of understanding, studying, and detailed information about what has been studied in the past. That's why the majority of it is done by people with PhDs. It isn't always easy to make that palatable to people without some modicum of understanding of science and the scientific method. Ultimately, whose responsibility should it be for making this information accessible to the public?

Cougar
2016-Feb-25, 03:22 AM
I was always under the impression that earth was formed by similar material as we know to exist in the asteroid belt and Oort cloud.....

I think the program may have been talking about how some (most?) of this stuff is primodial and hasn't changed since the early formation of the solar system, so it may represent part of the building blocks of the early planets?

kzb
2016-Feb-25, 01:35 PM
I see no reason to think that the inner Solar System was swept
clear of water and other volatiles before the inner planets formed.
I believe the formation of the inner planets began before the Sun
became bright enough to do any sweeping at all, and came to a
nearly complete halt when the Sun did become that bright.

-- Jeff, in Minneapolis

Perhaps we have to come clean and admit we are probably almost as bad as the TV docs! The honest answer is that there are still plenty of unknowns about planetary system formation.

I was giving what I believe is the prevailing picture at the current time:

The accretion disk is hot, and it gets hotter the nearer the centre you are. There is a "snow line" at some radius depending on the size of the disk. Volatile compounds become depleted inside this snow line, and this occurs while particle sizes are still small.

Jeff Root
2016-Feb-25, 07:12 PM
Isn't the disk opaque and thus shaded from sunlight and thus dark
and thus relatively cool wherever it is dense enough for accretion
to be occurring? If enough sunlight and/or solar wind is reaching a
forming planet to blow volatiles away, then the density of dust and
other non-volatiles must be too low for planet formation to occur.
If sunlight and/or solar wind is *not* reaching someplace in a disk,
then it doesn't matter how hot it is -- nothing will blow away.

-- Jeff, in Minneapolis

Noclevername
2016-Feb-26, 02:41 AM
Solar wind goes out to the heliopause, right?

Jeff Root
2016-Feb-26, 02:54 AM
Yes, the solar wind is stopped at the heliopause by the interstellar
medium, if it isn't stopped by something else first.

-- Jeff, in Minneapolis

kzb
2016-Feb-26, 02:33 PM
The truth is, the very earliest stages are hidden in the cloud. But the central area is hot before any protostar forms.

efanton
2016-Feb-26, 08:45 PM
It seems to me to suggest the earth was dry and barren because of a solar wind or hot centre of a proto solar system disk misses the point completely.

Water is one of the best chemical solvents we know. Even if there were no rivers, no lakes and no oceans there would still be massive amounts of water bound up in the early Earth that could or would be released later due to geologic or chemical actions.

Also is the solar wind strong enough to move liquid water if it is free floating in space? I can imagine it be strong enough to move single atoms nuclei or maybe gas, but would it exert enough force to actual move liquid?

If water molecules were bound to dust particles in space would the Solar wind have been able to move them to the outer solar system?

Amber Robot
2016-Feb-26, 09:51 PM
You wouldn't have liquid water free floating in space.

efanton
2016-Feb-27, 12:28 AM
You sure about that?

Although I said liquid water I do accept its more likely to exist as water frozen as ice


Since astronomers expected water vapor to be present even in the early universe, the discovery of water is not itself a surprise, Bradford says. There’s water vapor in the Milky Way, although the total amount is 4,000 times less massive than in the quasar, as most of the Milky Way’s water is frozen in the form of ice.

http://www.universetoday.com/87669/huge-resevoir-of-water-discovered-in-space-30-billion-trillion-miles-away/

Noclevername
2016-Feb-27, 12:33 AM
You sure about that?


Zero pressure means the boiling and freezing points of water overlap.

efanton
2016-Feb-27, 09:27 PM
Zero pressure means the boiling and freezing points of water overlap.

