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However we have nothing but guesses as to how often it might happen.

So far, we know of NO other planet with life on it.


Yes it's possible, but we currently have no way of knowing, as John pointed out. And I just wanted to explain why this is, what we know, what we don't currently know, what is likely, and what is extremely unlikely.

People often talk about the Universe as BIG, but not many people REALLY fathom how big it is! We're not even certain exactly how big it is. So, I want to start by scaling things back a bit; back to Galaxy level!

If you don't already know, our planet, Earth, exists in a solar system of 8 planets (including ours) and 1 former planet (Pluto). Our Sun, referred to as Sol as a means of distinguishing it, is a Star, one of innumerable others! Sol, the planets, Pluto, their associated moons and satellites and the cloud of debris known as the Kuiper Belt which exists beyond Pluto make up our Solar System. This is just ONE of 100,000,000,000 (one hundred billion) solar systems within our Galaxy, known as The Milky Way. I say 100,000,000,000 solar systems because we estimate that there are approximately 100,000,000,000 stars within our Galaxy. They may or may not ALL have planets.

To give you an idea of scale, Pluto is approximately 4 billion kilometres (approximately 2.5 billion miles) from Earth when they are at their closest! At their furthest from each other, they're about 7.5 billion kilometres (4.7 billion miles) from each other. That's huge! The fastest un-manned vessel from Earth to Pluto currently takes nearly 10 years to get there! A manned vessel would take FAR longer, (15-20 years) as the acceleration and speed of a manned vessel needs to be far less, otherwise you would kill the astronauts. If we could travel at the speed of light which is approximately 300,000km/second (which we can't, and is currently a scientific pipe-dream given the physics required to do so), a trip to Pluto would take a shade under 4 hours. To get through the Kuiper belt would take you another 4. So 8 hours to get out of our Solar System ONLY, and ONLY if we travel at the speed of light. A manned vessel, going by the numbers, would take up to 40 years JUST to clear the solar system!

Now, the closest star to our sun is Alpha Centauri. It is a measly 4.3 light years away; that is, if you could travel at the speed of light for just under 4.5 years, you'd get there! In REAL terms, that puts Alpha Centauri more than 42.5 TRILLION kilometres away!! Let's write the number down: 42,573,600,000,000 km!! That journey, with current manned technology is estimated to take between 50,000 and 150,000 years! That's a looong time to be cooped up! And only to go next door, relatively speaking!!

Our Galaxy, that is the Milky Way is 100,000 light years across! I say across; that means going the short way, straight through the middle. Which will take you 100,000 years at the speed of light. Which you can't do, firstly coz there's a ruddy great dirty black hole in the middle of it! Secondly, we want to check out stars on the way ANYWAY, because this whole thing is about life on other planets, so our path to get there is gonna be kinda zig-zaggy. We have, as I have said about 100 billion stars to check, so the whole she-bang is gonna take a lot longer, even if you COULD travel at the speed of light. Which you can't! Realistically speaking, if you do the math, in current manned technology, 100,000 light years translates into between 1 billion & 3 billion years! Ouch!

All this for the supposition that life COULD exist elsewhere (in our Galaxy alone, mind you)? Well, why not? Lets look at those numbers! It's a fair bet that the possibility of life on any given planet is probably 1 billion to 1! Long odds by anyones standards. So many things have to be JUST RIGHT for life to start. There IS some debate over whether that statement is accurate; our current experience tells us that what life NEEDS to exist are the sorts of things we currently find on Earth; Carbon, Hydrogen, Oxygen & Nitrogen. And abundance of liquid water is also considered essential. So we narrow it down to Earth-like planets. There might be one possibility of an Earth-like planet in any given Solar system. REALLY long odds!

But wait! Our Galaxy contains 100 BILLION stars! If our odds are 1 billion to 1, in our galaxy alone, there might be 100 stars WITH the right sort of planet where life got a foothold! Nice. Playing it strictly by the numbers, there is a good possibility of life elsewhere in our Galaxy. Finding it? Well, that's kind of the rub! We don't have the ability to look for it, and even if we did, where do we start looking? What are we looking for and will we recognise it when we see it? Hence John's answer; yeah there could be life, a damn good chance of it, but we don't know where, how or even if!

Something I'd like to add to this as well. Many people claim that Earth has been visited by aliens many times, or that they have had close encounters, or seen a ufo. There is a reason why the hard-core sceptics ARE so sceptic, and it has everything to do with what has just been discussed. Our own sun is a second generation star; First generation stars didn't have much in the way of planets. When the universe began, 99.9% of all matter was Hydrogen, with a smattering of Helium. Once things had cooled a bit, it was still essentially mostly Hydrogen, with a bit more Helium, and pretty much nothing of anything else. Hydrogen is FANTASTIC for forming stars (or gas giants), but if you want a rocky planet with things like heavy metals, water, minerals or things required for LIFE etc, you need a BIG fusion reactor to cook them in first. Which is essentially what a star (or our Sun) is! First generation stars are, by and large, long gone, and were extremely unlikely to have planets which supported life, given that these stars needed to cook the heavier elements required for making planets that could support life! So, second generation stars is where life is most likely at. It took about 4.5 billion years to get from the formation of our planet to us. Life actually appeared pretty quickly, within the first billion years, but then took another 3 billion to go from single celled bacterium and the like to complex, multi-celled organisms. It was a relatively short jump of about 500,000,000 years to go from them to us, but we were by NO means a given! Intelligent life is NOT the ultimate goal of evolution; evolution flows and fills gaps as required, survival being the ultimate aim, and a complex, thinking, abstract brain is not high on the list, unless absolutely necessary. So, we're really only talking about the expanse of time it took for 2nd generation stars to form, have rocky planets capable of supporting life form around them, and have life evolve to the point where they support intelligent life on their backs! Which is the same period of time it took to get to us! THEN you have to assume that life elsewhere has not ONLY gotten smart enough to LEAVE their planet (or to want to), but to then have developed the technology in order to GET to us, which has exactly the same number of problems associated with it as we have of locating life on other planets. Which includes, knowing where to FIND us! We live in a relatively sparsely populated part of our Galaxy (not many stars at all), and if you were to go looking for life, you'd probably hedge your bets and start looking in more densely populated areas. Again, going purely on numbers, you would be more likely to find life if you were able to maximise your search efforts.

So, even with the very likely POSSIBILITY of life on other planets, the probabilities that enough time has passed for a planet to get to appear and get to that stage, that it has gotten to a point for it to be sufficiently evolved, that intelligence has appeared, that it has the technological know-how, that it has had enough time to explore the galaxy (that it could KNOW even where to find us or where to look!) are vanishingly small! While the possibility of life INCREASES if you expand your search to include OTHER galaxies (the rest of the Universe), the probability that we may find it or that it could find us gets even smaller! Distances between galaxies are massive, with almost literally NOTHING in between. The distances are many times greater than the sizes of galaxies themselves! So even if you want to BELIEVE in little green men visiting Earth, the possibility for them to exist is fine; the probability that they already have is unlikely in the extreme! Sorry.

Danny Liwszyc

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โˆ™ 2011-12-08 06:00:30
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Q: Is life possible to another planet other than the Earth planet?
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