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Lukipela
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The Ancient One
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Now realize of course I'm relying on scientific theory for most of those conclusions, after all, we've never been beyond our own solar system (voyeger's close).
This is partly what bothers me with this. While we can observe the presence of planets in other solar systems, we can only observe differenent types of planetary "ecosystems"1 within our own solar system. And even within our own solar system, we really don't know that much about the planets. Drawing too many conclusions based on such a small sample is a tad risky.
That's the whole point, complex life like we find on earth. We can only speculate based on known life.
If we only speculate on known life, why are we not limiting our speculations to known planets and solar systems? If you can define how probable it is for another world to support human life, surely it could be coupled with a list that defines how probable it is that another world could support non-human life. After all, it's all speculation.
I actually agree with this.. partly. They do have to be met at once because that IS what is happening here on earth. All those criteria are being met right here and right now. if you change any variable, we don't have earth as we know it. For example do you realize the global effects of just several degrees in average global temperature would do to us? We see records of cyclic ice ages and warming trends in earth's history and most are caused by a small deviance in average global temperature.
I think what Ivan meant is that all those criteria must not be fullfileld at once. If A and B are required for life as we know it, that doesn't mean that A and B must have all come into existence at once. A could have happened first, giving rise to primitive life forms that then partially caused the occurence of B. They then further evolved/were changed in a system where both A and B were present, until they were unable to survive without both A and B.
Ahh, nice try, but if the other planets in the solar system had complex life, you might have a point..  The problem with your argument is that all people are pretty much the same. Two eyes, two ears etc. etc. Not a good analogy because Earth is the oddball in our solar system. Why haven't the other planets developed ecosystems and trive with life? Especially different life forms?
While it is highly unlikely that we ever found a buried martian civilisation, we might one day find primitive lifeforms on mars, or some moon (Clarke comes to mind). Also, keep in mind that time is of the essence. For all we know, there might once have been a great civilisation on Mars. Unlikely as it is, it isn't as if we've had a chance to do any archeological research there. If the Earth had been made barren by a civilisation a million years ago, would any visitor be able to determine that there had once been life there?
1 Well not real ecosystems since they are (AFAWK) devoid of life, but I couldn't find a better word.
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What's up doc?
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Death 999
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We did. You did. Yes we can. No.
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Not too close to center of galaxy, not too far out ,and in between galactic arms which keeps us out of nebuleas cloudsand high radiation.
Even if we were in a region with a lot of nebulas, the chances of passing too close to one would be insignificant.
(not to mention, provides a good viewpoint for human exploration of the universe).
The only places that aren't good for exploring the universe wouldn't have rocky planets anyway. I'm thinking here of the globular clusters, which exist in the halo. They are all first-generation stars.
Isn't it also odd that 95%+ of galactic matter is clumpped into the center and arms of the galaxy and earth is one of the rare final few precentile?
WTF are you talking about? Earth is in an arm. We're in the 95%, not the 5%. But that's just transient. You clearly don't even know what the arms ARE.
The arms are the high-pressure portion of a pressure wave that is proceeding around the galaxy at an astronomically slow rate. In the high pressure regions, nebulas are compressed to the point they collapse into stars. The stars are of all types, including the very bright blue stars. These burn out quickly, so you only find them near the peaks of the pressure waves.
As implied by calling them waves, they move in respect to the rest of the galaxy. On an evolutionary time scale, the arms have swept over us several times. Our present position in respect to them is insignificant.
And anyone who has a basic grip on galactic astronomy knows this. If your sources claimed this was signficant, they are so ignorant as to be useless as sources.
Not only that but our sun doesnt have a companion star which most systems have. Most bi or tri star systems would be far too radio active for life as we know it..
Bull. Most binaries are distant binaries, in which the second star would be too far away to be significant. It wouldn't even disrupt the inner part of our Kuiper belt.
Alpha Centauri is a binary star system. If you were to give us a binary star that was similar to Alpha Centauri's binary partner, it would be a bit brighter than Sirius.
All the other factors were given equally as much generosity imo. Solar habital zone, right mass, stabilizing moon, not too close to sun to mass lock like venus etc. etc.
Solar habitable zone? We have no data on how wide that is. And given the several chances our solar system got (about 3 planets in roughly the right area), it seems unlikely that a system would miss altogether.
