Signs of life on other planets

[Doghouse]

I've been reading lately about the newly discovered potentially life bearing planet, name escapes me but I'm sure everybody knows of it, and it got me to wondering, if such a planet were life bearing, how could we tell?

So, hypothetically, let's say there was an exact duplicate of Earth, at what distance would we be able to detect beings like us upon it?

For example, lights. From orbit at night the dark side of the Earth lights up, but how far away is that visible? From orbit it's all visible, but how about further away?

Also what about radio signals and such like? Futurama references notwithstanding, are we emitting anything that could be detected? Could Earth detect waves from a similar world? And if so over what kind of distance?

I'm a firm believer in bug eyed monsters, little green men and all that kind of thing, because the scale of the universe and robustness of life mean it's pretty much a given that somewhere there's got to be at least some squishy single cell alien life charging around. But I do wonder how, if ever, it could be found. I mean interstellar travel isn't really on the cards but it'd be nice to be able to see what's up elsewhere.

 

[sgrunterundt]

I read once that a 20m infrared telescope in orbit would be able to detect an ozone layer on planets at the nearest stars. I can't vouch for the accuracy.

Ozone would mean oxygen, oxygen would mean life, as it is too reactive to be sustained in an atmosphere by any other mechanism. (Now that I think about it, why couldn't there be a planet so abundant in oxygen that there are not enough reducing elements present to bind it all?)

 

[Duvelthehobbit666]

I read once that a 20m infrared telescope in orbit would be able to detect an ozone layer on planets at the nearest stars. I can't vouch for the accuracy.

Ozone would mean oxygen, oxygen would mean life, as it is too reactive to be sustained in an atmosphere by any other mechanism. (Now that I think about it, why couldn't there be a planet so abundant in oxygen that there are not enough reducing elements present to bind it all?)

We know that this planet has animals which breath oxygen to live. I would not assume that all life in this universe needs oxygen to live. Deep down in some strange places here on Earth, we have organisms which do not need oxygen to live and where oxygen is a poisonous to them . And looking for green wouldn't do it either. There are plenty of minerals which are green and who says that their "plant life" (used in the most loosely sense) has "chlorophyll" (again used quite loosely) which is green. I would say the best signs would be radio contact. I doubt that we could conclude that there would be life on that until we either get radio contact from them or we send down a probe and make actual photos of the planet.

 

[MRaverz]

The issue isn't how well life survives (and lets remember that about 99% of species which ever existed are extinct today), the issue is how rarely life starts up.

As far as we can tell, life only started on Earth once - it only needed to start once. For life (as we know it) to start on other planets, the planet needs to be 'Earth-like' and situated the right distance from the right sized stars for water to exist on the planet's surface.


Naturally, there is the possibility of very different types of life on other planets without water - ie. methane based life. However, nothing as such has been observed and it is generally agreed on that the best chances we have of finding life is by finding life in a similar situation to us.



On the issue of Gleise 581g, as I understand it the planet is thought to be tidal-locked to it's star. Therefore having one side of the planet constantly light and the other half constantly dark, whilst also having no conventional seasons. This, for me, raises doubts about whether plant life could arise on the planet and if it could - it would mean that one side of the planet could have a very different ecology to the other side.

 

[MRaverz]

I read once that a 20m infrared telescope in orbit would be able to detect an ozone layer on planets at the nearest stars. I can't vouch for the accuracy.

Ozone would mean oxygen, oxygen would mean life, as it is too reactive to be sustained in an atmosphere by any other mechanism. (Now that I think about it, why couldn't there be a planet so abundant in oxygen that there are not enough reducing elements present to bind it all?)

We know that this planet has animals which breath oxygen to live. I would not assume that all life in this universe needs oxygen to live. Deep down in some strange places here on Earth, we have organisms which do not need oxygen to live and where oxygen is a poisonous to them . And looking for green wouldn't do it either. There are plenty of minerals which are green and who says that their "plant life" (used in the most loosely sense) has "chlorophyll" (again used quite loosely) which is green. I would say the best signs would be radio contact. I doubt that we could conclude that there would be life on that until we either get radio contact from them or we send down a probe and make actual photos of the planet.

You don't need to go deep down into strange places, anaerobically respiring bacteria can be found by just digging into a river bank. Photosynthesising bacteria is also pretty easy to find.

