solar system creation

General physics and astronomy discussions not directly related to Celestia
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solar system creation

Post #1by Apollo7 » 22.07.2003, 01:57

Ok well using trusty Excel I've been creating a solar system and I'm trying to make it as realisticly as possible.
As an aside, is it even possible to get Excel to find something other than the square root of a number, i.e. a 3.5 root or a 4 root? I know Quattro Pro will do this, but will Excel?

Ok anyway the primary star is a single sun, of type G4 V. It has a radius of .828490 Sol and a Mass of .877077 Sol. The surface temp is 5740K and the Absolute Magnitude is 5.01.

I chose to create a sytem along the lines of Upsilon Andromeda, at least at first. The system includes three "Terrestrial Jovians" all within 1 AU of the parent star.

The first planet, Planet B - Nemesis orbits with a SemiMajorAxis of .064315 AU, a period 5.87 days and an eccentricity of .041064. I calculate other stats, like obliquity, Density et all but such bits of data are not relevant to this discussion. Planet C - Ragnarok orbits with a SMA of .298779 a period of 58.79 days, and an eccentricity of .084725. Planet D - Haydes has characteristics of SMA: .826884, Period: 270.69, Eccentricity: .117181. The masses for each planet (in Earth masses) are B: 166.5471, C: 35.61065 and D: 1124.091.

Now where I'm unclear is on the situation of massive moons orbiting these worlds. I created a moon for Nemesis, Asterion, and gave it the following relevant characteristics. Radius: .867432 E, Mass: .600584 E, Density: 5.0594962, with an average distance from Nemesis of 207,492.2 Km an Eccentricity of .204382, and an inclination of 7.170787 deg. Asterion does pass within the Roche limit of Nemesis, however from what I know its density is high enough to permit survival. That being said I do wonder as to weather it can survive as a moon of a Jovian world so close to its parent sun. I would imagine the perturbations would be enormus, since Nemesis is a little over half the mass of Jupiter, I question weather or not my neat system would survive for any length of time.

As for the other two worlds the questions still arise from perturbations and the relative proximity of each world to its neighbor. For Haydes, one of its moons, Therador swings on a highly eccentric inclined orbit that takes it nearly 3 million kilometers from the very massive planet it orbits. Again its a question of probability, my system looks neat but its difficult to ascertain if its even plasuable. Further, I placed sevearl Earth-like planets around Haydes, however, their seperation was often under 250,000km leads me to wonder if they could survive, considering the high densities and near Earthlike masses. Anyway I'd appreciate any input here, I can post my system when its read as well.

Cheers.
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Post #2by granthutchison » 22.07.2003, 02:19

You can get Excel to do any old root you want. For instance, for the 3.5th root of 7, use:

Code: Select all

7^(1/3.5)


What you're after is the Hill radius for your system - something that's just cropped up on another thread. It's the radius within which orbits can be expected to remain closed (ie not wander off into the Universe) despite the presence of a perturbing mass. If M is the mass of your star, m is the mass of your planet, D is the planet's distance from the star, and M>>m, then the Hill radius d is approximated by:

d = D[m/(2M)]^1/3

If your planet is within a 150th of the mass of the star, you get a better approximation from:

d = D[m/(3M)]^1/3

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Post #3by Evil Dr Ganymede » 22.07.2003, 03:29

I would be extremely surprised if your planets have moons. The tidal forces from the primary star would cause any satellites to spiral into the planets on a not very long geological timescale (the solar tides suck angular momentum out of the planet-satellite system). Hill spheres aren't particularly relevant to this effect.

That said, if the jovians formed further out with multiple satellites and spiralled in, I don't know what would happen - multiple bodies make it a hell of a lot more complicated. I suspect you'd still lose the moons through tidal forces though.

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Post #4by Apollo7 » 22.07.2003, 04:30

Ok so what I'm hearing is in this configuration moons of anykind are unlikely, and I can see the logic in that argument. What if, however, I removed all the jovians, save Haydes, and assigned moons to it? Would then the pertubations be less of a problem? Would the existance of close-in jovians preclude terrestrial worlds in much wider orbits? Thanks for the replies.

