Drake Equation??? Humbug!!!!!

ERRORIST · 2004-03-24 20:10:40

How will The finding of fossils or even life on Mars effect the equation????

SBird · 2004-03-25 21:20:53

The finding of fossils or life on Mars would definately make the Drake equation more favorable but not in a terribly helpful way. The problem with the Drake equation is that almost all of the numbers in it are unknown. Unfortunately, the only way to start filling in the numbers is to actually observe large numbers of other solar systems and find extra-terrestrial life and catalog it.

For example, before, we had absolutely no good way to know how common life was on other planets. If we find fossils or life on Mars, it's clear that life is possible on other planets but we still don't know how common it is. This is because it's a single example and its impossible to extrapolate anything meaningful about it.

For example, lets say that you live in a neighborhood. However, for whatever reason, you can't leave your house. You want to try and estimate how common other people living around you are. So, you send a robotic probe to the neighbor's house. Inside, noone's living there but there are clear signs that someone was living there at some time in the past.

Now, you have got a map of the city so you know how many roads there are. nfortunately, the map doesn't show houses. You can't actually see the other streets so you don't know if there are actually houses on those streets. Furthermore, even if there are buildings, you don't know if people live in them.

Before, you had no idea of people lived in those buildings but seemed likely. Now, you do know that it is possible but still have no good idea how many of them there are.

What we need for the Drake equation to be even remotely useful:
1: orbital telescopes capable of actually imaging earth-sized planets in nearby star systems.
2: a better understanding of how life evolved on this planet.
3: a better understanding of how solar systems form
4: a better understanding of how our galaxy formed
5: a better understanding of how human intelligence works and the probability of it evolving
6: a better understanding of how often intelligent creatures develop a technological society that wil try and communicate with us.

bolbuyk · 2004-05-13 07:25:46

The interesting idea of the Drake formula is that it begins with a valua (y^-1) and ends with a value (y). Between there factors with no dimension. If you could guess how many Earth-like planets there are, you could skip the first 3 (?) factors and make the formula shorter. It's credibility increases somewhat.

chat · 2004-06-10 04:49:15

I think the answers will start to come in the near future.

When we can detect small planets like earth, we will get a pretty good idea of what % to fill in most of the equations.

Figuring out what percent have life of those we find wont be to difficult.

But trying to figure out what percent have intelligent life will be much more difficult, unless they are a polluting tech species like our selfs.

From the planet finds of the last few years it seems to point to the fact that anywhere planets can be they are.

Multiple star systems are probably unsafe for life, asteroids collisions will be many on such a system.
Stars that spew radiation will also be bad places to look.

My guess is about 1/9 on all other equations other than planets, planets will be about 1/2.

This is what i believe the drake equation should look more like.

1 in 2 have planets.
1 in 9 has a correct sun type.
1 in 9 has a safe stable star.
1 in 9 has a planet in the right place and right size.
1 in 9 has the correct elements for an earthlike planet.
1 in 9 of those starts life.
1 in 9 maintains life.
1 in 9 have a large moon.
1 in 9 has enough land and sea mixture.
1 in 9 have creatures that migrate to the land.
1 in 9 gets inteligent life.
1 in 9 the inteligent life persists.
1 in 9 become a tech species.

Lots of life, very small numbers of inteligent life, nearly no other tech species to talk to.

lunarmark · 2004-06-11 03:04:48

From the discoveries of exoplanets made so far, (mostly all way above Jupiter in size) it is clear that there is a real spread of planetary orbits, some of them orbit very close to their sun, others very far away, this spread was a bit unexpected, and probably means that most planetry systems are statistically NOT like ours.

So far I think about 1 in 50 has a Jupiter planet in the same sort of region as in our solar system.

So at a guess it is near 1/50 than 1/9 - this is if we assume that Jupiter like planets have to exist in similar orbits to our own solar system, I think this because, for planets to be a similar distance to their sun ,the presolar disk must be of a simialr format to ours, therefore you would expect a similar planetery configuration to ours and hence a chance of an alien solar system.

