Is Gliese 581d a Goldilocks planet?

[narrator]

Hi, not sure if this belongs here or Astrophysics or... ??

http://au.news.yahoo.com/amazing-stories/a/-/article/9454275/could-exoplanet-be-a-haven-for-life/" , planet Gliese 581d. Sorry if this is old news, though the report is in today's Yahoo news here in Oz.

They say the planet probably has about twice Earth's gravity, and probably has water. Fictional stories sometimes talk about planets with greater or lesser gravity than Earth, but not double, which makes me wonder if they approach it too simplistically. With 2G, life forms (if they exist) are likely to be flatter and evolved to deal with what would be natural gravity to them. But surely the additional gravity would create geological and environmental problems that would go against sustaining life.

The interesting thing though is the new modelling for finding such planets. Under the old modelling, the article said there was a mistaken planet Gliese 581g, which the new method proved wrong.

From the science shows and articles I've watched and read, they say the two aspects for discovering and analyzing these planets are the gravity effect of the planet(s) on their star and when they're lucky enough to see one cross the face of the star. A really good science show demonstrated just how difficult the that is. Are there other aspects apart from these two?

I have difficulty comprehending how accurate the "wobble" method could be. At such distances, wouldn't it be like watching a ball-bearing move less than a hair's width, when that ball-bearing is as far away as the moon? Also, the star could have several planets, like ours, making such wobbles difficult to interpret, let alone see. And lastly, is our own "wobble" effect from our sun, moon and planets taken into account in such calculations?

Fascinating stuff anyway. Drivers, start your FTL's.

 

[bapowell]

But surely the additional gravity would create geological and environmental problems that would go against sustaining life.

Maybe against sustaining life like that on Earth, but who says that life, in general, has to look anything like what we have here on Earth? The difficulty with talking about the possibility of life on other planets is our limited experience with what, theoretically, constitutes "life". We are just now learning how robust it might be -- the recent discovery of arsenic in the DNA of microbes is one example of this, as are our seemingly constant discoveries of organisms thriving in niche environments that would be toxic and inhabitable to vast numbers of other species. As far as I know, there is no theoretical claim that life must be carbon based, that the units of heredity must look anything like DNA, or that the metabolic pathways common to life on Earth are by any means "necessary" for life.

 

[helios1]

Maybe against sustaining life like that on Earth, but who says that life, in general, has to look anything like what we have here on Earth? The difficulty with talking about the possibility of life on other planets is our limited experience with what, theoretically, constitutes "life". We are just now learning how robust it might be -- the recent discovery of arsenic in the DNA of microbes is one example of this, as are our seemingly constant discoveries of organisms thriving in niche environments that would be toxic and inhabitable to vast numbers of other species. As far as I know, there is no theoretical claim that life must be carbon based, that the units of heredity must look anything like DNA, or that the metabolic pathways common to life on Earth are by any means "necessary" for life.

Since we have a very good idea of what life looks like, adding more complexity doesn't make sense, especially since our growing acceptance of alien life is enhanced by study of our simplest forms. Planets, moons, stars, and comets are all made of basic raw materials, why should life be any more exotic?

 

[Negeng]

Since we have a very good idea of what life looks like...QUOTE]

Well I do not know if we have a good idea of what life looks like, especially since we keep getting surprised by discoveries like the ones bapowell mentioned. Really we only have one planet to study life right now and that is like having an experiment with only one trial. Multiple trials in an experiment help weed out the fluke results, but we do not have such a luxury and life on our planet could be an exception to what life forms might be like in the rest of the Universe.

 

[helios1]

"life on our planet could be an exception to what life forms might be like in the rest of the Universe".

Then what would we look for? Would we recognize it as life?

 

[Negeng]

Then what would we look for? Would we recognize it as life?

So far the best idea I have heard is that we look for planets with gasses in their atmosphere that would normally react with other elements in the ground. Take Oxygen for example, it only exist in the air because plants put it there, otherwise it would combine with elements on the ground and not be in the atmosphere. I am certain there other such gasses as well and this would expand our search a little (and I would be the first to admit that it would expand it by a only a little).

