Earth - Moon System
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Astrobiology, Extrasolar Planets, milky way, SETI

If the Earth is Rare, We May Not Hear from ET

8 Feb , 2010 by

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If civilization-forming intelligent life is rare in our Milky Way galaxy, chances are we won’t hear from ET before the Sun goes red giant, in about five billion years’ time; however, if we do hear from ET before then, we’ll have lots of nice chats before the Earth is sterilized.

That’s the conclusion from a recent study of Ward and Brownlee’s Rare Earth hypothesis by Duncan Forgan and Ken Rice, in which they made a toy galaxy, simulating the real one we live in, and ran it 30 times. In their toy galaxy, intelligent life formed on Earth-like planets only, just as it does in the Rare Earth hypothesis.

While the Forgan and Rice simulations are still limited and somewhat unrealistic, they give a better handle on SETI’s chances for success than either the Drake equation or Fermi’s “Where are they?”

“The Drake equation itself does suffer from some key weaknesses: it relies strongly on mean estimations of variables such as the star formation rate; it is unable to incorporate the effects of the physico-chemical history of the galaxy, or the time-dependence of its terms,” Forgan says, “Indeed, it is criticized for its polarizing effect on “contact optimists” and “contact pessimists”, who ascribe very different values to the parameters, and return values of the number of galactic civilizations who can communicate with Earth between a hundred-thousandth and a million (!)”

Building on the work of Vukotic and Cirkovic, Forgan developed a Monte Carlo-based simulation of our galaxy; as inputs, he used the best estimates of actual astrophysical parameters such as the star formation rate, initial mass function, a star’s time spent on the main sequence, likelihood of death from the skies, etc. For several key inputs however, “the model goes beyond relatively well-constrained parameters, and becomes hypothesis,” Forgan explains, “In essence, the method generates a Galaxy of a billion stars, each with their own stellar properties (mass, luminosity, location in the Galaxy, etc.) randomly selected from observed statistical distributions. Planetary systems are then generated for these stars in a similar manner, and life is allowed to evolve in these planets according to some hypothesis of origin. The end result is a mock Galaxy which is statistically representative of the Milky Way. To quantify random sampling errors, this process is repeated many times: this allows an estimation of the sample mean and sample standard deviation of the output variables obtained.”

Forgan simulated the Rare Earth hypothesis by allowing animal life – the only kind of life from which intelligent civilizations can arise – to form only if homeworld’s mass is between a half and two Earths, if homesun’s mass is between a half and 1.5 times our Sun’s, homeworld has at least one moon (for tides and axial stability), and if homesun has at least one planet of mass at least ten times that of Earth, in an outer orbit (to cut down on death from the skies due to asteroids and comets).

The good news for SETI is that a galaxy like ours should host hundreds of intelligent civilizations (though, somewhat surprisingly, there is no galactic goldilocks zone); the bad news is that during the time such a civilization could communicate with an ET – between when it becomes technologically advanced enough and when it is wiped out by homesun going red giant – there are, in most simulations, no other such civilizations (or if there are, they are too far away) … we, or ET, would be alone.

But it’s not all bad news; if we are not alone, then once contact is established, we will have many phone calls with ET.

To be sure, this is but a work-in-progress. “Numerical modeling of this type is generally a shadow of the entity it attempts to model, in this case the Milky Way and its constituent stars, planets and other objects,” Forgan and Rice say; several improvements are already being worked on.

Sources: “A numerical testbed for hypotheses of extraterrestrial life and intelligence” (Forgan D., 2009, International Journal of Astrobiology, 8, 121), and “Numerical Testing of The Rare Earth Hypothesis using Monte Carlo Realisation Techniques” (arXiv:1001:1680); this too will be published in IJA, likely in April.