As for sun type, the observations are a little biased at the moment as they are purposly looking at 'sunlike stars' to find planets, it may be that many more star stages and types can maintain habitable planets. I think your about right with the rest being aprox 1/9, either way we are talking just a few potential habitable planets within our own galaxy.

The real issue is that, we can only hope to communicate with around 20% of the stars in the galaxy due to the vast distances involved and the square law of radio signal propagation (i.e it becomes far too weak to recieve once its crossed just a fraction of the galaxy'.)

Secondly we would have to point an antenna at excactly the right place and time for a civilisation to be in a technical position to hear it, the odds of that are near infinite)

Basically my reading of the Drake, is that it matches reality (i.e it predicts silience!): we will never communicate with any life outside our own solar system, unless it happens to exsist on the nearest few thousand stars to us, and the odds of that are REALLY not good!

Our best chance is to optically spot planets and characterise thier atmosphere, with obscenly large telescopes and then refine our studies to these planets. :bars2: :bars2:

chat · 2004-06-11 04:44:02

lunarmark,

I agree.
It is tough to say what is a safe star for life to exist at.
A hot blue star, red giant or white dwarf might still have conditions and zones that are safe for life.

With our limited knowledge of how a planetary system works, we might be surprised to find out that even though a Jupiter sized planet is close to a star it can still have an earthlike place.

I think your right though that 1/9 is a generous guess.
Even in our solar system if we play planet billiards and move earth to mars or Venus or any of those combinations we probably don't get a habitable planet.

It is going to be a quiet galaxy and a long hunt to talk to anyone other than our selfs teraforming worlds.

Lets not forget though that radio communications might not be the ultimate way to talk.
Those civilizations that have persisted for millions of years probably have a much faster way to talk, we just are not ready to listen yet.

The numbers do point to the fact that if we are not alone, the next door neighbors are not listening or are so far away they don't care, or consider us so primitive they wont talk to us.

Gennaro · 2004-06-11 23:18:25

So far I think about 1 in 50 has a Jupiter planet in the same sort of region as in our solar system.

On what reasoning would you base such an assumption? To me it looks like this: wobble method is particularly suited to find Jupiters in bizarre close orbits. So it's only natural most discovered systems are of this type.
At the same time we actually haven't found that many planetary systems yet (somewhere above one hundred), compared to the number of star systems extending out to the bulk of the range of discoveries, and in fact, if you have followed the news, the rate of new discoveries is seriously dwindling!

This suggests to me that we might already be running out of close/highly eccentric gas giants nearby and that most planetary systems might actually be quite like our own. Absence of proof is not proof of absence. (Oh, feels so good at last having a reason to write the last sentence! )

As for star systems forming planets, I take it as common sense to suppose this to be the rule. There are always more of the little lumps than the big lumps, on every scale this pattern is the same.
Finding stars without planets might actually end up being the rare and special case.

Lastly, stable orbits around binaries as close as Alpha Centauri have both been predicted and more or less proven by the discovery of a gas giant around Gamma Cephei A. (Gamma Cephei A and B, or Errai, have a marginally larger minimum distance than Alpha Centauri A and B.)

geo_flux · 2004-06-12 18:13:54

You're assuming that Earth life is normal. We could be galactic freaks with all other life evolving inside mega planets or suns or deep space. The truth is we know absolutely nothing about life out there.
The only fact we have is that we cant see or hear anyone else out there.

chat · 2004-06-13 04:55:17

geo_flux,

At the moment all we can assume is that life on earth is a normal process for places like earth.

For places not like earth that harbor life, life will be very different.
I believe you are right about other places we don't expect to have life.

I'm of the opinion that our solar system is not a freak, it is a normal place, with a normal average sun, with average planets, in an average place in the galaxy, in an average galaxy.

Other solar systems will range from the bizarre to the familiar, but most will resemble ours.

If we think of our system and shift all the planets into different orbits, how many non life arrangements do we come up with?

9x8x7x6x5x4x3x2x1

Or is our arrangement of planets pretty normal, and we only need to think of moving 3 of them.
earth Venus and mars to get a planet that can harbor life?.