So what does that mean in reality

Water vapour, water ice or mixture of both?

kzb
2016-Feb-29, 12:28 PM
It seems to me to suggest the earth was dry and barren because of a solar wind or hot centre of a proto solar system disk misses the point completely.

Water is one of the best chemical solvents we know. Even if there were no rivers, no lakes and no oceans there would still be massive amounts of water bound up in the early Earth that could or would be released later due to geologic or chemical actions.

Also is the solar wind strong enough to move liquid water if it is free floating in space? I can imagine it be strong enough to move single atoms nuclei or maybe gas, but would it exert enough force to actual move liquid?

If water molecules were bound to dust particles in space would the Solar wind have been able to move them to the outer solar system?


I wouldn't say it misses the point completely. The fact is you have rocky planets close in and gas/ice giants further out. You have to come up with a viable theory to explain that. Yes there are exoplanet hot Jupiters and mini-Neptunes, but astronomers are adamant they could not form in their current locations. They formed further out, and migrated inwards later on.

It is thought that protostar formation leads planet formation. The protostar is orders of magnitude more luminous than the star it will eventually become. Ice within a certain distance would sublime into gas. At this stage, the average particle size is small (cm) so water should be effectively removed at high temperature. It would then be shifted out by the particle wind. It could also be photodissociated.

I believe that is the prevailing theory. However, it has to be said that in the protostar phase, possibly pre-formed icy planets close enough in get stripped of atmosphere and ices due to the intense luminosity and radiation. Possibly some water survives trapped under the surface. But bear in mind planets of any size will still be red hot at this stage.

efanton
2016-Feb-29, 04:35 PM
Maybe I am misunderstanding this completely.

As I understand it the universe was almost uniform at its beginning. From this uniformly distributed helium the first stars were created. Only when these stars died was the materiel required for a second generation of stars and planetary formation possible. I assume that means the material required for planetary formation was flung outwards at speeds far in excess of what any solar wind could combat or the gravity of the dying stars core could retain. Logically following from that we have planetary material travelling in all possible directions and continuously travelling per Newtons laws until gravitational forces from other stars grab this material.

If the above is right then the material that create proto planetary discs is travelling towards proto stars at speed far in excess of the force exerted by any solar wind.
As it originated beyond the 'heat boundary' (im sure there a technical term for this so please let me know) this material would clump but also would be very cold. One would imagine that planetoid or proto planets are already in formation long before they ever got even close to being into stable orbits around a proto star or a proto planetary disc.
These planetoids or proto planets would already have bound within them huge reserves of water ice. Until they got into stable orbits it seems logical to assume they would be travelling inwards towards a star faster than any solar wind could repel them until a stable orbit was found. It seem logical then that some planets would be well on their way to formation as a proto planetary disc with a proto star in it centre was forming, while others would form later from the dust and smaller material within the proto planetary disc.

Maybe I have it all wrong, and if I have please point out where. But if the above was correct for some proto planets the solar wind seems to be fairly irrelevant.Yes some of the surface material and water would be removed due to the proto stars heat but one would imaging the large bulk would remain unaffected, gravity wins, not the solar wind.
For the rest of the material (dust, small rocks etc) that has not yet already been absorbed by the proto planets or proto star I can see the proto star having the effects kbz has suggested.

Amber Robot
2016-Feb-29, 05:26 PM
So what does that mean in reality

Water vapour, water ice or mixture of both?

It'll be either water molecules amongst all the other molecules or water ice on dust grains. Liquids won't survive in the near vacuum of space.

Eclogite
2016-Feb-29, 05:44 PM
Maybe I am misunderstanding this completely.You may be.

Stars and their accompanying planetary systems are formed simultaneously from the collapse of Giant Molecular Clouds. These GMCs consist of very fine dust and gas, much of it originating from supernovae. Gravitational instability in the cloud, or possibly pressure waves generated by a supernova, lead to collapse of a portion of the cloud.