 

[Drakkith]

"life on our planet could be an exception to what life forms might be like in the rest of the Universe".

Then what would we look for? Would we recognize it as life?

I think it is safe to say that almost any form of life will be readily recognizable. At least compared to sterile environments where no life would be found.

 

[bapowell]

Since we have a very good idea of what life looks like, adding more complexity doesn't make sense, especially since our growing acceptance of alien life is enhanced by study of our simplest forms.

You miss my point. We have a very good idea of what life looks like on earth. To suggest that we know about life more generally than this shortsighted at best, delusional at worst.

 

[DaveC426913]

I think it is safe to say that almost any form of life will be readily recognizable. At least compared to sterile environments where no life would be found.

No it's not.

Sure, if you were walking around on the planet kicking over rocks. But remember our extremely limited viewpoint - light years distant at the very best. We can only spot life by the chemical signatures we might see in the atmo, and it's very difficult to distinguish natural processes from biological ones. We're having this very diffculty on the end of our cosmic noses - Mars, some 10 million times closer.

 

[Drakkith]

You miss my point. We have a very good idea of what life looks like on earth. To suggest that we know about life more generally than this shortsighted at best, delusional at worst.

No, I understand your point. I have no idea what it will LOOK like, or what form it will take, or whatever. But I would bet that it will be farily obvious. Any form of life should readily change its environment.

 

[DaveC426913]

But surely the additional gravity would create geological and environmental problems that would go against sustaining life.

Nah. Realistically, we're talking bacteria, lichens.

Finding complex large-scale life on our first foray into the world of exo-biology would a lottery win writ cosmic.

 

[helios1]

Carbon based, DNA genome, highly conserved metabolic pathways. This has been the basic recipe for nearly one third the entire life of the universe so it just makes sense to expect to find what works best.

 

[DaveC426913]

Carbon based, DNA genome, highly conserved metabolic pathways. This has been the basic recipe for nearly one third the entire life of the universe so it just makes sense to expect to find what works best.

A sample of one does not a probability make.

(Though my money is on a COH amino acid based molecule.)

 

[Drakkith]

Carbon based, DNA genome, highly conserved metabolic pathways. This has been the basic recipe for nearly one third the entire life of the universe so it just makes sense to expect to find what works best.

I can't tell if this is sarcasm or not.

 

[helios1]

So we look for earthlike planets in the universe, with earthlike properties, occupying earthlike space, full of earthlike water, covered by an earthlike atmosphere and expect to find life looking like nothing on earth.

 

[Drakkith]

So we look for earthlike planets in the universe, with earthlike properties, occupying earthlike space, full of earthlike water, covered by an earthlike atmosphere and expect to find life looking like nothing on earth.

I see the irony lol...

 

[DaveC426913]

So we look for earthlike planets in the universe, with earthlike properties, occupying earthlike space, full of earthlike water, covered by an earthlike atmosphere and expect to find life looking like nothing on earth.

Well, Earthlike or no, all the chemicals out there we have right here on Earth. And there are precious few combinations that are capable of producing complex molecules.

Because DNA life is dominant here does not mean we shouldn't expect to see any molecular candidates here. And we don't, really.

Further, C O and H are very common in the universe and hang out in gangs.

The cosmic scales of molecular opportunity are not balanced, they weigh very heavily in favour of
- the lower few dozen elements,
- the most common elements,
- the most reactive elements,
- water, which is virtually unique in the universe.

While there could be other forms out there, COH life has these huge advantages.

 

[narrator]

Nah. Realistically, we're talking bacteria, lichens.

Finding complex large-scale life on our first foray into the world of exo-biology would a lottery win writ cosmic.

True enough I suppose. Though if there were cellular life, would you expect it to evolve, or is evolution a bit of a lottery at such low levels of life?