As for the right mass, again, we have two planets that are heavy enough to form a thick atmosphere without being too heavy to 'run away' like the gas giants. TWO out of a figure the order of ten.
I don't see the significance of the moon. We don't even need it for tides (The sun's tides are 1/3 as strong as the moon's, or something like that).
And Venus is not tidally locked, though its day is really long, that I'll grant.
Now realize of course I'm relying on scientific theory for most of those conclusions, after all, we've never been beyond our own solar system (voyeger's close).
If you were relying on scientific theory, you'd be a lot more accurate.
Oh, sure if any of these things were different life as we know it[ would be impossible, but it doesn't mean all kinds of life would be impossible. That's the whole point, complex life like we find on earth.
Oh, like the extremophiles that live in oceanic vents? Hmm, couldn't possibly have life that was a little toastier than it is here, then, eh?
Even if we only include life that actually is known to occur, we find that it is quite capable of tolerating situations that you do not admit it can.
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« Last Edit: September 06, 2006, 04:08:57 pm by Death 999 »
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RTyp06
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The only places that aren't good for exploring the universe wouldn't have rocky planets anyway. I'm thinking here of the globular clusters, which exist in the halo. They are all first-generation stars.
Why wouldn't there be any rocky planets there? because the dust disk hasn't built planets yet?
What I'm describing is the fact that the earth is placed in a position in the galaxy where we can view the galactic center, view the outer edge, see distant spiral galaxies and draw conclusions about our solar system position and shape of the milky way. From almost any other point other than the mid galactic plane, it's difficult to draw conclusions. Galactic arms and center are too crowded with dust and super huge stars.
WTF are you talking about? Earth is in an arm. We're in the 95%, not the 5%. But that's just transient. You clearly don't even know what the arms ARE.
Each spiral arm describes a logarithmic spiral (as do the arms of all spiral galaxies) with a pitch of approximately 12 degrees. There are believed to be four major spiral arms which all start at the Galaxy's center. These are named as follows, according to the image at right:
2 and 8 - 3kpc and Perseus Arm
3 and 7 - Norma and Cygnus Arm (Along with a newly discovered extension - 6)
4 and 10 - Crux and Scutum Arm
5 and 9 - Carina and Sagittarius Arm
There are at least two smaller arms or spurs, including:
11 - Orion Arm (which contains the solar system and the Sun - 12)
http://en.wikipedia.org/wiki/Milky_Way
I'm talking about the Major Arms.. Chocked with dust and super heavy, hot suns..Not:
The Orion Arm is a minor spiral arm of the Milky Way galaxy. The solar system and Earth are within the Orion Arm. It is also referred to as the Local Arm or the Orion Spur.
..wich is sparsely populated in comparison to the major arms.
Bull. Most binaries are distant binaries, in which the second star would be too I disagree.
Source?
Solar habitable zone? We have no data on how wide that is. And given the several chances our solar system got (about 3 planets in roughly the right area), it seems unlikely that a system would miss altogether.
I believe running water is the criteria.
As for the right mass, again, we have two planets that are heavy enough to form a thick atmosphere without being too heavy to 'run away' like the gas giants. TWO out of a figure the order of ten.
Which planets are you referring to? Besides I was talking about tidal lock where one orbiting body presents the same side to the parent object. Venus and Mercury are very, vey close to this. The drag from the sun slows their rotation. Many moons including our own exhibit this pattern.
As for size of the earth, large enough to exert enough gravity and enough mass to maintain a molten core which churns up and releases fresh chemicals onto the surface. In turn the molten iron core also provides protection from cosmic rays.
I don't see the significance of the moon. We don't even need it for tides (The sun's tides are 1/3 as strong as the moon's, or something like that).
Interesting but tides are nessicary for the moderate climate we enjoy. Somthing I don't think the sun would provide nearly as well.But even if it did, it is believed by many scientists that the moon stabilizes our rotation and axis tilt. Without the stabilizing moon our seasonal changes would be drastic.
And Venus is not tidally locked, though its day is really long, that I'll grant.
Not yet,but full tidal lock is therorized and predicted.
Oh, like the extremophiles that live in oceanic vents? Hmm, couldn't possibly have life that was a little toastier than it is here, then, eh?
Even if we only include life that actually is known to occur, we find that it is quite capable of tolerating situations that you do not admit it can.