At the center of the collapse lies a protostar and around it is an accretion disc. Material in the disc collapses onto the protostar, which is highly luminous because of conversion of the kinetic energy of accretion to heat. A strong temperature gradient is present in the disc that determines what minerals will condense at particular distances. Water is not something that is readily incorporated into the refractory minerals that predominate in the inner part of the disc where the terrestrial planets form.

That is a greatly simplified description of the process, but the bottom line is that it is unlikely that significant water will be present during initial formations of the inner planets.

Jeff Root
2016-Feb-29, 07:00 PM
The portion of a giant molecular cloud which collapses is roughly
spherical. It collapses because it is cold. As it collapses its density
increases, which increases the frequency of collisions between
particles. Depending on the distribution of matter and its motions,
it could either first begin collapsing at the center to a protostar, or
it could first begin collapsing to a disk. If the matter predominantly
falls to the center of the sphere, solar wind from the young star could
blow away all the rest of the dust and gas, preventing formation of
any planets at all. If the matter predominantly remains in the outer
parts of the disk, it could form planets of any size at any distance
from the center before the central protostar begins giving off solar
wind. Multiple stars can form. It all depends on the distribution of
the particles and their motions as the cloud collapses.

A disk forms if the outer parts of the spherical cloud are dense
enough for the particles to collide frequently enough. Then there
is a rapid collapse because the density of the disk is far greater
than the density of the spherical cloud. The constant collisions
force the particles into circular orbits. As long as there are no
significant local concentrations of mass within the disk, the
particles will remain in circular orbits. But particles can stick
together, so clumping begins, and those clumps can grow to
any size that the distribution of matter and momentum allow,
until solar wind blows the remaining unconsolidated particles
out of the system. A result is that planets tend to end up in
roughly circular, coplaner orbits.

-- Jeff, in Minneapolis

efanton
2016-Mar-01, 08:27 PM
thanks for the responses.

and thanks Eclogite, temperature gradient was the term I was searching for when I said 'heat boundary'


I find the standard model supplied as explained by Jeff Root very unsatisfying. I understand science is what it is, not what you would like it to be but the standard model seems to be a model idealised in a closed bubble. It doesn't seem to take account of material that has already combine before the proto star or proto planetary disc starts forming.

Here again I might misunderstand the reality of super novae. When these stars 'explode' or eject material, is this material vaporised or are we talking about lumps, boulders or possibly something bigger?

It strikes me that although I accept the explanation given by Jeff, it seems to be missing the possibility of large sized material and even planetoids being gravitationally captured by proto planetary discs. The standard theory seems to assume that every planetary disc starts from square one. Surely you would think that as successive generations of solar systems form they are likely to start with a lot more larger pieces of material rather than simply dust grains,

Noclevername
2016-Mar-02, 12:32 AM
Here again I might misunderstand the reality of super novae. When these stars 'explode' or eject material, is this material vaporised or are we talking about lumps, boulders or possibly something bigger?


Plasma, mostly, at those temperatures. No solid objects are coming out of a supernova.

efanton
2016-Mar-02, 12:34 AM
thanks Noclevername.
thats what I assumed, but assuming is not knowing.

kzb
2016-Mar-02, 12:37 PM
Efanton wrote:
I might misunderstand the reality of super novae. When these stars 'explode' or eject material, is this material vaporised or are we talking about lumps, boulders or possibly something bigger?

There's no lumps or boulders. Previous to becoming a supernova, the object was a large star. it was very hot and everything would have been in the gas phase. In fact it is more likely to be in the plasma phase (so hot that even atoms are dissociated into nuclei and electrons). Anyway, the key point is, there is nothing solid ejected by a supernova at the time it explodes.

As the ejected material cools, the heavier elements condense into tiny dust grains. The average size is about 0.1 micrometers, i.e smaller than most bacteria. No large chunks at this stage. There are also chemical species formed, like water, plus many carbon-containing compounds.

