More about "earth-like" planet Gliese 581g

[Martin]

The technical article was just posted. It confirms earlier findings and gives more detail.

 

http://arxiv.org/abs/1009.5733

 

====quote from 1009.5733 abstract ===

"...The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and 67-day planets previously announced by Bonfils et al. (2005), Udry et al. (2007), and Mayor et al (2009). The observations also indicate a 5th planet in the system, GJ 581f, a minimum-mass 7.0 M_Earth planet orbiting in a 0.758 AU orbit of period 433 days and a 6th planet, GJ 581g, a minimum-mass 3.1 M_Earth planet orbiting at 0.146 AU with a period of 36.6 days. The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star."

==endquote==

 

SciAm has a news item.

http://www.scientificamerican.com/article.cfm?id=habitable-exoplanet-gliese-581

 

It's a bit puzzling why they say "squarely in the middle of the habitable zone". Maybe someone here can comment. Water freezes at 273 kelvin, so the equilibrium temperature they give, 228 kelvin, seems quite cold.

With a mass of 3 Earths it could retain a nice dense atmosphere, with greenhouse effect. Might be geologically active---hot springs--some hospitable local environments. Any ideas?

 

=============================

 

I see! it is a small reddish star so the habitable zone is in close to the star and the planet is almost certainly not rotating but is instead TIDALLY LOCKED. Always the same face to the star.

 

That means that it would have a whole range of temperature from quite hot on the front to quite cold on the back====and there would be some GOLDILOCKS LONGITUDES where the temperature is just right!

 

==quote from SciAm==

Nevertheless, Earthlings would not mistake Gliese 581g for their home planet—in addition to its so-called super-Earth dimensions, it orbits a star far smaller and dimmer than the sun, and its average surface temperatures would vary dramatically, from well below freezing on its night side to scorching hot on the day side.

 

But somewhere between those temperature extremes, which Vogt estimated might range from –35 to 70 degrees Celsius, would exist stable climatic bands, which Vogt called "eco-longitudes," within which liquid water might persist. Because the planet is probably tidally locked, showing only one hemisphere to its star just as the moon does to Earth, the temperate band between permanent daylight and permanent night might afford life a toehold. "There is a continuum of temperatures in between that are stable," Vogt said.

==endquote==

 

==from page 31-32 of the technical article==

An equally important consideration is the actual surface temperature Ts . The

equilibrium temperature of the Earth is 255 K, well-below the freezing point of water, but

because of its atmosphere, the greenhouse effect warms the surface to a globally-averaged

mean value of Ts = 288 K. If, for simplicity, we assume a greenhouse effect for GJ 581g

that is as effective as that on Earth, the surface temperatures should be a factor 288/255

times higher than the equilibrium temperature. With this assumption, in the absence of

tidal heating sources, the average surface temperatures on GJ 581g would be 236 – 258 K.

Alternatively, if we assume that an Earth-like greenhouse effect would simply raise the

equilibrium temperature by 33 K, similar to Earth’s greenhouse, the surface temperature

would still be about the same, 242 – 261 K. Since it is more massive than Earth, any putative

atmosphere would likely be both denser and more massive...

==endquote==

Edited September 30, 2010 by Martin

[D H]

That means that it would have a whole range of temperature from quite hot on the front to quite cold on the back====and there would be some GOLDILOCKS LONGITUDES where the temperature is just right!

That is assuming the planet is not librating so much as to make these goldilocks zones migrate so much over the 37 day orbit as to make the planet uninhabitable. This planet is a bit too much like the joke about the two statisticians who went duck hunting.

 

But it is a good start on our hunt for a life-bearing planet, and it is very close.

 

 

 

[Martin]

That is assuming the planet is not librating so much as to make these goldilocks zones migrate so much over the 37 day orbit as to make the planet uninhabitable. This planet is a bit too much like the joke about the two statisticians who went duck hunting.

 

But it is a good start on our hunt for a life-bearing planet, and it is very close.

 

Never heard the joke but I assume that one of the statisticians aimed at the average of the ducks---their mean location---and so hit no ducks at all.