3x2x1

If ours solar system is average, then 1 in 6 places that have planets will have a place that can start our sort of carbon based life.

If ours is not an average solar system, then the outlook for any life is very bleak, unless as you say we are the freaks.

lunarmark · 2004-06-14 09:23:43

You say our planet is probably not a freak, I think it probably is a freak. Look at the reletivly close distance to Mars and Venus, and look how different they are to us!

We are only habitable because we have a moon exactly the right size to keep our orbit stable, otherwise seasons would vary greatly, and day night might end up like Venus's 255 days or so, which would hinder life's development.

Its also our magnetic field (which is still very strong compared to others) which shields life from most harmful solar radiation (i.e protons etc) this also prevents the atmosphere from being stripped like Mars.

All these things to me make Earth a special place, and maybe suggests that we are indeed, largley one of a kind.

I would say that 'life' is probably widespread as bacteria but when you consider it took billions of years for intelligence to form, even with our very stable planet.

- we aint gonna find anyone else anytime soon.

chat · 2004-06-14 18:41:52

lunarmark,

What if a few billion years ago we had 3 earth like planets in our solar system?

Earth Venus and mars, only earth was in the right place.

Venus boiled and lost it's hydrogen, we see the product of a wet world being to hot.

Mars froze, and we see a cold desert, the product of a world to cold.

In my thoughts other than earth having a large moon, all 3 planets are pretty similar, or were a few billion years ago.

We might be just a normal planet, with a few extra goodies, good for the life on our planet.

Earth might be duplicated in general 25 billion times in our galaxy alone, or just 1.
And mostly water worlds don't need a moon, or a magnetic field.

We might be in for a shock when they can start to see earth like places with multiple joined telescopes.

I think we will find all sorts of them, and have to rethink everything we know.

lunarmark · 2004-06-15 09:27:57

Indeed We MIGHT find all sorts of things.

But we KNOW that life (that is all the life we have studied) needs a stable band of temperatures otherwise all known life either goes dormant or dies!

This isnt to say that other forms of life couldnt potentially exist but at the moment we have to go by what we see in the world around us, and Venus and mars appear sterile, (at least to anything other than Bacteria - possibly).

There is a big difference between an eviroment that can support life and one in which life can thrive & evolve into complex intelligent forms. (There are organisms on Earth that could potentially [survive] on mars, at least for a while, but could it evolve into humans in 3 billion years time - no)

I would argue that early life is actualy quite fragile (and there appears to have been many near extinction events in earths history).

If you factor in the fact that a habitable planet needs an orbit actually [very] similar to Earth's maybe with a moon and enough water then the potential number of alien habited worlds is even less.

The truth is we dont know enough about the number of planets like our own to make an accurate judement It could even be for example that if it wasn't for the other 8 planets we might have way too much water for intellegent life to form (i.e no land mass=no humans) or if earth was smaller we would have no atmosphere - so we might even need a solar system that is exactly same as ours for life to start! even less odds!

chat · 2004-06-16 04:17:12

lunarmark,

I agree that finding places that have life wont be to difficult.
But will that host planet have a moon, land/water, a magnetic field,a stable circular orbit,a few billion years of no disasters and creatures that make it to the land, then have an unusual frail species like our selfs happen.

When we start looking for all those things, we wont find many that resemble earth.
Maybe 1 in a billion, but that is still 250 in our galaxy.
Probably 245 of the 250 are dominated by dinosaur like creatures.

I also agree that its all speculation right now.
I also think only a handful of intelligent species exist per galaxy, finding any of them will be a hurculean task, even when we have the instruments to look.

For the lack of better information, it looks like its our job to colonize the galaxy until someone says we cant.

lunarmark · 2004-06-16 08:09:57

The interesting thing is how important is the ratio of Land & water?

Too much water and you would surley only have 'dumb' sea creatures too much land and it would presumably be difficult for life to start (since it is assumed that life started in the sea or in some sort of early water based liquid soup).