I saw a doco once that did the math on life forming, even on a perfect planet like Earth. They said that the odds were so small as to make it highly unlikely, making us better than lottery winners. They went on to suggest that at such odds, it's possible we're unique in our universe (in having any life at all).

 

[DaveC426913]

True enough I suppose. Though if there were cellular life, would you expect it to evolve, or is evolution a bit of a lottery at such low levels of life?

It would certainly evolve. But the jump to multicelled life is a huge one. Note that bacteria are doing just fine here after 3 billion years.

 

[narrator]

It would certainly evolve. But the jump to multicelled life is a huge one. Note that bacteria are doing just fine here after 3 billion years.

Why would it "certainly" evolve? Here on our planet, a part of the engine of evolution is said to be caused by the effects of gamma radiation (from our sun) on DNA, but (for example) the star that the article in the OP talks about is a red dwarf, for which the radiation effects could be substantially less likely to aid or provoke evolution.

 

[DaveC426913]

Why would it "certainly" evolve?

Because life does that. I'm not sure it would be life if it didn't.

I'm not just being flip; I'm trying to imagine a mechanism that generated life from chemistry, and created a perfect replicating system in an enironment that was perfect to support it, never changing, so never driving reproduction and death rates.

 

[Ryan_m_b]

Why would it "certainly" evolve? Here on our planet, a part of the engine of evolution is said to be caused by the effects of gamma radiation (from our sun) on DNA, but (for example) the star that the article in the OP talks about is a red dwarf, for which the radiation effects could be substantially less likely to aid or provoke evolution.

Radiation really isn't the only driver of evolution, even back in the times of abiogenesis. As you say it is only a part. All that is required for evolution to occur is replication with error and environmental attrition.

 

[Cosmo Novice]

Because life does that. I'm not sure it would be life if it didn't.

I'm not just being flip; I'm trying to imagine a mechanism that generated life from chemistry, and created a perfect replicating system in an enironment that was perfect to support it, never changing, so never driving reproduction and death rates.

I agree with Dave here. Life (the only cosmic example we have, granted) by its very nature seeks to adapt to its environment to become more succesful. This is true whether applied to single cell or complex multicell lifeforms. For life not to evolve would require an unchanging environment (on a cosmic magnitude given the timescales required for evolution) and also require that the life occupying the environment was at its biological peak - ie there would be nothing life could do to further its chances of survival and it COMPLETELY dominated its condition of environment.

So to summarise if life did not change to adapt to its surroundings then essentially it would not be life - or not what we recognise as life. I do not think in any environment there would be life in any form that doesn't adapt to conditions of environment - while not to say that all life WILL evolve into complex lifeforms this is to say I think all life WILL change in reaction to environmental changes - whether this is evolution to higher lifeforms or devolution for survival.

 

[Ryan_m_b]

For evolution to stop the following criteria (from the Hardy-Weinberg Equilibrium) must be met

1) A population must be large
2) No mutations may occur
3) Mating must be random
4) No migration
5) No differential reproductive success

However even if evolution did stop said species would have had to evolve to those conditions first. I highly doubt an organism can fully form into these conditions

 

[Tanelorn]

I fully agree with helios. I don't know why everyone is looking for weird alien life biological designs. I suspect that there is a lot of primitive life out there but very few highly intelligent civilisations. Such civilisations could also be very short lived on cosmologocal timescales.

 

[Ryan_m_b]

I fully agree with helios. I don't know why everyone is looking for weird alien life biological designs. I suspect that there is a lot of primitive life out there but very few highly intelligent civilisations. Such civilisations could also be very short lived on cosmologocal timescales.

Who knows? We've got no idea how long lived a technological civilization can be (having only one to observe that hasn't yet ended) and what would effect that. As for primitive life we're limited by our ability to detect it from a distance of light years with only telescopes.

 

[Cosmo Novice]

I fully agree with helios. I don't know why everyone is looking for weird alien life biological designs. I suspect that there is a lot of primitive life out there but very few highly intelligent civilisations. Such civilisations could also be very short lived on cosmologocal timescales.

