Suitable stars and the Drake Equation discussions

Is it just me, or does it seem that most discussions about the Drake Equation are overconfident about the number of habitable planets?

It seems to me that too many examples of the Drake Equation in action don't screen out unsuitable stars. Only lower F-type, G-type, and upper K-type stars in the main sequence seem suitable. Hotter stars are too-short-lived, and dimmer stars lack a real habitable zone due to issues like tidal locking and the impact of solar flares at close range. Some people say dim orange and red dwarfs (middle K-type through all type M stars) could harbor a civilization, but I think that's REALLY stretching things. In my Enhanced Drake Equation Calculator app (free on Google Play), I give a default value of 10% as the fraction of stars of the correct spectral type.

Most discussions of the Drake Equation omit the Galactic Habitable Zone. The inner portion of the galaxy is too dangerous, and the outer portion is short on metals. In my enhanced Drake Equation calculator, I give a default value of 9% as the fraction of stars in the Galactic Habitable Zone.

I've never seen an example of the Drake Equation in action that took into account the ages of stars. Remember the 4.6-billion year time lag between the birth of our sun and the beginning of our interstellar communication capability. If this slow speed of evolution is typical, then stars younger than our sun are unlikely to harbor a civilization simply because there hasn't been enough time yet. Thus, most civilizations would have to orbit stars at least as old as our sun. But the metallicity in the galaxy may have been considerably lower in the first 4+ billion years of the history of our galaxy's thin disk. Additionally, the sun has a higher metallicity than most other stars its age. It's possible that we are part of the first group of civilizations to form, and the most vibrant days of the galaxy are ahead of us. In my Enhanced Drake Equation app, I give a default value of 40% as the fraction of stars in the Galactic Habitable Zone that are old enough to harbor a civilization. Of course, the real value could be considerably lower.

Dear Jason Hsu:

On Thursday, August 9, 2012 9:39:07 AM UTC-7, Jason Hsu wrote:
....
I've never seen an example of the Drake Equation
in action that took into account the ages of
stars. Remember the 4.6-billion year time lag
between the birth of our sun and the beginning
of our interstellar communication capability.

Was only ~2.2 billion years from the Theia encounter, that wiped out whatever might have been on Earth before.

If this slow speed of evolution is typical,
then stars younger than our sun are unlikely
to harbor a civilization simply because
there hasn't been enough time yet.

Migrate from other stars. We will try and spread out, so why not others?

Thus, most civilizations would have to orbit
stars at least as old as our sun.

Disagree.

But the metallicity in the galaxy may have
been considerably lower in the first 4+
billion years of the history of our galaxy's
thin disk. Additionally, the sun has a
higher metallicity than most other stars its
age.

Since it is a second generation...

It's possible that we are part of the first
group of civilizations to form,

Very doubtful. We are seeing high metallicity in galaxies 500 million years after the Big Bang. So we could easily be 8 billion years younger than the first civilization.

and the most vibrant days of the galaxy are
ahead of us.

Let us hope we are equal to the task of watching that come true.

David A. Smith

Le 09/08/12 18:39, Jason Hsu a écrit :
Is it just me, or does it seem that most discussions about the Drake Equation are overconfident about the number of habitable planets?

It is just you.


It seems to me that too many examples of the Drake Equation in action don't screen out unsuitable stars.

Only lower F-type, G-type, and upper K-type stars in the main sequence seem suitable.

What are the observations that lead to this result?

Hotter stars are too-short-lived,

Only extremely short lived ones. In our planet, life appeared almost
immediately after the formation of our planet, so life starts quite
quickly.

Intelligence needed 4 billion years to appear but we do not know at all
why, and under what circumstances a global ecological system like our
own develops intelligent beings.

Are they developed shortly before the host star makes life impossible?
Our sun will make life impossible on Earth in 1 billion years.
Intelligence appears on earth after 4 billion years, only 1 billion
before life becomes impossible because of the star evolution.

In short, we have no data.

and dimmer stars lack a real habitable zone due to issues like tidal locking and the impact of solar flares at close range.