Any large chunks can only form later on, as these tiny particles clump together. This is more likely to happen as the cloud is compressed into a disk, because then they are closer together and orbiting at similar speeds to each other.

efanton
2016-Mar-02, 08:46 PM
There's no lumps or boulders. Previous to becoming a supernova, the object was a large star. it was very hot and everything would have been in the gas phase. In fact it is more likely to be in the plasma phase (so hot that even atoms are dissociated into nuclei and electrons). Anyway, the key point is, there is nothing solid ejected by a supernova at the time it explodes.

While I accept that this is the case for the star, and as I already posted I assumed that there would be no solid matter ejected from the dying star, I also was thinking along the lines of a thermonuclear bomb. The bomb itself and anything close to it gets vaporised, but the pressure wave produced destroys and hurls way anything but the most solid of structures for miles around it. If supernovae did a similar thing (obviously on a much bigger scale) then it would not be unreasonable to expect large chunks of material to be ejected from a solar system experiencing a super nova.

Jeff Root
2016-Mar-02, 10:32 PM
Space is big. Really big. The planets and asteroids and pieces
thereof that get scattered out of solar systems by supernovae or
gravitational slingshots are widely scattered throughout space
compared to the relatively small volume of a protoplanetary disk.

-- Jeff, in Minneapolis

kzb
2016-Mar-03, 01:02 PM
There's at least one case of a planet orbiting a neutron star (remnant of a supernova) been found.

It's certainly an interesting topic, what happens to the planets after a supernova. Depending on its distance and other variables, a planet could be (a) vaporised, (b) remain in orbit (albeit a changed one), or (c) find itself unbound to the system.

If it ends up gravitationally unbound, it will wander around as a "rogue planet". Some people think there may be lots of rogue planets, but they say most of them come from being ejected from forming planetary systems, not as ejects from supernova systems.

What you seem to be theorising is that planets are captured, rather than formed in the protoplanetary disk. There are lots of problems with that model. One I can think of offhand is, where are these rogue planets now? If this capture mechanism is how the solar system came about, there should be a constant stream of rogue planets passing near the solar system, and new planets should be captured periodically. Is there evidence of this?

efanton
2016-Mar-03, 02:07 PM
Yes I was suggesting rogue planets, asteroid and other bodies being used in the formation of new solar systems


One I can think of offhand is, where are these rogue planets now? If this capture mechanism is how the solar system came about, there should be a constant stream of rogue planets passing near the solar system, and new planets should be captured periodically. Is there evidence of this? .

Currently we are told a supernova event occurs in a single galaxy every 500 year approximately. If we assume that just one large object and many many smaller object such as asteroids, comets etc, becomes unbound then it would not be a 'constant stream' but certainly sufficient for them to become a factor in any model regarding the formation of a new solar system. our Galaxy the Milky Way is 13+ billion years old, with one object per supernova becoming unbound you are talking 26 million plus large objects having become rouge plus countless asteroids, comets and smaller object. Obviously if more than one large object is ejected the numbers go up rapidly

I find it hard to believe that all these rouge objects have nothing to to with solar system formation. If these enter a proto planetary disc surely their larger size dictates the formation of new planets at the same time the proto star is forming. A small asteroid might not be big, but it is likely to be big enough to gravitationally attract the dust grains and smaller material and grow rapidly.

We also have to take account that in the earlier generations of stars SN's would have been far more frequent but this frequency is deteriorating with subsequent generations.
All these unbound object are likely at some point, to become incorporated into solar systems, some after these solar system have formed, some as they are forming.

Jeff Root
2016-Mar-03, 08:25 PM
I'm pretty sure the most likely interaction between a rogue asteroid
and a protoplanetary disk is that the asteroid would pass through the
disk one time, disrupting it very slightly, never to return. It would not
likely be captured unless it was moving very slowly and roughly in
the plane of the disk, so that it encounters a lot of material.