Nobody says those animals can't live in extreme situations. But that's a far cry from the diversity and absolute density of life we find here in every possible enviornment. We have yet to find such a remarkable eco-system such as found
here anywhere else.
Thats an interesting fact in it's own right. If life is so versatile and so tenatious at surviving and evolving, why isn't mars teaming with polar bears and pine trees (or the mars equivilant) ?
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« Last Edit: September 07, 2006, 01:18:40 am by RTyp06 »
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Lukipela
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The Ancient One
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As far as we can tell all the criteria must be met for anything more complex than perhaps a neamatode. Can you think of any animal surviving on mars (or any other planet) more complex than a bacteria?
Assuming Mars at it's present state, and life as we know it, no. But as I said, you're only working with known life, and a small sample of known planets. Granted, as Ivan said another Earth is probabyl very unlikely to coem along, but that doesn't mean other forms of life are equally unlikely.
We have no reason to suspect that the cellular process in complex life today is any different than the beginning of life.
Nor does it need to be. There are plenty of bacteria around to day that can do just fine without many things we need. Oxygen, sunlight, and so forth. Some of them produce oxygen, among other things. So they might only need A, but produce B. Later lifeforms then evolve/specificallymutate to take advantage of this new circumstance B, and cannot survive without it.
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Death 999
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We did. You did. Yes we can. No.
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The only places that aren't good for exploring the universe wouldn't have rocky planets anyway. I'm thinking here of the globular clusters, which exist in the halo. They are all first-generation stars. Why wouldn't there be any rocky planets there? because the dust disk hasn't built planets yet?
This is really sad, but okay, I'll teach you astrophysics.
The globular clusters, as I said, are all first-generation stars which formed roughly simultaneously. This means that when they formed, the only thing around was Hydrogen. Okay, a tiny amount of helium and an even tinier amount of lithium. That was it. You can't make rocky planets out of that.
Supernovae in the cluster would create heavier elements, but since the other stars had already formed by that point, there is no drag to help them form up into planets. They would just scatter off of the other stars' gravity wells.
What I'm describing is the fact that the earth is placed in a position in the galaxy where we can view the galactic center, view the outer edge, see distant spiral galaxies and draw conclusions about our solar system position and shape of the milky way.
You can see the galactic center and distant spiral galaxies from anywhere in the galaxy. We couldn't see the outer edge ourselves until like 50 years ago or so.
Anyway, the ease with which one can do extragalactic astronomy has nothing to do with the development of intelligent life.
From almost any other point other than the mid galactic plane, it's difficult to draw conclusions. Galactic arms and center are too crowded with dust and super huge stars.
WTF are you talking about? Earth is in an arm. We're in the 95%, not the 5%. But that's just transient. You clearly don't even know what the arms ARE.
does not conflict with my explanation. The arms move independently of us. They sweep over us. The arms have raised density/pressure, which triggers the formation of stars.
I'm talking about the Major Arms.. Chocked with dust and super heavy, hot suns.
It's not choked with dust. If it were, it would be DIM. It's dense with hydrogen and number-dense with bright stars. The bright stars are deadly to be around, yes; but they only form where there are nebulas. The nebulas are orbiting with us, and their collapse is triggered by the pressure wave. The nebula in our area already got triggered a long time ago, making our system; so there isn't another one around to wreck us later.
Bull. Most binaries are distant binaries, in which the second star would be too I disagree. Source?
Wait a cotton-picking moment. You disagree before you've even looked at the evidence. Great.
http://www.stellar-database.com/fields.html
says that
Bear in mind that any planets in a multiple star system must be closer to the star they are orbiting than 25% of the Periastron distance between that star and its nearest neighbor; otherwise, their orbits wouldn't be stable and they'd fly off into deep space. Note, this is a pessimistic rule of thumb since one star may be substantially larger than the other, which would help bind other objects into the system.
I'll go down the database, from closest to furthest... (note, this does bias the data, in the direction of HIGHER density and more close binaries, because we are in a dense neighborhood)
periastron separations (i.e. the closest they get)
Alpha - proxima centauri periastron separation: 11.4 AU
UV Ceti: 4.12 AU
Sirius: 8 AU
Epsilon Eridani: 1.36 AU
EZ Aquarii: < 1.22 AU
Procyon and its companion: 9.544 AU
61 Cygni: 51 AU
Struve 2398: 26.26 AU
Groombridge 34: 146 AU
DO Cephei: 5.7 AU.
