Habitable Planets: How many in the Milkyway?


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Profile Johnney Guinness
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Message 977346 - Posted: 11 Mar 2010, 6:10:51 UTC

This is a good article that, using todays current data, attempts to work out how many Habitable Planets are in the MilkyWay;
http://www.centauri-dreams.org/?p=11625

One estimate suggests that there might be 45.5 billion terrestrial planets in the habitable zones of host stars in our MilkyWay galaxy. There are lower estimates of 50 million Habitable Planets in the MilkyWay.

3 or 4 years from now NASA's Kepler telescope will help give us a far more accurate estimate. Kepler has just finished its first year in orbit.

John.
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Message 998147 - Posted: 23 May 2010, 4:10:39 UTC

My estimate is that there is one. Or more.
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Profile Johnney Guinness
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Message 998320 - Posted: 23 May 2010, 22:33:50 UTC

Its interesting, the figures were done as estimates for habitable planets around stars in the Milkyway. Near the end of the article, they take the end figure and use it to do an estimate for the whole visible universe.

The number works out to 10^18, or 10 million trillion habitable planets in the universe.

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Profile William Rothamel
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Message 998335 - Posted: 24 May 2010, 0:17:50 UTC
Last modified: 24 May 2010, 1:02:37 UTC

i suspect it is much lower. If there were 15 conditions necessary for life and each turned out to be 10% probable for a mother star then how many would that make in the galaxy and in the universe. Certainly less than one in the Milky Way, and how many in the 100 billion galaxies each with 100 billion stars?

I propose the following conditions for a planet that might have intelligent life that we might say is somewhat like our own place in the Universe.

There are probably many more --can you add some ??

We are defining planets that are habitable now to intelligent life.

Star on the main sequence with a lifetime of at least 10 billion years
Star with at least 5 billion years under it's belt
Star with plants orbiting at the right distance to allow a stable temperature cycle conducive to life
Star with planets that are in a near circular orbit
Star that has outer giants to protect from asteroids and planets for the inner planets.
Planet that has a large moon to create tides and stabilize the spin of the planet
Abundant water delivered by comets to habitable planets
Star that is not a binary to allow stable planetary orbits
Planets that have evolved an oxygen-rich atmosphere
Planet that has Gravity that will be conducive to life-not crushing and strong enough to hold an atmosphere.
Planet that is rocky as opposed to gaseous
Planet that does not have a crushing atmospheric pressure.
Planet that is not completely water covered.
Stars that have moderation of gamma ray emissions
Planets that have a magnetic field to deflect harmful radiation.
Planets with non-crossing orbits which might fling habitable planets out of stable orbits.

Now, if we want to estimate how many habitable planets that harbor intelligent life that we might detect we would have to add another bundle of conditions. The nearest galaxies to us are on the order of 200 thousand light years away-- The nearest spiral Galaxy--Andromeda is 2,500,000 light years away. Can't imagine detecting a signal from that distance.

I suspect that we would conclude that habitable planets are not abundant in the Galaxy, (probably not in a detectable range) and that we will never be likely to detect another civilization. I am still hopeful but my eyes are wide open.

Hubble and newer telescopes might put some of my conditions at a high probability per star--i will eagerly await these data and hope to live long enough to clear up a portion of the vast uncertainty pertaining to this question. I wager it is worthwhile to expend resources on these questions.

Profile Johnney Guinness
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Message 998674 - Posted: 25 May 2010, 2:55:50 UTC
Last modified: 25 May 2010, 3:01:39 UTC

Bill there are just too many variables and not enough money to scientifically narrow them down. As we know with the Drake equation, you can fill in whatever values you want, and that's not very scientific.

We only have one example, us!. So we are trying to do statistics with only one sample, and that called guessing.

But!!!!... On the statistics of just "one", we know "life" is possible. And we know that life is incredibly versatile and resilient. Life on earth is abundant in many many forms.

On that simple basis, with the money mankind is willing to spend on this stuff, we are doing our best to find other life. We are trying to find it locally on Mars, Europa, Titan, Enceladus, etc,etc. Within a few years, within your lifetime Bill, Kepler or another telescope will confirm another earth-like planet. If there is one other earth-like planet, then there are billion's of them!!! If there are billion's of earth-like planets, then on our statistics of one, life will have occurred on a second planet. If this is the case, then life is everywhere!!!

This WILL happen in your lifetime Bill, and we will all be able to smile. Kepler telescope should have results within 3 years tops, if not much sooner! They have a year and a quarter's worth of data at this stage.

John.
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Message 998783 - Posted: 25 May 2010, 22:23:25 UTC - in response to Message 998674.

Johnney, My son,

Perhaps an exobiologist could comment on other conditions for life to form on our world (or any world) and evolve to somewhere where we are at now in a few billion years. Certainly, I have posted what I suspect are essentials for such a chain of development to take place. Some of these may be non-essentials; but there are, I suspect many more that I don't know about which point to the uniqueness of Earth. I do not pretend to have any expertise in this area other than to extrapolate what I think has happened here. There may well be 'life" on Europa or Titan but I am betting against it being any more intelligent than a squid.