1) Not all dimmer stars have a zero habitable zone. A big planet
that is tidally locked to a dim star and has a thick atmosphere can
redistribute the feeble heat from the star into
the night side making overall temperature quite OK.

2) Very low temperature stars offer a wonderful environment in their
surface. The atmosphere of recently discovered stars offers an ideal
environment stable for billions of years.

Keck spotted "CFBDSIR J1458+1013B," a brown dwarf 75 light-years from
Earth with a mass of 6-15 times that of Jupiter, and from observations
realized that this very dim object must have a temperature of less than
100 degrees Celsius (212 F) -- about as hot as boiling water.
http://news.discovery.com/space/ultr...er-110312.html

3) Solar flares are a repetitive phenomenon that living beings can
very well adapt to for instance by living under a sea or underground.
Have you taken into your calculations this things?

Some people say dim orange and red dwarfs (middle K-type through all type M stars) could harbor a civilization,

Yes

but I think that's REALLY stretching things.

Again, what observations lead to this conclusion?
What theoretical reasons?

In my Enhanced Drake Equation Calculator app (free on Google Play),
I give a default value of 10% as the fraction of stars of the correct
spectral type.

And by what calculations you arrive at that figure?


Most discussions of the Drake Equation omit the Galactic Habitable Zone.

Yes. Maybe because it is not relevant?

The inner portion of the galaxy is too dangerous,

Dangerous for whom?
For living beings adapted to the outer portions of the galaxy of course!

The central point here is that life elsewhere is NOT life as WE know it!

and the outer portion is short on metals.

What observations lead you to that conclusion? Have we discovered
planets in the outer portions of the galaxy? Can we say for sure
that planet population in the outer parts of the galaxy are less than
in the inner portion?

We have NO DATA for any of your suppositions.


In my enhanced Drake Equation calculator, I give a default value of 9% as the fraction of stars in the Galactic Habitable Zone.

Again, you take that value out of where?


I've never seen an example of the Drake Equation in action that took into account the ages of stars.

Remember the 4.6-billion year time lag between the birth of our sun and the beginning of our interstellar communication capability.

We have absolutely no interstellar communication capability.


If this slow speed of evolution is typical, then stars younger than our
sun are

unlikely to harbor a civilization simply because there hasn't been
enough time yet.

We have no idea of why and when a global ecological system evolves
intelligence.

Is it a coincidence that we have appeared after 4/5ths of the lifespan
of life has been reached?

Maybe in a system with a shorter lifespan things develop quickly, much
more quickly than on earth?


Thus, most civilizations would have to orbit stars at least as old as our sun.

Absolutely not. From the first multi-cellular beings to humans there was
a much shorter time span of just 500 million years.

Did the 3 500 million years of uni-cellular life happen because life
NEEDS that time to evolve them?

Or did it happen because life does not NEED to develop them because it
has more time, the sun being a longer lived star?

We do not know.

But the metallicity in the galaxy may have been considerably lower in the

first 4+ billion years of the history of our galaxy's thin disk.

Maybe, it depends on how many big stars were created in the first 4
billion years of the galaxy life. If there were a lot of huge stars
at the beginning of the galaxy life, they synthesize metals quickly
with life spans of only a few million years.

We have no data to assert anything like galaxy composition 8 billion
years ago.

Additionally, the sun has a higher metallicity than most other stars its age.

So what?

It's possible that we are part of the first group of civilizations to form,

"Civilization" ?

Our primitive society mainly busy with slaughtering themselves in
endless wars?

Where science, art, and all the most noble capacities of the human
spirit are despised for more interesting things like making war,
polluting, destroying the planet?

and the most vibrant days of the galaxy are ahead of us.

I agree with that, only if we are able to evolve, what looks quite
difficult.

In my Enhanced Drake Equation app, I give a default value of 40% as the

fraction of stars in the Galactic Habitable Zone that are old enough to harbor a civilization.

Of course, the real value could be considerably lower.


Or higher.

We have NO DATA.

