Gliese 581 e

[Dominick]

Gliese 581 e is a planet, an extrasolar planet. This means a planet orbiting another star than our precious Sun. Gliese 581 e is hardly the first known extrasolar planet as there are 346 (http://exoplanet.eu/catalog-all.php)of them to date, Gliese 581 e being the most recently discovered one.

Gliese 581 e however is interesting because of its size. It's only 1.9 times the mass of Earth. In other words, we're now on the verge of discovering Earth size planets in other star systems. While it's not the case with Gliese 581 e it's only a matter of time before a planet of roughly that size will be discovered into that region around a star which is considered to be 'habitable' (needless to say that this is from an anthropocentric viewpoint).

The sheer abundance of discovered planets in stellar systems combined with the discovery of (almost) Earth sized planets makes the suggestion plausible that locations with at least the potential of extraterrestrial life are in fact abundant in the universe. The ancient idea that life on earth is something special is crumbling further and further.

[Michael]

How important is "earth-size" ???

I mean, planets that are 100 or 1000 times earth size have 'gravity issues' that likely make our kind of life impossible. But what's the problem with one that is 1.8 times the size of earth? Gravity shouldn't be that far out of our range to interfere with our kind of life development.

So why is 1.8 times Earth size still too large? I'm curious. :ummm:

[partofme]

I would think it might be too large for life to develop exactly as we have but I see no reason why something couldn't evolve into a different sort of species with gravity that strong. That's just me guessing but there could be a reason I just can't think of.

[Donkey]

How important is "earth-size" ???

I mean, planets that are 100 or 1000 times earth size have 'gravity issues' that likely make our kind of life impossible. But what's the problem with one that is 1.8 times the size of earth? Gravity shouldn't be that far out of our range to interfere with our kind of life development.

So why is 1.8 times Earth size still too large? I'm curious. :ummm:
Indeed. We are so biased toward our own version of life. Who's even to say that life will be Carbon based on other planets? Hospitable my ass.

According to Richard Dawkin's, for early life on Earth, Oxygen was a brutal toxin.

[Greendruid]

The other factor to considering the gravitational affects, and to my mind a more important factor, is the density of the planet in question. If it's made up of mostly squishy gases (unlikely, given its size) then there's really very little density and, thus, little mass and, thus, little gravitational pull. The earth has a pretty dense centre, though it is supposedly in liquid form (don't know, I've never been despite the claims of many Christians that I was spawned there). At any rate, I can't see why the 1.8 volume difference is a huge problem. I would also think distance from its star/sun is pretty important too. Oh, and the relative power and heat intensity of its star/sun.

I'm sure that someone here could tell me the formula for this but the moon is about 1/4 the size of earth and probably less dense yet it's gravity is only about 80% of earth's. I'm sure humans could adapt to this and the proposed newly "found" planet. Regardless, it's probably too bloody far for us to worry about that. Sounds a little like a Superman scenario though - perhaps this is the mythical Krypton from which Kal-El hails! :rofl:

[SMadsen]

It'll be interesting when we get clear enough views of other planets so that we'll be able to discern the elements and detect signs of life, such as high levels of oxygen, which movements will get into the biggest hype. It's only a matter of time before the Phelps kids make banners saying "God hates NASA".

[Dominick]

Well, given how planetary systems form, there are really (and roughly) only two types of planets, viz. small rocky ones and big gaseous ones. Since these extrasolar planets are discovered by 'wobbles' in the star's movement due to gravitational interaction with said planets, it logically follows that the biggest (gaseous ones, think Jupiter or Saturn type) are getting discovered first. That's a first reason why size matters; simply because the resolution of the technique has increased to the point where Earth sized ones can be detected.

The big gaseous ones can't have life "as we know it" for many reasons. The wrong chemicals in the wrong phase (liquid or metallic hydrogen), enormous athmospheric pressure (e.g. at a depth of 20,000 km into the Saturnian atmosphere the pressure is 3 million times that of Earth's atmosphere), no surface to live on, too cold, etc., etc. If there were some form of life there (electric ? metallic?) it's quite possible we wouldn't even recognize it as such when staring straight at it. For now that is science fiction.

The little rocky ones don't guarantee the potential for life either. They can't be too close to their sun (actual distances are dependent on the nature of the star) or too far for reasons of excessice or insufficient heat. They can't be too small because they would lack the gravitational pull to retain an atmosphere. This is a rather complex issue of heat vs. gravity. (Heat is equivalent to amount of random motion; when the temperature, and thus the motion, of molecules or atoms exceeds certain statistical limits, those molecules or atoms will overcome the gravitational pull of the planet and be lost into space).

Then there is the issue of water. It is assumed that life requires water to emerge. And that water must be liquid at least some of the time. That further narrows down the range of distance from its star where a planet should be located.

As for an upper limit to gravity, I'm not aware of some strict limit other than that a massive planet would be ipso facto gaseous and thus uninhabitable.

The focus on carbon-based life isn't necessarily geo- or anthropocentric. It's simply the best element for the job. Its chemical properties are best suited; it can make more bonds than other elements, and it's the lightest and thus most abundant element that fits the bill. The other ones (in the same column as C on the periodic table of elements) are both less abundant and less reactive. It's not chemically impossible though to theoretize an organic system based on e.g. Silicium. It's just not nature's way to use something that requires more energy and is less suited when there's a better candidate.

Oxygen is indeed a byproduct of life and not the other way around. Oxygen is far too reactive to exist in large quantities on a lifeless planet. It wasn't until already existing lifeforms started producing oxygen continuously that lifeforms that needed oxygen could evolve.