V577 Monoceri: 3.857 AU
etc. As you can see, the median separation from these 11 samples is Sirius, with 8 AU separation. Over 50% of the stars involved would have enough room to fit Earth in; the role of Jupiter in our system would obviously be taken by the other star.
And then of course there's the possibility of using a trojan orbit. You can fit two planets in very easily in that case.
Solar habitable zone? We have no data on how wide that is. And given the several chances our solar system got (about 3 planets in roughly the right area), it seems unlikely that a system would miss altogether. I believe running water is the criteria.
I know. I didn't say we have three planets in the habitable zone, I said in the right area. Planetary orbits are forced to be spaced out somewhat, and that increases the chances that one will happen to be in the Goldilocks zone.
As for the right mass, again, we have two planets that are heavy enough to form a thick atmosphere without being too heavy to 'run away' like the gas giants. TWO out of a figure the order of ten. Which planets are you referring to?
Venus. Earth. We have of order ten planets. Four are gas giants. Four are rocky inner planets. The rest are ice dwarfs.
Of the rocky inners, two have a substantial atmosphere.
Besides I was talking about tidal lock where one orbiting body presents the same side to the parent object. Venus and Mercury are very, vey close to this. The drag from the sun slows their rotation. Many moons including our own exhibit this pattern.
The drag from the sun? Drag. From. The. Sun.
LOL
The slowing is due to an interplay between tides and frictional losses in the mantle and core. Tidal lock sets in when the planet has been distorted to an egg shape so that one side is significantly more attracted than the rest of the planet.
As for size of the earth, large enough to exert enough gravity
Umm... you mean heavy enough to maintain an atmosphere? As I already pointed out, two out of four rocky planets in this system qualify.
and enough mass to maintain a molten core which churns up and releases fresh chemicals onto the surface.
That would be where tides become important, actually. Tides are what keep volcanism active, not our mass. See below. And above. Jupiter's moon Io has a lot more volcanism than Earth, and it has a tiny mass, comparatively speaking.
In turn the molten iron core also provides protection from cosmic rays.
The atmosphere does that. The high energy cosmic rays pierce the magnetic field like it wasn't even there, and wham! Atmosphere? Nearly nothing gets to the ground. Sure, UV gets through, but that passes straight through the magnetic field with no interaction.
Interesting but tides are nessicary for the moderate climate we enjoy. Somthing I don't think the sun would provide nearly as well.
One third as much, as I said. If you have a real argument for why we tides one third as large would be a problem, I'd really like to hear it.
But even if it did, it is believed by many scientists that the moon stabilizes our rotation and axis tilt. Without the stabilizing moon our seasonal changes would be drastic.
Hmm.. axial tilt of other planets... among the rocky inner planets, we have the LARGEST axial tilt, slightly larger than that of Mars and 6 times larger than that of Venus. In fact, the only planet in the entire solar system with an axial tilt substantially larger than ours is Uranus, and that's so far out its tidal interactions with the Sun are insignificant.
This is inconsistent with the 'we'd begin wobbling way too much' theory.
And Venus is not tidally locked, though its day is really long, that I'll grant. Not yet,but full tidal lock is therorized and predicted.
Well, it's jolly well taking its time! If it takes more than 6 billion years, is that enough to prevent the formation of complex life? NO.
Oh, like the extremophiles that live in oceanic vents? Hmm, couldn't possibly have life that was a little toastier than it is here, then, eh?
Even if we only include life that actually is known to occur, we find that it is quite capable of tolerating situations that you do not admit it can. Nobody says those animals can't live in extreme situations. But that's a far cry from the diversity and absolute density of life we find here in every possible enviornment.
If your ecosystem was most easily measured in cubic meters I don't think you'd have a lot of large complex life with tons of biodiversity either.
I was just making a point, which you missed: life can tolerate temperatures of near the boiling point of water.
We have yet to find such a remarkable eco-system such as found here anywhere else.
... not that we have a lot of places besides Earth to look, do we?
Thats an interesting fact in it's own right. If life is so versatile and so tenatious at surviving and evolving, why isn't mars teaming with polar bears and pine trees (or the mars equivilant) ?
Because the chances of life successfully forming are not particularly close to 100% even in eligible cases?
Because Mars is too hot for ammonia-based life?