We are just speculating, witout any means to make a scientific
assertion of this problem.

We do not even know if there is any life in our own solar system!

Life could be present in Mars, Europa, Encedalous, Titan, the clouds
of Venus, ignoring all other places that we know nothing about like
the moons of Neptune, Uranus, etc!


jacob

Le 10/08/12 12:23, jacob navia a écrit :
2) Very low temperature stars offer a wonderful environment in their
surface. The atmosphere of recently discovered stars offers an ideal
environment stable for billions of years.

Even cooler is Spitzer's candidate brown dwarf, detected 63 light-years
from Earth with a mass of approximately seven times the mass of Jupiter,
appears to have a temperature of 30 degrees Celsius (86 F)!

That's cooler than the surface temperature of Las Vegas strip that
features up to 45 Celsius (113 F), obviously too hot for any
intelligent life to exist.

I'm not optimistic on the prospects of interstellar space colonization. First, there is the Relativity problem, and then there is the matter of protecting occupants from stray atoms and grains of dust (which would punch holes in the spaceship near light speed). I think that the only thing that would motivate civilizations to colonize other star systems is the death of their parent star.

As for metallicity in the early days of the galaxy, it was mostly confined to the galactic core, and it took time for the metals to spread out into the thin disk. So I still think there's a limit on how early life could have formed and how early the first civilizations could have formed.

It's possible that the evolution of life is faster on other worlds than it was here, but I prefer to make conservative assumptions until they're proven wrong. Even if it turns out that evolution can be fast enough to allow an upper F-type or even a lower A-type star to give rise to a civilization, such stars are grossly outnumbered by the lower-F through upper K group.

I still have a hard time seeing how dim red dwarfs can harbor a new civilization. True, a thick atmosphere can distribute the heat from the sunlit half of the planet to the dark half, but I think that such a planet would have a better chance of being another Venus than another Earth.

I am aware that Mars may have had life at one time, and there could even be alien fish swimming in the waters inside Europa. Again, I prefer to make conservative assumptions. If there really was life on Mars, and if there really is life inside Europa, then that would justify the more optimistic guesses for the ne term of the Drake Equation. However, that would also mean justifying the more conservative guesses for some of the later terms. There's a BIG difference between microbes and the complex life we see on Earth today. All of those extremophiles that live in boiling water, strong acids, strong bases, extreme brine, etc. are microbes.

I'm sure that simple life is commonplace but complex life is much rarer. I think that there are hundreds of millions of worlds in the galaxy with microbes, but only a few percent have complex life. There are so many things that can foil the establishment of complex life: a star that is too short-lived, marginal conditions on the planet, too many mass extinctions from crashing asteroids/comets, too many nearby supernovas, etc.

I can't imagine how we can expect a civilization to form in a brown dwarf, even one at room temperature. A brown dwarf is mostly hydrogen and helium and would have much more in common with a hot Jupiter (or even our own Jupiter) than it would have with the Earth.

Dear Jason Hsu:

On Friday, August 10, 2012 10:07:38 AM UTC-7, Jason Hsu wrote:
I'm not optimistic on the prospects of
interstellar space colonization. First,
there is the Relativity problem,

Not a problem further in, or in clusters, where stars are fractions of a light year apart. *We* are in a special place in that respect... in a sort of void.

and then there is the matter of protecting
occupants from stray atoms and grains of
dust (which would punch holes in the spaceship
near light speed).

Use a linebacker asteroid, no problem. Can even harvest what it collects.

I think that the only thing that would
motivate civilizations to colonize other
star systems is the death of their parent
star.

Look at what has motivated any species to move outside its current environs. Look at what has caused us to populate other continents.

As for metallicity in the early days of the
galaxy, it was mostly confined to the
galactic core, and it took time for the metals
to spread out into the thin disk. So I still
think there's a limit on how early life could
have formed and how early the first
civilizations could have formed.

You stand alone, without substantial support. A water ball could have had nothing much heavier than oxygen, and started life.

It's possible that the evolution of life
is faster on other worlds than it was here,
but I prefer to make conservative
assumptions until they're proven wrong.