If applying a Kardashev scale and looking at anything pre type1 civilisation then I agree that one would expect civilisation lifespans to be small on a cosmological scale. If a civilisation could extend past type2 civilisation (somewhere between type 2 and type 3) then it could be expected to have cosmologically long timescales.

Interestingly Kardashev didnt extend the scale past type3 but anything post type3 civilisation could be assumed to have very long timescales as the sort of timescales involved in developing a civilisation of that type would by its nature exist over a very long timeframe.

While I concur with you that the basic biological life will be numerous across the cosmos (I still speculate we will find microbacterial life within our local system - possibly a jovian moon) however I disagree that their are "very few" developed civilisations - given the size of U and the probabilities involved. (Even when we assume earthlike environments only for intelligent life, which still may not be the case.)

 

[DaveC426913]

While I concur with you that the basic biological life will be numerous across the cosmos (I still speculate we will find microbacterial life within our local system - possibly a jovian moon) however I disagree that their are "very few" developed civilisations - given the size of U and the probabilities involved. (Even when we assume earthlike environments only for intelligent life, which still may not be the case.)

Yeah, the confounding factor then becomes: if they are too far away to observe, they are as good as non-existent anyway.

So that limits our useful sphere dramatically - depending on how patient you are and how good your eyesight - hundreds of ly or less.

 

[Cosmo Novice]

Yeah, the confounding factor then becomes: if they are too far away to observe, they are as good as non-existent anyway.

So that limits our useful sphere dramatically - depending on how patient you are and how good your eyesight - hundreds of ly or less.

True, but any civilisation which develops to anywhere between type2 and type3 civilisations on the Kardashev scale may be detectable (assuming development within our galaxy) this is assuming current energy harvesting theories on a large scale (such as Dyson Spheres)

The more I think about this the harder I think it may be for an advance civilisation to hold itself together (over multiple star systems) Assuming superluminal travel can be achieved how could a civilisation hold itself together in multiple time frame references - as they would be spread across space/time. Ok now I am confusing myself... :)

Very interesting :)

 

[narrator]

One cell does not a case make. I'm guessing that all life on Earth developed from a single cell. And so all species on this planet inherit the nature of evolution "as we know it" from that single cell. It's easy to look at all life on this planet and think it represents some universal evolutionary principle, but when you look at its origins from that single cell, you could be drawing a wrong conclusion.

On the flip side, whatever caused that cell to first appear could be considered part of the "adaption" process, and hence, any formation of life might inherently mean adaption. Or is that a bit of a stretch?

I recall a documentary that I saw adding up all the odds; firstly for having a planet that fits into the goldilocks zone requirement, second for having the cosmic environment just right for sparking life, and finally for having something actually ignite that spark.

We got lucky all those millions of years ago when something happened to precipitate that first cell forming. The guy in the doco said it was near impossible odds. So, for the number of possible planets in our OU that fit the criteria, and then to have the almost impossible happen, it suggests (as the doco guy suggested) that having any life on this planet at all is more unique than we may believe.

 

[Nik_2213]

Now slightly OT due thread derailment...

The star's wobble that is interpreted as orbiting planets is detected using Doppler effect ( ~ 1 metre / sec), often referenced to a standard element's spectrum. IIRC, that used to be a halogen gas, but current instruments seem to use thorium or just an extraordinary optical grating...
http://en.wikipedia.org/wiki/High_Accuracy_Radial_Velocity_Planet_Searcher

Following the links, the next-generation instruments should be sensitive to stars' cyclical motion ~ 10 cm/sec...

 

[Ryan_m_b]

True, but any civilisation which develops to anywhere between type2 and type3 civilisations on the Kardashev scale may be detectable (assuming development within our galaxy) this is assuming current energy harvesting theories on a large scale (such as Dyson Spheres)

The more I think about this the harder I think it may be for an advance civilisation to hold itself together (over multiple star systems) Assuming superluminal travel can be achieved how could a civilisation hold itself together in multiple time frame references - as they would be spread across space/time. Ok now I am confusing myself... :)

Very interesting :)

I've never been too convinced by Kardashev scales. It seems to assume that there is a linear progression that technological civilizations will follow. I'm not even convinced that humanity would build a Dyson sphere if they had the capability let alone aliens.