The disruption might be enough to either trigger or briefly halt
formation of planetoids in a very small part of the disk. The gravity
of an asteroid smaller than Ceres is extremely tiny. My opinion is
that bodies with the mass of Earth or greater would very rarely be
thrown out of a solar system. Such bodies have not shown up in
microlensing searches. Even if there are a lot of very small bodies
flying around the galaxy, their effect on evolution of protoplanetary
disks would probably be negligible.

-- Jeff, in Minneapolis
.

efanton
2016-Mar-03, 08:37 PM
good point about any rogue object being in the same plane as a planetary disc, that's something I never considered.

kzb
2016-Mar-04, 12:23 PM
Another thing to consider is that on the cosmic time scale, protoplanetary disks don't last very long. There are only a few million years during which planet formation is possible. So these disks are quite ephemeral in the scheme of things.

The disk formation seems to be an orderly process, with a rotating gas cloud (along with it entrained micrometer dust particles) collapsing into a thin rotating gas/dust disk.

Any macroscopic objects wandering the galaxy would arrive at random angles and velocities. Like Jeff says, they're very unlikely to be travelling at just the right angle and velocity to be captured into the disk in a circular orbit, and in the plane of the gas disk.

As stated above, there is only a very limited time slot available for them to be captured also.

So if this seeding mechanism is how planets form, you would expect planetary systems to be rare. But it's now known for a fact they are not, in fact they are pretty well universal.

zyxwv99
2016-Apr-14, 12:33 AM
The solar system formed from a bit of molecular cloud that contained plenty of water. Percentage-wise it wasn't much, but in absolute terms it was enough for many, many oceans. This wasn't just hydrogen that could potentially bind with oxygen: molecular clouds in general contain actual water.

Current theories on where Earth got its water are usually described as "dry earth" and "wet earth." The most extreme version of dry earth has the planet getting nearly all its water from comets during the Late Heavy Bombardment. A more moderate version of dry earth has a substantial amount arriving from the mantle rocks of asteroids, both actual water and hydroxyl (which can turn into water if something happens to it).

The most widely accepted wet-earth scenario starts with particles of cosmic dust (the size of cigarette-smoke particles) floating around in space, with hydrogen, oxygen, or water bumping into them occasionally, then binding with the dust in processes called "adsorption" and "chemisorption." Various theories have this happening at temperatures of 450-750 K in the early protoplanetary disk. The result is a mineral called olivine, which can be up to 20% water and hydroxyl. Protoplanetary disks have been found with spectral lines consistent with olivine.

Then there's the question of how much of this water could survive the various heating events on the road to becoming a planet. Shortly after the solar system began forming, it was contaminated by radioactive fallout (probably from a supernova) containing a lot of aluminum 26. Particles that were very small at the time got heavily contaminated. Those that grew to 20 km or more within 1-2 million years would have heated up to white hot and molten. Studies indicate that most of the water would have been driven out, but some would have survived.

Assuming the same happened in other heating events (compression, friction, iron 60 and other isotopes) an initial water content of 1.25% could have been reduced to 0.1%, leaving us with one ocean and three more in reserve locked up in the mantle. In some models we started out with 5% and may have 10 extra oceans down below. Plus whatever we got from asteroids and comets.

Meanwhile, the whole business of the frost line is a little complicated. The latest is that the frost line started out at zero (when the First Core was still forming). Then it went way out there (35-50 AU in one model, 8-12 AU in another). Then, when the sun began to blow away gas and dust, the frost line moved in to 0.65 or 0.83 AU depending on the model. That persisted for a few million years before it migrated out to something vaguely resembling its current position.

During the dusty-gassy disk phase material was spiraling in so that it's hard to say where Earth started forming. Maybe beyond the Kuiper belt or half way to the Oort cloud. Later, other mechanisms kicked in that could cause outward migration, so maybe we started inside the orbit of Mercury.

In other words, they haven't figured it out yet.