.... and even ignore reasonable input, as to how your opinions are too limited.

....
I can't imagine how we can expect a
civilization to form in a brown dwarf, even
one at room temperature. A brown dwarf is
mostly hydrogen and helium and would have
much more in common with a hot Jupiter (or
even our own Jupiter) than it would have with
the Earth.

So? Because Jupiter has little oxygen in its atmosphere, if Europa has oxygen in abundance, so does Jupiter. You are drawing too many lines in the sand based on too little personal research.

Your assertions are describing civilizations we can breed with, rather than all possible civilizations.

David A. Smith

On 09/08/2012 2:42 PM, dlzc wrote:
Dear Jason Hsu:

On Thursday, August 9, 2012 9:39:07 AM UTC-7, Jason Hsu wrote:
...
I've never seen an example of the Drake Equation
in action that took into account the ages of
stars. Remember the 4.6-billion year time lag
between the birth of our sun and the beginning
of our interstellar communication capability.

Was only ~2.2 billion years from the Theia encounter, that wiped out whatever might have been on Earth before.

The Theia encounter (if it happened), would've happened only a few
hundred million years after formation, maybe let's say 4.5 billion years
ago. Pretty much right at the beginning of the formation, so almost no
difference.

But the metallicity in the galaxy may have
been considerably lower in the first 4+
billion years of the history of our galaxy's
thin disk. Additionally, the sun has a
higher metallicity than most other stars its
age.

Since it is a second generation...

It's possible that we are part of the first
group of civilizations to form,

Very doubtful. We are seeing high metallicity in galaxies 500 million years after the Big Bang. So we could easily be 8 billion years younger than the first civilization.

However, they don't exactly know in which part of those early galaxies
that metallicity is showing up. It could be happening entirely within
the inner sections of the galaxy near the bulge, which is a dangerous
place. Once the metallicity spreads to outer parts of the disk, where
orbits are more stable because stars are spread out farther from each other.

and the most vibrant days of the galaxy are
ahead of us.

Let us hope we are equal to the task of watching that come true.

I'm sure at some point the the far outer parts of the galaxies will
become habitable too, not just the middle parts.

Yousuf Khan

On 09/08/2012 12:39 PM, Jason Hsu wrote:
Is it just me, or does it seem that most discussions about the Drake
Equation are overconfident about the number of habitable planets?

It seems to me that too many examples of the Drake Equation in action
don't screen out unsuitable stars. Only lower F-type, G-type, and
upper K-type stars in the main sequence seem suitable. Hotter stars
are too-short-lived, and dimmer stars lack a real habitable zone due
to issues like tidal locking and the impact of solar flares at close
range. Some people say dim orange and red dwarfs (middle K-type
through all type M stars) could harbor a civilization, but I think
that's REALLY stretching things. In my Enhanced Drake Equation
Calculator app (free on Google Play), I give a default value of 10%
as the fraction of stars of the correct spectral type.

I could see some Super-Earths, especially waterworlds, orbiting red and
orange dwarfs at a little further than habitable zone (let's say at the
Mars-analog orbits), which might be able to retain enough greenhouse
warmth from their star, without being too close to get tidally locked,
nor affected by their solar flares. I think perhaps only large red
dwarfs or orange dwarfs need apply, perhaps down to 50% Solar masses at
least.

Also some really large planets might be able to produce a lot of
internal heat that might supplement the heat from a weak star.

I think the definition of a habitable zone itself is fluid, it depends
at least as much on the properties of a planet in that zone as much as
it does on the star. Our comfortable preconceptions of what ranges are
the habitable zone may only be a special case for our solar system.

Most discussions of the Drake Equation omit the Galactic Habitable
Zone. The inner portion of the galaxy is too dangerous, and the
outer portion is short on metals. In my enhanced Drake Equation
calculator, I give a default value of 9% as the fraction of stars in
the Galactic Habitable Zone.

