Great big Jupiter-like planets are one thing, but the Holy Grail of extrasolar planetary discover is going to be another Earth - complete with life. We're not there yet, but astronomers announced the next best thing yesterday: ...

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Such an exciting discovery! I can't wait for Darwin to reveal more!

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Fraser. Cool. definitely cool. For decades the uniqueness of our solar system was indisputable. Then the first exoplanets. Then a lot more. Now smaller ones,possibly one with water at the triple point. Within the century, a starship descending through an atmosphere to find or seed life? cool definitely cool. ...and they all thought I was crazy. Pete.

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Cool! Time for me to go grow some gills now....

Sagebrusher;975442. Uh, Uh, Uh,Uhhh! How soon you forget. All humans have vestigial gills during the first trimester. Been there. Done that. Pete.

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Well... sticking the relevant values (from http://www.solstation.com/stars/gl581.htm ) into my trusty world-building spreadsheet, I see a few interesting possibilities.

For starters, this new planet is obviously tidelocked. Though its orbit is pretty eccentric (solstation.com says it's e=0.28 ± 0.06) so I wonder if it'd be in a 3:2 resonance or something, like Mercury. If it was in a 1:1 then wouldn't its orbit be completely circular? So I wonder if something's pumping its eccentricity up (probably the other planets in the system).

I can't get a radius 1.5 times that of Earth to yield a mass of 5.03 earths with an earthlike density (5500 kg/m3). Given that density, the radius has to be 10,926 km to get the same mass, and you'd need a very large (probably unrealistic) proportion of the planet's mass to be water. But I suspect that the density would actually be higher even with a thick water layer, because a more massive planet will self-compress more. A very rough guesstimate (based on plugging numbers into my internal structure spreadsheets) would be that the density of the planet could be about 7950 kg/m3 with a radius of 9659 km (1.514 earths) and 5.30 earth masses (3e25 kg) - such a world would have about 800 km of water and high pressure ice on top of a rocky body with a radius of about 8860 km, that has an earthlike outer/inner core with a combined radius of about 4950 km. The surface gravity would be 2.19g.

The odd thing is that the blackbody temperature of an object with albedo 0.0 at a distance of 0.073 AU from a star with luminosity of 0.013 Sols is 348K. With an earthlike albedo of 0.3 it drops to 318K (45°C). with an albedo of 0.5 it drops to 293K, and with an albedo of 0.7 (venus-like) it drops to 258K. Earth's blackbody temperature (including its albedo) is 254K, the greenhouse effect pushes that up to the generally accepted average tempeature of 288K. So I guess if it's really cloud-covered (which it probably would be if it was a panthalassic world covered in very deep oceans) then its albedo would be higher and it can be more habitable? That said, wouldn't it have a much thicker atmosphere too, which would increase the greenhouse effect and therefore the temperature? It might actually be a hot, steamy "moist greenhouse" environment on the surface in that case.

The really interesting thing is that it'd probably be massive enough to retain helium in its atmosphere over geological timescales (assuming flares don't blow it away, though solstation doesn't mention if the primary is actually known to flare). I don't think it can retain hydrogen though (if it could, it'd be a gas giant). But I wonder what a planet that can hold helium in its atmosphere would be like - would it still have its primordial helium envelope? Would it all mix with other gases, or could you have a breathable atmosphere at the bottom of a thick helium layer? Anyway, my calculations say that the minimum molecular weight of gas retained by Earth around Sol over billions of years is 5.52, and the MMW retained by this planet over the same timescales would be 2.08 (which means it can hold Helium (MMW 4) for that long, but not Hydrogen (MMW 2), though it can hold it for shorter timescales).

I could be barking up the wrong tree completely here (I hope not, I got all the equations for my spreadsheets from textbooks and journal papers!), but it's interesting to think about...

I didn't think that an Earth size planet would be discover within at least 10-15 years. This is great! Maybe they'll discover life outside our planet or even communicate with them (at least I hope so) during my lifetime (I think another 50 years to go for me).

