Inhabitable Planets Too Close Together?

SWM wrote:100 million planets is still plenty. That's an average of 1 out of 400 stars, which is actually fairly high. Assuming a star density similar to that in the Solar neighborhood, that means 1 habitable planet per 100,000 cubic light-years, or an average separation of 46 light-years between habitable planets.

Tenshinai wrote:Isn´t it 1 out of 4000?

SWM wrote:Sorry, you're right. 1 out of 4000 stars.

JohnRoth wrote:The press release says there are 10 billion stars in the galaxy, while the Fount of All Knowledge says 100 to 400 billion. (http://en.wikipedia.org/wiki/Milky_Way ) Their comment is that 1% to 2% of all systems would have a planet which could host multi-cellular life. Either their estimate of the number of stars in the galaxy is incorrect, or the press release isn't telling the full story (What! A press release is wrong? Egads, what is the world coming to!)

I'm translating "complex" into "multi-cellular" here. That doesn't include planets with life that's still in the single-cell stage. To interpret this, remember that the Great Oxygenation Event occurred prior to the origin of multi-cellular life here on Earth.

Replying to myself.

The paper itself is open access. There is no mention of how they got the 10 billion stars in the galaxy. However, the 100 million number does occur in the Conclusions, and the 1.7 percent seems like it's reasonable considering their calculations. I wasn't able to find the supplementary materials, however.

Hi John Roth,

Back at the bar I think the estimated ratio of inhabited systems in the SL might have been as high as 1/50 or 2% of the stars, to explain the SL's density of 1 inhabited system with a radius averaging ~14.717 LY each, assuming the SL's radius of 150-200 LY was a 50/50 proposition.

L

JohnRoth wrote:**quote="SWM"**100 million planets is still plenty. That's an average of 1 out of 400 stars, which is actually fairly high. Assuming a star density similar to that in the Solar neighborhood, that means 1 habitable planet per 100,000 cubic light-years, or an average separation of 46 light-years between habitable planets.**/quote**

Tenshinai wrote:Isn´t it 1 out of 4000?

SWM wrote:Sorry, you're right. 1 out of 4000 stars.

JohnRoth wrote:The press release says there are 10 billion stars in the galaxy, while the Fount of All Knowledge says 100 to 400 billion. (http://en.wikipedia.org/wiki/Milky_Way ) Their comment is that 1% to 2% of all systems would have a planet which could host multi-cellular life. Either their estimate of the number of stars in the galaxy is incorrect, or the press release isn't telling the full story (What! A press release is wrong? Egads, what is the world coming to!)

I'm translating "complex" into "multi-cellular" here. That doesn't include planets with life that's still in the single-cell stage. To interpret this, remember that the Great Oxygenation Event occurred prior to the origin of multi-cellular life here on Earth.

Replying to myself.

The paper itself is open access. There is no mention of how they got the 10 billion stars in the galaxy. However, the 100 million number does occur in the Conclusions, and the 1.7 percent seems like it's reasonable considering their calculations. I wasn't able to find the supplementary materials, however.

JohnRoth wrote:
The press release says there are 10 billion stars in the galaxy, while the Fount of All Knowledge says 100 to 400 billion. (http://en.wikipedia.org/wiki/Milky_Way ) Their comment is that 1% to 2% of all systems would have a planet which could host multi-cellular life. Either their estimate of the number of stars in the galaxy is incorrect, or the press release isn't telling the full story (What! A press release is wrong? Egads, what is the world coming to!)

I'm translating "complex" into "multi-cellular" here. That doesn't include planets with life that's still in the single-cell stage. To interpret this, remember that the Great Oxygenation Event occurred prior to the origin of multi-cellular life here on Earth.

You´re mixing up definitions there i think.

"could host multi-cellular life" is nothing the same as "life-giving planets".
The second means it´s capable of independently generating life, the former that complex life can survive on it.

That´s how i read it at least.

I finally got a chance to read the original article. I want to clarify a couple of misconceptions in the discussion here.

The article does not say that there are 10 billion stars in the galaxy. What it actually says is that the authors assume the existence of 10-100 billion planets in the galaxy. Assuming that the percentages match the 600+ known planets at the time of publication, that means about 1% of them are as capable of evolving life as Europa. That leads to their estimate of at least 100 million planets in the galaxy on which life could evolve. Note that does not mean 100 million star systems, since more than one could occur in a single system (they count Earth, Mars, and Europa in that category).

Tenshinai wrote:

JohnRoth wrote:
The press release says there are 10 billion stars in the galaxy, while the Fount of All Knowledge says 100 to 400 billion. (http://en.wikipedia.org/wiki/Milky_Way ) Their comment is that 1% to 2% of all systems would have a planet which could host multi-cellular life. Either their estimate of the number of stars in the galaxy is incorrect, or the press release isn't telling the full story (What! A press release is wrong? Egads, what is the world coming to!)

I'm translating "complex" into "multi-cellular" here. That doesn't include planets with life that's still in the single-cell stage. To interpret this, remember that the Great Oxygenation Event occurred prior to the origin of multi-cellular life here on Earth.

You´re mixing up definitions there i think.

"could host multi-cellular life" is nothing the same as "life-giving planets".
The second means it´s capable of independently generating life, the former that complex life can survive on it.

That´s how i read it at least.

The authors are quite specific that they're interested in a preliminary estimate of planets that might be able to have evolved "complex", that is, multi-cellular, life, not planets that could have evolved single-cell life but can't get beyond it. To do this they created an evaluation methodology. Whether that formula is anything more than vigorous arm-waving is something we're going to have to wait a long time to see.

Their index isn't intended to evaluate whether the planets that are habitable by interstellar colonists. The data is available, so if that's your interest have at it.

SWM wrote:I finally got a chance to read the original article. I want to clarify a couple of misconceptions in the discussion here.

The article does not say that there are 10 billion stars in the galaxy. What it actually says is that the authors assume the existence of 10-100 billion planets in the galaxy. Assuming that the percentages match the 600+ known planets at the time of publication, that means about 1% of them are as capable of evolving life as Europa. That leads to their estimate of at least 100 million planets in the galaxy on which life could evolve. Note that does not mean 100 million star systems, since more than one could occur in a single system (they count Earth, Mars, and Europa in that category).

Read my comment to Tensani - the authors are interested in complex, that is, multi-cellular, life, not lots of single-cell organisms. In any case, Mars does not make their cut, and Europa probably doesn't make it either.

My problem is that I'm still not seeing where they get that 10-100 billion planets that they ran into their formula to get 100 million planets that make their cutoff.

JohnRoth wrote:

SWM wrote:I finally got a chance to read the original article. I want to clarify a couple of misconceptions in the discussion here.

The article does not say that there are 10 billion stars in the galaxy. What it actually says is that the authors assume the existence of 10-100 billion planets in the galaxy. Assuming that the percentages match the 600+ known planets at the time of publication, that means about 1% of them are as capable of evolving life as Europa. That leads to their estimate of at least 100 million planets in the galaxy on which life could evolve. Note that does not mean 100 million star systems, since more than one could occur in a single system (they count Earth, Mars, and Europa in that category).

Read my comment to Tensani - the authors are interested in complex, that is, multi-cellular, life, not lots of single-cell organisms. In any case, Mars does not make their cut, and Europa probably doesn't make it either.

My problem is that I'm still not seeing where they get that 10-100 billion planets that they ran into their formula to get 100 million planets that make their cutoff.

I read the article. Both Mars and Europa do make their cut.