PDA

View Full Version : The Odds of an Earth-Like World...



RalofTyr
2008-Mar-06, 08:33 PM
So, we all know that planets are 99% probable of forming around a star. Now, let's factor in how many are actually in the star's Habitiable Zone. First, determine the ranges of possible orbits and the size of the HZ. In G and F stars, it will be greater. In K and M stars, it will be less. (the HZ) Now, factor in the extra-solar planets and excluded any who's orbit would prevent that, excluding exoplanets that might have an Earth-like Moon. Now, factor in the spiral effect of these exoworlds that might have vaccuumed up the terrestrial worlds and there you have the probable numbers of earthlike worlds near us. It is my gut feeling, that finding an earthlike world within ten or twenty light years would be an amazing feat of luck.

I have hopes the E.Eridandi hosts an early earth, however, it's HZ is so small and they chances that a world is orbiting within it, are slim. Same goes for Proxima Centauri. Also, the planet we know exists there has a high eccentric orbit, meaning, perhaps, something happen causing someone of similar mass to either get ejected or spiral in.

cress
2008-Mar-06, 11:16 PM
So, we all know that planets are 99% probable of forming around a star.

You have to be a little careful making generalisations like this. For G- and K-type single (i.e. not binary, etc.) stars, the lower bound for the proportion that have planets is 20-25%. There is no reliable upper bound (other than 100%!) yet; this may mean that these stars have planets we can't yet detect, it may mean they don't have planets at all. We don't know. For all other classes of star, there are no worthwhile stats at all. It's too early in the search.

What we do know is that the likelihood of there being a planet increases with stellar metallicity. The converse to this tells you that some stars have fewer (and therefore, possibly no) planets.

I fully expect that 20-25% to keep on climbing, but there's no reason it should level out anywhere near 100%.

Not to put a dampener on the rest of your post. I have every faith we will find at the very least tens of Earths eventually, and there's plenty of reason to be optimistic.

mugaliens
2008-Mar-07, 01:19 PM
So, we all know that planets are 99% probable of forming around a star. Now, let's factor in how many are actually in the star's Habitiable Zone. First, determine the ranges of possible orbits and the size of the HZ. In G and F stars, it will be greater. In K and M stars, it will be less. (the HZ) Now, factor in the extra-solar planets and excluded any who's orbit would prevent that, excluding exoplanets that might have an Earth-like Moon. Now, factor in the spiral effect of these exoworlds that might have vaccuumed up the terrestrial worlds and there you have the probable numbers of earthlike worlds near us. It is my gut feeling, that finding an earthlike world within ten or twenty light years would be an amazing feat of luck.

I have hopes the E.Eridandi hosts an early earth, however, it's HZ is so small and they chances that a world is orbiting within it, are slim. Same goes for Proxima Centauri. Also, the planet we know exists there has a high eccentric orbit, meaning, perhaps, something happen causing someone of similar mass to either get ejected or spiral in.

Three words (well, two, actually), courtesy of Carl Sagan: "Billions and Billions."

As for my vote...

Ok, here's poking out a figure. Within this galaxy, I say there might be a thousand. However, the development of such life forms might be in such stages that either they'll never recognize us of we'll never recognize them.

I'll tell you what - I'd love to be a language specialist working with one of these kids...

rucs_hack
2008-Mar-07, 01:41 PM
While I realise they are advantageous, why would a moon like ours be required?

It does provide tides, and I know they are important, but why wouldn't life emerge without one?

Further, on the tides point, the Moon was closer in the past, so tides would have been severe. Certainly they haven't always been as they are now. Therefore I am given to think that looking at how the moon effects us today is not a good way of estimating the effect of the moon on the emergence of life.

kzb
2008-Mar-07, 04:30 PM
I've found a reference that says Earth-like planets are probably favoured by LOW metallicity, not high.

That's because high metallicity is correlated with "hot Jupiters", which have a bad effect on otherwise habitable planets in the system.

Current computer models of system formation say that low metallicity causes many small bodies to form, rather than a few very large ones.