I guess you might say that I have had an epiphany that has led me from the notion of abundant life in the Galaxy to probably none other. it's hard to prove a negative so i will await evidence from SETI and enjoy "playing the Lottery"

You are right that in time we would know more of the probabilities that a given star has planets that fit the mold for likely development of intelligent life.

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Message 998950 - Posted: 26 May 2010, 16:51:55 UTC
Last modified: 26 May 2010, 16:57:14 UTC

Bill,
I look out my window in front of me and i see green trees, new summer plant growth, white puffy clouds moving slowly across the pale blue sky. For the last few weeks i have watched 5 new born kittens run across my yard playing every day. The beauty that plays out in front of my eyes every day leaves me speechless.

I'm actually physically unable to imagine this has not happened on other planets. We are in Heaven, right here, right now, and its beautiful. This is my epiphany, we are at one with nature in this beautiful universe.

John.
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Message 999507 - Posted: 29 May 2010, 9:00:48 UTC
Last modified: 29 May 2010, 9:28:39 UTC

It will most likely be proven in the future that life is abundant in the Galaxy.
Look for advanced life in the outer limbs of the galaxy where conditions are more stable.

Given that life appeared very early in the Earth's history, and it appears most of what we see out there is made of the same "stuff" as our solar system,
odds are that there are habitable planets in the millions in our galaxy alone.

It's all down to the cosmic lottery, where a planet lies in relation to the output from it's parent sun, the so called goldilocks zone.

Life once started is tenacious and will eek out a living in its most basic form.
However, given a very suitable stable habitat, it will flourish into the beautiful things we see around us.

I call it the Cosmic Incubator, the hand of God if you will.

Saying we are alone, even in our own Galaxy, is the height of crass stupidity IMHO, or religious mania,
and this is based on deduction, not proof.

My own opinion is that all we see in the cosmos has an ultimate purpose,
and that is to bring forth life, period.

When I stand outside at night and observe the jaw dropping cosmic theatre above my head, I am in awe of the possibilities that exist on this galactic canvas that has been put in place for us by god knows who or what, and the countless stories of civilisations that have come and gone, countless variations on the life theme, and the eons that have had to pass for all this to exist.

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Message 999971 - Posted: 2 Jun 2010, 14:54:34 UTC
Last modified: 2 Jun 2010, 14:56:13 UTC

SETI@home has sent me a mail message linking to a debate between Dan Werthimer and Geoff Marcy just on this subject. I watched it a couple of times to be sure I had understood the positions of the two debaters, and it seems that Werthimer is more optimistic while Marcy, an astronomer hunting for planets on other stars, is rather pessimistic. But it was very interesting anyway, and I thank SETI@home for sending me the message.
Tullio
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Message 1001274 - Posted: 6 Jun 2010, 14:58:00 UTC - in response to Message 999971.

T,
Ciao Piasano.

I would welcome some comments on my list of conditions for intelligent life to form as it relates to the probabilty of a given star to harbor a planet that would support such life.

I would also expect that others might add or subtract from the list I started.

Incidently it looks like Jupiter just recently absorbed another massive comet or asteroid hit--sort of "taking one for the team" so to speak. In the early universe and solar system formation there must have been many more comets and other bodies flying around. We needed early comets to bring water and then we needed a shield later on so that life that was started would not be wiped out by the effects of a massive collison.

Bill

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Message 1001322 - Posted: 6 Jun 2010, 17:49:55 UTC

Well, other necessary but not sufficient conditions for life to develop could be the relative strength of the four basic interaction, the division of matter between fermions (which obey the Pauli exclusion principle) and bosons. All of this is included in the Gaia hypothesis, which I find very appealing even if it cannot be proven. I find also very appealing the panspermia hypothesis of Arrhenius, recently taken newly in consideration by Hoyle, Narlikar and Wickramasinghe. I find it almost impossible to think that life originated here on this small planet. But, until we find it somewhere else, that's all we know.
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Message 1001327 - Posted: 6 Jun 2010, 18:21:11 UTC - in response to Message 998335.

I propose the following conditions for a planet that might have intelligent life that we might say is somewhat like our own place in the Universe.

Star on the main sequence with a lifetime of at least 10 billion years
Star with at least 5 billion years under it's belt
Star with plants orbiting at the right distance to allow a stable temperature cycle conducive to life
Star with planets that are in a near circular orbit
Star that has outer giants to protect from asteroids and planets for the inner planets.
Planet that has a large moon to create tides and stabilise the spin of the planet
Abundant water delivered by comets to habitable planets
Star that is not a binary to allow stable planetary orbits
Planets that have evolved an oxygen-rich atmosphere
Planet that has Gravity that will be conducive to life-not crushing and strong enough to hold an atmosphere.
Planet that is rocky as opposed to gaseous
Planet that does not have a crushing atmospheric pressure.
Planet that is not completely water covered.
Stars that have moderation of gamma ray emissions
Planets that have a magnetic field to deflect harmful radiation.
Planets with non-crossing orbits which might fling habitable planets out of stable orbits.