Even if you optomistically ended up with 250 possible earth like worlds, with stable temperatures and water/land mix, you would still have to have the right amount of extinction events (remember without extinction events the world would probably be still ruled by dinosaurs!) and you would have to wait 5 billion years from creation for intelegent/humanoid type life to evolve, so the chances of there being other habitable worlds in our galaxy at this moment in time are extreemly small, when the drake equation starts pointing to 5 - 10 communicative habitable worlds, then this really doesnt leave much room for error.

Hence the reason Seti has made no contact and I suspect never will.

Gennaro · 2004-06-16 13:14:00

The interesting thing is how important is the ratio of Land & water?
Too much water and you would surley only have 'dumb' sea creatures too much land and it would presumably be difficult for life to start (since it is assumed that life started in the sea or in some sort of early water based liquid soup).

I agree. I've been thinking about this as well. Wouldn't be surprised though if the ratio 'base' could still be quite wide. If we stick to a world with plate tectonics, contrary to perhaps common perception, the way I've got it is that oceanic and continental crust aren't exactly the same (as in being an arbitrary feature of a plate covered by water or not). Actually, continental plates are made up of lighter material than oceanic plates and hence 'float' on the former. Since water and various silicates are also such common elements it would be likely to suppose that planetary ratios tend to be quite uniform, to a large extent following gravitation (just a theory).
So within a certain range, say from a gravitation somewhere below Mars to somewhere above Earth, dry worlds, continental worlds and ocean worlds might all be quite equally represented (depending of course on a lot of interconnected local factors).
There are limits of course. A rocky planet significantly heavier than Earth might be hopelessly submerged in water since it attracts so much more of it. Likewise there ought to be a general lower limit where water can't be maintained at all. (I won't go into atmospheres, liquid water zones, photodissasociation etc, because it will make the post too long and I'll probably just end up confusing myself and the issue beyond salvation anyway.)

So maybe this land/water ratio problem isn't really that much of a problem after all, provided plate tectonics, which we will need in the first place.

Also, am I correct in supposing that the moon is instrumental primarily in relation to plate tectonics, having robbed so much of the lighter elements which would otherwise have thickened earth's crust considerably?
If so, plate tectonics is the crucial point, not our large moon in itself. The moon only accounts for how plate tectonics came about on our world. Could there not be alternatives to this scenario?

Even if you optomistically ended up with 250 possible earth like worlds, with stable temperatures and water/land mix, you would still have to have the right amount of extinction events (remember without extinction events the world would probably be still ruled by dinosaurs!) and you would have to wait 5 billion years from creation for intelegent/humanoid type life to evolve, so the chances of there being other habitable worlds in our galaxy at this moment in time are extreemly small, when the drake equation starts pointing to 5 - 10 communicative habitable worlds, then this really doesnt leave much room for error.

Not sure I agree. The main threshold is evolution of multi-celled organisms. This in turn requires an oxygen rich atmosphere since probably only oxygen suffice for the high metabolism of metazoa. The oxygen enrichment of earth's atmosphere by cyanobacteria lasted for about 2 billion years, i.e roughly from Earth Age 2.3 billion to 4.3 billion. Then suddenly, when time was ripe, multi-celled organisms made their debut some 540 million years ago and from there on evolution has just went along on rails. If major extinctions are important for evolution, well, there will be more than enough going around for everyone in any normal star system. I doubt you can even reach the multi-celled stage and not eventually develop intelligence, since the microbal advantages for survival have already largelly been lost by then.

So considering Tau Ceti, which I believe is considerably older than our star, I'd say chances might be even better of finding intelligence having evolved there than around the abnormally massive and radiation spewing system of Sol. Naturally a disadvantage would be the tighter water zone of a G8 sun (about a third of ours).
:bars3:

Edit: I might be mistaken about the age of Tau Ceti. Just checked at solstation.com and it only says it may be more than 3 bilion years old. Probably some misrecollection on my part due to lower amount of heavy elements in system.

lunarmark · 2004-06-17 07:20:39

Gennaro,

Dont worry I have never seen the same star age listed twice!, or indeed a stars distance listed twice the same, they seem to differ on a regular basis depending on the author. (goes to show how little we actually know about distant stars!)