Cougar
2008-Mar-07, 04:33 PM
While I realise they are advantageous, why would a moon like ours be required? It does provide tides, and I know they are important, but why wouldn't life emerge without one?
I swear I read somewhere - I thought it was in a Paul Davies book, but I went back and couldn't find it - that without the moon, the tilt of Earth's axis would not just wobble like a top as it does now, but there would be nothing to stop the spin axis from "tipping" or rolling all the way over again and again. (Imagine if this happened now!... well, it would be slowly, in the next several hundred thousand years or more...) This may not be totally devastating to primitive life on a planet, but it seems for life to get very "far," there has to be some degree of stability in the environment. I admit I could be totally wrong with this scenario. Maybe I dreamed that I read it. But I swear....

John Mendenhall
2008-Mar-07, 05:46 PM
Ok, here's poking out a figure. Within this galaxy, I say there might be a thousand. However, the development of such life forms might be in such stages that either they'll never recognize us of we'll never recognize them.



Sounds like a reasonable figure. Of greater concern might be the major impact rate. Lifeforms here on Earth took at least several major extinctions caused by impacts. Based on what we've seen here, and intelligent life forms as we know them, it looks like an impact free 40 to 60 million years is required. There may not be many planets that impact free.

agingjb
2008-Mar-07, 06:08 PM
Indeed, if the "half-life" of a complex biosphere is 100 million years, then after 4 billion years the fraction left will be 1/2^40, or perhaps 1/10^12.

There are, maybe, 10^11 stars in our galaxy.

cress
2008-Mar-07, 06:45 PM
That's because high metallicity is correlated with "hot Jupiters"...,
Yes.


...which have a bad effect on otherwise habitable planets in the system.
No. That was the assumption up until a few years ago, but two separate groups have since checked it out, and found it's not the case. (Nice little review on arxiv. (http://uk.arxiv.org/abs/0710.3730)) In fact, it turns out a hot Jupiter mixes the system up and delivers more water to such worlds, so they might actually be a help for some systems.

I suspect the reference you've found pre-dates these studies, which are fairly new, but obviously that's a guess.


Current computer models of system formation say that low metallicity causes many small bodies to form, rather than a few very large ones.
I'd like to see a link for this, if possible, and I'm not really sure what you mean by 'small' - small as in 'terrestrial', or small as in 'super-terrestrial but not a gas giant'?

Clearly if you put less solids into your disc at the start, you get less solids out at the end. However, I'd expect that to show up as the size of the objects, rather than their number - you simply can't grow them as big, because there's less to feed them. It's not at all obvious to me that that should translate to there being more of them once the formation period is over, and I'd like to see evidence if that's the case. To me, it says the system evolves as normal, but a little slower, and runs out of building blocks earlier on. Initially you get many small bodies, as you would anyway; they simply hang around in the simulation a little longer because they can't grow as fast. No-one has managed to model all the different phases of planet formation in a single simulation, so sure, you'll find more cores left at the end if it's not progressing as fast.

JustAFriend
2008-Mar-09, 02:03 AM
This is another case where guessing is just useless.

Until we can accurately map out the planetary systems of a few thousands or tens of thousands of stars to know what the ACTUAL percentages are in planetary formation, you're just spitting into the wind throwing around numbers.

....there's just a lot in the Universe we just don't know yet....

kzb
2008-Mar-11, 06:12 PM
Cress- I think it's the paper I linked to above that argues the case about low metallicity causing the formation of many small bodies, rather than a few large ones. By small bodies it means terrestrial (rocky) planets rather than gas giants.

http://www.space.unibe.ch/taps/doc/willy.benz.pdf

You imply the situation is merely about RATE, ie the end product is the same, it may just take longer to get there with lower metallicity. As I understand it though, the slower rate of accretion definitely gives a different end-point. That's what these models show anyway.

However, it's only computer modelling, who knows really.

kzb
2008-Mar-11, 06:25 PM
Cress- i've now skim-read the paper you linked to. Thanks for pointing this out, you were right I have not seen it before.