[D H]

Never heard the joke but I assume that one of the statisticians aimed at the average of the ducks---their mean location---and so hit no ducks at all.

Correct. "Two statisticians went duck hunting. A mallard flew by. The first statistician shot, missing 10 feet to the right. The second shot, missing 10 feet to the left. They gave each other a high five: 'Direct hit!'"

[lemur]

so would any regions on this planet exhibit seasons? If not, and there was no day/night cycle, it would be strangely static to be there, I think. I wonder if plants can even grow without night-time and seasons.

[D H]

It depends on how much libration the planet undergoes, and that in turn depends largely on the eccentricity of the orbit. Too much of that and those supposedly habitable zones are going to swing from too hot to too cold. We don't yet know. Claiming a 100% chance of the chance of life on that planet is 100% out of line (right now). Just a tad more research is needed.

 

That said, this is a very good start in our hunt for another planet that can bear life.

[Airbrush]

There was no mention of Kepler, so was this discovered by wobble? How long until Kepler delivers similar discoveries? Does Kepler's field of vision include nearby stars or only a region of stars very far away? What range of distances are the stars in Kepler's field of vision?

 

Gliese 581 is the 86th star in distance from us at 20 ly. Would Gliese 581g have tremendous winds at the border between the hot and cold sides?

Edited October 2, 2010 by Airbrush

[lemur]

Are there any actual photos of this planet/star or are there only artistic renderings? That's all I can seem to find on google anyway.

[insane_alien]

too small to view directly.

[Martin]

Would Gliese 581g have tremendous winds at the border between the hot and cold sides?

 

I suppose the prevailing surface winds at the border would be hotwards (toward the hot spot).

I'm just thinking along similar lines to you. It makes sense. And highaltitude winds would blow coldwards, towards the cold spot.

 

By analogy to what I guess the windpattern would be like on Earth if it were not for the Coroloris effect of Earth's rotation. The surface winds would blow towards equator (hotwards) and then heated air would rise and return to polar regions (coldwards).

 

I don't know how powerful the winds would be at the border. As I imagine it, with a dense atmosphere (given planet mass is 3 x earth) they would be powerful and steady.

They might make the planet uninhabitable (just my imagination, not knowledge) by drying out the border regions and transporting all the water to a big icecap on the cold side.

 

Someone else with more expertise correct any speculative misconceptions please.

[Mr Skeptic]

Strong dense constant winds, sounds to me like the perfect place for a wind farm.

[Martin]

Strong dense constant winds, sounds to me like the perfect place for a wind farm.

 

That's a point. There's apt to be a lot of available energy, if there were complex life-forms able to utilize it.

But those same conditions (as I imagine it) might make it hard for complex organisms to evolve in the first place!

 

I suppose there are always caves, and cracks in the rock, and craters---providing shelter where primitive single-cell goo can develop. Microbes have colonized all sorts of niches on earth from hot to cold and wet to dry. But if there are these strong winds always blowing across the borderland from cold to hot, transporting water, as vapor, hotwards away from the borderlands, and then bringing the vapor back at higher altitude to be cycled down on the border and colder regions as precipitation. If there is this constant maybe gale-force rainstorm&blizzard---and maybe even sandstorm---how does even multicell life get started? Could ocean exist btw?

 

Have to go. But anyway the windfarm idea is excellent

[DanielC]

Hello,

 

I'm new in this forum. I just thought this thread and I thought I might reply. I am currently doing a masters in astrophysics and I'm very interested in exoplanets.

 

It's a bit puzzling why they say "squarely in the middle of the habitable zone". Maybe someone here can comment. Water freezes at 273 kelvin, so the equilibrium temperature they give, 228 kelvin, seems quite cold.