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« Last Edit: September 07, 2006, 06:30:30 pm by Death 999 »
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RTyp06
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The globular clusters, as I said, are all first-generation stars which formed roughly simultaneously. This means that when they formed, the only thing around was Hydrogen. Okay, a tiny amount of helium and an even tinier amount of lithium. That was it. You can't make rocky planets out of that.
Supernovae in the cluster would create heavier elements, but since the other stars had already formed by that point, there is no drag to help them form up into planets. They would just scatter off of the other stars' gravity wells.
Fascinating, but rather pointless..really. I disagree that the only bad place to view the universe around us is are places without rocky planets. And as you pointed out, this isn't a criteria for complex life just an interesting side note.
You can see the galactic center and distant spiral galaxies from anywhere in the galaxy. We couldn't see the outer edge ourselves until like 50 years ago or so.
I disagree.. How would we be able to differentiate between distanant objects and close objects in densely packed places in our galaxy such as the core? We have difficulty with this as is.
Anyway, the ease with which one can do extragalactic astronomy has nothing to do with the development of intelligent life.
Agreed, was just an interesting side note, such as the moon perfectly covering the solar disk during a total eclipse that has allowed us humans to confirm some aspects of the theory of realitivity.
does not conflict with my explanation. The arms move independently of us. They sweep over us. The arms have raised density/pressure, which triggers the formation of stars.
We don't know this and is purely theroretical. In fact some scientists have tried to use this as an explanation for the cyclic global weather changes (ice ages). Earth is not inside a major galactic arm and never have been throughout human recorded history. And we ARE in a realitivly clear area of space, a minority place outside the vast mass of the galaxy.
It's not choked with dust. If it were, it would be DIM. It's dense with hydrogen and number-dense with bright stars. The bright stars are deadly to be around, yes; but they only form where there are nebulas. The nebulas are orbiting with us, and their collapse is triggered by the pressure wave. The nebula in our area already got triggered a long time ago, making our system; so there isn't another one around to wreck us later.
It is choked with dust. There is a reason we called it the "Milky Way' when viewing our galaxy edge on.
Wait a cotton-picking moment. You disagree before you've even looked at the evidence. Great.
You didn't present any evidence and it is my understanding that most binary star systems are theorized to be tidally locked., not just in resonance with each other which can be achieved at much greater distances.
Also to illustrate my point:
Visual binary stars have a large true separation, and consequently usually have orbital speeds too small to be measured spectroscopically from far away. Conversely, spectroscopic binary stars move fast in their orbits because they are close together; usually too close to be detected as visual binaries.
http://en.wikipedia.org/wiki/Binary_star
Hubble and Spitzer are finding these close binaries at an alarming rate. I understand that it wasn't until modern times where we had powerful and orbital telescopes that we drew the conclusion that most stars we see are part of a binary or more system.
I'll go down the database, from closest to furthest... (note, this does bias the data, in the direction of HIGHER density and more close binaries, because we are in a dense neighborhood)
I agree we are in a fairly dense area (number of nearby stars) of our galaxy but still maintain it's nothing compared to the core and the desnse major galactic arms.
etc. As you can see, the median separation from these 11 samples is Sirius, with 8 AU separation. Over 50% of the stars involved would have enough room to fit Earth in; the role of Jupiter in our system would obviously be taken by the other star.
Brown dwarfs occupy the mass range between that of the lowest mass stars (anywhere between 75[1] and 80 Jupiter masses) and large gas-giant planets.
http://en.wikipedia.org/wiki/Brown_dwarf
Now imagine that mass sitting in an orbit somewhere between Jupiter (5.2 AU) and Saturn (9.5 AU). I think it might have a significant effect on the inner solar system.. Don't you? And that's just a brown dwarf which is on the low end of the scale for star masses. So most of those binary stars you listed are much, much more massive.
I know. I didn't say we have three planets in the habitable zone, I said in the right area. Planetary orbits are forced to be spaced out somewhat, and that increases the chances that one will happen to be in the Goldilocks zone.
Just because the odds of a planet residing in the goldilocks zone may not be extreme, what about size? Size matters, despite what women tell us..
Venus. Earth. We have of order ten planets. Four are gas giants. Four are rocky inner planets. The rest are ice dwarfs.
Of the rocky inners, two have a substantial atmosphere.
Wether a planet has an atmosphere or not is of course not solely decided by mass. I believe the chemicals that constitute the atmosphere are very important as well as the gravitational pull.