To summarise, hot-Jupiter inward migration takes place BEFORE terrestrial planet formation is complete. Contrary to what others have said, the giant planet does NOT sweep up, or eject, the majority of the planet-forming material on its way through -in fact 86% is left over (in the example given).

Volatile (ie water-rich) material initially towards the outer part of the accretion disk is scattered inwards.

So we should not write off Earth-like planets in hot-Jupiter systems. Very interesting.

Fazor
2008-Mar-11, 07:47 PM
WRT life on other planets;

I'd venture to say that the greatest challenge is discovering a way to explore the vastness of the universe...which is a feat that will require us to overcome physics as we now know it (for instance, the "speed limit" of c...which as you know doesn't necessarily mean violating it, but could include finding a way to circumvent it).

If/when we can do that, I'd all but grantee we find life elsewhere.

We can argue about the statistics and probabilities of earth-like planets, but there's no way to put a number on the possibility that totally different life forms could exist in totally different conditions, dependent on different variables than ourselves.

Noclevername
2008-Mar-11, 07:52 PM
WRT life on other planets;

I'd venture to say that the greatest challenge is discovering a way to explore the vastness of the universe...which is a feat that will require us to overcome physics as we now know it (for instance, the "speed limit" of c...which as you know doesn't necessarily mean violating it, but could include finding a way to circumvent it).

Or maybe a means of extending or suspending our own existence so that the long travel time is no longer a major inconvenience.

Fazor
2008-Mar-11, 08:17 PM
Or maybe a means of extending or suspending our own existence so that the long travel time is no longer a major inconvenience. Even that I doubt though. Makes for good sci-fi, but in terms of realistic value, what is the value of sending a crew into "deep sleep" so that when they make their discoveries and return, civilization will be hundreds of years ahead, and whatever nation, organization, whatever that sent them most likely would no longer exist?

It's just not a very feasable means of exploring our universe.

Noclevername
2008-Mar-11, 08:22 PM
Or maybe a means of extending or suspending our own existence so that the long travel time is no longer a major inconvenience. Even that I doubt though. Makes for good sci-fi, but in terms of realistic value, what is the value of sending a crew into "deep sleep" so that when they make their discoveries and return, civilization will be hundreds of years ahead, and whatever nation, organization, whatever that sent them most likely would no longer exist?

It's just not a very feasable means of exploring our universe.

It is a feasible means of exploring our universe. It's not a feasible means of returning information to the planet of origin. But if you bring your organization with you, this is a non-problem.

Fazor
2008-Mar-11, 08:45 PM
But if you bring your organization with you, this is a non-problem.
True, but exploration for the pure sake of the explorer would likely have to be a private venture...and Fazor, sitting here bored in his office chair, makes no distinction between a possibile civilization that he can never know exists, and a discovered civilization that he can never know exitsts.

And hooray for Fazor refering to himself in the third person! :)

Noclevername
2008-Mar-11, 11:09 PM
True, but exploration for the pure sake of the explorer would likely have to be a private venture...

Yes, but private ventures in a post-scarcity economy (such as a fully developed Solar System would likely be) can be arbitrarily large.

RalofTyr
2008-Mar-11, 11:29 PM
WRT life on other planets;

I'd venture to say that the greatest challenge is discovering a way to explore the vastness of the universe...which is a feat that will require us to overcome physics as we now know it (for instance, the "speed limit" of c...which as you know doesn't necessarily mean violating it, but could include finding a way to circumvent it).

If human beings could stop aging and atain a sort of immortality via cybernetics, what's a few centuries in space to someone that can live for thousands of years?

clint
2008-Mar-12, 01:20 PM
Yes, but private ventures in a post-scarcity economy (such as a fully developed Solar System would likely be) can be arbitrarily large.

What do you mean by post-scarcity economy? There will always be practical limits on our resources.

I do agree that in a fully explored and colonized solar system, it probably will look like the logical next step to venture beyond.
If it seems far-fetched today, that's only because our short-term challenges are so much closer to Earth...

kzb
2008-Mar-12, 01:23 PM
I wonder what life would be like in a system with a Hot Jupiter. It is alleged in the paper Cress linked to above, that having a hot jupiter in the system is no barrier to having a habitable planet there. The orbit in the habitable zone should be stable.