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By
Hi! When I was only six (or so), I went out one clear but windy night with my uncle and peered through the eyepiece of his home-made 6" Newtonian reflector. The dazzling, shimmering, perfect globe-and-ring of Saturn entranced me, and I was hooked on astronomy, for life. Today I'm a freelance writer, and began writing for Universe Today in late 2009. Like Tammy, I do like my coffee, European strength please. Contact me: [email protected]



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The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
February 8, 2010 6:12 AM
Your quote says; “The Drake equation itself does suffer from some key weaknesses: it relies strongly on mean estimations of variables such as the star formation rate [SFR];” The only reason this was originally in the Drake equation is simply that planets need stars, and if the SFR is high, therefore there are more planets. IMO the complexity here is mostly in our understanding the stages of evolution of the SFR overtime in galaxies. Where the planet being formed are mostly after several generation of stars so the metal content (elements heavier than hydrogen and helium) of the galaxy is high enough so rocky Earth-like are able to form. Over time, the SFR decreases or declines in number… Read more »
gopher65
Member
gopher65
February 8, 2010 6:57 AM

I’ve seen articles recently that claim that life is less likely to evolve on planets that are less than ~2 Earth masses due to the inherent axial instability of such planets and the lack of ease of plate tectonics being maintained for a reasonable amount of time *cough*Venus*cough*.

In fact, the articles are claiming that Earth itself might be a special case, where a low-mass planet was able to form life due to unusual circumstances (a large moon to stabilize the axis, etc).

I wonder how this would have affected their simulation, if at all? Are higher mass planets less likely to form, more likely, or about the same?

Molecular
Member
Molecular
February 8, 2010 7:29 AM

I find it easier to go with the thought that for every star that shines in the night sky, there’s a distinct probability that, it too, has a solar system with planets, and on one of those planets (not necessarily Earth-sized), there’s a good chance that it has some form of life, be it intelligent, or not.

We are wasting less time exploring the REAL Universe, rather than inputting values into a simulation, while lacking knowledge about how life can even come into to being.

One can point in the direction that clearly indicates the prospects of a drinking fountain, or, dry up completely thinking that boulders act as sponges holding lakes. smile

Aqua4U
Member
February 8, 2010 10:33 AM

IF Earth is the rarest and ONLY ‘advanced’ civilization in our galaxy.. there are still quite a few other galaxies out there! In which, faster than light inter-dimensional communication or travel may have been developed? Then the rarity of advanced lifeforms might make communications all that much more precious and sought after?

Aqua4U
Member
February 8, 2010 10:37 AM

At least.. that’s what my ‘spirit guides’ tell me.

CrazyEddieBlogger
Member
February 8, 2010 7:53 AM
There’s a big piece missing IMO, which is what happens to a civilization after it achieves interplanetary travel, and before its star dies out. While I do suspect that meaningful interstellar travel is impossible, long-term colonization is not technically impossible – hibernation + travel at even 1% the speed of light are not impossible. If you do the math on this hypothesis (assume 5000 years to make an interstellar hop, and 5000 years to boot a colony so it can spawn again), you’ll find out that the first species to achieve these technologies will populate the galaxy within an evolutionary blink of an eye. Which means the civilizations in the galaxy (which will be divergent from a common… Read more »
CrazyEddieBlogger
Member
February 8, 2010 8:00 AM
oops, didn’t finish typing… So the bottom line from this is that the first species to achieve these technologies “wins”, though there are interesting variations on what happens next, still within the bounds of the hypothesis. (and it works even for slower travel time – even for 0.1% speed of light travel) What it doesn’t cover, and we have no way to imagine, is what happens after long period of technology. We’re obviously living in very interesting times – we only developed math and science 300 years ago. We can’t imagine what happens after 3000. If scientific discoveries continue at the current rate, then we might be teleporting across the galaxy. If basic scientific discovery dries up and… Read more »
SteveZodiac
Member
SteveZodiac
February 8, 2010 9:04 AM

The factors we needed to get where we are are so many I could almost (stress, almost) feel sympathy for the creationists.