The fact is, however, that the only complex life we have is dependent on oxygen. So we assume that it is most likely that we'll find oxygen-based lifeforms.

 

[AndroidAR]

On the issue of Gleise 581g, as I understand it the planet is thought to be tidal-locked to it's star. Therefore having one side of the planet constantly light and the other half constantly dark, whilst also having no conventional seasons. This, for me, raises doubts about whether plant life could arise on the planet and if it could - it would mean that one side of the planet could have a very different ecology to the other side.

Actually, while it's quite doubtful that life will arise on either the sun-baked, or dark-side sides, there is an area where day transitions to night, near the terminator, where there will be constant dusk/dawn (like the north/south poles during their summer solstices), where the temperatures would be intermediate between the 2 sides, and liquid water could exist.

 

[SagansHeroes]

On the issue of Gleise 581g, as I understand it the planet is thought to be tidal-locked to it's star. Therefore having one side of the planet constantly light and the other half constantly dark, whilst also having no conventional seasons. This, for me, raises doubts about whether plant life could arise on the planet and if it could - it would mean that one side of the planet could have a very different ecology to the other side.

Actually, while it's quite doubtful that life will arise on either the sun-baked, or dark-side sides, there is an area where day transitions to night, near the terminator, where there will be constant dusk/dawn (like the north/south poles during their summer solstices), where the temperatures would be intermediate between the 2 sides, and liquid water could exist.

I am sure I read recently that some Nasa scientists modelled the weather patterns of a tidally locked planet and found that it can still generate enough atmospheric motion (wind/currents/jet streams etc.) to keep the planets overall temperature a little more... consistent/stable.

I think the real question isn't so much, could life flourish in the extremes of the sun baked side and the dark side, I'm pretty sure we already know that it can (looking at the plethora of extremophiles on earth; deep sea vents, huge pressures in deep waters, no sunlight, no oxygen, living in ice, acid, rock etc.) The REAL question would be, how well/easily could life start off in the first place there. Considering we aren't 100% sure how it kick started here... is hard to tell.

 

[dav37777777]

i saw a program on tv years ago astrologers were looking for similar earth type planets by taking photos of space everyday and then they put the photos together like a movie to detect what planets wobble. this spectral wobble was important because it showed that the planet was rotating in an orbit

 

[AndroidAR]

i saw a program on tv years ago astrologers were looking for similar earth type planets by taking photos of space everyday and then they put the photos together like a movie to detect what planets wobble. this spectral wobble was important because it showed that the planet was rotating in an orbit

(Emphasis mine)

Astronomers, not astrologers. Astrologers aren't the ones who look in a telescope and make discoveries.

Also, taking photographs and comparing them (a la finding asteroids or other objects in our solar system), wouldn't actually be any good, considering that the size of the wobble would be near undetectable, not even a fraction of a pixel change, and that's just with the larger planets. Earth-sized planets would cause a wobble so undetectable optically that we'd probably have an easier time directly imaging the object. Instead, redshift measurements are used to detect the wobble (aka, changes in radial velocity) in the star, and we've only recently begun to be able to find near-Earth sized planets because our instruments and understanding have only recently become sensitive and good enough to do so.
Even given our current tools, the smallest planets around normal stars are still quite a bit more massive than Earth. Gliese 581 e (in the same system as Gliese 581 g, the planet of attention) is the least massive known planet around a normal star, and it is still almost 2 times more massive than Earth.

 

[MRaverz]

On the issue of Gleise 581g, as I understand it the planet is thought to be tidal-locked to it's star. Therefore having one side of the planet constantly light and the other half constantly dark, whilst also having no conventional seasons. This, for me, raises doubts about whether plant life could arise on the planet and if it could - it would mean that one side of the planet could have a very different ecology to the other side.

Actually, while it's quite doubtful that life will arise on either the sun-baked, or dark-side sides, there is an area where day transitions to night, near the terminator, where there will be constant dusk/dawn (like the north/south poles during their summer solstices), where the temperatures would be intermediate between the 2 sides, and liquid water could exist.