IMO, this is the greatest discovery to date. Gas giants, stars, black holes, dark matter, etc... are cool, but to find an Earth size planet with a possibility of water or land, which can hold life, is so much better. The potential for life on that planet may be very realistic. However, intelligent life on that planet is another matter. I'm not sure if there was, is, or will ever be intelligent life on that planet, but it sure does give hope that planets like our own Earth, that can hold life, are abundant in the universe. We are not alone!

Btw, I read that the mean temperature on that planet is 0 to 40 degrees celsius. I've lived in -50 to 45 degrees celsius before on various points of the Earth so that planet would be a great getaway for me. Time to start packing...

This is amazing!! I cant believe it, I cant wait untill we learn more about this or more info is released!, It sounded like(on the today show) that they werent for sure if it is inhabitable?what do you think? well, I hope there is life there, and I hope like someguy44 that we will comunicate or get there or something in my life time, about 60-70years hopefully. This is Awesome!!

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EDG, I must say that was a very intersting post. Is there some possible variation that you could potentially figure out involving a more dense planet than earth, specifically maybe a large iron core similar to mercury. I think it is probably the most logical explanation given the formation of the planets. With the heavier elements settling first, the planet may only be 1.5 times the diameter of earth. Id be interested to see the calcs based on a core proportional with Mercury, simply because if it was larger, it would be a much more dense planet than earth due to the large amount of gravitational compression

My newspaper reports a gravity of 1.6, that of Earth.

On communication, is SETI still up? Would it be worth swinging the array in that direction?

Anyone heard reports on age yet? If it is a few million years different than Earth that should effect the state of any life there.

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That was actually incorporated into the numbercrunching I did . The thicker rock mantle and iron core means that the centre of the planet is denser - the materials the model planet is made out of are a saltwater (1050 kg/m3) shell, silicate mantle (3600 kg/m3), Fe-FeS outer core (5965 kg/m3) and a solid Fe core (8000 kg/m3). Once you include the pressure from the material above them, the density of those materials gets much higher, which makes the whole planet's bulk density higher too (to about 7950 kg/m3).

As it is, the outer core of the model contains 20% of the mass of the planet and is about half the radius of the planet (4947 km), and the inner core contains 10% of the total mass of the planet and is about a third of the radius of the whole model planet (3096 km). By comparison, earth's outer core is about half of our planet's radius. If we made that proportional to Mercury's core then the outer core would have to be about 75% of the radius of the model, or about 7250 km, which would require an obscene amount of iron and iron-sulphides - 80% (about 2.4 earth masses) of the planet's mass would have to be core material! As it is, in my model planet the core's mass is 1.5 times that of the whole earth!

(just to be clarify again, my model planet is entirely putative, not peer-reviewed (though it is based on equations published in journals and textbooks about planetary interiors), and makes a lot of assumptions that may or may not be valid - it's just an educated guesstimate, one possibility among many possible configurations of material and internal structure).

What's fun to think about (though highly unrealistic) is what sentient and technological beings on this world would be thinking about us based on what TV signal have made it their way. Seeing that this planet is about 20 or so light years away it means right now they are getting 1987 television broadcast.

The following is a link to Wikipedia that list various TV show and events that occurred in 1987

1987_in_television

Hmm... Thanks to Star Trek I bet they're wondering why we haven't dropped by to say "Hello" yet. Of course, having watched all those years of television I'm sure by now they hope we don't or are preparing an invasion fleet to destroy us because of it.

EDG, can I ask, why do you assume the planet will be panthalassic?

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I did some quick calculations on the amount of energy this planet would recieve from it's star.

Our sun puts out 3.9e26 W of power, and since this star is 1.3% as luminous it'll put out 5.07e24 W of power. The planet is 14 times closer to it's star then the Earth, so it's orbital radius will be 1.07e10 m:

4*pi*(1.07e10)^2 = 1.44e21 m^2

5.07e24 W / 1.44e21 m^2 = 3514 W/m^2

So 3,514 Watts per square meter of energy is recieved by this planet. Compare that to the Earth which gets 1,380 W/m^2, and Venus which gets 2,660 W/m^2. That's 2.5 times more sunlight then the Earth recieves and 32% more sunlight then Venus!

