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Have the aliens landed?; Have the little green men made contact, or is it a figment of our imagination?
Topic Started: Mar 12 2010, 02:42 PM (5,488 Views)
Holben
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T.Neo
Apr 10 2010, 05:44 AM
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So, we have lots of stars. Each probably has more than five planets, of which one or two will be suitable.


It doesn't work that way. Firstly, some stars are just not suitable here. This includes variable stars, O class stars that blow away their protoplanetary disks, stars in globular clusters and the galactic core, low metallicity stars that don't accrete planets as easily, stars in the vicinity of O class stars (yep, they blow away the protoplanetary disks of other stars as well) and certain binary arrangements.

Secondly, planetary system evolution is... odd. All that can be safely said is that every planet, and every planetary system, is different. No two planetary systems are the same. So while you may get a few planets in the habitable zone, there's no telling that they're habitable- they might be too small or might have suffered an event in their past that made them uninhabitable, like Venus. There might be gas giants in the habitable zone instead- they might not form moons massive enough to be safe abodes for life (there are certain theories that sub brown-dwarf mass objects won't form large enough moons at all)

The formation of suitable planet(s) for life around a star is tricky - there are plenty of forces that can affect it.
Yes. So the proportion of stars that are 'good' is one of the major values. I think Mr. Drake said about 10%- so 0.1?

I don't see why globular clusters and the galactic core shouldn't harbour life, so long as they aren't having their stars ripped apart by a supermassive black hole. I mean, the stars forming there are safe enough, usually red dwarf types, which aren't exposed to masses of radiation.

On second thoughts, the dominance of extrasolar gas giants in habitable zones and closer means there are probably many potential planets thrown out into interstellar space.

Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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T.Neo
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Yes. So the proportion of stars that are 'good' is one of the major values. I think Mr. Drake said about 10%- so 0.1?


Perhaps.

From numbers in the stellar neighborhood, G class stars make up 7.6%, K class stars, make up 12.5% and M class stars 76%. I don't know if Drake included M stars in his calculations.

Obviously not all of those stars are suitable, and complex life may not be as common around M stars as it could be around G and K class stars.

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I don't see why globular clusters and the galactic core shouldn't harbour life, so long as they aren't having their stars ripped apart by a supermassive black hole. I mean, the stars forming there are safe enough, usually red dwarf types, which aren't exposed to masses of radiation.


I've read that the radiation is the primary concern. Not sure if it is a valid one.

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On second thoughts, the dominance of extrasolar gas giants in habitable zones and closer means there are probably many potential planets thrown out into interstellar space.


Close-in gas giants may not be dominant, it's probably just that we keep on detecting them due to the nature of the detection techniques used.

Either way, there's a possibility for habitable planets to form after migration, or for gas giants in the habitable zone to have large moons that could host life.

A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork.
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I don't see why globular clusters and the galactic core shouldn't harbour life, so long as they aren't having their stars ripped apart by a supermassive black hole. I mean, the stars forming there are safe enough, usually red dwarf types, which aren't exposed to masses of radiation.


I think it's the same reason for stars in the main parts of the arms, the stars die to quickly.
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Holben
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But the largest stars, the ones which use their fuel fastest, are greater in trhe satellite galaxies we have, and that's also why we see more supernovae. REd dwarves and kin exist mainly at the centre of the galaxy.

Radiation from the galactic core will be stronger over there, but also there will be more stars in the way. :D

I suppose, since large planets are easier to detect, and close planets are easy to detect, that may be. But before we detected them, we didn't even think they were possible! (aside from a few).
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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T.Neo
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I suppose, since large planets are easier to detect, and close planets are easy to detect, that may be. But before we detected them, we didn't even think they were possible! (aside from a few).


Indeed, but think of all the things in biology that were regarded as impossible at one time or another...

But now we know planetary migration happens quite often, and gas giants might form closer in than has been thought.
A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork.
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Holben
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T.Neo
Apr 11 2010, 04:13 PM
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I suppose, since large planets are easier to detect, and close planets are easy to detect, that may be. But before we detected them, we didn't even think they were possible! (aside from a few).


Indeed, but think of all the things in biology that were regarded as impossible at one time or another...