But I just wonder what it would be like. The giant planet (which in many systems has many times the mass of Jupiter) would be giving off a stream of hot gas like a comet, but presumably much larger and more intense than any comet we've seen. This would be a permanent fixture in the night sky, and our planet would be regularly passing through it.

Every few days we would see a black disc move across the face of the sun, and presumably the orbit of our planet would be affected, being pulled in and out as the giant planet orbits.

I guess we would also be wondering what would happen to us when the giant planet finally spirals into the sun?

John Mendenhall
2008-Mar-12, 04:47 PM
I guess we would also be wondering what would happen to us when the giant planet finally spirals into the sun?



Didn't one of our posters do a recent simulation replacing Venus with Jupiter? As I recall, Earth stayed ok, and Jupiter was stable, but unexpectedly after a while Mars departed the solar system!

kzb
2008-Mar-12, 06:35 PM
I can't see why Mars would be ejected !? It seems counter intuitive, but then I've no experience of these models so I really can't comment.

I wonder what the effect of the tides on the star are like? If you have an 8-Jupiter mass planet orbiting close-in to the star, there will presumably be a stellar bulge following the planet around. Will this have an effect on mixing in the star's layers?

What effect would it have on space weather? You have a giant planet with a giant magnetic field, interracting with that of the star.

mugaliens
2008-Mar-12, 06:49 PM
Sounds like a reasonable figure. Of greater concern might be the major impact rate. Lifeforms here on Earth took at least several major extinctions caused by impacts. Based on what we've seen here, and intelligent life forms as we know them, it looks like an impact free 40 to 60 million years is required. There may not be many planets that impact free.

Good point. I've often wondered whether Earth is as young as we think it is. It may have cooled, life formed, then took such a huge impact that it turned the entire surface into hot lava, such subsequently cooled and was moved around by plate tectonics.

I know the current theory, but I also wonder if the entire surface hasn't subducted under plates several times, and that what we think was the "beginning" land mass that later divided between North America and Europe as well as between South America and Africa didn't actually exist until some impact on the opposite side of the planet cause some sort of upheaval. Perhaps all (or nearly all) land was underwater.

How do we really know that Earth isn't 8 billion years old, instead of just 4 byo?

John Mendenhall
2008-Mar-12, 07:30 PM
I can't see why Mars would be ejected !? It seems counter intuitive, but then I've no experience of these models so I really can't comment.

Again, as I recall, the guy running the simulation was equally surprised. But after several trials, it was consistent.

If I get chance to look it up, I'll edit in the link.

RalofTyr
2008-Mar-12, 10:32 PM
What effect would it have on space weather? You have a giant planet with a giant magnetic field, interracting with that of the star.

Jupiter's magnetic field would probably cross earth.


Good point. I've often wondered whether Earth is as young as we think it is. It may have cooled, life formed, then took such a huge impact that it turned the entire surface into hot lava, such subsequently cooled and was moved around by plate tectonics.

I know the current theory, but I also wonder if the entire surface hasn't subducted under plates several times, and that what we think was the "beginning" land mass that later divided between North America and Europe as well as between South America and Africa didn't actually exist until some impact on the opposite side of the planet cause some sort of upheaval. Perhaps all (or nearly all) land was underwater.

How do we really know that Earth isn't 8 billion years old, instead of just 4 byo?

The oldest known rocks are about 3.8billion years old. Found in Australia and Greenland. It was called Rodina, and it was located either on the equator, running N/S or on the pole as a single polar land mass. As for the ones before, it's anyone's guess, but there are two ways the Earth has had continents, spread out and one. It seems to be the continents nature to group together and the Earth's nature to break them apart.

Most evidence points to an age of 4.5billion years for earth.

As for the continents, using geophysics, we can only go back about a billion years.