Honestly, what are the chances that this is more Earth-like then Venus-like? I know that Venus is the way it is mostly due to it's overly thick atmosphere, but all things being equal it seems like this planet will have a much better chance at being Venus like then Earth like. Also, consider what would happen to the Earth if the sun all of a sudden increased in brightness by 2.5 times. I don't think it would take too long for Earth to start looking a whole lot more like Venus.

This doesn't seem like a very good contender for an Earth like planet. What do you guys think?

*Note: I'm basing this off of the fact that I read that this star is 1.3% as luminous as the sun. If I got wrong information, then obviously my calculations are all wrong. Is 1.3% correct?

Well, compared to Jupiter, Venus is very Earth-like. But it all depends on the amount of greenhouse gasses in its atmosphere. If it's rich with CO2, like Venus, it'll be a hellworld, but if it's thinner, it might be perfectly comfortable. We can't know until we analyze its atmosphere.

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I supposed discussions have already happened on what it would take to develop intelligent life.

Do they need certain chemicals and 'normal' temperatures etc?

It seems to me they would just need lots of cells capable of firing electrical impulses. Our brains run up to 75mV (.075 volts), I think that would be possible with a great range of chemistry and temperature.

The variations may also influence the rate of evolution. Shorter lifespans, more nutrients. Anyone else ever read 'Surface Tension'?

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Hmm, seems I have alot to discuss in this post lol.

I think its up for debate about the classification of what type of planet that this would be like. Again its coming down to atmospheric content in terms of C02, as well as the temperature of the star that it rotates around, which I believed it was said to be cooler than the sun. Keeping in mind, one factor that hasn't been said in this is whether or not the planet is tidally locked, or has some form of orbital resonance. With that being said, if this planet is tidally locked, its going to have one baked side and one frozen side. Although, liquids could redistribute the heat, its still going to be frozen if one side receives no sunlight.

And Pinemartin,

As far as developing intelligent life, there are so many criteria that need to be met even for the most basic life forms to thrive. Based on current standards, the planet will need a magnetic field to protect from the sun's radiation. Secondly is the presence of water, to redistribute heat. Thirdly it has to be within the habitable zone. Im assuming that a planet that size will successfully have cleared out enough surrounding debris to form a stable neighbourhood. With that being said, these are currently accepted standards on what scientists thing life on earth needed to survive. I would still like to think that other standards exist to form different bases of life forms other than carbon...ie something like the conditions on Titan where liquid methane or nitrogen breathing organisms would exist that force us to expand our theories.

Can't liquid methane transfer heat as well as water? Any liquid or dense gas should work well for that. As well the cooler temperatures may assist life because of the superconductivity speeding the electrical pulses.

As to a magnetic field, would being tidally looked block the radiation on one side?
Would the temperatures near the terminator on the cold side be okay for life and thus avoid the radiation issue?

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The 3-planet solution gives an eccentricity for planet 2 (i.e. the >5 Earth mass one) of 0.16, not 0.28 (that number was for the 2-planet solution). However, they do state explicitly in their paper that the eccentricity is not well constrained. In fact, a circular orbit actually gives a lower reduced chi-square than letting the eccentricity be a free parameter.

It's more massive than earth, and panthalassic worlds are theorised to be more massive (being basically an earth mass or two of rock + thick water/ice layer), so it seems a possibility.

I suspect that if it's rocky then it'd be a lot more massive and would easily hold onto hydrogen, and we'd be looking at a more massive gas giant instead of a low mass world.

It may not be panthalassic at all, but it seems like one of the more realistic possibilities .

Ah I see. Thanks for the clearup.

Aren't these two positions mutually exclusive? I don't see how it could have more insolation than Venus and yet still be considered within the star's habitable zone.

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It's gotten to the point where careful investigation is needed just to tell parody from reality. I think that means reality is broken.- Noclevername.

Pinemarten ...