[Dominick]

The other factor to considering the gravitational affects, and to my mind a more important factor, is the density of the planet in question. If it's made up of mostly squishy gases (unlikely, given its size) then there's really very little density and, thus, little mass and, thus, little gravitational pull. The earth has a pretty dense centre, though it is supposedly in liquid form (don't know, I've never been despite the claims of many Christians that I was spawned there).
Density an sich is essentially a result of the initial formation of planets. There's very little variation in the density of rocky planets (between 5.24 and 5.517 for the solar system with the exception of Mars but that planet is an anomaly in that regard because it is presumed to have had a cataclysmic history). It's therefore not of primary, but of derived importance.

[Michael]

Indeed. We are so biased toward our own version of life. Who's even to say that life will be Carbon based on other planets? Hospitable my ass.

According to Richard Dawkin's, for early life on Earth, Oxygen was a brutal toxin.
I agree that we are rather 'anthrocentric' here, but I don't think we actually can be anything else but.

Sure life may exist in ginormous gaseous planets, breathing chlorine, or they might be some sentient energy fields - but we don't know how to look for or evaluate that kind of thing.

What we do know is that life can function in an earth-like environment, so it is reasonable, rational and logical for us to look for life-possibilities on 'earth-like' planets first.

[Michael]

Great post Dominick! :thumbsup:

As for an upper limit to gravity, I'm not aware of some strict limit other than that a massive planet would be ipso facto gaseous and thus uninhabitable.
Yes, this is what I thought. I should think that a planet size of 50% to 200% of Earth-size would be the most likely candidate - though, as Greendruid pointed out, orbital distances may also be important, though, sun sizes vary as well - apparently ours is a rather small one, so maybe being further out with a larger sun might be more similar to 'earth-like' than matching the orbital distance. I'm just speculating here of course. :)

Oxygen is indeed a byproduct of life and not the other way around. Oxygen is far too reactive to exist in large quantities on a lifeless planet. It wasn't until already existing lifeforms started producing oxygen continuously that lifeforms that needed oxygen could evolve.
Thanks for this clarification. I didn't think oxygen was an 'original' element in the proverbial 'primeval soup' of life creation.

[drgoodtrips]

This is kind of interesting - saw it on slashdot this morning

http://www.eurekalert.org/pub_releases/2009-04/nios-sga042309.php

[Dominick]

This is kind of interesting - saw it on slashdot this morning

http://www.eurekalert.org/pub_releases/2009-04/nios-sga042309.php
Good idea, but only applicable when you're orbiting the planet. None of these extrasolar planets has ever been visually seen. Their existence is derived from
applying relativity to the motion of the star.

[Dominick]

By the way, the theory about formation of planets is not cast in stone. Which is rather obvious since it was entirely derived from a single example. Amongst all those discovered exoplanets there are some really weird specimens, such as this (http://news.bbc.co.uk/2/hi/science/nature/8020594.stm) one, i.e. a Jupiter-sized planet whose orbit takes it never further away from its Sun-like star than the Earth but also 10 times closer than already sunbaked Mercury.

[andrewl]

Gliese 581 e is a planet, an extrasolar planet. This means a planet orbiting another star than our precious Sun. Gliese 581 e is hardly the first known extrasolar planet as there are 346 (http://exoplanet.eu/catalog-all.php)of them to date, Gliese 581 e being the most recently discovered one.

Gliese 581 e however is interesting because of its size. It's only 1.9 times the mass of Earth. In other words, we're now on the verge of discovering Earth size planets in other star systems. While it's not the case with Gliese 581 e it's only a matter of time before a planet of roughly that size will be discovered into that region around a star which is considered to be 'habitable' (needless to say that this is from an anthropocentric viewpoint).

The sheer abundance of discovered planets in stellar systems combined with the discovery of (almost) Earth sized planets makes the suggestion plausible that locations with at least the potential of extraterrestrial life are in fact abundant in the universe. The ancient idea that life on earth is something special is crumbling further and further.

Its very exciting that we have the potential to someday photograph earth-like planets, and its potentially not that far off.

You probably meant 'special' in the sense of being "unique", but i think life on earth is something special regardless of how much life, intelligent or otherwise, exists elsewhere in the universe (in the qualitative but non-religious sense).

Its no less fragile.

Andrew

[Dominick]

Its very exciting that we have the potential to someday photograph earth-like planets, and its potentially not that far off.
I wouldn't get too optimistic. Not only is the required resolution orders of magnitude beyond present capabilities, there's also the glare of the corresponding star that outshines everything else.


You probably meant 'special' in the sense of being "unique", but i think life on earth is something special regardless of how much life, intelligent or otherwise, exists elsewhere in the universe (in the qualitative but non-religious sense).
Yes, I understand and it probably always will remain so no matter what happens in the future. It's extremely unlikely that apart from maybe some really simple lifeforms any earthly species will exist on another planet even if there are millions of them harbouring life.


Its no less fragile.
That I vehemently agree with.

[SMadsen]

By the way, the theory about formation of planets is not cast in stone. Which is rather obvious since it was entirely derived from a single example. Amongst all those discovered exoplanets there are some really weird specimens, such as this (http://news.bbc.co.uk/2/hi/science/nature/8020594.stm) one, i.e. a Jupiter-sized planet whose orbit takes it never further away from its Sun-like star than the Earth but also 10 times closer than already sunbaked Mercury.
Wow, talk about climate changes! :)

Gotta be a binary system somehow, as suggested in the article.