Slow burning G2 star
Planets at all
Goldilocks planet position
Unusually large moon for Axial stabilising,
Plate tectonics
Inexplicably large amounts of water
Iron core dynamo for radiation shield
Jupiter keeping large rocks away
several attempts over a billion years at decent oxygen levels

and there are more I can’t think of ATM

Lawrence B. Crowell
Member
Lawrence B. Crowell
February 8, 2010 9:07 AM
There are other factors as well. These include stellar systems of planets which can support a stable orbit of a planet in the “goldilocks zone.” A gas giant who’s orbit is less than 3AU from a G-class star would exert too great a perturbation on the orbit of a 1AU terrestrial planet. From extrasolar systems found so far the statistics on Lyapunov exponents (chaos time parameters of sorts) on extrasolar system data does not look very favorable. I wrote a paper on this and a version is in my book on the physics of interstellar probes. I estimate there are only around 1000 planets at all similar to Earth in the galaxy. As for intelligent life or civilizations… Read more »
CrazyEddieBlogger
Member
February 8, 2010 10:46 AM

I think requiring a large moon and other such mechanisms is over-doing it.

I can see how some other civilization that grew on the “equatorial” ring of a gravitationally locked planet will argue that that’s the only way to evolve life, since a rotating planet will have extreme “day-night” cycle that will SURELY prevent any organism from developing.

Or, a civilization in a super-Earth imagining that the levels of radiation we tolerate here will SURELY kill any complex life form, and so life can only develop on massive planets with soupy atmosphere.

I like the wider definition of habitable, which is supporting the conditions for complex chemistries.

Lawrence B. Crowell
Member
Lawrence B. Crowell
February 8, 2010 10:49 AM

Faster than light comunications and travel are very unlikely. This violates a whole lot of things. Maybe then again the problem is:

LC

CrazyEddieBlogger
Member
February 8, 2010 11:21 AM

Hehe LC… I can watch that clip endless times…

The extra touch above and beyond the text is just so delicious…

Aqua4U
Member
February 8, 2010 2:52 PM

LC… LOL! Been there, done that.. remember the ‘Meat Puppets’?

A gold fish in a small bowl might think the laws of physics were very limited.. if he could think? Thing is, that gold fish is alive, and therefore possesses SPIRIT in a body, which is infinite…. so he doesn’t worry about how big his universe is.

ND
Member
ND
February 8, 2010 1:07 PM

Putting aside the violation of physics as we know it, I think a lot of people are assuming faster than light travel and communications will make large distances irrelevant. There might be limitations to it as well where FTL communications with other galaxies could take hundreds of years, as if communicating with systems in our galaxy. Also if there is FTL communications going on right now, we most likely cannot pick up on that. But then again the rather solid physics we understand make this a moot point.

But, our wishes and desires of space travel wants FTL.

mrdpearl
Member
mrdpearl
February 8, 2010 1:33 PM

Well, as Carl Sagan said in his TV series Cosmos: “Somebody has got to be first”
The mirth I find in discussing “other” life forms on “other” planets is that we are not certain how it all started here in the first place!

Vedic
Member
Vedic
February 8, 2010 1:34 PM

Arthur C. Clarke I think put it very well:

“Either we are alone in this Universe or we’re not, and both possibilities are terrifying.”

Drunk Vegan
Member
February 8, 2010 1:38 PM

“And even with a recovery after then the increased solar irradiance will be 700 million years start to make things a bit too toasty for complex life. By 1.5 billion years Earth will start to look a whole lot like Venus.”

If we haven’t figured out how to successfully colonize and terraform other planets 700 million years from now, or at the very least, bump Earth’s orbit a bit to cool it down, or, heck, even re-engineer the sun – well, then of course we deserve to die.

Of course it won’t be *humans* who are facing that dilemma in 700 million years, it will be a species descended from us, and probably heavily genetically engineered.

Andy F
Member
February 8, 2010 2:26 PM

The Universe continues to throw shocks and surprises at us. Hence, I don’t think there is any reason for life, intelligent or otherwise, to exhibit attributes or requirements that our common sense dictates it should possess.

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