Is Gliese 581d a Goldilocks planet?

[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?

 

[DaveC426913]

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

Hang on, I'll be back in a minute...

 

[DaveC426913]

Yep. There's atmospheric oxygen out there!

 

[Chronos]

The presence of oxygen in an exoplanet atmosphere would be very exciting. It would be very difficult to explain without biogenic replenishment over long periods of time. Actually, ozone is what they look for. It is easier to detect spectroscopically than oxygen, and ozone without oxygen would be improbable. From a chemistry standpoint, carbon is the logical building block for life. An incredible array of molecules can be formed with carbon bonds, and carbon is abundant in the universe. It makes sense to base any search for ET on a proven winner on earth. There is no known non-carbon based life form on Earth to my knowledge.