But now we know planetary migration happens quite often, and gas giants might form closer in than has been thought.
For example, bacteria and other microbes.


Yeah, i looked at planetary migrations for gas giants. But they siad they'd eventually merge with their star.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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@Fakey Huh? Any way here are my estimates on my favorite equation.

As interesting as microbial life or multicellular alien life would be, what scientists would really like to find is intelligent, communicable aliens. One scientist named Frank Drake organized a meeting in 1961 with about a dozen scientists with specialty areas ranging from astronomy to biology to talk about the possibilities of life beyond Earth. At this meeting Dr. Drake came up with an equation used to estimate the number of intelligent civilizations in our galaxy. The equation , N = R*Fp x Ne x Fl x Fi x Fc x L is know as the Drake equation.
In order to find N (the number of intelligent civilizations) we must know the number of sun like stars that are born each year or the R* rate of star formation. Sun like stars are yellow g-type stars. We know that about 20 new stars are born each year. NASA has estimated that around 7 sun like stars are born each year.
The next element of the equation is Fp, the fraction of stars with planets. As I discussed earlier about 200 planets have been found outside of our solar system. Only one of these planets was small and rocky. The technology today is very limited in its ability to find Earth like planets. The situation is only going improve as technology advances such as with the launch of the Terrestrial Planet Finder and the Kepler spacecraft. I’m going to agree with Drake's original guess of 0.5 or half of the sun life stars have planets.
Ne , the number of Earth like planets. Within our own solar system at least 3 planets other than Earth possibly could have life of their own, or at least could support it. The word planet is misleading though because their are "moons" possibly capable of supporting life as well. Mars certainly is a planet within the habitable zone but Titan and Europa are denoted as "moons" of Saturn and Jupiter. This raises the value of Ne to at least 2 or every solar system with planets will have at least 2 planets capable of supporting life.
Fl , the frequency life actually arises on a planet. One of the main problems with the Drake equation is that the farther to the right you go the more uncertain we become about the value of the variables. We have yet to find any form of alien life so we can only speculate on the value of the term Fl. Life on Earth is capable of surviving a variety of difficult conditions, amino acids were found on meteorites, and organic molecules have been found on the surface of Titan. As amino acids are the building blocks of life this opens up more possibilities. Given the right circumstances, I am fairly optimistic that live would and could arise on another world. I will guess that Fl is 1 or all planets capable of supporting life will develop life at some point in their lifetime.
Fi , The fraction of planets with intelligent life. In the 4.6 billion years life has existed on Earth, humans have only existed for about 100,000 years, a blink in the evolutionary history of life on Earth. This means that planets will probably have to have to host life for a fairly long time before intelligent life develops. However, if we look at the example of the octopus, a relatively old species, we realize that it has the largest brain of all invertebrates. The octopus’s brain is in fact even larger than some vertebrates. This means that planets could possibly develop smart creatures earlier in their history. The fossil record has also demonstrated that some creatures gradually evolve to have larger brains. Clearly intelligence has an obvious advantage. I think that given enough time a planet with life will develop an intelligent species, leaving the value of Fi at around 100 percent or all planets with intelligent life will, in time, develop intelligent life.
Fc, the fraction of intelligent species capable of interstellar communication. A few species on Earth are considered to be intelligent, like the dolphin, the chimpanzee and the gorilla, the parrot, and the octopus. As an example of this group of animals, the dolphin is able to communicate with other members of it's speices and is able to do many different tricks and other sophisticated actions humans associate with intelligence. But although the dolphin is intelligent it lacks the ability to create tools so it will never be able to develop technology, a neccessity for interstellar communication. As a human civilization we have only very recently developed technology that allows us to communicate between the stars. The inventions that let us accomplish this are the radio and the laser. Could alien life develop these technologies? Assuming the intelligent species has some way to manipulate tools, some form of "graspers", and has some way to communicate with other members of it's species it is very likely to develop science. If you look at human history on Earth, many early civilizations had science. For instance the highly religous Aztecs had extremely accurate measurements of the planets. All it takes is for one person to make a monumental discovery, like Albert Einstein's Theory of Relativity. I believe that the course of science in any alien civilization will eventually lead to the radio, the laser or some other form of interstellar communication. But the question remains even if a species does develop technology capable of interstellar communicatication, will it communicate? Skeptics of the Drake equation have said that very few societies will broadcast signals because they are not interested in talking to other foriegn civilizations or because they may fear alien invasion. I personally believe that one of the aspects of intelligence is curiosity. For example, if James Clerk Maxwell had never been curious about the nature of electricity we would not have cars, computers, IPODs, lightbulbs, ovens, televisons, or any other modern inventions. If primitive societies had never been curious about fire we would still be living in the stone age. I think it is reasonable to assume that intelligence and curiousity are connected. So if there are other civilizations out there they probably are searching for us! The alien invasion concept, although possible, is unlikely ( more on this next ). With this reasoning I believe the value of Fc to be about 0.95 or 95 precent of intelligent species will communicate.