The continents have only existed for a short while. Continents break apart, then fuse with other continents to form another continent.

clint
2008-Mar-13, 10:40 AM
I wonder what the effect of the tides on the star are like? If you have an 8-Jupiter mass planet orbiting close-in to the star, there will presumably be a stellar bulge following the planet around. Will this have an effect on mixing in the star's layers?
What effect would it have on space weather? You have a giant planet with a giant magnetic field, interracting with that of the star.

You wonder about the star??
Imagine the effects of a Venus with 8 times Jupiter's mass on planet Earth!! :eek:

kzb
2008-Mar-13, 06:17 PM
clint wrote:
<<You wonder about the star??
Imagine the effects of a Venus with 8 times Jupiter's mass on planet Earth!! >>

I see what you're saying, but we can only go with the computer modellers. They say that stable orbits CAN exist in the habitable zone, in the presence of hot Jupiters. I think the majority of such planets are orbiting well within the orbit of Venus, or even Mercury come to that. They tend to have orbital periods of just a few days.

But I'd guess there must be some effect on the orbits of the terrestrial planets, they would not be smooth ellipses as in our system.

Chunky
2008-Mar-13, 06:23 PM
isnt the Habitable Zone objective? like this is OUR habitable zone where OUR planet life can live.

but at differant distances from the sun arnt other habitable zones created?

for other based lifeforms?

Trocisp
2008-Mar-13, 06:35 PM
Good point. I've often wondered whether Earth is as young as we think it is. It may have cooled, life formed, then took such a huge impact that it turned the entire surface into hot lava, such subsequently cooled and was moved around by plate tectonics.

I know the current theory, but I also wonder if the entire surface hasn't subducted under plates several times, and that what we think was the "beginning" land mass that later divided between North America and Europe as well as between South America and Africa didn't actually exist until some impact on the opposite side of the planet cause some sort of upheaval. Perhaps all (or nearly all) land was underwater.

How do we really know that Earth isn't 8 billion years old, instead of just 4 byo?We get the number 4 billion not from earth, but from extra-terrestrial objects in the solar system that we've found on earth. We've dated them.

Earth's history is 3.8 billion years at most and as few as 30 or 40 minutes at minimum. :p

astromark
2008-Mar-13, 06:40 PM
The chances of planetary development is 'obviously' common. We can ponder the life zone probabilities till the cows come home and it changes nothing and achieves even less. We have excepted the possibility of planetary stability without divine intervention... I will not prejudge what may or may not be found. I will await the actually factual information. It is where we are looking and will find 'Life'... I get the felling we will be speculating until then. Not that I do not enjoy a good 'wonder if' column. I am optimistic that we will find or be found.;)

John Mendenhall
2008-Mar-13, 07:15 PM
Earth's history is 3.8 billion years at most and as few as 30 or 40 minutes at minimum. :p

Isn't the pre-Earth's hit by the Moon-maker at 4.3 billion years ago?

clint
2008-Mar-14, 12:12 AM
clint wrote:
<<You wonder about the star??
Imagine the effects of a Venus with 8 times Jupiter's mass on planet Earth!! >>

I see what you're saying, but we can only go with the computer modellers. They say that stable orbits CAN exist in the habitable zone, in the presence of hot Jupiters. I think the majority of such planets are orbiting well within the orbit of Venus, or even Mercury come to that. They tend to have orbital periods of just a few days.

But I'd guess there must be some effect on the orbits of the terrestrial planets, they would not be smooth ellipses as in our system.

It's amazing that Earth's orbit could stay stable in this scenario,
but actually what I had in mind were more the impact on planet Earth itself:
tides, weather, earthquakes, radiation, etc.

You mentioned the effects on the star,
but this 'Super-Jupiter' would be much closer to Earth...

