Earth is rare

[mooware]

http://www.space.com/scienceastronomy/rare_earth_040803.html<br /><br />It seems to me that it's just as much conjecture to say earth is rare, than to say earth is common.<br /><br />We only have about 100 extrasolar planets to gauge on. What our Galaxy has something like 400 billion stars?<br /><br />

 

[5stone10]

Sure - you could take either polar opposite position - Rare Earth vs. Common Earth, and stick to it to the bitter end.<br /><br />But why be so boring !

 

[mooware]

As with most things it's probably someplace in the middle. Not to common, but not too rare.<br /><br />Kinda like lukewarm water. lol..<br /><br />

 

[fortytwo]

These two stories (out on the same day) are SO DIFFERENT it's almost comical...heh, you can even see the difference in the links.<br /><br />http://www.space.com/scienceastronomy/rare_earth_040803.html<br /><br />http://www.space.com/scienceastronomy/mars_microorganisms_040803.html<br />

 

[5stone10]

Actually I'm talking about the position papers/books that are already out there - to the point where I'm ready to puke.<br /><br />There are any number of people who are positioning themselves to be able to say "I told you so" - when there is barely any hard data in yet. <br /><br />As 42 points out above - it is almost comical.

 

[summoner]

My problem with the first "rare earth" article is that the data set they use may be very skewed to begin with. They admit that most of the planets that we have found are giants orbiting near the star. Once we have a more complete look at many different solar systems then we can make a much more accurate prediction. <div class="Discussion_UserSignature"> <p> </p><p> </p><p> </p><p> <br /><table cellpadding="0" cellspacing="0" style="width:271px;background-color:#FFF;border:1pxsolid#999"><tr><td colspan="2"><div style="height:35px"><img src="http://banners.wunderground.com/weathersticker/htmlSticker1/language/www/US/MT/Three_Forks.gif" alt="" height="35" width="271" style="border:0px" /></div>

 

[mooware]

Agreed. We just don't have enough to go on to say one way or the other.<br /><br />Although, i think it's reasonable to assume that Earth is not the only habitable planet in the entire universe.

 

[qzzq]

And we want earthlike planets, because they may harbor (intelligent) life, but maybe most life in the Universe can be found on the moons of the Jupiters they keep finding. Maybe it's only a sum of a couple of factors; liquid water/warmth, the right chemical composition, enough gravity to hold an atmosphere and not too many extinction level events. Hmmm, that last one will be tough next to a gas giant who acts like the system's vacuum cleaner...<br /><br />O well, 1 percent of all the stars in the Universe is still a staggering number of opportunities.<br /><br />We need bigger and better (space) telescopes. Then the hunt for earthlike planets can truly begin. <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>

 

[aaron38]

The point of the article didn't seem to be so much that the Earth itself is rare, but that the basic design of our solar system is rare.<br /><br />Are they saying that there's absolutely no way a system can have a habitable world if it has a hot Jupiter? Do we know enough yet to make such a bold statement?

 

[projectorion]

It looks like Stars rich in metal are most likely to harbor planets but our direct knowledge of extrasolar systems is restricted to Gas Giants. In fact Gas Giants so big they are virtually proto-suns. Until we have a better picture of terrestrial planetary formation its all just educated guesswork. The rarity of Earths would however explain the fact that ET isn't knocking on our door. The universe is still young and wild. Civilisations meeting one another are probably still very rare events. Perhaps a good thing for us.

 

[qzzq]

<i>Are they saying that there's absolutely no way a system can have a habitable world if it has a hot Jupiter?</i><br /><br />No, a Jupiter in any system is a good thing, but for terrestrial planets, with the right conditions for liquid water - the star's habitable zone- , to evolve, that Jupiter needs to be at some distance from its parent star. The extra-solar planets we've found so far are orbiting their star at a too close a distance, making it unlikely a earthlike planet could survive, being caught between the star's and the gas giant's gravity. <br /><br /><i>Do we know enough yet to make such a bold statement?</i><br /><br />As far as I know, detection of these planets is more indirect than direct. You can measure the wobble a star experiences when a massive object orbits it. Another means of detection is when a gas giant passes its parent star and blocks it light somewhat. This way, <i>only</i> massive planets can be detected. So yes, it might be far too early to say anything that in hindsight makes sense. <div class="Discussion_UserSignature"> <p> </p><p>***</p> </div>