The drag from the sun? Drag. From. The. Sun.
LOL
Yeah? Not seeing the humor...
The slowing is due to an interplay between tides and frictional losses in the mantle and core. Tidal lock sets in when the planet has been distorted to an egg shape so that one side is significantly more attracted than the rest of the planet.
Thank you for describing the mechanics of tidal locking but what causes it? Yeah, that's right, the gravity of the parent object... Perhaps "drag" isn't the best choice of words but the principle stands. The moon is in tidal lock because of the earth's gravity irregardless of the specific details...
Umm... you mean heavy enough to maintain an atmosphere? As I already pointed out, two out of four rocky planets in this system qualify.
Mass and atmospheric chemical composition are both important factors. If mass didn't matter, many of the small moons would have thick atmospheres.
That would be where tides become important, actually. Tides are what keep volcanism active, not our mass. See below. And above. Jupiter's moon Io has a lot more volcanism than Earth, and it has a tiny mass, comparatively speaking.
So what happened to mars? Why does it boast the largest volcanos in the solar system yet has two small insignificant moons with little to no tidal effect? IO is an extreme case and you are clearly correct, but do you really think the moon or sun tides are solely responsible for earth's molten core? And what about mercury? Surely the sun's tidal effect would make that little rock a molten mess? How about venus without a moon and has much evidence of a volcanic past (if not current)..
The atmosphere does that. The high energy cosmic rays pierce the magnetic field like it wasn't even there, and wham! Atmosphere? Nearly nothing gets to the ground. Sure, UV gets through, but that passes straight through the magnetic field with no interaction.
Im not talking about UV that the OZone takes care of...
Then, during the decade from 1927 to 1937 a wide variety of experimental investigations demonstrated that the primary cosmic rays are mostly positive charged particles,
http://en.wikipedia.org/wiki/Cosmic_rays
Hmm.. axial tilt of other planets... among the rocky inner planets, we have the LARGEST axial tilt, slightly larger than that of Mars and 6 times larger than that of Venus. In fact, the only planet in the entire solar system with an axial tilt substantially larger than ours is Uranus, and that's so far out its tidal interactions with the Sun are insignificant.
Yes and our tilt still wanders. Some scientists theorize it would be much worse than is without the moon.
This is inconsistent with the 'we'd begin wobbling way too much' theory.
I'm not aware of this theory and is not my argument. It is believed the earth had a much more erreatic wobble before the moon was formed and the moon's tidal interaction has stablized the earth to a certain degree. I'm not saying the earth was completely chaotic and out of control.
If your ecosystem was most easily measured in cubic meters I don't think you'd have a lot of large complex life with tons of biodiversity either.
I was just making a point, which you missed: life can tolerate temperatures of near the boiling point of water.
Yes I'm aware of extremophile life. One would think from a darwinian standpoint though that if microbes had reached the other planets they'd have had enough time to build ecosystems and alter their respective atmospheres in a similar fashion as found here on earth, would they not?
Because the chances of life successfully forming are not particularly close to 100% even in eligible cases?
Because Mars is too hot for ammonia-based life?
Um .. OK..
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Death 999
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We did. You did. Yes we can. No.
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Luki, you can talk about astrophysics. It's not the topic, it's the approach.
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Death 999
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We did. You did. Yes we can. No.
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I disagree that the only bad place to view the universe around us is are places without rocky planets.
We can see straight through the other arms quite a distance from here (otherwise how did we know about the other arms of this galaxy?) so clearly we could see out of them from inside.
Consider the consequences of your conclusion before you disagree.
I disagree.. How would we be able to differentiate between distanant objects and close objects in densely packed places in our galaxy such as the core? We have difficulty with this as is.
What... the... frell...
Do you have any clue how we actually tell how far away the stars are? The only problem the core would pose to observations is that we'd be dead and no planetary system could form due to the absurd density. Aside from that, there are no obstacles to getting the trigonometry done to calculate the distances. Which is what you were talking about. Oddly enough.
[it] was just an interesting side note, such as the moon perfectly covering the solar disk during a total eclipse that has allowed us humans to confirm some aspects of the theory of realitivity.
Which we would have been able to confirm by other methods about... twenty years later even with no moon whatsoever. Gravitational lensing, anyone?
does not conflict with my explanation. The arms move independently of us. They sweep over us. The arms have raised density/pressure, which triggers the formation of stars.