 

There is a difference between "equilibrium temperature" and "surface temperature". Earth's equilibrium temperature is 255 K which is also below freezing. More interesting is the surface temperature. For Earth that is 288 K and for Gliese 581g the current guess is about 247 K. That's still below freezing, but it is not nearly as bad as it sounds. For reference, this value puts the planet's temperature right in the middle between Earth and Mars. We know that Mars once had liquid water, so Gliese 581g probably has/had water. Furthermore, what went wrong with Mars is that it was just a bit too far from the sun and it didn't have enough gravity to hold on to its atmosphere. Gliese 581g doesn't have either of these problems, so it's a pretty exciting candidate.

 

That is assuming the planet is not librating so much as to make these goldilocks zones migrate so much over the 37 day orbit as to make the planet uninhabitable. This planet is a bit too much like the joke about the two statisticians who went duck hunting.

 

If you can, read the paper by Joshi, M. 2003 Astrobiology, 3, 415. He did a climate simulation of a tidally locked planet. His main finding is that they'd actually be quite habitable. As long as it has a decent atmosphere and and active hydrology, the temperature differences between cold and warm parts are not too extreme. Basically, the more water the better. So, for example, if Gliese 581g has a very deep ocean, I wouldn't worry much about libration.

so would any regions on this planet exhibit seasons? If not, and there was no day/night cycle, it would be strangely static to be there, I think. I wonder if plants can even grow without night-time and seasons.

Earth plants need a day/night cycle, but there is no fundamental reason why alien plants have to be like that. Evolution makes life adapt to whatever conditions are prevalent in the area. I'm not a biologist, but I'd imagine that not having a night would not be much of a bother for Gliesean flora. I imagine that Gliesan astronomers are ignoring big type G stars because obviously a planet with a day/night cycle could not support life

 

 

There was no mention of Kepler, so was this discovered by wobble? How long until Kepler delivers similar discoveries? Does Kepler's field of vision include nearby stars or only a region of stars very far away? What range of distances are the stars in Kepler's field of vision?

 

No Kepler. Yes, this was discovered by wobble. Kepler should deliver similar discoveries in a couple of years. AFAIK Kepler's field only includes pretty far away stars.

 

Gliese 581 is the 86th star in distance from us at 20 ly. Would Gliese 581g have tremendous winds at the border between the hot and cold sides?

 

Actually, it is the 116th star. Wikipedia is wrong on this one. The paper I mentioned earlier (Joshi 2003) does not predict very strong winds at the border. It actually predicts the strongest winds at the substellar point (where the star is straight up). His paper assumes a planet somewhat warmer than Gliese 581g and it predicts mean wind speeds of 15 m/s, which is a strong wind, but it's not a hurricane.

 

Are there any actual photos of this planet/star or are there only artistic renderings? That's all I can seem to find on google anyway.

 

We don't have the technology to photograph a planet like this. In 8 years, when the E-ELT comes online we'll be able to photograph these planets - and by that I mean that we'll have one pixel or two. That will be a very cool time because when we can get a pixel of light from a planet, you can do spectroscopy and figure out what the atmosphere is made of. And if it is very far away from chemical equilibrium (like ours) that would be a tell-tale sign of life.

 

 

too small to view directly.

 

Actually, that's not the problem. The problem is that it is right next to something really really bright.

 

That's a point. There's apt to be a lot of available energy, if there were complex life-forms able to utilize it.

But those same conditions (as I imagine it) might make it hard for complex organisms to evolve in the first place!

 

I suppose there are always caves, and cracks in the rock, and craters---providing shelter where primitive single-cell goo can develop. Microbes have colonized all sorts of niches on earth from hot to cold and wet to dry. But if there are these strong winds always blowing across the borderland from cold to hot, transporting water, as vapor, hotwards away from the borderlands, and then bringing the vapor back at higher altitude to be cycled down on the border and colder regions as precipitation. If there is this constant maybe gale-force rainstorm&blizzard---and maybe even sandstorm---how does even multicell life get started?

 

If the model from Joshi is valid (see above), the winds will not be particularly strong. The strongest winds are in the hottest spot, and with an average of 15 m/s. And that model was assuming an Earth-like energy flux. Since Gliese 581g is colder than Earth its winds would be correspondingly slower than that.

 

Could ocean exist btw?