 

[aaron38]

Okay, let's say the solar system formed differently. Jupiter formed closer in, in the habitable zone. So yes, this would prevent an Earth from forming.<br /><br />But Jupiter has lots of moons and we would have to assume that the extra-solar hot Jupiters would have some moons as well. Those moons would then be in the habitable zone correct?<br /><br />So while you won't get an 'Earth', you might still get habitable worlds.

 

[fortytwo]

I think gas giants need to be further away from the sun or they would lose most of their atmosphere to solar wind. <br /><br />There was a theory that only small rocky planets are close to the Sun and gas giants farther away, but the discovery of Pluto kinda shot a hole in this.

 

[g_riff]

There may be many moons in the habitable zone, but I suspect that a large Jupiter planet would gravitationally attract too many asteroids for its moons to have a stable enough environment. There would just be too many impacts on the moons. Besides, if moons were easily habitable, I would suspect us to find ourselves inhabiting one such moon, since they must be far more numerous throughout the universe. But we're not, which adds to my suspision that moons aren't habitable. <br /><br />As for how rare an earth-like planet may be, I think the study the OP linked to would be valid if Jupiters like ours were just as easy to find as hot Jupiters, but I don't think they are, and that skews the data. There could be a lot more undiscovered "cold" Jupiters than hot ones. Personally, though, I think that there are a lot of very specific factors that are required to produce a planet capable of evolving complex lifeforms. Probably a lot more factors than we even know of yet. Which makes me think that other earths may be very rare.

 

[g_riff]

>Not a good argument; by this reasoning you might wonder why everyone on Earth is not a member of the largest nation, China. <br /><br />Well, if China had, say, 100 billion people, and the rest of the world only had 100 million, then I would be very surprised not to find myself a member of that nation. But China doesn't even have a majority of the world's population, so it's not surprising at all that I'm not from there. I believe my reasoning stands, at least assuming that there are far more moons in the universe than terrestrial planets. It's called the anthropic principle. <br /><br /> />I tend to agree, but there is very rare, and very very rare. If there is one Earth per million stars, that would make a couple of hundred thousand Earths in our galaxy alone. <br /><br />I agree, our universe is incredibly vast, so there are probably lots of earths out there. However, even one in a million seems very optimistic to me - if you consider that most stars aren't suitable and that many parts of the galaxy are unsuitable, I think there may be fewer earths in this galaxy than most people realize. Of course, all of that is speculation. There is no way, right now, to know for sure.

 

[kmarinas86]

I think that the number of habitable planets are much greater if we go beyond the number of planets where life has evolved. A highly advanced civilization could turn a few moons around their gas giant into an earth-like planet. However much time it takes, an advanced civilization would have the necessary technology and scientific knowledge to start new humanities, etc. in other star systems.

 

[aries4548]

...the only reason that Earth-like conditions enter into the scenerio regarding 'other life is that is the only life we know. There is one, and only one fact regarding life in the Universe. It has occurred once. We do not have the slightest idea what to even look for. What would radio signals mean, hopefully 5 light years worth of television signals have not been picked up, that would be embarressing! It is questionable that carbon based life is the only life to ever have proliferated on this planet. We're talking the Universe here people, let us not delude ourselves about what we actually know. How many places in the Universe support life? Of those, how many developed intelligent(of any kind) life, of those, how many became technologically advanced, of those, how many developed the capability to annihilate themselves, of those, how many remain? And one last thought. If an Advanced Other Life observed Earth for a lunar cycle or so, what would they see, and what would be the incentive to make contact?

 

[mooware]

Well, in short I really think given the vastness of the universe it's impossible to say earth is rare, as it is impossible to say earth is common.<br />

 

[mooware]

On another note.<br /><br />Let's take this on a more "local" level. Let's confine our search for the probability for earth like planets within 20ly of our location. <br /><br /><br /><br />

 

[aries4548]

...I agree with everything you say, assuming it is prefaced with: to the best of our knowledge.

