18 replies to this topic

[Still Waters]

www.bbc.co.uk said:

Scientists have outlined which moons and planets are most likely to harbour extra-terrestrial life.

Among the most habitable alien worlds were Saturn's moon Titan and the exoplanet Gliese 581g - thought to reside some 20.5 light-years away in the constellation Libra.

The international team devised two rating systems to assess the probability of hosting alien life.

Read more...

[HMS Dreadnought]

The water under Saturns moon is what I find most interesting a bit possibility for some kind of life there I think  

[scowl]

HMS Dreadnought, on 24 November 2011 - 03:58 PM, said:

The water under Saturns moon is what I find most interesting a bit possibility for some kind of life there I think  

If you believe the "recipe" version of life, Enceladus has many of the ingredients. Unfortunately it doesn't appear to have a wide range of environmental conditions that promotes life.

[skookum]

Some major speculation on the Gliese planets.  Other than we have detected them we truly have no idea what they are like, bar an estimate of temperature.  They have rated them more earth like than Mars.  For all we really know they could be gas planets.

[itsnotoutthere]

meaningless.

[HMS Dreadnought]

scowl, on 24 November 2011 - 07:27 PM, said:

If you believe the "recipe" version of life, Enceladus has many of the ingredients. Unfortunately it doesn't appear to have a wide range of environmental conditions that promotes life.

Would a different type of life be able to exist under different enviromental conditions though?

[scowl]

HMS Dreadnought, on 25 November 2011 - 10:47 AM, said:

Would a different type of life be able to exist under different enviromental conditions though?

We don't know of any other "type" of life, so no one can answer that question with any authority.

[bison]

The existence of the highest-rated extrasolar planet, Gliese 581g is in considerable doubt. Some  re-examinations of the radial velocity data do not find it at all. More radial velocity measurements will be needed to settle this matter. It is considered very unlikely that the planet, assuming it does exist, is a gas planet, like a smaller version of Neptune. With a mass of ~3.1 to 4.3 times that of Earth, it would be very unlikely to gravitationally retain  such a large amount of the necessary light gasses. This is particularly so, since the planet is tidally locked to its star, with the same side always heated. This would increase the erosion from its atmosphere of the  lighter gasses via stellar radiation.  It's atmosphere would probably be somewhat denser than Earth's, but not greatly so, and made up of the heavier gasses typical of terrestrial planets-- nitrogen, oxygen, carbon dioxide, argon, and the like.

[scowl]

bison, on 25 November 2011 - 06:57 PM, said:

This is particularly so, since the planet is tidally locked to its star, with the same side always heated.

The "freeze and fry" planets seem like the worst combination of extreme conditions for life.

[bison]

scowl, on 25 November 2011 - 08:17 PM, said:

The "freeze and fry" planets seem like the worst combination of extreme conditions for life.

It's been calculated that atmospheric circulation could, in some cases substantially even out the extremes of temperature. This is what happens on Venus, which rotates so slowly as to be practically tidally locked. It's almost as hot all over the planet, as around the sub-solar point. They believe  this could happen in much less dense atmospheres, too. Perhaps down to 1/10  the density of Earth's atmosphere. Given a planet well centered in its habitable zone, like Gliese 581 g is supposed to be, and tolerable temperatures might exist over much of the surface. Possibly a torrid zone, like our tropics, around the sub-stellar point, and a frigid zone opposite it on the planet, like one of our polar areas.

[Dom3434]

I think we truely have no idea what conditions life could manifest from distant planets. for instance a organic being that uses photosynthesis as a way of reciving energy and no need of eating for nutrition. just a thought.... but then you wouldnt need a atmosphere that has more oxeygen than carbon dioxide it would be vise versa. Like i said just a thought, in another galaxy the laws over there might be completly different from the laws over here.

[Colonel Rhuairidh]

itsnotoutthere, on 24 November 2011 - 09:54 PM, said:

meaningless.

helpful as ever.

[Colonel Rhuairidh]

Dom3434, on 26 November 2011 - 01:30 AM, said:

I think we truely have no idea what conditions life could manifest from distant planets. for instance a organic being that uses photosynthesis as a way of reciving energy and no need of eating for nutrition. just a thought.... but then you wouldnt need a atmosphere that has more oxeygen than carbon dioxide it would be vise versa. Like i said just a thought, in another galaxy the laws over there might be completly different from the laws over here.

i suppose the question is whether there'd be likely to be the resources and the raw materials needed to build a technological Civilisation, and then whether any intelligent beings would evolve in a form to be able to construct anything out of them; for that I suppose you'd need a physical body at the very least, and, people seem to consider, another thing that would be essential would be Thumbs. Without Thumbs, you wouldn't get anywhere.  

Edited by 747400, 26 November 2011 - 08:42 PM.

[scowl]

bison, on 26 November 2011 - 12:44 AM, said:

It's been calculated that atmospheric circulation could, in some cases substantially even out the extremes of temperature. This is what happens on Venus, which rotates so slowly as to be practically tidally locked. It's almost as hot all over the planet, as around the sub-solar point.

Because it has a fluid and crushingly dense atmosphere that can't help but quickly conduct heat around the entire planet.

Quote

They believe  this could happen in much less dense atmospheres, too.

I haven't read that and I can't find any example that supports that. Every model I've seen shows that thinner atmospheres away from the sun either quickly lose their heat to space before they can conduct it around the planet or trap the heat creating intense temperatures, depending on their distance from their sun. For example, lock the Earth to the sun and you end up with water becoming a greenhouse gas and it becomes something close to Venus.

It's really hard to make an atmosphere that's balanced like the Earth's. The tremendous amount of water here is very important and any kind of fluid on a planet would help.

[bison]

The Wikipedia article on Gliese 581 g has a reference to efficient heat transfer in even a 100 Millibar atmosphere, assuming  sufficient greenhouse gases.  There is also a link in the article to a scholarly article about this study.  (footnote 23).  link to the relevant section of the above Wikipedia article: http://en.wikipedia....bitability  see subsection on atmospheric effects, first paragraph.