L the lifespan a civilization communicates. After the invention of the radio in 1895 by Guglielmo Marconi, an incredibly destructive device was tested in Alamogordo, New Mexico. With the force equivalent to 22,000 tons of conventional high explosives, the atomic bomb was born. The device was so powerful that J. Robert Openheimer in observing it said "Now I am become Death, the destroyer of worlds." a quote derived from the Hindu scripture. Humankind now has numerous weapons capable of destroying life on a massive scale and even destroying our own species. The varible L in the Drake equation deals with how long humans as a species will broadcast detectable signals into space. In the history of life on Earth life has come very close to being destroyed on numerous occasions. In the Permian era roughly ** million years ago, 90 precent of life on Earth was completely wiped out by a massive meteoroid impact. But life recovered. One of the most amazing abilities of life is its skill of being incredibly adaptable. As I talked about in my first section, we have found lifeforms adapted to an array of incredibly harsh conditions where they continue to thrive. The animals and plants that did survive the Permian extinction went on to reclaim the planet and eventually evolved into modern humans. People too have faced epidemics, earthquakes , famine, nuclear disasters, tidal waves and war yet still have been able to establish themselves as the dominate vertebrate on the planet. How long as a species will we survive and thus continue to communicate? On our current evolutionary path we've been communicating by radio for just over 100 years. This is likely to be the miniumum ammount of time a species will communicate. Of course the lifetime of our civilization , which serves as an example for other civilizations, is likely to be much longer. Dr. Drake's estimate was 100,000 years. For this varibable I will give a high of 100,000 years and a low of 1000 years.
N the number of intelligent civilizations in our galaxy. After multipling every varibable in the equation for both the pessimistic and optimistic veiw of the equation , I came to an interesting conclusion, the varible L greatly effects the answer to the equation. For the opptimistic answer I came to 665,000 intelligent civilizations within the milky way galaxy. With this estimate we will probably find direct evidence of an alien civilization with the next 25 years. But with the pessimistic estimate of 6650 civilizations we are not likely to contact an alien race unless we discover a way to travel to other star sytems within a resonable amount of time. Beacause of the large diference between the two values of N , the drake equation does not give a solid answer to how many civilizations are within the milky way , but more of an educated guess. As our understanding of the different factors that contribute to the drake equation incresses so will the accuracy of our guess.

Sorry for the long post.

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Pando
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I think that 665,000 intelligent aliens in the Milky Way is a bit optimistic, considering that the Milky Way is only 100,000 light years across. You also forgot that not every planet will necessarily evolve brain-like structures, and also just because intelligence is common on Earth it doesn't mean on a planet with "brained" animals they will evolve to be intelligent. So I would guess 1,000 to 100,000, without doing the Drake Equation.
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Holben
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And out of those, how many use the same technique for contact and how many would want to?
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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Pando
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Radio wave seems the best technique for short range. But for long range communication you would have to use a stronger radiation, like UV, X-Ray, or Gamma.
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Holben
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I mean they would probably use lasers.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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For communication?
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T.Neo
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Probably, and probably in a wavelength that the star emits least.

Good luck finding a targeted transmission out of the entire sky...
A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork.
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Holben
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Well, soon we'll have spaceships capable of interstellar travel. They can set up receivers all over the place.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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