Cheers.
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Post #5by Evil Dr Ganymede » 22.07.2003, 04:49

Apollo7 wrote:Ok so what I'm hearing is in this configuration moons of anykind are unlikely, and I can see the logic in that argument. What if, however, I removed all the jovians, save Haydes, and assigned moons to it? Would then the pertubations be less of a problem? Would the existance of close-in jovians preclude terrestrial worlds in much wider orbits? Thanks for the replies.


At the distance that Haydes is from the star, you can probably forget about moons, unless the system is pretty young. It's more likely to have them than the other jovians though.

As for your latter question - I don't know. We don't even really know how the close-in Jovians get there. If they spiral in from further out, then any terrestrial worlds in the way would probably be destroyed.

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Post #6by Apollo7 » 22.07.2003, 06:20

Well you make good points, however: I am not a proponent of the spiral-theory, it seems to me like it could happen but if thats how it works, it would beg the inevitable question of why it did not happen here. I tend to believe we need to rethink or ideas on how gas giants form, it seems a process of collapse out of the nebula, like a star, is the most likely (read: simplest) explination. But, I wont lose any sleep if I'm wrong either.

I will redesign the system and take some new looks at just how the systems form, Celestia is useful for me as I am a writer and the program allows me to visualize the systems I create, beyond just having them on a spreadsheet, which is, of course, extremely useful. I'll get back to the drawingboard and see what else I can come up with, thanks for the input though, since I'm not in school for this stuff yet I still learn as I go.

Cheers.
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Post #7by Evil Dr Ganymede » 22.07.2003, 07:49

Well, I'm a fairly experienced system builder (on paper at least. I've made loads of systems for the Traveller RPG, and I'm a stickler for realism), so I'll gladly offer advice :).

There are some pretty nifty books out there to help you build planetary systems - Stephen Gillett's "Worldbuilding" is a must-have. Some of the sci-fi RPG books are pretty useful too. There are a few copies of 'Worldbuilding' left on Amazon.com at:

http://www.amazon.com/exec/obidos/tg/detail/-/158297134X/ref=pd_bxgy_img_2/104-0328134-5487131?v=glance&s=books

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Post #8by granthutchison » 22.07.2003, 12:56

Evil Dr Ganymede wrote:The tidal forces from the primary star would cause any satellites to spiral into the planets on a not very long geological timescale (the solar tides suck angular momentum out of the planet-satellite system). Hill spheres aren't particularly relevant to this effect.
Neat. They can't settle into synchronous rotation with both the primary and the star, but both raise massive tides, so energy has to be lost. Makes sense, now you've said it. :wink:
As to the Hill radii, plugging in some low Jovian masses to Apollo7's system shows the satellites orbiting within the Hill radii - so they're orbits might wander a bit, but in the longer term they're definitely going to go in, rather than out, as you say.

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Post #9by granthutchison » 22.07.2003, 18:27

Evil Dr Ganymede wrote:At the distance that Haydes is from the star, you can probably forget about moons, unless the system is pretty young.
Hang on, though. At Haydes' distance from its star, the stellar tides are going to be of very similar magnitude to those on the Earth's Moon - only 1.5 times more, if the Moon were transplanted to the Haydes system. Admittedly the forces experienced by an Earth-sized body will be larger, but its inertia will scale faster than the tidal forces with increasing radius.
Stellar tides on the Moon have failed to counteract the outward impulse generated by lunar tides on the Earth - so the Moon has moved steadily outwards over geological time. Shouldn't we expect something similar to happen at Haydes? The highly eccentric moon would then quickly circularize its orbit at pericentre distance and become a synchronous rotator, but might then be drifting outwards at a rate that would depend in some complex way on its distance from Hyades, and Hyades' rate of rotation.

I guess I'm missing something again, but I don't know what it is :cry:

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Post #10by Apollo7 » 22.07.2003, 23:29

I'm not sure how much this matters, but the central star in this scenario is less massive than the sun, if I recall it was about 827% as massive. Someone mentioned the Hill Radius here and after some work I got my spreadsheet to calculate that for me. I guess my only real concern was creating systems which simply could not exist for any length of time.

I've since gone on looking at other configurations and possibilities. It is too bad that planets like 51 Pegasi B and Tau Bootis B probably do not have moons. They would be exceedingly interesting to study in the event that they did. Of course the possibility of Terrestiral moons orbiting gas giants is facinating in of itself, which is why I feel using Celestia for that means is a good thing.