 

According to Joshi's model, yes. His models included both a water world, and a half-water / half-land world. Both were habitable, but the water world had a better climate (not surprising).

Edited October 3, 2010 by DanielC

[japan rocks/andromeda]

it suprised me when i first learned about gliese581g

[lemur]

it suprised me when i first learned about gliese581g

 

really? I felt it coming on some level. It's as if Earth is ready to expand and reproduce itself across the universe and all that was needed was a first sign that a fertile bride is there somewhere, maybe not this planet but just over the horizon of discovery.

[DanielC]

it suprised me when i first learned about gliese581g

 

I think it surprised most scientists. I don't think any astronomer expected to find a planet like that so soon and so close. These guys really preempted the Kepler mission. We were expecting to get the first Earth-like planets in a couple of years, and we were expecting that they'd be very far away.

 

We should still look forward to the Kepler results though. Kepler will give us a good idea of how common Earth-like planets are. Then we'll know, for example, if Gliese 581g is a freak accident or if there are probably more planets like it within 20 ly.

[Airbrush]

Within a year or two we should have an estimate of how common Earth-like, or habitable, planets are in the Kepler field of vision. Then can we say that is also how common they are in our neighborhood?

 

How about that advanced space telescope going up in around 2014 which will be able to measure atmospheres on these planets? Then they can tell more about living conditions there.

[MRlogic]

the question is if can support human life. or even an atmosphere. do u know how we came across the planet?

[Airbrush]

Gliese 581g may be like a perpetual fire storm on the hot side, vacuuming and burning everything from the border region. Then the cold side is a huge ice cap, perhaps.

[DanielC]

Within a year or two we should have an estimate of how common Earth-like, or habitable, planets are in the Kepler field of vision. Then can we say that is also how common they are in our neighborhood?

 

Basically, yes. The idea is that the stars in Kepler's field of vision should be representative. So whatever it finds should be at least indicative of what you can expect around here as well.

 

How about that advanced space telescope going up in around 2014 which will be able to measure atmospheres on these planets? Then they can tell more about living conditions there.

 

Which telescope are you referring to? The only one I know that will be able to do that is the E-ELT which will come around 2018. Is this what you are thinking of? I just want to make sure I know what you're talking about before I say anything.

 

the question is if can support human life. or even an atmosphere. do u know how we came across the planet?

 

We came across the planet by the wobble method. The question about *human* life is really too specific for any meaningful answer right now.

 

Gliese 581g may be like a perpetual fire storm on the hot side, vacuuming and burning everything from the border region. Then the cold side is a huge ice cap, perhaps.

 

Look at my reply earlier, where I mentioned the work by Joshi (2003). His model suggests that actually the planet would be reasonably nice. If it has a good amount of ocean, or a thick atmosphere, the temperature range should not be too extreme and the planet should actually be fairly habitable. Basically, the more water it has the better. A thick atmosphere can also do a lot to equalize the temperature in a planet. Look at Venus. It has a ridiculously long day, but the temperature is actually quite uniform thanks to the thick atmosphere and strong winds.

[Airbrush]

Nice explanation DanielC. Thanks for the info. I had mistaken the Webb telescope would have that capability. Sorry we have to wait until the end of this decade for better telescopes. Besides E-ELT, the best I can find is ATLAST which could be operational 2025 - 2035.

 

"The greatest leaps in our understanding of the universe typically follow the introduction of radically new observational capabilities that bring previously unobserved phenomena into view. Some, such as the unambiguous detection of life on an Earth-like planet orbiting another star, will be profound yet conceivable. Others are entirely beyond our imagination. All forever change our view of our place in the universe. ATLAST is envisioned as a flagship mission of the 2025 - 2035 period, designed to address one of the most compelling questions of our time. Is there life elsewhere in our Galaxy? It will accomplish this by detecting "biosignatures" (such as molecular oxygen, ozone, water, and methane) in the spectra of terrestrial exoplanets."

http://www.stsci.edu/institute/atlast

 