Though we're strongly drifting into the Fermi paradox here

 

[narrator]

Now slightly OT due thread derailment...

The star's wobble that is interpreted as orbiting planets is detected using Doppler effect ( ~ 1 metre / sec), often referenced to a standard element's spectrum. IIRC, that used to be a halogen gas, but current instruments seem to use thorium or just an extraordinary optical grating...
http://en.wikipedia.org/wiki/High_Accuracy_Radial_Velocity_Planet_Searcher

Following the links, the next-generation instruments should be sensitive to stars' cyclical motion ~ 10 cm/sec...

Wow! Thanks Nik.. I wondered about that. How much does our own Sol wobble? I imagine it would not be so simple, with so many planets in our system.

 

[narrator]

Though we're strongly drifting into the Fermi paradox here

Speaking of which, I thought I heard on the news the other day that SETI is about to increase their searching. Not sure what was meant by that though..

 

[Nik_2213]

"...with so many planets in our system."

My guess is it would simplify to 'Jupiter plus error-bars' as our inner planets are too small and even Saturn is too small and too far out to have much effect. More importantly, their slow orbits (12 yr & 30 yr) mean it would take a long, long time to spot, then quantify their cyclic Doppler effects...

Uh, Google found ~13 m/s due Jupiter and ~3 m/s due Saturn.

FWIW...
http://en.wikipedia.org/wiki/Gliese_581 for intro. (YMMV)
http://en.wikipedia.org/wiki/Doppler_spectroscopy may not be up to date.

 

[narrator]

"...with so many planets in our system."

My guess is it would simplify to 'Jupiter plus error-bars' as our inner planets are too small and even Saturn is too small and too far out to have much effect. More importantly, their slow orbits (12 yr & 30 yr) mean it would take a long, long time to spot, then quantify their cyclic Doppler effects...

Uh, Google found ~13 m/s due Jupiter and ~3 m/s due Saturn.

FWIW...
http://en.wikipedia.org/wiki/Gliese_581 for intro. (YMMV)
http://en.wikipedia.org/wiki/Doppler_spectroscopy may not be up to date.

Great info and links. I love the graphics in that first link. It also prompted me to wonder the effects of centrifugal force. 581d may be in the habitable zone, but its centrifugal force may throw off atmosphere or have some other counterproductive effect, making it less viable. Is my thinking right there?

 

[Negeng]

One cell does not a case make. I'm guessing that all life on Earth developed from a single cell. And so all species on this planet inherit the nature of evolution "as we know it" from that single cell.

I am not so sure about that, because of the arsenic life forms.

I fully agree with helios. I don't know why everyone is looking for weird alien life biological designs.

I can explain that. If we narrow our search too much we could end up not looking at places that have life. As a side note if there is a planet with life on it, it most likley does not have Oxygen in its sky. The only reason why Earth's sky is the way it is, is because plants make that way and there is no hard fast rule that says plants have to evolve. Remember proabilty is an important component of evolution.

 

[Ryan_m_b]

I am not so sure about that, because of the arsenic life forms.

If you are referring to the GFAJ-1 bacteria reported by NASA that was a massive cock up on behalf of their press office. They had no evidence that arsenic had been included into any part of the cell, let alone replacing the phosphate in DNA as their press office's video implied!

http://en.wikipedia.org/wiki/GFAJ-1#Criticism

 

[DaveC426913]

I am not so sure about that, because of the arsenic life forms.

Yes, that is blown way out of proportion. There aren't really "arsenic-based life forms". It's muuuch more suble than that.

I can explain that. If we narrow our search too much we could end up not looking at places that have life.

Yes but if we're roaming across the American Midwest in search of horses, does it really make sense to expend resources looking for a zebra?