Anyway After checking out Upsilon Andromedae the actual seperations are more on the order of B .05 AU, C 1 AU and D 2.2 AU. I'll be doing some redesigns and calculations, hey at least its fun right? heh. Well after dinner I'll see what else I can come up with.
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Post #11by Evil Dr Ganymede » 23.07.2003, 09:32

Grant - here's how I understand it. In order for the 'spiralling in' process to start, the satellite has to be synchronously locked to its planet and the planet has to be locked to the satellite (like the Pluto-Charon system). At this stage, the satellite is basically in a geosynchronous orbit. After that, the solar tides become dominant and try to tide-lock the planet to the star. This slows the planet's rotation down, which increase the geosynchronous distance, moving that orbit out from the planet. However, the satellite itself can't keep up with the expanding geosynchronous orbit, so its orbit starts to evolve a satellite that's orbiting within it - it starts to spiral in towards the planet (like Phobos is doing around Mars). As it approaches the planet, its orbital evolution speeds up since the planet's rotation is still slowing down, and eventually the satellite hits the planet or breaks up around it.

The Earth-Moon system hasn't got to that stage yet - the moon's still evolving outward from Earth. It may not even get that far, it depends on whether or not the Moon is lost into interplanetary space before it reaches the 'outer geosychronous orbit' (IIRC that the Earth would have a rotation period of somewhere around 60 days by this point, equal to the Moon's extended orbit)

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Post #12by Apollo7 » 23.07.2003, 11:16

Hmm theres a point that I seldom here about, it is a fact that the moon is recieding at about 4 cm a year, with a nearly-negligable (but measurable) increase in the Earths rotation period occuring as a result. I'm wondering if the solarsystem has enough survival time in it for the moon to escape the Earth's grasp. With only 5 billion years or so to go, is that enough time? And if the moon did elude Earth's gravitation would it not become a hazard of "biblical" proportions to the beings of Earth (if there are any) at that time?

I read a paper on the survivability of moons if infact their parent jovians spiral in towards the primary star due to drag from the infant nebula. The ability for the planet to retain or lose its moons depended not just on the hill radius of the system, but upon what fraction of the hill radius the moons orbit occupied and weather or not the moons revoultion was prograde or retrograde. It was an interesting read but the gist of it was. Prograde moons are easilly lost during inward migration (especially if their orbit extends to .1 the Hill Radius), but retrograde orbits are far harder to shear away from the planet. If I recall the paper concluded retrograde moons within .1 the Hill Radius would survive the passage inward up until about .1 AU. So still this all but certainly rules out moons for planets like 70 Virginis B, 51 Pegasi B, or 55 Cancri B. Of course if the system is young and there is an abundant supply of detritus (Planetesimals, Asteriods and the like) then perhaps there could be many transient, but ultimately totally unstable configurations possible.

As I recall the recent spate of moons found around Jupiter are all thought to be recent, unstable captures of Jupiter, and not stable at all. So perhaps gas giants, effecient as they are at attracting small bodies, would have a near innumerable ammount of possible configurations throughout the lifetime of a star system.

In reference to what the good Evil Doctor said, am I to understand that once a moon achieves geostationary orbit about its homeplanet, (e.g. the pluto-charon system) that then the star begins working on the planet to tide-lock the planet to the star? If so that would be quite an interesting phenomina to observe.

Another question I'm pondering right now is the limit of terrestrial world building that may occur in space. Some have suggested the spate of Epistellar Jovians now known to exist could be super-terran type worlds of emese proportions, but rocky surfaces. Is there any reason (or any process) in the physical universe that would prevent or preclude the formation of Terrestrial Worlds above a certain size? 51 Pegasi B is thought to weigh in at .46 Mj, is it entirely inpossible that this planet is a super-Earth? It does seem logical that at the extreme close distances involved with the Epistellar Giants that such a region would prefer a mix of dust and metals as opposed to the very light (but plentiful) supply of H, D, and He. So one could immagine a large planetessimal forming at .05 AU from a sun-type star, becoming very massive, however being unable to capture the nebular-envelope proper as the star may eject the lightest gasses before accretion is complete, thus leaving only heavier elements for the taking. Am I off base on this hypothesis?

Anyway the system I've currently designed includes 4 gas giants, a quasi-terrestrial world and two Plutino-type vagrants.