Hard to say how much metalicity is actually needed to form terrestrial
planets. We only know what we see in our solar system and those nearby,
which we can assume may have been formed in similar conditions as our
Sun. However, further out there may be different conditions and they
still may be forming planets.

I've never seen an example of the Drake Equation in action that took
into account the ages of stars. Remember the 4.6-billion year time
lag between the birth of our sun and the beginning of our
interstellar communication capability. If this slow speed of
evolution is typical, then stars younger than our sun are unlikely to
harbor a civilization simply because there hasn't been enough time
yet. Thus, most civilizations would have to orbit stars at least as
old as our sun.

The first 3 billion years was wasted in single-cell form. Complex life
only started about 600 million years ago, probably after the last
Snowball Earth. If other planets undergo quicker transitions from
single-cell to complex life, then they could save upto 3 billion years.

But the metallicity in the galaxy may have been considerably lower in
the first 4+ billion years of the history of our galaxy's thin disk.
Additionally, the sun has a higher metallicity than most other stars
its age. It's possible that we are part of the first group of
civilizations to form, and the most vibrant days of the galaxy are
ahead of us. In my Enhanced Drake Equation app, I give a default
value of 40% as the fraction of stars in the Galactic Habitable Zone
that are old enough to harbor a civilization. Of course, the real
value could be considerably lower.

Don't the Drake equations already have factors to take these into account?

Yousuf Khan

Dear Yousuf Khan:

On Friday, August 10, 2012 6:56:22 PM UTC-7, Yousuf Khan wrote:
....
The first 3 billion years was wasted in
single-cell form. Complex life only started
about 600 million years ago, probably after
the last Snowball Earth. If other planets
undergo quicker transitions from single-cell
to complex life, then they could save upto
3 billion years.

That is probably when the first DNA "virus" infected an RNA host cell. Corresponds reasonably well with the formation of free oxygen (at 500 million years).

If such is drifting on the stellar wind, being in a void as we are, could slow how long it took to get here. Cooler stars might be easier to let this stuff in...

David A. Smith

Yousuf Khan wrote:
On 09/08/2012 2:42 PM, dlzc wrote:
Dear Jason Hsu:

On Thursday, August 9, 2012 9:39:07 AM UTC-7, Jason Hsu wrote:
...
I've never seen an example of the Drake Equation
in action that took into account the ages of
stars. Remember the 4.6-billion year time lag
between the birth of our sun and the beginning
of our interstellar communication capability.

Was only ~2.2 billion years from the Theia encounter, that wiped out
whatever might have been on Earth before.

The Theia encounter (if it happened), would've happened only a few
hundred million years after formation, maybe let's say 4.5 billion
years ago. Pretty much right at the beginning of the formation, so
almost no difference.

The Late Heavy Bombardment era was around 3.8-4.1 billion years ago, maybe
this is what he meant. The Moon was heavily cratered, and presumably so was
the Earth, resetting the clock for evolution of life. The LHB does have
some criticisms that I won't go into, but the Theia event almost certainly
happened very early on and is the only viable explanation so far for the
existence of Earth's large Moon and the similarities of lunar and
terrestrial isotope signatures, for example.


But the metallicity in the galaxy may have
been considerably lower in the first 4+
billion years of the history of our galaxy's
thin disk. Additionally, the sun has a
higher metallicity than most other stars its
age.

Since it is a second generation...

It's possible that we are part of the first
group of civilizations to form,

Very doubtful. We are seeing high metallicity in galaxies 500
million years after the Big Bang. So we could easily be 8 billion
years younger than the first civilization.

However, they don't exactly know in which part of those early galaxies
that metallicity is showing up. It could be happening entirely within
the inner sections of the galaxy near the bulge, which is a dangerous
place. Once the metallicity spreads to outer parts of the disk, where
orbits are more stable because stars are spread out farther from each
other.
and the most vibrant days of the galaxy are
ahead of us.

Let us hope we are equal to the task of watching that come true.

I'm sure at some point the the far outer parts of the galaxies will
become habitable too, not just the middle parts.

Yousuf Khan

--
Mike Dworetsky

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