We don't know this and is purely theroretical.
What is purely theoretical?
The arms are where the brightest stars are. This is what makes them bright. The density of other stars is roughly even as you proceed around the disk. Neutron stars, i.e. the remnants of bright stars, are distributed around the disk approximately evenly. Therefore, bright stars have formed around the disk fairly evenly. Thus, the formation of bright stars has moved around the disk. The only reasonable mechanism which could cause this is a gas density wave.
In fact some scientists have tried to use this as an explanation for the cyclic global weather changes (ice ages).
Use what as the explanation? The movement of the arms? Interstellar dust clouds and such, sure; but at any rate the movement of the arms through the galaxy is not so fast as our ice age transitions.
Earth is not inside a major galactic arm and never have been throughout human recorded history. yeah, that's, what, 10,000 years tops? That's how long it takes light to get from the core to here. On the time scale of the movement of the arms that's NOTHING. A hundred million years, now you're talking.
And we ARE in a realitivly clear area of space, a minority place outside the vast mass of the galaxy.
So you keep saying.
Local density of stars: roughly 0.1 per cubic parsec.
There are a number of dense star clusters, 'open clusters', which have substantially higher star density, from 0.3 to 10 stars per cubic parsec. However, there are only a few thousand such open clusters in the galaxy and each one contains only a few hundred stars, a few thousand on the upper end. Total? A million stars, roughly. Compared to the 100 billion stars in the galaxy, that's nothing.
Note, by the time you get up to 0.3 stars per cubic parsec, you're already in 'cluster' territory, which implies that this is unusually high density.
Also, there are globular clusters. However, these are not in the disk at all, forming a halo around the galaxy. Their number should not be dismissed completely, but it should be fairly clear that there are quite a few stars not in the halo.
Then there's the core. Core stars are indeed much more dense, so if the average you are speaking of includes core stars, that would explain everything. But the core is inappropriate for a wide variety of reasons all at once.
Disk stars are the name of the game, not core, not halo. The open clusters account for a tiny fraction of the disk. The rest is around our density or less.
It's not choked with dust. If it were, it would be DIM. It's dense with hydrogen and number-dense with bright stars. It is choked with dust. There is a reason we called it the "Milky Way' when viewing our galaxy edge on.
Umm, that's STARS. You know, the bright things that emit lots of light. Not the dark stuff that absorbs light and reemits in the infrared, that we call 'dust'.
As I tried to say to you earlier.
and it is my understanding that most binary star systems are theorized to be tidally locked., not just in resonance with each other which can be achieved at much greater distances.
Those would be the really tight binaries. See below.
Visual binary stars have a large true separation, and consequently usually have orbital speeds too small to be measured spectroscopically from far away. Conversely, spectroscopic binary stars move fast in their orbits because they are close together; usually too close to be detected as visual binaries.http://en.wikipedia.org/wiki/Binary_starHubble and Spitzer are finding these close binaries at an alarming rate. I understand that it wasn't until modern times where we had powerful and orbital telescopes that we drew the conclusion that most stars we see are part of a binary or more system.
Looking at a list of spectroscopic binaries...
http://lheawww.gsfc.nasa.gov/~corcoran/sb8.html
Most of these periods are really short, like 0.8 days, 4 days, etc. These stars are close enough to act like one central mass from the point of view of a planet as far out as we are.
So, I still don't see a problem.
And on top of that, a lot of these stars are stars which otherwise would be too dim to support life; but with the extra boost of a similar neighbor, could do the trick. Great!
I agree we are in a fairly dense area (number of nearby stars) of our galaxy but still maintain it's nothing compared to the core and the desnse major galactic arms.
I agree that the core is way too dense, but the density of arms or not is irrelevant, since we have been in arms and not in arms several times each on evolutionary time scales! So our not being in a dense region now is not a selection factor.
Now imagine that mass sitting in an orbit somewhere between Jupiter (5.2 AU) and Saturn (9.5 AU). I think it might have a significant effect on the inner solar system.. Don't you?
Hard to say, actually. It's in the regime where i'd really want a calculation instead of handwaving or even back-of-the-enveloping.
Just because the odds of a planet residing in the goldilocks zone may not be extreme, what about size? Size matters, despite what women tell us..