My system is designed as follows:
Star: RB722208, F9V, 1.12Ms, 1.14Rs, 6050k temp.
Comfort Zone: 1.218 A.U.
Brightness: 1.48Bs
Lifetime: 7.13Gy

The Star translated into Celestia pretty well, however the temperature values reported in the program seem to be rather underestimated, this is ok however.

The Planets are currently as follows:
B: Mirage, 23Me, 4.5Re, .064AU
C: Illusion, 138Me, 8Re, 1.22AU
D: Deception, 20Me, 3.14Re, 3.5AU
E: Magic, 684Me, 14.2Re, 9.2AU
F: Illumination, 73.44Me, 7Re, 17.7AU
G: Faith, .02Me, .36Re, 32.1AU
H: Truth, .0007Me, .15Re, 45.2AU

The planet Illusion swings in and out of the comfort zone, however its size and mass were not condusive to Earth size worlds, it does have a large moon but it is more Mars like. Mirage is a Jovian, where as Deception is a Terrestrial world. Despite the similarity in mass, Deception is composed of a mix of ice and rock and has a mean density of 3.51gm/cm^3. In this configuration Illumination revolves in a retrograde motion with a period of roughly 74 years.

Anyway, I'll post more later, cheers.
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Post #13by Evil Dr Ganymede » 23.07.2003, 19:29

Apollo7 wrote:Hmm theres a point that I seldom here about, it is a fact that the moon is recieding at about 4 cm a year, with a nearly-negligable (but measurable) increase in the Earths rotation period occuring as a result. I'm wondering if the solarsystem has enough survival time in it for the moon to escape the Earth's grasp. With only 5 billion years or so to go, is that enough time? And if the moon did elude Earth's gravitation would it not become a hazard of "biblical" proportions to the beings of Earth (if there are any) at that time?

I think it's going to take longer than the remaining lifetime of the solar system to reach the outer synchronous orbit. I did have some numbers for this somewhere but I've lost them :oops:

In reference to what the good Evil Doctor said, am I to understand that once a moon achieves geostationary orbit about its homeplanet, (e.g. the pluto-charon system) that then the star begins working on the planet to tide-lock the planet to the star? If so that would be quite an interesting phenomina to observe.

Yep. Thoough for Pluto-Charon, the solar tides are so miniscule as to be non-existent. That system's staying in the 'double-locked' state.

It does seem logical that at the extreme close distances involved with the Epistellar Giants that such a region would prefer a mix of dust and metals as opposed to the very light (but plentiful) supply of H, D, and He. So one could immagine a large planetessimal forming at .05 AU from a sun-type star, becoming very massive, however being unable to capture the nebular-envelope proper as the star may eject the lightest gasses before accretion is complete, thus leaving only heavier elements for the taking. Am I off base on this hypothesis?

The problem is that there's lots of hydrogen and helium spread throughout the protostellar nebula, not just in the outer regions. As a terrestrial world grows, its gravitational influence increases and it can hold on to lighter gases. All it's got to do is grow to a certain mass, and then it's able to hold onto the H and He around it - and there's a LOT more of that than there is dust. So it would be far more likely to snowball in size to become a gas giant rather than a super-terrestrial, unless you somehow have some means to prevent it from picking up H and He. I'm not sure being dead close to a star would do the trick. I'd guess that the biggest a 'naked' terrestrial world can get is a few times the mass of the Earth - not tens or hundreds of times as massive.

Mirage is a Jovian, where as Deception is a Terrestrial world. Despite the similarity in mass, Deception is composed of a mix of ice and rock and has a mean density of 3.51gm/cm^3.


There's a hell of a lot more rock there than ice then. At 20 earth masses, that's a ridiculously huge world... I don't think it's remotely realistic, especially at that distance from the star.
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Post #14by granthutchison » 23.07.2003, 19:57

Evil Dr Ganymede wrote:I think it's going to take longer than the remaining lifetime of the solar system to reach the outer synchronous orbit.

Yep, Solar System Dynamics puts this at ~50 billion years, at which point the Moon would have moved out to 87 Earth radii and the Earth would be rotating once in 47 days. Then another 50 billion for the solar tidal effect you just described to bring the Moon back in again to the Roche limit.
The same book contains some good stuff on how to estimate the rate of evolution of rotation speed and orbital radius, in particular how long it would take to reach doubly synchronous rotation for various initial planet/satellite parameters.