Edited: just in case anybody's interested in debating this further, I just started a new thread (http://www.bautforum.com/questions-answers/71560-what-would-hot-jupiter-do-earth.html)

Trocisp
2008-Mar-14, 03:40 AM
Isn't the pre-Earth's hit by the Moon-maker at 4.3 billion years ago?
http://en.wikipedia.org/wiki/Oldest_rock
2.5-3.8 billion.



http://en.wikipedia.org/wiki/The_Moon#Formation
Several mechanisms have been suggested for the Moon's formation. The formation of the Moon is believed to have occurred 4.527 0.010 billion years ago, about 3050 million years after the origin of the solar system.

clint
2008-Mar-14, 05:17 PM
Yes, but private ventures in a post-scarcity economy (such as a fully developed Solar System would likely be) can be arbitrarily large.

Sorry to insist, but I didn't know this concept and I'm curious:

What do you mean by post-scarcity economy? There will always be practical limits on our resources.


I just looked it up on wikipedia (http://en.wikipedia.org/wiki/Post_scarcity), but I think it sounds a bit Utopian.
Why do you think a fully developed Solar System would be post-scarcity?

Trocisp
2008-Mar-14, 05:40 PM
The only ways to absolutely ensure a post scarcity economy are;
1) Kill anyone who can't provide a surplus.
2) Separate two groups (One would be Post Scarcity and one would be Slave labor).
3) Full automate almost all food production. But this isn't a sure thing, because that would free people up for more "free time" (reproduction).

Anything else is just hopeful thinking.

Noclevername
2008-Mar-14, 08:50 PM
An open Solar system means no limits on energy-- just build an arbitrarily large solar collector, simple foil can focus sunlight on a photocell or thermocouple array-- and little limit on materials, as there's plenty of variegated mass in small gravity wells, you just need to get there, which only requires energy (see previous example).

By the time (or more likely, before the time) the Solar System is fully developed in several centuries-- in fact, as part of the process of it becoming fully developed-- we will have almost certainly also developed the technologies of automation in mining, manufacturing, and, yes, food production as well, as well as sythesizing complex chemicals from asteroidal/cometary materials, as far as they can physically go. So the need for human labor will also be minimized.

Given this, there's few practical limits on the size or complexity of spacecraft a private group can construct. Even a relativistic colony ship is plausible under those conditions.

Van Rijn
2008-Mar-14, 09:13 PM
An open Solar system means no limits on energy-- just build an arbitrarily large solar collector, simple foil can focus sunlight on a photocell or thermocouple array--


There would be a limit, just a very large one by present standards. I'm a bit uncomfortable with the term "post-scarcity" too. The wikipedia definition of scarcity is:

In economics, scarcity is defined as the condition of human wants and needs exceeding production possibilities. In other words, society does not have sufficient productive resources to fulfill those wants and needs. Alternatively, scarcity implies that not all of society's goals can be fully attained at the same time, so that trade-offs are made of one good against others.

I could imagine, if there is a stable population, a situation where essentially all needs are taken care of. I'm not so sure about wants. As long as there are finite resources, there would be trade-offs.

clint
2008-Mar-14, 11:19 PM
There would be a limit, just a very large one by present standards ... As long as there are finite resources, there would be trade-offs.

Exactly my point.
Resources will never be infinite.
So, by definition, there will always be scarcity.

For a stone-age hunter and gatherer, our food supply would look unlimited.
From his perspective it is, because it's difficult to starve to death today unless you want to (at least in a developed country)
But at the same time our standards have risen, so the normal guy still cannot afford just any kind of food or beverage there is.

Same for energy.
For a 16th century explorer travel from London to New York in 6h instead of 6 weeks, and for a tiny fraction of the cost, would have seemed like paradise.
(or to have fire, air conditioning, light, heating, all at the flick of a switch)
However, we are far from having unlimited fuel or energy at our disposal.

Or take computers.
Who could have imagined any use for 2GB RAM memory just 10 years ago (or 20 years if you are a very advanced user),
- there weren't even permanent storage devices with that capacity on the market.
Now, I'm already thinking my PC is getting kind of slow.

If you take economic history as a guide,
it's hard to imagine that we will ever run out of ideas how to use up bigger resources.
We will just keep inventing new and more resource-hungry technologies.
So there will always be practical limitations on what we can afford.

RalofTyr
2008-Mar-15, 06:38 AM
...till the cows come home...