The element issue you mention with the moon Is about right, I think without it, our geology on earth would be somewhat different!

The moon also helps life in other ways too, it must have blocked quite a few large meteors/comets in its day (i.e its a cosmic hoover!), some of the craters on the moon are staggeringly massive. They would have set life back a long way had they hit us.

The other thing is the nice stable smooth orbit and short day/night we enjoy is partly down to the moon, (its gravitational mass helps keep our climate from being too extreeme). In addition tidal action must have conributed to life in some way e.g currents and water flow essential to spreading life around, as well as perhaps adding to continental plate movemt by 'tidal' force on the earths crust.

it would be interesting to see a model of the earth with a moon and without and see how the earth is different, my bet is earth would be quite a different place without the moon.

If this is the case then it changes the Drake equaton, because the chances of an exo-planet similar to ours having a moon of similar size, composition and distance with all the other factors is I would have thought quite low.

Its not even safe to assume that all planets like ours would probably have a moon, since the moon was formed by a giant collision with the earth, that has its own probabilites attached too, what if the impactor had hit Mars or Jupiter, RESULT: bigger earth and a completley different Earth....

atomoid · 2004-06-17 16:14:09

...it would be interesting to see a model of the earth with a moon and without and see how the earth is different, my bet is earth would be quite a different place without the moon.
If this is the case then it changes the Drake equaton, because the chances of an exo-planet similar to ours having a moon of similar size, composition and distance with all the other factors is I would have thought quite low.
Its not even safe to assume that all planets like ours would probably have a moon, since the moon was formed by a giant collision with the earth, that has its own probabilites attached too, what if the impactor had hit Mars or Jupiter, RESULT: bigger earth and a completley different Earth....

Without the moon Earth might look something much more like Venus (though perhaps not as hot), because it has no moon, Venus has no plate techtonics, about a year-long day/night cycle,

I've heard that the moon imparts a stabilizing effect, limiting the extremes of the procession of the equinoxes. Does the moon effects the interior magma flow of earth and perhaps stabilize the magnetic field as well?

Perhaps its not so uncommon in the universe for such planetoid impacts to occur and a good part of the time they end up forming a stable moon, given that the masses are in pretty close orbit and velocity since they originated in the same system, its just the slow orbital harmonics that slowly eases them together. Such a planetoid was probably in a somewhat, though not permanently stable orbit between Earth and either Mars or Venus until it was eased into collision, the resultant excess wreckage of this (the moon being almost entirely composed of Earth's crust after it was spalled outward by the impact vibrations on a 5-hour-day Earth), the impacting planetoid remnant might have wandered in another such orbit for eons until it impacted Mars i a simialr fashion. Im under the impression that Mars was likely hit by a large planetoid early on as well, from looking at the difference between hemispheres which dont happen to be aligned equatorially (a large impact could have imparted this).

Gennaro · 2004-06-17 19:32:52

Gennaro,
Dont worry I have never seen the same star age listed twice!, or indeed a stars distance listed twice the same, they seem to differ on a regular basis depending on the author. (goes to show how little we actually know about distant stars!)

Thanks for bailing me out!

The moon also helps life in other ways too, it must have blocked quite a few large meteors/comets in its day (i.e its a cosmic hoover!), some of the craters on the moon are staggeringly massive. They would have set life back a long way had they hit us.

Hm, many impacts on the moon are very old I believe. Most of the big ones, if I recall correctly, were due to the final great bombardment early in Earth's history, when all planets were duly peppered for a while. I doubt if the moon has served significantly as a vacuum cleaner for Earth. It's mass is just too small for that.

In addition tidal action must have conributed to life in some way e.g currents and water flow essential to spreading life around

This is an interesting point. I wonder what would have the biggest impact: tidal bulge or temperature differences for shallow warm/deep cold water at the poles for creating global currents? Tidal flows in themselves don't seem so enourmously important to me. Some interaction between sea and land should always take place, I reckon, even without any moon. Storms and such.

Without the moon Earth might look something much more like Venus (though perhaps not as hot), because it has no moon, Venus has no plate techtonics, about a year-long day/night cycle.