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Post #15by Evil Dr Ganymede » 24.07.2003, 01:01

Aha. Thanks Grant, I knew I'd seen the numbers somewhere... (darn good book, that).

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Post #16by Apollo7 » 24.07.2003, 05:35

Is there any data out there on the lower-limit on atmospheric pressure (in millibars) is necessary for human resperation? It occurs to me that in the Universe, there will be a definate distinction between a world that is habitable, and a world that is suitable for the creation of life. Additionally since water stays liquid at temperatures above suitability for human life it is additionally possible for the existance of uninhabitable life-bearing planets.

But anyway I digress, I will re-work Deception, I want a good sized, non-gas giant world in that area and will do my best to rectify the current situation. If I may inquire for a moment, given the right pressure and temperature would it not be possible to have extremely cold planets where one can find oceans of nitrogen, or perhaps oxygen? Is there any physical reason why this could not be so?

Well I have some work to do, see you guys soon, thanks for the great input.
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Post #17by Evil Dr Ganymede » 24.07.2003, 08:08

Apollo7 wrote:Is there any data out there on the lower-limit on atmospheric pressure (in millibars) is necessary for human resperation? It occurs to me that in the Universe, there will be a definate distinction between a world that is habitable, and a world that is suitable for the creation of life. Additionally since water stays liquid at temperatures above suitability for human life it is additionally possible for the existance of uninhabitable life-bearing planets.

It's all down to oxygen pressure. I think that's calculated by taking the total pressure of the atmosphere, and multiplying by the percentage that is oxygen. So Earth has an oxygen pressure of 0.21 atmospheres. IIRC, humans can tolerate an oxygen pressure of between 0.05 and 0.3 atmospheres without masks and protective gear, though they'd be having trouble at the extremes there.

But anyway I digress, I will re-work Deception, I want a good sized, non-gas giant world in that area and will do my best to rectify the current situation. If I may inquire for a moment, given the right pressure and temperature would it not be possible to have extremely cold planets where one can find oceans of nitrogen, or perhaps oxygen? Is there any physical reason why this could not be so?


Not of oxygen - you need life to make large amounts of oxygen. But liquid nitrogen oceans are certainly a possibility. You just need something REALLY cold, like Triton, an atmosphere that can allow the liquid to exist and not evaporate away, and the right temperature range. Other liquids are a possibility - there might be oceans or lakes of liquid ethane on the surface of Titan. Ammonia might be another possibility somewhere else too.

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Post #18by granthutchison » 24.07.2003, 18:09

Apollo7 wrote:Is there any data out there on the lower-limit on atmospheric pressure (in millibars) is necessary for human resperation?
There are no permanent human habitations above ~5000m, where the partial pressure of oxygen is around half sea-level, which is equivalent to 100 millibars O2. People at that altitude tend to die relatively young, in heart failure, because of the proliferation of red blood cells to carry extra oxygen - this makes the blood more viscous and harder to pump around the circulation.
Partial pressure of oxygen at the summit of Everest is 70 millibars, and at that altitude you can only survive by massive hyperventilation which can't be sustained for more than a few days - most people are incapable of sustaining it at all. It also requires a period of acclimitization - if you were exposed to a 70-millibar oxygen mix right now, you'd lose consciousness and die, because you'd be be incapable of hyperventilating to the necessary extreme without shutting down your cerebral circulation - low circulating carbon dioxide constricts the blood vessels in your brain, which is why you feel dizzy if you hyperventilate. So you need to work up the hyperventilation slowly, over a week or two, so that your blood vessels have a chance to reset themselves to the new CO2 level. (This is why the standard 4-day rush up Kilimanjaro kills a few people a year.)

Me, I wouldn't buy a ticket to anywhere with a partial pressure of oxygen less than 0.15.

Grant

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Post #19by Apollo7 » 25.07.2003, 02:39

Ok so for resparation, one would need about .15 atmospheres of Oxygen available. This makes sense.

In referance to Triton I remember in a book called "Out of the Cradle", which was published before Voyager 2's 1989 Neptune Encounter, one of the illustrations of Triton showed the moon covered in pools of liquid nitrogen. With the approach of Cassini to Saturn under a year away, there is also a chance we'll find liquids of some kind on Titan. Although there are plenty of skeptics, Titan does seem to at least be a candidate. Of course I'm biased, Titan is my favorite moon.