As a side note if there is a planet with life on it, it most likley does not have Oxygen in its sky. The only reason why Earth's sky is the way it is, is because plants make that way and there is no hard fast rule that says plants have to evolve. Remember proabilty is an important component of evolution.

Which is why we look harder for methane than for oxygen.

 

[Nik_2213]

"... but its centrifugal force may throw off atmosphere..."

Uh, no. Earth had an estimated 6-hr day length just after the mega-impact that sloughed what became the Moon. It took a long time for tidal drag to slow the spin which, IIRC, can be followed by counting growth lines in fossilised stromatolites etc. There had to have been an extensive atmosphere at that point...

 

[narrator]

"... but its centrifugal force may throw off atmosphere..."

Uh, no. Earth had an estimated 6-hr day length just after the mega-impact that sloughed what became the Moon. It took a long time for tidal drag to slow the spin which, IIRC, can be followed by counting growth lines in fossilised stromatolites etc. There had to have been an extensive atmosphere at that point...

No, I mean the centrifugal force of a 66 day year, such a tight circle around its sun. I guess it wouldn't throw off atmosphere (just as Venus doesn't) but I'm thinking it could have other negative effects.

 

[Filip Larsen]

Just in case anyone is interested in reading about the actual method and assumptions for this Gliese 581d analysis employed by the french team, the paper can be found at http://arxiv.org/abs/1105.1031

 

[narrator]

Woohoo! Thanks Filip.. downloaded the pdf :)

 

[Nik_2213]

"...the centrifugal force of a 66 day year"

IMHO, compared to the effect of a solar flare or absence of a magnetosphere, the orbital velocity hardly counts if planet is in temperate zone...

 

[andiamaj1431]

why should we look for Earth like planets to find life? whos to say that life cannot exist on a planet with liqiud methane or sulfur atmosphere, we are limiting the possibiltiy of life else where in the universe to our own genetic standards of what's livable

 

[DaveC426913]

why should we look for Earth like planets to find life? whos to say that life cannot exist on a planet with liqiud methane or sulfur atmosphere, we are limiting the possibiltiy of life else where in the universe to our own genetic standards of what's livable

Our methods of detection right now are in their infancy. We have only a few ways to determine - at multi-light year distances - life from non-life (eg presence of atmospheric oxygen). It is hard enough to do for the metabolic processes of life we know. It will be impossible to do for metabolic processes we can't even conceive of. How would you even know if it's life you're detecting?

 

[Hurkyl]

No, I mean the centrifugal force of a 66 day year, such a tight circle around its sun.

There is no centrifugal force.

 

[DaveC426913]

There is no centrifugal force.

This thread has been resurrected after ~6 months. Only the last post before mine is much use.

However, as for centrifugal force, what he's really thinking of is tides, he just doesn't know it.

As the planet whizzes around its parent, its oceans/surface/atmo will indeed rise up on the dark side of the planet - just like they will on the sunward side.

 

[narrator]

However, as for centrifugal force, what he's really thinking of is tides, he just doesn't know it.

As the planet whizzes around its parent, its oceans/surface/atmo will indeed rise up on the dark side of the planet - just like they will on the sunward side.

Thanks Dave, yes indeedy, tides and other gravitational effects.

I've been away from the forums for a while, but I did see a report that suggested Dune-like planets (like the sci-fi) could be more likely for prospects of life. They mentioned Mars and how such planets typically have water at their poles. They suggested that blue planets are rarer and Dune-like planets could be more common.

As an aside, it reminded me of the idea that life on Earth may have originated on Mars and brought to Earth via meteors.

 

[andiamaj1431]

Our methods of detection right now are in their infancy. We have only a few ways to determine - at multi-light year distances - life from non-life (eg presence of atmospheric oxygen). It is hard enough to do for the metabolic processes of life we know. It will be impossible to do for metabolic processes we can't even conceive of. How would you even know if it's life you're detecting?

im not sure, but did they use the detection method on Earth to see if it could detect life? was it accurate?