Why should Earth have had a year long day/night cycle without the moon? Surely, tidal-locking from the sun would have no meaningful effect at the distance of Earth or even Venus? (The long day/night cycle is probably due to some coincidence. This is a matter that should be easy to calculate to a high degree of exactitude.) Mercury isn't even totally tidally locked (yet), only about two thirds.
Anyway, Mars has a nearly identical day/night cycle to Earth and it has no large moon. Indeed, the moon helps breaking the Earth a bit if I'm right.

Perhaps its not so uncommon in the universe for such planetoid impacts to occur and a good part of the time they end up forming a stable moon, given that the masses are in pretty close orbit and velocity since they originated in the same system, its just the slow orbital harmonics that slowly eases them together.

This I believe. As for tides, some such rythmical effect I can only presume would result, even if the mass of such a moon would be considerably divergent from ours and if it was created/captured in some other way.
Moons are quite common after all. Even Pluto has one.
Right now, perhaps there is even some alien species somewhere, living on a larger double planet pair like Pluton/Charon inside their star's water zone, having misgivings about the prevalence of intelligent life in the galaxy, since after all, double planets can't be considered all that common.

chat · 2004-06-18 03:29:56

Gennaro,

One big calculation is missing from the drake equation.
Life on moons.

In my opinion life on moons will be much more common that life on earth like systems.

Move any of the gas giants to earths orbit, and each one has a potential life sustaining moon, or a few of them.

Why look for duplicates of an earth like system, when a much simpler way exists to have a safe stable moon that harbors life.

Earth like places might be rare, but earth like moons might not.

The moon calculation could drastically alter how many worlds have life in our galaxy.

lunarmark · 2004-06-29 03:51:48

chat,

Intersting point about life on moons, the only moons I would credit with possible life would be Europa and Titan. Titan is strange because it shouldn't really have an atmosphere for its size, hopefully we shall find out more when the Hugyens probe lands later this year.

Yes, you may not need a planet (or gas planet) to be in the so called 'habitable zone',since tidal/gravitational action can cause heating, as this is seen on some of the jovian moons, where volcanoes/heat are triggerd by the gravity from jupiter.

This would drastically effect the drake equation, if only we could find a moon with life supporting potential, like europa for example, if there was a warm ocean below the ice...

Whether life can actually start, on a moon, is another question however, what are the exact ingredients needed for life to evolve, can they occur on a small planetary body with limited atmosphere and intense radiation or do you need a stable earth sized world?

And what about that radiation, the radiation on europa is very intense and would kill all known organisms very quickly... if the moon was far enough away for the radiation to not be a problem, then there probably would be no gravitational heating?

chat · 2004-06-29 04:43:21

lunarmark,

Counting the days to when Hugyens arrives.
Think the probe is going to find a strange place when it splashes down.

Good point about the tidal action on Io, and good point about the radiation.

I guess if the moon was big enough for a magnetic field then the radiation isn't a large factor.

I think wherever the moon might be it will need to be a decent sized place, maybe 70% earth size or larger to have all the goodies earth has.

The tidal action idea does open up a lot of potential places that haven't been considered for life.
With a bit more tidal action at Europa we probably get a very different world.

Large moons that don't require tidal action for heating, that are in an earth type orbits of its star, will probably be the main places for life.
But non earth type orbits might still have tidal moons with life.

I bet aliens don't even look for earth type systems, they probably don't think something like earth/moon is feasible.

lunarmark · 2004-06-29 05:12:56

Chat,

I am counting every second also, this could be one of the most exiting space landings for a long while if it comes off, (and it is a high risk landing), it will be simply stunning. There are a lot of unknowns however, like will the chutes be big enough to slow it down, have they calculated the atmospheric drag well enough (beagle 2 didin't!), even will there be enough light to see. fingers definatley crossed!

The magnetic field point is an interesting one..

To keep an atmosphere in a high radiation enviroment you need a magnetic field.

