PDA

View Full Version : Lookin' for life in all the wrong places...



ToSeek
2003-Aug-04, 04:27 PM
Search for life could include planets, stars unlike ours (http://www.sciencedaily.com/releases/2003/08/030804075326.htm)

dgruss23
2003-Aug-04, 04:37 PM
"We have no idea how evolution would proceed on any planet other than our own," Gould said. "If we find a planet around a shorter-lived star, we may be able to test what would happen to evolution under those circumstances."

Can't they do that anyway? I assume computer simulations are the way they will test the circumstances. For these large stars they should be able to determine where the habitable zone is and do their simulations from that - regardless of whether or not any planets exist in those habitable zones.

tracer
2003-Aug-04, 10:00 PM
Yeah, but it's one thing to say "Here's how life might evolve on a hypothetical planet of thus-and-such a size at thus-and-such a distance from this here star."

It's quite another to be able to say "Here's how life might evolve on this here planet orbiting this here star."

dgruss23
2003-Aug-05, 07:18 PM
It makes a difference when you're selling it to the public, but they say they have "no idea" how life evolves except on Earth. The habitable zone of the star can be calculated regardless of whether or not a planet exists in it. So from a scientific point of view - if they're interested in understanding how life would evolve on planets around this particular type of star - they can predict how life might evolve on a planet of any size they choose within that habitable zone. So if how life evolves is the question, then the actual discovery of those planets only provides more fine-tuned data for a specific case. What discovering these planets would do is give them some statistics on the % of stars that have such planets.

jkmccrann
2005-Nov-01, 04:34 PM
Can't they do that anyway? I assume computer simulations are the way they will test the circumstances. For these large stars they should be able to determine where the habitable zone is and do their simulations from that - regardless of whether or not any planets exist in those habitable zones.

Perhaps, they can run simulations based on a narrow understanding of how life evolves, given our own circumstances, but isn't there going to be an inherent bias in anything they do towards carbon-based life-forms? Can we say for sure that other life-forms don't for sure exist out there in the Universe?

If we can say that, that's definitely news to me. All I guess I'm getting at is that whatever they come up with, who can know for sure whether their results are really reliable or not, our understanding of the Universe is simply too narrow to come up with any categorical results in this field I would posit.

steve1
2005-Nov-02, 06:36 PM
Gould in his "Wonderful Life" was quite clear that those series of random, accidental events which lead to current life on earth were important in creating a huge variety of life. And that if any of those events were changed, esp. early ones, the present kinds of species on the earth would have been greatly changed. So whole phyla and types of life are very likely very sensitive to conditions.

Our visual systems are cued basically to the brightest light from our sun, that of visible light. If a sun were orange yellow, or even a deep tangerine, one would expect the visual systems of creatures there to be modified, as well.

The chlorophylls, pigments and other light capturing compounds in plants are pretty specifically attuned to our sun's spectrum as well. Chlorophyll might not even be present around some orange suns. The plants there might use some other equivalent compound to capture photon energy to grow. The auxiliary pigments would likely be changed as well.

Metallacity differs from system to system as is known from stellar spectra. Some will be metals rich. Others metals poor. Life will reflect these changes. If Cd, As, and Tl, for instance were enriched on some planets, we'd not be able to live there, easily. And if some planets were deficient in Co, Mb, and some other trace elements, unless we brought in our own elements as dietary supplements, we might die. Iodine excess, too, can create serious illnesses.

So, considering that more than 3 factors create unpredictable chaotic outcomes, the hugely differing conditions and compositions of planets in a liquid water zone around a star would create conditions hardly likely to create species & phyla as we know them, altho 'carbon/nitrogen/water life as we know it would still be there.

course, this all must be carefully tested by direct observations. :)

Enzp
2005-Nov-03, 07:00 AM
I think also that to model evolution elsewhere, we would need to know not only the basis of life there, but also the selective pressures and environment such life exists with.

over the years i have seen many speculative ecosystem proposals, and they usually take a factor or two and base a whole fauna upon them. For example on a low gravity world they assume animals will be very large, and on high gravity worlds animals will be tiny. But here on earth, even within mammals we range from the largest whales down to tiny little shrews. Obviously gravity is not a major factor.

We can predict something that resembles us, but the crystal people living on the sulphur cliffs will feel left out.

Would our models - given earth-like conditions - result in Dolphins AND spiders? Spanish moss AND sequoias? Steak AND portabellas?

Zogski
2005-Nov-05, 10:42 PM
Gould's book is great, and unfortunately I've met some hard-core "determinists" who became very aggressive when exposed to his ideas. Some people like to think that WE are the "goal" of Life.

But life at the beginning seems to have created an initial set of design or parts, just like construction blocks... and it has experimented with it. Call it the "Global Reality Show": at each extinction event, a few of these designs were eliminated and lost forever. Survival of the most broadly dispersed, resiliant to environment change, and genetically diverse. Survival of the fittest? Locally.

Since many features of living creatures evolved more than once during evolution, I would tend to say that given a specific set of conditions (temperature, density of air, gravity, luminosity), we can predict some of the features that are likely to emerge.
For instance:
- The human eye is very similar to the octopus eye (...and the octopus eye is of a superior design, with no blind spot!)
- Both mammals (bats, flying squirrels) and birds evolved wings.
- Dolphins and fishes have evolved fins, although they don't use the same technique for swimming.

I'd say some features would be very common, though, even in very exotic environments :
1. left-right symmetry in mobile organisms
2. in most cases, a tube-like design, like in chordates (since simplest lifeforms would be "living food processors", tubes)
3. an immune system
4. a flow of internal liquids, probably moved with pumps or vascular systems
5. reproduction and death

Other than that... I wouldn't bet on sexual reproduction, eyes, vocal communication, a moral system that's even remotely related to ours, lifespan, respiration and nose (gas exchange), "eating" organs, hygiene, smell (!), ...