 

[nexium]

Hi steve: I agree, Wheel stations and similar unattached habitats have some advantages. Planets, mid size moons asteroids and comets also have some advantages. Perhaps most important is a very large supply of raw materials, and a good heat sink to get rid of waste energy.<br /> Suppose we gentically modify humans so they can thrive at 1/15 th bar = 1 psi mostly oxygen. If the presurized interior of the space habitat is one billion square inches, divide by 12 squared =6,944,444 square feet. That will comfortably accomodate less than 100 humans long term/not enough to do big, complex projects. The total pressure is 1/2 million tons, trying to burst the habitat. This does not make for thin, light weight construction, especially if we want a large safety factor and considerable resistance to radiation and micro meteorites. Technology of the next decade will put a dent in some of these problems.<br /> 100 feet below the surface of an asteroid, solves most of these problems and the walls are raw materials. Neil

 

[thnkrx]

I ran a sort of back of the envelope calculation on this, using Tarter&Turnbulls `HabCat' as a base, which claims something on the order of 12,000 `habstars' within a 450 lightyear radius. Because of issues of massive radiation near the galactic core and reduced metallicity for stars out at the galactic fringe, Habstars are thought to orbit about the galactic center in a sort of `belt' or band something on the order 5000 lightyears `wide' and 20,000 lightyears from the galactic center. Taking the Habcat as a base, turning the area represented from a sphere into a cube (almost doubling the area and number of Habstars within), then this band would have 12000x2=24,000x5=~125000 habstars per 900 lightyear `slice'. (Stellar distribution, age, and tye varies even within this habitable belt.) The number of Habstars for the galaxy overall comes into the 10's of millions range - and this is actually being conservative.<br /><br />Murmers from the planet hunters seem to be that about half of these stars will actually have planets. About 10% of the 130+ planets discovered so far have stable orbits that would permit the formation and stable existence of terrestrial planets in that systems habitable zone. Turnbull and Tarter state that some systems with hot jupiters are also candidates, though we'll leave them out for the time being, and the planet hunters seem to be thinking that there are many more systems with worlds in stable orbits at acceptable distances - but we'll leave those out as well. Hence...figuring 10 million possible Hab stars, half with planets - thats five million. Ten percent of that comes out to around 1/2 million systems that could have terrestrial planets in stable orbits at acceptable distances (in the habzone). <br /><br />

 

[nexium]

I agree: For 5 or ten inhabitants with back up supplies for 5 or 10 months. With present technology the mass of wall, floor and ceiling materials needed increases with the square of the number of inhabitants, perhaps even faster employing the colonists in large scale projects inside the habitat. Neil

 

[nexium]

While it is true, we can travel between habitats with a billionth the mass of a planet with much reduced energy, it is typically at very low relative speed, and time is money even for machines, unless they have life expectancies of thousands of years, with only rare, low cost mantainance. Recent man made structures and machines have rarely remained viable even one century, but I don't think we have to do planned obsolesence.<br /> A craft leaving a habitat following Earth by 60 degrees, needs to accelerate perhaps 10,000 miles per hour to get to the habitat following Venus by 60 degrees in 10,000 hours, then use fuel to slow down a bit to make a gentle landing as areo braking is not possible. For some departure dates the path will be longer than 100,000,000 miles, especially if the initial accelleration is to less than 10,000 miles per hour. If we wish to make this trip in a week instead of a year, enormous amounts of energy are needed even though the gravity wells are close to negligible. Sorry about the over simplified navigation.<br />To get to a habitat 59.999 degrees behind Earth takes little time or energy, but is it practical to station keep habitats that closely spaced in solar orbit? Neil

 

[spayss]

"First we got rid of geocentrism with Galileo and Kepler.Then we got rid of homocentrism with evolutionary facts. Now we have to get rid of geocentrism. "<br /><br /> The logic is a false one and not scientific. Just because a or b has been proven false it doesn't make c any more or less false.<br /><br /> (just being picky) Otherwise, interesting posting.