To have a magnetic field, the planet would need a molten core, therfore it would have to be earth sized (since anything much smaller would have a cooled :. solidified core by now)

The other thing though, is the type of radiation, presuably it would from be 'juptier orbit trapped protons etc' (ie particles) in which case a magnetic field will stop it, but high energy xray/gamma/cosmic showers not so sure!

so its unlikely unless of course there exsits a mechanism whereby a small moon still has a liquid core due to 'tidal action', and manages to keep its atmosphere. this could be what is happening on Titan. Titan is [very] cold however.

chat · 2004-06-30 04:04:03

lunarmark,

Titan is going to be stranger than we think.
I picture a place with lakes of methane, methane bergs, methane snow covered mountain peaks, methane snow and rain.

It will look just like northern Canada, just a few degrees colder *lol*

If we are lucky enough to have the probe survive and take a picture of the sky, it will be an awe inspiring view.

Moons around gas giants.
I believe you are right that a life sustaining moon orbiting a gas giant will need to be near earth sized to sustain its atmosphere.

I guess at 70% or larger will suffice, but any tidal action from the host gas giant might allow for a smaller place to hold an atmosphere, and allow it to be in a colder more distant orbit of the star.
Maybe 50% and larger if it has tidal action.
The magnetic field is a must for any moon orbiting a gas giant.
Without a magnetic field the moon will be a pretty nasty place.

The early results of solar systems we are finding, seem to point to whatever can be out there for solar systems, is out there.

Allowing that gas giants can be in an orbit similar from Venus to mars or beyond, and can have moons much larger than our system has.
It seems the most logical place for life, and by far the most logical place for intelligent life.

With a near earth sized moon, at least when we find gas giants in the right places they will wabble.
We should be able to know those earth size moons are there before we can see them.

If i was looking for life sustaining moons orbiting gas giants at other stars.
I would look at au units .5 to 2.5, and moon size about he same .5 earth size to about 2.5 earth size.

Beyond 2.5 au sunlight decreases quickly, so i believe advanced life will not exist.
Beyond 2.5 earth size the internal heating will make it tough for life.

I guess when we find the first moon the drake will need a big rework.

Earthfirst · 2004-06-30 09:52:53

A planet does not need a liqued iron core in order to have a mag field. For example io has an induced one because it passes right jupitor mag lines, every time it cross a mag field of opposite polarty is induced and last for a while. In the other moon liqued salt water flowing makes a mag field on ganymed. Also fossil fields in the past when a planet had a strong field but lost because it cooled, a weak one remains because the iron core keep it like a big bar mag. Also fossel field remain on the surface in colled lava rork. Mars has small local fields. Mars still might have a mag field, but it is too weak and small to leave the planet rock sphere. Mercury has one 1% of earth strenght.
Moon around jupitor have a lot of ice, except io. If a moon got large enough mass, around jupitor than it it would be larger diameter than earth since it will have lots of ice. If tidal heating and the mass was large enoung than you could have a lage ocean world with a thick atmosphere like earth. This dint happen at jupitor. Io tidal heating was too great gravity too low, It lost its atmosphere and ocean, europa lost a lot of its water untile tide heating lessen and the ocean froze protecting it remaining water. On the other moon they are big in diameter but low in gravity, Heating never total melt there water into an ocean at the surface, but enough for it to get a core, of metal.
My guess if a moon got to the gravity of like mars it would have been able to hold on to its atmosphere and ocean. An earth gravity maybe, but with larger diameter. Remember all the moons are close to the earth moons gravity, but have very different diameters.

clark · 2004-06-30 16:48:43

Anybody able to figure out what the L1 & L2 points might look like for some of these Jupiter+ sized extrasolar planets?

Perhaps a smaller world formed in the same orbit as the Jupiter planet- not sure what effect that would have on the tidal forces and angular momentum, but perhaps it could work out.

The reason I ask is that a current theory being proposed about the Moon formation has a Mars sized planet forming at the L1 or L2 point in the Earth orbit- sometime in the past, it fell out of that stable orbit and crashed into Earth, thus creating a bigger Earth and the Moon we have now.

Maybe something similar happened in one of these other solar systems, only the smaller planet didn't crash...

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