I do wonder however, why Ganymede was unable to accrue any real atmosphere, when it is bigger and more massive than Titan. Pherhaps moons of that size and composition can only gain substancial atmospheres where the ambient temperature is low enough, and therefore the molecular motion slow enough to allow retention.

In some ways I am surprised there are no missions to revisit Uranus or Neptune even on the drawing boards, with New Horizons on the way perhaps revisiting Neptune/Trition is a bit redundant, but I would say that the environs and systems of the outer giants are very much worth further in-depth exploration. Already Mercury MESSENGER is being fabricated, and Mars always gets alot of play, the seasonal changes visible in Neptune's atmosphere could be reason to go back, but then if Hubble can see the changes perhaps such missions will be obsolete (to large degree) when the NGST launches.

befpre I run I want to pose a question. In a purely hypothetical situation if two massive, earth sized planets engaged in a head on colission in space, would they not both explode? Considering that their interiors (which are under vast ammounts of pressure) would suddenly be exposed to the vacuum of space, I would think that nearly all of the mass would vaporize and create a spectacular explosion. And thus in the process turning most of both planets mass to dust. Am I on the right track here?
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Post #20by Evil Dr Ganymede » 25.07.2003, 03:05

Apollo7 wrote:In referance to Triton I remember in a book called "Out of the Cradle", which was published before Voyager 2's 1989 Neptune Encounter, one of the illustrations of Triton showed the moon covered in pools of liquid nitrogen. With the approach of Cassini to Saturn under a year away, there is also a chance we'll find liquids of some kind on Titan. Although there are plenty of skeptics, Titan does seem to at least be a candidate. Of course I'm biased, Titan is my favorite moon.

Well, they did find some suspiciously flat areas on Triton that looked like they might have been liquid once... lemmee see if I can find some pics online.. Here you go: http://photojournal.jpl.nasa.gov/catalog/PIA02208 - take a look at that area on the right of the image there.

I do wonder however, why Ganymede was unable to accrue any real atmosphere, when it is bigger and more massive than Titan. Pherhaps moons of that size and composition can only gain substancial atmospheres where the ambient temperature is low enough, and therefore the molecular motion slow enough to allow retention.

I suspect one reason might be Jupiter's magnetic field, which would strip atoms off the atmosphere very rapidly. Surface temperature is probably also a factor too. Though it's an interesting question. The surfaces and interiors of Ganymede and Titan probably aren't that different... I guess the compositional differences (more methane and ammonia on Titan) must really be important!

In some ways I am surprised there are no missions to revisit Uranus or Neptune even on the drawing boards, with New Horizons on the way perhaps revisiting Neptune/Trition is a bit redundant, but I would say that the environs and systems of the outer giants are very much worth further in-depth exploration. Already Mercury MESSENGER is being fabricated, and Mars always gets alot of play, the seasonal changes visible in Neptune's atmosphere could be reason to go back, but then if Hubble can see the changes perhaps such missions will be obsolete (to large degree) when the NGST launches.

It also takes ages for missions to get there (especially with an Ion Drive. I have to marvel at the irony of replacing chemical rockets that take forever to get the probe to its destination via a circuitous route through the solar system with an ion drive that takes forever to get the probe to its target directly!), and it's hard to get into orbit around Uranus and Neptune anyway. You need a lot of fuel to slow yourself down, and you'd have to time a mission to Uranus to get there when its equator is facing us to make it easier to be captured into a stable orbit.

befpre I run I want to pose a question. In a purely hypothetical situation if two massive, earth sized planets engaged in a head on colission in space, would they not both explode? Considering that their interiors (which are under vast ammounts of pressure) would suddenly be exposed to the vacuum of space, I would think that nearly all of the mass would vaporize and create a spectacular explosion. And thus in the process turning most of both planets mass to dust. Am I on the right track here?


I doubt they'd 'explode' in the sense you're talking about (they'd obviously explode anyway, in the sense of being destroyed by the impact). Don't forget, there'd be a massive overpressured shockwave passing through the planets, putting the interiors under MORE pressure (and melting it totally in the process, probably). It'd be messy, either way ;)


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