I thought of this question not too long ago and I was wondering if anyone could tell me the answer:
We know - generally - how life develops from chemicals and how there has to be certain conditions that satisfy the initial stages, so, how come there is no life on the moon? The earth is a perfect distance from the sun to have life, the moon isn't that much further, so how come in the last 4.5 billion years or so life never started there? Venus is too close and mars is too far but the moon isn't that far away where life would be impossible - I would think.
So, I think the answer may have to do with the moon's gravity and how it's too weak, but, does that really matter? If we looked deep into space would we find life only on planets that have the same gravity?
What Mark said. To expand on that a little, though, the lack of water and of a noticeable atmosphere really goes back to gravity. The mass of the moon is just too low to hang on to an atmosphere at its distance from the Sun. Pluto has a similar mass, and has a little more atmosphere, but it's 200 degrees C colder out there, too.
It seems then that there really is a fine 'knife edge' as to how life can form. I was under the impression that as long as the planet is somewhat close to a heat source that life could easily start...?
It takes more than just warmth to support life. All the suggested pathways we have involve some solute at least. We'd also need to have a reasonable mix of chemicals. Neither of those would last long on the moon.
is that we only have one sample of life to work and make judgements from. All life that we can see seems to be built on one set of basic principles. And it looks to us like you need water, carbon, a set temperature range, some form of atmosphere (even if disolved in a liquid base) and some protection from extreme radiation.
But remember, that is based only on a sample of one.
Is there the possibility of life based on a whole different set of processes?
Would we recognize it if we ran into such a thing?
It appears that life requires a planet of roughly earth size, and similar tempreture levels to earth. Whether that is a 'knife edge' or not depends not on the conditions needed but also on the likelyhood of those conditions.
Are planets of suitable size common in star systems? Is the distribution of planets in our solar system typical of other solar systems? Answer: we don't really know, but current models of planet formation suggest that both answers are 'yes' for main sequence stars.
Note also that life starting and life continuing are different matters.
I'm not sure that Earth-like conditions are necessary for life. You would certainly need a solution with a diverse mix of chemicals, but there may be a number of different pathways to get to self-replicating molecules. Just because Earth happens to be warm, but not too warm, and its atmosphere is just so doesn't mean that this is the only place life could exist.
There may be life on Europa and other moons in the solar system, even though those moons are far from the sun because of heat generated by tidal forces between the moon in question, the planet it orbits around, and other moons. Europa, one of Jupiter's moons, is believed to have liquid water underneath its icy crust for this reason, and the movement of this water gives the crust its cracked appearance. Titan, Saturn's largest moon, is smaller than Earth but has a thicker atmosphere, because it is colder. It may also have lakes or seas of liquid hydrocarbons, which may include liquid methane. Simple organic compounds such as methane may have the ability to work as a solvent like water at low temperatures, allowing for chemical reactions that could lead to simple life forms.
Other possible pathways for life besides the one used on Earth might include silicon based life forms, since silicon shares some of carbon's properties, and boron-nitrogen compounds, since these can behave in ways similar to carbon as well. I'm no expert, and I don't know for sure if these methods are feasible, but all I'm saying is that there may be more than one way to get life.
I believe that life will exist anywhere it can. Because even the simplest life form is self-replicating, it should reproduce itself until it runs out of space and resources. It may be hard to identify something as living or nonliving, for example, self replicating molecules may not be considered living unless they are bound by membranes. There is a continuum between living and non-living in which it is debatable whether or not something is alive.
While we're on the subject of heat etc., the moon's varying temperatures would make stable life almost impossible.
Beacause there is very little atmosphere, and the surface of the moon does not hold heat well, the air temperature on the side away from the sun - the lunar "night" or "winter" - is about -88C (surface temp. -193C). This rockets to 58C (surface temp. 111C) in the lunar "afternoon" or "summer".
This varied climate would probably put paid to any water-based life, which covers life as we know it, so the prospect of life on the moon is rather dim.