New research has found that a planet's axis of rotation may be stable enough, even without the presence of a large moon, to allow life to flourish. It's often been said, in recent years, that the poles of a planet without a large moon to help stabilize it would tend to wander markedly, making for severe climate changes detrimental to life. This seemed to sharply limit the number of otherwise habitable planets that could make good abodes for life, especially complex forms of life. If this new work holds true, the number of potentially habitable planets could increase substantially. http://www.physorg.com/news/2011-11-life-alien-planets-require-large.html

Interesting theory Michael,
Sound very reasonable to me anyway.

John.

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though a moon would encourage spawns of sea creatures like we have on earth. Otherwise most sea turtles anda multitude of other creatures that rely on tides would be easily killed by predators. THough one would have to guess that since sea turtles base their egg laying on moon cycles that the lack of the moon would allow it to mate and spawn at any time which would also force the turtles to form a different means of arriving at their spawning grounds etc etc etc

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In a rich man's house there is no place to spit but his face.
Diogenes Of Sinope

Skil,
The earth has four tides a day, two from the moon and two from the sun. They base their mating on the combination of the cycles. Length between the spring tides has to be long enough for the incubation of the eggs.

[edit]Forgot the eccentricity of the orbits also are cycles they use.

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That is true on our world since we have the moon. On another planet, life would evolve specifically to adapt to conditions there. Because tides help here doesn't necessarily mean that tides are a requirement.

A large moon is most likely necessary to stabilize the spin of a planet.
Tides may also be necessary to start life on land.

A large moon is most likely necessary to stabilize the spin of a planet.
Tides may also be necessary to start life on land.

We haven't been to any other solar systems yet, so we don't know if that's fact. It would also be pretty limiting to think that life on other planets would develop the same way we did. It's plausible that life could adapt to the climate shifts. We cannot assume that because this is how life evolved on our planet, it's how life must evolve on other planets. Every solar system is almost certainly unique from all others.

That is true on our world since we have the moon. On another planet, life would evolve specifically to adapt to conditions there. Because tides help here doesn't necessarily mean that tides are a requirement.

I think you have the right idea. There is no way anyone can say for certain what is required for a planet to support life, beyond water and an energy source.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

A large moon is most likely necessary to stabilize the spin of a planet.
Tides may also be necessary to start life on land.

That is what has been assumed in recent years. A closer look now makes this look much less certain. If tides are necessary, it should be recalled that they could be supplied by the star a planet orbits. In our system, solar tides are about 1/3 as large as Lunar ones. Tidal ranges are quite dependent on localized geography. Areas with large tidal ranges could be utilized by life on other planets to compensate for relatively weak stellar tides. Stars with nearer in habitable zones would have life bearing planets with higher stellar tides. Michael

That is true on our world since we have the moon. On another planet, life would evolve specifically to adapt to conditions there. Because tides help here doesn't necessarily mean that tides are a requirement.

It's not just a matter of the creatures that use the cycles to spawn. You also have the creatures that feed on those that spawn with this regularity. elimination of cyclical spawns would eliminate and I would think hinder animal species from developing their brains.

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In a rich man's house there is no place to spit but his face.
Diogenes Of Sinope

I think you have the right idea. There is no way anyone can say for certain what is required for a planet to support life, beyond water and an energy source.

That is true but I suspect that there may be more than a dozen requirements for intelligent life to develop and survive that is comparable to ourselves. I suggest the following:

Magnetic field to ward off cosmic rays.
Temperatures that don't freeze or boil the entire planet
Outer gas or rocky giant planet to protect from comets and meteor hits.
Stable , nearly circular orbit to limit temperature extremes
Axis tilt and spin to allow for reasonable temperature cycles
Oxygen atmosphere with enough Nitrogen to prevent burning the place down.
Non-crushing gravity, sufficient to hold water and atmosphere from vaporizing into space (Mars?)

The next question is how far away from us is such a planet and how many are there in the Milky way. I think that there may only be a hand full. Exobiologists, better telescopes, probes and time will hopefully answer these questions in some of our lifetimes.

Several billion years ago Mars no longer had a molten core thereby preventing it from having a magnetic field. Solar winds slowly eroded the atmosphere of Mars to become what it is today. A certain requirement for life on the surface of a planet is that it must still have a molten core of metal like Earth to create that magnetosphere.

Don't get me wrong. That's certainly not a requirement for life at all. The water inside Enceladus is completely closed off (except for one known vent) and is protected from solar winds. It's atmosphere is negligible. However, it likely gets heat from radioactive decay and the tidal forces created from it's orbit around Saturn. The bottom of our ocean has some life down there and has similar conditions likely found in Enceladus. This is why this moon is the best candidate for life off of Earth.

Oxygen atmosphere with enough Nitrogen to prevent burning the place down.

Live on earth started without O2... At this time O2 was very toxic for all lifeforms.
the first cyanobacteria used H2S as e- Donator. But 3- 2,8 billion years ago- most of the H2S was depleted.
So the cyanobacteria used H2O as e- Donator, and this form of photosynthesis created O2. a mass extinction followed.
later the organisms learned to detoxify O2 (mitochondria) and use O2 for their own metabolism.
the big advantage:
- greater energy efficiency (metabolism creates much more energy (ATP) by using O2 than under anaerobic conditions)
- ozone (O3) which protects from UV- radiation

But is O2 really necessary for the evolution of high developed organisms?

plants and plant like life came way earlier than any animal and plants are Notorious for their use of CO2 in metabolism. When animals(single celled organisms) began to develop the earth was already full of plant life. The plant life also created a nifty byproduct in its respiration. Oxygen, which we animals gleefully use(d).

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In a rich man's house there is no place to spit but his face.
Diogenes Of Sinope

that's true. Everthing we see now is the result of an 3,8 billion year old coevolution and symbiotic interactions between the organisms on earth.
the plant fixate the CO2 by creating carbohydrates and create energy via the light reactions (therefor they use H20 and create O2).
heterotropic orangisms like us burn the carbohydrates by using O2 and creating CO2 and H2O.- the cycle is closed.
A very efficient system.
But maybe life on other planets use different biochemical ways.

Just like we need to be open minded about the possibility of getting around the speed of light barrier for interstellar travel we also need to be open to the possibility of life springing up in circumstances that are totally alien to us. Maybe even to the point of not being carbon/oxygen/water dependent.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

i think so too.
that's a very interessting topic.

What we need to do is to start life here on earth with the current idiom. Then we need to see if life can start in another chemical environment.

I'm wondering if anyone has repeated the http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment with the complete mix as on early earth. Not just the lightning energy source, but a nice lava into the sea, a tidal zone, UV into the atmosphere and a black smoker at the bottom of the sea.

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