I answered this already. Sheesh. 2/4 rocky planets are of an appropriate size to hold an atmosphere. If you count the giants, it's still 2/8, hardly a showstopper. This automatically includes all factors, including size.
Wether a planet has an atmosphere or not is of course not solely decided by mass. I believe the chemicals that constitute the atmosphere are very important as well as the gravitational pull.
Well, yeah. That's a great selection criterion. Mars has an appropriate-looking chemistry. Its problems are that it is too cold and too little. So, 2/3. And there are the moons of Jupiter, which again have all the right stuff.
The individual ingredients are not looking terribly uncommon.
Yeah? Not seeing the humor...
drag from the sun? That connotes atmospheric drag, which in the vacuum of space, even with a solar wind, is completely negligible. I gave you the mechanism, and 'drag from the sun' isn't a part of that.
Perhaps "drag" isn't the best choice of words but the principle stands. The moon is in tidal lock because of the earth's gravity irregardless of the specific details...
And you ignored my main point, which was that Venus is in fact not tidally locked. Back in the beginning of life, it would have been spinning much more; and as it slowed down, life would have adapted.
Umm... you mean heavy enough to maintain an atmosphere? As I already pointed out, two out of four rocky planets in this system qualify. Mass and atmospheric chemical composition are both important factors. If mass didn't matter, many of the small moons would have thick atmospheres.
I spoke of actual planetary atmospheres. This automatically takes all factors into account, including mass.
By the way, there is a moon with a fairly thick atmosphere, Titan. And life could form underwater, too, in Europa or a similar body.
So what happened to mars? Why does it boast the largest volcanos in the solar system yet has two small insignificant moons with little to no tidal effect?
1) I meant tectonic activity, not volcanism. My bad. Volcanism is due to excess heating in the core, which can be due to radioactivity or an increase in compression. Increases in compression can in turn be due to tides or just due to the planet's not having settled down yet.
2) Mars has enormous volcanoes because it had too LITTLE tectonic activity, not too much. If you have an upwelling and let it sit in the same place for a few billion years, you get a massive volcano. Whereas our ring of fire is a ring because the plates keep moving away.
And what about mercury? Surely the sun's tidal effect would make that little rock a molten mess? How about venus without a moon and has much evidence of a volcanic past (if not current)..
Mercury is in a stable resonant orbit, which would minimize the impact of the tidal forces on tectonics. It has already been pulled as much as it's going to be.
Venus has slightly stronger tides from the sun than the Earth does from the moon (2/3 the orbital radius, 3/2 to the third power is 27/8 ~ 3 )
Re: Cosmic rays
yes, cosmic rays are largely charged particles. This does not conflict with what I said. These particles are so hyperrelativistic that they pass through our magnetic field with little effect. Then they hit the atmosphere and BAM, particle shower. You can't find these things on the ground. Go on a tall mountain, and you can. Go in space, even in our magnetosphere, and you need radiation shielding.
Yes and our tilt still wanders. Some scientists theorize it would be much worse than is without the moon.
Perhaps they are pointing out that our axis would precess much more quickly. Sure, that would be so; but the solar-system 'longitude' part of the orientation of north is completely unimportant.
Otherwise, they're ignoring the point I made, which seems an awfully odd coincidence if there is no motivating mechanism.
In other words, if it did it more, would it really be worse?
This is inconsistent with the 'we'd begin wobbling way too much' theory. I'm not aware of this theory and is not my argument.
Oh, really?
It is believed the earth had a much more erreatic wobble before the moon was formed and the moon's tidal interaction has stablized the earth to a certain degree. I'm not saying the earth was completely chaotic and out of control.
Gee, it sounds exactly the same as your argument! I didn't say 'completely chaotic'. I said 'way too much'. As in, it would be a severe enough problem to prevent the formation of life. If it isn't a problem, why are you even bringing it up?
You are trying to argue that Earth was extremely uncommonly well-suited to the formation of life, aren't you?
Yes I'm aware of extremophile life. One would think from a darwinian standpoint though that if microbes had reached the other planets they'd have had enough time to build ecosystems and alter their respective atmospheres in a similar fashion as found here on earth, would they not?
Darwinianly, they would alter themselves. You're thinking of Gaia, not Darwin. There is no reason to suspect that these creatures would not form a Gaia which reinforced the satus quo rather than bringing them for some reason to an Earthlike system.
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