Bill your looking to add some more stuff to this list, but i dispute many of the things on your current list.

Star on the main sequence with a lifetime of at least 10 billion years
Star with at least 5 billion years under it's belt

No way, if life can find a habitable place, it could evolve a reasonable level of intelligence within a few million years.

Star with planets that are in a near circular orbit

This also might not be necessary. As is suggested in the "Avatar" film, you could have habitable exo-moons around a gas giant planet with an elliptical orbit. The habitable zone has tonnes of variables. For all we know, there could be intelligent life living in the warm water under Saturn's moon Enceladus. There is no reason why human like creatures could not evolve to live under water.

Planets that have evolved an oxygen-rich atmosphere
Planet that has Gravity that will be conducive to life-not crushing and strong enough to hold an atmosphere.

On earth,we have lots of creatures living under the massive crushing pressure of the deep oceans. And there is no reason why life could not evolve to breath gases other than oxygen. Methane could be a source of energy for creatures.

John.
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Message 1001764 - Posted: 8 Jun 2010, 11:41:17 UTC - in response to Message 1001327.

"No way, if life can find a habitable place, it could evolve a reasonable level of intelligence within a few million years."

The only bit I disagree with Johnny is the above.
I suspect there are many evolutionary dead ends out there in the cosmos.
Life for lifes sake with little intelligence other than to survive.

There are many species here on earth that have remained unchanged for millions of years and if they dominate the ecosystem, like the dinosaur family, the evolution of advanced beings would be repressed, perhaps indefinitely unless removed.

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Message 1001998 - Posted: 9 Jun 2010, 2:53:51 UTC - in response to Message 1001327.

Johnney,

Good comments. Here are my thoughts. We have evolved in a few million years from beings that are the result of a few billion years prior evolution. The planet would have to cool and attract water from comets. early life would have to create an atmosphere. That's why I say that a star would have to be about as old as our sun to harbor planets with intelligent life. I wont quibble about a billion years or so ;but I don't see how the stellar nurseries could be producing life right away.

There would have to be a source of energy that would come from either internal heat or from a sun. A cold moon would have to have internal heat to power the engines of life. That life would have to be sub-terranian or under an ocean.

I am assuming that intelligent life that developed on a water-only planet would not be able to develop written language and; though intelligent, would not progress to where they could communicate among the stars. I am assuming that they could not develop electronic communication under water.

Admittedly most of my musings are extrapolations of our current situation here on Earth. I see an extremely delicate balance here that allowed us to exist and evolve--I am asking what are the conditions necessary for intelligent life to evolve, and also how prevalent those conditions might be among the stars that have planets.

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Message 1003269 - Posted: 11 Jun 2010, 22:24:49 UTC

This might help you :)

http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html

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Message 1003285 - Posted: 11 Jun 2010, 23:17:50 UTC
Last modified: 11 Jun 2010, 23:21:36 UTC

Drake equation next step:
SETI and SEH (Statistical Equation for Habitables)
by Claudio Maccone
Co-Chair, SETI Permanent Study Group, International Academy of Astronautics


73 & clear skies from Bruno IK2WQA - brmoret_at_libero.it
FOAM13 Astronomical Observatory, Tradate (Italy)
Founder SETI@home Berkeley's Staff Friends Club
Founder SETI ITALIA Team G. Cocconi

Profile William Rothamel
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Message 1003312 - Posted: 12 Jun 2010, 0:39:37 UTC - in response to Message 1003269.

Thankyou fred but my quarrel with the Drake equation is the uncertainty of the estimate of what percentage of suns have habitable planets. I believe that more than a handful of conditions are necessary. It could be many dozens as I believe that we have a very delicate set of conditions for intelligent life to develop. I took a guess at a few of them and suspect that there would be some deletions and many more additions to the list.

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Message 1003322 - Posted: 12 Jun 2010, 0:54:01 UTC - in response to Message 1003285.

With such a large standard deviation. I could conclude that at a 95% confidence level that there are zero habitable planets in the Milky Way.

To be fair, there would be infinite uncertainty as to how many Planets have what probabilities of possessing the requirements for intelligent life. First we need a valid list of requirements and then a lot more telescope data .Then, time will allow us to make better estimates as we find more planets, their compositions, temperature, orbits, etc .

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Message 1003755 - Posted: 13 Jun 2010, 19:11:34 UTC - in response to Message 1003322.

First we need a valid list of requirements and then a lot more telescope data .Then, time will allow us to make better estimates as we find more planets, their compositions, temperature, orbits, etc .


I think, you are absolutely right!
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