How Much of Space is Habitable?

[wolram]

i have had setti runninig for about six months, i suppose there
is always a chance no matter how slim.
the thing is how much of space is habbitable? a supernova will
sterilize several light years of space around it, maybe some
areas are to hot or to cold, there must be many other things
that can stop life forming or killing it, so would anyone have
an estimate 10% 20%?

 

[wolram]

http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=27243

Darwin is unlikely to be launched before 2014 and, in the meantime, astrobiologists will have to rely on calculations to estimate the number of Earth-like planets. Such estimates, however, are prone to error! "The number of Earth-like planets in the Milky Way was put at 2.4 million this morning, but had dropped to 48 this afternoon," Malcolm Fridlund, ESA's study scientist for Darwin, told the meeting during a summing up.

 

[Labguy]

I have always wondered why, when searching for "ET" life, Earth-like planets are always mentioned. It ain't going to be like Star Trek, where every planet just happens to have an atmosphere we can breath and inhabitants are human-sized bipeds with a few wrinkles or bumps on their heads.

What about a planet like one of our gas giants?? Large gravity makes the inhabitants about the size of a peanut, they breath methane and H₂SO₄ just fine and orbit around their planet in ships the size of a shoebox. Life doesn't only mean bipeds breathing oxygen and nitrogen. So, why are we trying to limit our estimates to "Earth-like" planets? Them little peanut creatures might be far more advanced than we are. No?

Labguy

 

[wolram]

http://mcdonaldobservatory.org/news/releases/2002/0107a.html

Bursts of radiation that can cause biological mutations, or even deliver lethal doses, can come from flares given off by the planet’s parent star or from more remote cosmic events (e.g., supernovae and gamma-ray bursts). The magnitude of the effect on life and evolution on a planet is related to how much protection it gets from its atmosphere. The work presented today concentrates on the transmission of high-energy X-rays and gamma-rays through planetary atmospheres.

 

[wolram]

http://www.spaceref.com/news/viewnews.html?id=463

As such, from the perspective of a substantial portion of the life on Earth, the ability to live in an aerobic (oxygen rich) world confers upon our own species the distinction of being an extremophile. But there are other things that organisms can "breathe". The bacterium Shewanella putrefaciens uses metal atoms in its metabolism in the same fashion as we use oxygen atoms. As such, it "breathes" metal - in this case, manganese.

hi LABGUY if your interested in the diversity of life have
a look at this, these little b****s can live of almost
anything and anywhere

 

[Nereid]

why not underground life?

There's been another of those dethronings in the last few years - there's far more Earth life below ground than above, as measured in tonnes, let alone number of living things.

IIRC, the Earth's crust, to a depth of several kilometres (and more?), teems with life. It's mostly bacteria, and much of it doesn't depend on scraps falling from the photosynthetic table. Of course, the density - bacteria per cubic metre - is low, but the available space is so much greater than the surface +/- a metre or two!

If the basic requirements for such life are primarily geophysical - the right chemicals and a temperature ultimately due to radioactive decay - life would be quite immune to mere nearby supernovae, and even colliding asteroids would have to be pretty big to cause extinction (it could happen though; enough energy to melt the crust to a depth of 3 km, say).