My issue wasn't primarily about the presence of water on the planet, but that life on Earth exists harmonically with our day/night cycle. Therefore if life were to exist on Gleise 581g, it would likely have a very different ecology. For example, flowering plants on Earth have a cycle whereby their flowers open during the day and close during the night, animals tend to sleep (or wake) at night. On Gleise 581g, the system would be different. Life could either exist in total day or total night - a situation which plant life, as we know it, would not be able to survive in.

Perhaps life could exist around the terminator, venturing into the dark side when needing to sleep and into the light side when needing to hunt?

 

[Master_Ghost_Knight]

The problem with all this isn't that we can't tell by looking at it, the problem is we can't look at it.
It is possible to identify in special circumstances potential life forms by a spectral analysis (it may not match clorophile but it may comback complex organic molecules), we can do that from space and even in some cases identify the species and the apropriate fase of development (to see if it is good for ripe), however this requiers to have a decent enough resolution of the planets surface to be able to even do such analysis and that is something that we simply don't have. This is jut an example, people working on the field may know hundreds of other ways to do it, but if we can't gather a minimal ammount of data those methods simply can't work.

 

[Unwardil]

On the subject of the question of 'can life start on a planet or not' remember, that what we think of as life uses 4 basic proteins... But it could have started just as easily if only 2 of those proteins were present. Or if they were different. The makings for DNA were present on the earth and they were so useful for making life that all life became DNA based. There's absolutely no reason to presume this must be true on other planets.

 

[SagansHeroes]

a situation which plant life, as we know it, would not be able to survive in.

I don't know if we can really say whether or not plant life would not be able to survive... there hasn't been a time on earth where part of the earth stayed facing the sun long enough for plants to evolve a way to deal with it.
Plants that have alREADY evolved on earth can't I guess. But as stated before, there have been models showing that wind currents can/would still exist on tidally locked planets, spreading the warmth/cool love around.... although there are obviously other issues with never seeing night/day...

 

[Dragan Glas]

Greetings,

If life has managed to evolve, then it's certain that it will have spread throughout most of the planet - the (very!) strong winds would transport micro-organisms to other parts of the planet, which might then evolve into "extremophiles", enabling them to survive in otherwise hostile parts of Gliese 581g.

The strongest winds would occur at the equator, with progressively less strong winds as one travels to the poles. Correct me if I'm wrong - someone with the relevant expertise - but I'd imagine that the temperature difference between the "day" and "night" sides at the poles would be small, perhaps allowing a more uniform ecology.

You'd probably get something similar to the tundra's lichens and/or the low-lying plants which occur in the Burren in Ireland - these grow between the cracks in rocks, having evolved to stay below the surface-level of the rocks due to the very high winds which act like a scythe for any flowers which grew above the surface in the past. Fungi - and others which rely on the wind to spread their seed/spores - would possibly evolve.

Any flying insects would probably be "ground-huggers", similar to the insects which visit flowers in the Burren.

If there were anything more advanced - reptiles/mammals - they'd probably resemble the Inland Taipan ("Fierce Snake") with it's extremely lethal toxin to ensure that its potential meal doesn't escape very far

There are some interesting ideas to be found here.

Kindest regards,

James

 

[MRaverz]

a situation which plant life, as we know it, would not be able to survive in.

I don't know if we can really say whether or not plant life would not be able to survive... there hasn't been a time on earth where part of the earth stayed facing the sun long enough for plants to evolve a way to deal with it.
Plants that have alREADY evolved on earth can't I guess. But as stated before, there have been models showing that wind currents can/would still exist on tidally locked planets, spreading the warmth/cool love around.... although there are obviously other issues with never seeing night/day...

Hence the words 'as we know it'.

 

[Doghouse]

To return to the topic somewhat, how could we actually detect such creatures, at the distance we are? Does an organism have to have evolved to use technology and shoot radio waves off into space for us to detect it, or are there tell tale signs?

 

[AndroidAR]

To return to the topic somewhat, how could we actually detect such creatures, at the distance we are? Does an organism have to have evolved to use technology and shoot radio waves off into space for us to detect it, or are there tell tale signs?

The best option we currently have is to either listen for radio signals from that planet's vicinity (assuming they are technologically capable and using radio communication) or to send a signal and hope for a reply. Other than that there really isn't any way we can detect life on a planet from such a massive distance. Even just 4 billion miles from Earth, our own planet is just a "pale blue dot."