Alright, you are in NZ and you are using a midwestern US phrase.

agingjb
2008-Mar-15, 09:10 AM
Resources are certainly finite; it's just a question of ensuring that they are slightly greater than needed for the population, or that the population is slightly smaller than the number that can be supported by the resources.

m1omg
2008-Mar-15, 11:11 AM
Exactly my point.
Resources will never be infinite.
So, by definition, there will always be scarcity.

For a stone-age hunter and gatherer, our food supply would look unlimited.
From his perspective it is, because it's difficult to starve to death today unless you want to (at least in a developed country)
But at the same time our standards have risen, so the normal guy still cannot afford just any kind of food or beverage there is.

Same for energy.
For a 16th century explorer travel from London to New York in 6h instead of 6 weeks, and for a tiny fraction of the cost, would have seemed like paradise.
(or to have fire, air conditioning, light, heating, all at the flick of a switch)
However, we are far from having unlimited fuel or energy at our disposal.

Or take computers.
Who could have imagined any use for 2GB RAM memory just 10 years ago (or 20 years if you are a very advanced user),
- there weren't even permanent storage devices with that capacity on the market.
Now, I'm already thinking my PC is getting kind of slow.

If you take economic history as a guide,
it's hard to imagine that we will ever run out of ideas how to use up bigger resources.
We will just keep inventing new and more resource-hungry technologies.
So there will always be practical limitations on what we can afford.

on PCs-Its a dirty trick from pc manufacturers. because the system is intentionally bloated to make people "need" new computers, my old 386 is subjectively faster in applications like text editing than my new computer and 400 mhz pentium ii 64 mb ram with windows 95 is faster than 2 ghz core duo with 512 mb ram, i have new pc just because of games and movies, otherwise you really DON'T need any "greatest 2 ghz 4 gb ram pc", if you want to do work, browse web, listen to music and play earlier generation 3d games you can be absolutely satisfied with pentium 133 mhz with winblows 95 (or 16 mhz with atari falcon if you play only vintage games and don't need Flash)

really, try it, and clear that propaganda nonsense "that you need faster computer" from your head that corporations are trying you to belive to make a lot of bucks

even nasa still uses old 386-pentium 1 or 68k mac computers because they know that they simply don't need to upgrade, why?to play quake 4 on the space shuttle :D?

Trocisp
2008-Mar-15, 01:40 PM
NASA does need to upgrade their PC's. But not to newer, faster models.

To newer, less power intensive models (on the shuttles, at least).

clint
2008-Mar-15, 05:52 PM
It all depends on what you want to do with your PC, of course.
I work a lot with 3D virtual worlds and simulations, and you cannot have enough RAM/velocity for that ;)

In the case of NASA,
I suppose the use of old computer models is more due to the long-term nature of many of their missions, isn't it?

Trocisp
2008-Mar-16, 11:29 PM
Backwards compatability isn't all that hard, but the big thing, especially for shuttles, is that you could get equal power for less weight, which would be quite a lot of cash saved over time.

danscope
2008-Mar-17, 03:05 AM
While I realise they are advantageous, why would a moon like ours be required?

It does provide tides, and I know they are important, but why wouldn't life emerge without one?

Further, on the tides point, the Moon was closer in the past, so tides would have been severe. Certainly they haven't always been as they are now. Therefore I am given to think that looking at how the moon effects us today is not a good way of estimating the effect of the moon on the emergence of life.

Hi, Many overlook the importance of our Moon. Just imagine, for a moment,
the incredible amount of seawater that is moved each day , thanks to our moon.
The currents and shifts thus created tend to cleanse and stimulate the lhousands of bats and estuaries along the coasts of everything, islands, capes, penninsulas, rivers etc, each of which enjoys his life giving stirring.
In Boston the is a daily tide change of 8 to 9 feet. That's a lot of water
to flood in and out of an area. Trust me, we must needs have our wonderfull
moon.....no question. Without it, the stagnant mess would be miserable.