"Dubbed E-ELT for European Extremely Large Telescope, this revolutionary new ground-based telescope concept will be 42 metres in diameter and will be the world's biggest eye on the sky. With start of operations planned for the end of the decade, the E-ELT will tackle the biggest scientific challenges of our time, and aim for a number of notable firsts, including tracking down Earth-like planets around other stars in the "habitable zones" where life could exist one of the Holy Grails of modern observational astronomy."

http://www.eso.org/public/teles-instr/e-elt.html

Edited October 8, 2010 by Airbrush

[DanielC]

Nice explanation DanielC. Thanks for the info. I had mistaken the Webb telescope would have that capability. Sorry we have to wait until the end of this decade for better telescopes. Besides E-ELT, the best I can find is ATLAST which could be operational 2025 - 2035.

 

The James Webb telescope is very interesting too. Although it can't image planets directly like the E-ELT, it can do important things that the E-ELT cannot do. The Webb is an infrared telescope. Infrared light is important because it can penetrate through dust clouds which normally block visible light. So, for example, it can look inside a planet-forming region which is all surrounded by dust. Learning how planets form would help us know how common they are in the universe. So this is related to how common Earth-like planets and life are in the universe. And the E-ELT will be completely useless for this kind of observation. Any telescope with a segmented mirror is useless for infrared, because the little cracks between the mirrors emit enough heat to completely ruin the observations.

 

There are other exciting things happening soon. The Kepler mission is already in space and it seems to be finding planets by the week. The first planets it finds are the ones in very close orbits, but in a couple of years it should find a good number of Earth-like planets in Earth-like habitable zones. When that happens, we'll have an idea of how common Earth-like planets in the HZ are. And we'll have a catalog of interesting planets ready for the E-ELT to take a peek at when it comes online, so we can probe them for bio-signatures. By the end of the decade we might have found life outside of Earth (fingers crossed).

[creationist]

hi group!! in responce to Gliese 581g being Earth-like,as many of you pointed out,it is not Earth-like at all,most certainly a toxic hell where no life can exist. the so called ''goldilocks zones'' probably dont exist either,a life bearing planet needs many overlapping vectors to sustain life. Earth acts as a huge organism,where all life is interconnected,and dependent on all the others,for instance,if you wiped out all the plankton,the entire food chain would fall apart,rendering the Earth almost devoid of ambulatory creatures. it is plain that Gliese 581g doesnt have this ability.

[DanielC]

hi group!! in responce to Gliese 581g being Earth-like,as many of you pointed out,it is not Earth-like at all,most certainly a toxic hell where no life can exist.

 

At best, this is an argument about scemantics. As an astronomer, I consider a planet "Earth-like" if it is a rocky planet with a surface gravity similar to the Earth and it is located in the region where liquid water can exist. Incidentally, you have no basis on which to claim that it is "most certainly a toxic hell". How do you know that?

 

the so called ''goldilocks zones'' probably dont exist either,

 

The "Goldilocks zone" certainly exists. The term comes from the children's story "Goldilocks and the Three Bears" where Goldilocks eats the little bear's soup because it was neither too warm nor too col. Every star has a region around it where liquid water can exist. This is what is referred to as the Goldilocks zone.

 

 

Earth acts as a huge organism,where all life is interconnected,and dependent on all the others,for instance,if you wiped out all the plankton,the entire food chain would fall apart,rendering the Earth almost devoid of ambulatory creatures.

 

Not entirely true. If you wiped out all humans, the rest of the earth would be better off.

 

it is plain that Gliese 581g doesnt have this ability.

 

Why not? Nobody can make that assertion.

[imatfaal]

We need to take all of the predictions of water and goldilock's zone with a massive pinch of salt - I heard Prof Andrew Fitzsimmons on the radio a few days ago trying to calm the media hype. "the signal is around the same level as the noise, as the uncertainty" - "it needs work to be positive that the planet actually exists" - "water: complete conjecture". The exciting part is that of the nearby stars surveyed we have now found two very distinct possibilities for rocky planets in fairly near orbits - hopefully we will find one soon that transits across the face of its star and we can get an idea of hte atmosphere