SETI already scanned this star ! See the Wiki links, etc, etc, linked on my Blog ...

http://djbarney.wordpress.com/

Of course now I can almost hear the crunching of gears as a thousand telescopes swing towards Gliese 581, including SETI, for a closer look, if I'm not mistaken.

Folks, with this kind of info... (the first of it's kind EVER, period!) I wonder if we might see some very interesting developments now there is somewhere TO scrutinise, if you see what I mean. Up till now we've had a whole sky to swing the scope around. Now, there this. (I know .. there WERE intelligent decisions being made about what to scan before ... but this is new).

Anyone got this up in Celestia ? My version already has a textured version of one of the Planets around Gliese in it, but not C yet.

Where are the interviews with discoverers ? Why are'nt they being paraded down central avenue in ticker tape parades ! (LOL! I know, silly example, but you know what I mean).

IMO the silence is DEAFENING! There are 20 replies on this thread. Should'nt that be 20,000 ? Where is everyone ?

DJ Barney

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Ah, I just found this....

Most Earth-like planet to date revealed.

159 replies ... more like it.

Still, it still seems a little quiet.

DJBarney

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definitely an amazing discovery! my favorite part is the fact that the sun would be 20 times larger in the sky. in almost all science fiction when they show show far off solar system the size of the sun(s) or moon(s) is usually similar to our perspective from earth. but the perspective from this planet would be unbelievable - to see the sun so huge in the sky. it makes me dream.

Thank you for the response on the SETI angle (pun intended), the other thread on this subject seemed to ignore my query.
I did take the time to peruse the first three pages of it, but it seems to be mostly speculation and paragraphs of calculations that have already been done.
Not many facts on the discovery itself.

I also heard there is a Canadian satellite that may be able to provide a better second look.

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Pinemarten.....

Glad to be of help

I often end up looking at the sociological / cultural aspects of these kind of discoveries, while nodding to the Scientific facts.

I wonder if this discovery is so huge that we're in a psychological "bottoming out" phase where thee are so many questions that it's going to take a few weeks and months to pull things together! Not that it is'nt fascinating in the meantime!

DJ Barney

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The details for this planet in Celestia are available here
http://celestia.cvs.sourceforge.net/...extrasolar.ssc

note that this will produce a rocky world for 581 c, which is one of the possibilities for this planet; another is a hot-water-world, which would be larger and cloudier (but stiil the same mass).

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This is actually in reference to EDG's multiple posts as well. Don't have a planet builder, but accepting as roughly accurate the radius and mass given in the stories for 581c (1.5 times that of Earth and 5 times that of Earth respectively), I get a surface gravitation of something like 2.2 and a density roughly 1.5 that of Earth. I expect an iron core primarily because of its size and mass. If the star emitted as much energy as the sun, then at its distance the planet would receive something like 200 times as much energy as the Earth receives from the sun, so the question is how much fainter is Gliese 581 than the sun.

Can't the eccentricity of the orbit be determined by the wobble? EDG says it has been, if I read right. Wouldn't it be surprising if a planet that close wasn't tidelocked?

I suspect we are somewhat provincial in our notions of what constitutes life, able so far to credit it only when it occurs in our familiar format. On Earth, life fills every available niche. I would be surprised if it were different for the universe. And intelligence: We are the most intelligent creatures in the universe? That sound likely? To me it sounds somewhat human-centric, a bit reminiscent of the Earth-centered astronomy of centuries ago.

Do not of course have evidence for these latter speculations. Just a personal sense of what is probable. Could be wrong. Would take bets, though.

Jack,
I completely agree with your last post. You would have to think somewhere around the trillions of stars in one of the millions of galaxies, that conditions would exist so that other intelligent life could evolve. Calling ourselves intelligent or the most intelligent life out there is very human in nature, like the earth centred solar system theory. However, with that being said, Im not so sure you can even call us intelligent. I mean what intelligent race kills each other off with no motives other than different beliefs? Either that just look at the global issues that are arising as a result of our current society. Just my personal view, but those are two reasons as why I don't deem the human race as intelligent. The average human is smart, but in groups, dumb.

If that's the case it sounds like there's something wrong with their model fitting procedure.