Best regards, Dan

Noclevername
2008-Mar-17, 11:55 AM
Trust me, we must needs have our wonderfull
moon.....no question. Without it, the stagnant mess would be miserable.


Miserable for those lifeforms who evolved on a planet with a Moon and are adapted to its presence. We have no evidence of how life would or could adapt to conditions without lunar tides.

Chunky
2008-Mar-17, 01:23 PM
isnt the Habitable Zone objective? like this is OUR habitable zone where OUR planet life can live.

but at differant distances from the sun arnt other habitable zones created?

for other based lifeforms?

i was forced to quote myself.



?

Trocisp
2008-Mar-17, 02:17 PM
Johnathan, there's a thread about life on Europa. If it happens to be possible that life can arise based on geothermal heat alone - there wouldn't be a real "habitable" zone, just a habitable zone for planets that dont create enough of their own heat...

kzb
2008-Mar-17, 06:25 PM
clint wrote:
<<You mentioned the effects on the star,
but this 'Super-Jupiter' would be much closer to Earth...>>

In most cases, it wouldn't be, not as I understand things anyway. Hot Jupiters are typically less than 0.1AU from their star. However, johnathan wrote:

<<isnt the Habitable Zone objective? like this is OUR habitable zone where OUR planet life can live.

but at differant distances from the sun arnt other habitable zones created?>>

Again, as I understand things, the "habitable zone" is generally taken to be the range of distances from the star within which liquid water can exist on the surface of the planet, and so "life as we know it" could exist. Of course life may well be found outside this zone, as Trocist has pointed out -but I wouldn't want to live there.

Going back to the original point, it is true that stars much smaller than our sun will have habitable zones much closer in than ours. As we look at smaller and smaller stars, at some point, hot Jupiters, at say 0.05AU, will start to interfere with planetary orbits in the habitable zone. Perhaps the planetary modellers think this is a sufficiently rare occurence that they don't have to mention it.

clint
2008-Mar-18, 08:10 AM
Hot Jupiters are typically less than 0.1AU from their star.

Is there really any reason Hot Jupiters should be mostly that close to their stars?
Or is it just that these ones are easier to detect, so far?

kzb
2008-Mar-18, 06:12 PM
clint wrote:
<<Is there really any reason Hot Jupiters should be mostly that close to their stars?>>

I guess it depends on if there is a strict definition of a Hot Jupiter ?! If it's more than a certain distance away it will no longer be "hot". I believe from what I've read that the inward migration generally continues until the giant planet is perhaps 0.05AU from the star. It then stabilises at this distance, the orbit is circularised by tidal effects and the rotation becomes either tidally locked, or in resonance with the orbit.

Although I've also read other papers where the planet continues into the star. That in itself is an interesting topic, as the planet will pollute the outer layer of the star as it burns up, and potentially give a false high metallicity reading to the star.

<<Or is it just that these ones are easier to detect, so far?>>

Well in terms of detecting planets in general, I'm sure this must be the case. I read something the other week that estimated the discovery efficiency of planets at about 4%.

clint
2008-Mar-19, 08:02 AM
...I believe from what I've read that the inward migration generally continues until the giant planet is perhaps 0.05AU from the star. It then stabilises at this distance, the orbit is circularised by tidal effects and the rotation becomes either tidally locked, or in resonance with the orbit...

Does this mean all planets within the orbit of a Hot Jupiter get kicked out, eventually?
Or might an additional inner planet stabilize a Hot Jupiter's orbit a little bit farther out than 0,05 AU?

I was thinking of that exo-system (was that 55Cancri?) with a Neptune-sized planet within the orbit of a Hot Jupiter...

kzb
2008-Mar-19, 12:52 PM
I really don't know clint. All I can say is that some computer modellers have got something published which says (1) water rich terrrestrial planets can form, and (2) orbits in the habitable zone are stable, both in the presence of Hot Jupiters.

Now perhaps you're a bit skeptical of computer models just like me. I'd like to ask the question, was the existence of hot Jupiters PREDICTED by any planetary formation models BEFORE they were actually discovered??

I don't think they were, but perhaps someone knows different.