Weekend Feature: "Dead Zones of the Universe" --Do They Support the 'Rare Earth' Theory?

 

          


While the Kepler Space Telescope has discovered 3,030 exoplanets with 709 confirmed that revolve around a star, new findings from diverse fields are being brought to bear of the central questions of the 21st century: How common is life in the universe? Where can it survive, Will it leave a fossil record? How complex is it? The list below moves several key features of the Universe off the chart of likely places to search for life.

In stark contrast to the optomism underlying the Kepler Mission, the zones and regions of the known Universe listed below are the ones that astrobiologists have concluded have little or zero chance of supporting life as we know it. The listing of "dead zones" was compliled for Rare Earth -- Why Complex Life is Uncommon in the Universe by University of Washington scientists Peter D. Ward (Professor of Geological Sciences and Curator of Paleontology) and Donald Brownlee (Professor of Astronomy and member of the National Academy of Sciences).

Early Universe: The most distant known galaxies are too young to have enough metals for formation of Earth-size inner planets. Hazards include energetic quasar-like activity and frequent super-nova explosions.

Elliptical Galaxies: Stars are too metal-poor. Solar mass stars have evolved into giants that are too hot for life on inner planets.

Globular Clusters: Although they contain milllions of stars, the stars are too metal poor to have inner planets as large as Earth. Solar mass stars have evolved to gaints that are too hot for life on inner planets.

Small Galaxies: Most of the stars are too metal deficient.

Centers of Galaxies: Energetic star building and black-hole processes prevent development of complex life.

Edges of Galaxies: Most stars are too metal poor.

Planetary Systems with "Hot Jupiters": Inward spiral of the giant planets drives the inner planets into the central star.

Planetary Systems with Giant Planets in Eccentric Orbits: Unstable environments. Some planets lost to space.
Future Stars: Uranium, potassium, and thorium too rare to provide sufficent heat to drive plate tectonics.

The "Rare Earth" theory says that there is no hope of finding alien life in space because conditions on all other planets are too hostile, according to Howard Smith, a senior astrophysicist at Harvard. Smith made the claim after an analysis of the 500 planets discovered outside our Solar System that showed that extreme conditions are likely to be the norm, and that the hospitable conditions on Earth could be unique.

“We have found that most other planets and solar systems are wildly different from our own. They are very hostile to life as we know it,” he said.

Smith pointed to stars such as HD10180, which sparked great excitement when it was found to be orbited by a planet of similar size and appearance to Earth, but turned out to be superficial similarities. The planet lies less than two million miles from its sun, meaning it is roasting hot, stripped of its atmosphere and blasted by radiation. Many of the other planets discovered to date have highly elliptical orbits which cause huge variations in temperature which prevent water remaining liquid, thus making it impossible for life to develop.

Claiming that we're the only life in existence is a combination of ignorance and self-importance that should have a livejournal, not a scientific journal.  The important work is getting ourselves out there and seeing who and/or what we can find.

Recent figures place the total number of stars in the Milky way at an astounding three trillion.  Which leads to this question, given such a ginormous figure, what does it mean to be rare? Even if the Earth is a one in a million occurrence, that means there are still 3 million Earthlike planets in the Galaxy (assuming one Earthlike planet per star).

On the other hand, if the Earth is a one in a billion occurrence, then there are still 3,000 Earths in the Milky Way. 

We also have to keep in mind that the 3 trillion stars only accounts for what exists right now. There have been well over a billion trillion stars in our past Universe. As Charles Lineweaver  of the Planetary Science  Institute  and the Research School of Astronomy and Astrophysics  at the Australian National University has noted, planets began forming in our Galaxy as long as 9 billion years ago. We are relative newcomers to the Galaxy.

Recent breakthreoughs in the chemical analysis of the Universe suggests that we live in a Universe exceedingly friendly to life. What we see in the physical laws and condition of the Universe runs contrary to the expectations of the "Rare Earthers."

Indeed, we are discovering that the Galaxy is littered with planets. Scientists have already cataloged well over 500  extrasolar planets -- a number that increases by a factor of 60 with each passing year. Yes, many of these are are so-called "hot Jupiters," but the possibility that their satellites could be habitable cannot be ruled out. Many of these systems have stable circumstellar habitable zones.

And shockingly, the first Earthlike planet was discovered in 2007 orbiting the red star Gilese 581. It's only 20 light-years away, 1.5 times the diameter of Earth, is suspected to have water and an atmosphere, and its temperature fluctuates between 0 and 40 degrees Celsius.

If we are one in a billion, then, and considering that there are only 0.004 stars per cubic light-year, what are the odds that another Earthlike planet is a mere 20 light-years away?

Indeed, given all this evidence, the Rare Earthers are starting to come under attack. Leading the charge these days is Alan Boss who recently published The Crowded Universe. Boss estimates that there may be billions of Earthlike planets in the Milky Way alone.

"I make the argument throughout the book that we already know that Earths are likely to be incredibly common -- every solar-type star probably has a few Earth-like planets, or something very close to it," says Boss. "To my mind, at least, if one has so many habitable worlds sitting around for five billion or 10 billion years, it's almost inevitable that something's going to start growing on the majority of them."

The Kepler space telescope has mapped more than 1,200 planets in one tiny corner of our Milky Way Galaxy. Based on that sample, scientists say that there are approximately 50 billion planets in the entire galaxy based on a conservative estimate of one planet per star in the galaxy, including 500 million that are theoretically capable of sustaining life.

In astronomer Milan Cirkovic's view, truly advanced technological civilizations (ATCs: those who survive the bottleneck presented by the threat of self-destruction through warfare or asteroid impact or other accidents) will tend to be located at the outskirts of the Milky Way. The very traits that make  ATCs capable of migrating and utilizing resources with high efficiency will tend to make them systematically hard to detect from afar.

Benjamin Zuckerman, an astrophysicist and a professor in the Department of Physics & Astronomy at UCLA, proposed in 1985 that stellar evolution of stars far older than our Sun is an important motivation for civilizations to undertake interstellar migrations.  It seems implausible that any but the most extreme conservative societies would opt to wait to be forced to migration by slow and easily predictable process such as their star leaving the Main Sequence.

Kepler has discovered over 3,000 exoplanets in alien star systems, in an area that represents around 1/400th of the Milky Way. By extrapolating these numbers, the Kepler team has estimated that there are at least 50 billion exoplanets in our galaxy -- 500 million of which sit inside the habitable "Goldilocks" zones of their suns, the area that is neither too hot nor too cold to support life.

Astronomers estimate that there are 100 billion galaxies in the Universe. If you want to extrapolate those numbers, that means there are around 50,000,000,000,000,000,000 (50 quintillion) potentially habitable planets in the universe.

What do you think?

The Daily Galaxy via planetquest.jpl.nasa.gov

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Comments

[Pete]

I believe ATC's have already sent robotic probes to investigate our planet. Thats why people see UFO's.

[prizm1]

The common view in all this is that if we only had a star ship that we would be able to resolve this question by "getting out there".

The real problem is not in having a star ship that could travel across the galaxy in a relatively short period of time, but in knowing which direction to go. Contrary to the sense that most people develop from watching Sci Fi space shows on a constraining 2D video screen, space is unfathomably and incomprehensibly vast. The volume of the Milky Way alone is sexdecillion (10^51) cubic miles.

That is 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 cubic miles.

Even if three million earth-like planets exist in this galaxy, finding such such a world with common-intelligent life would be nearly impossible. Lets say that we travel in our new star ship to the other side of the galaxy in our search for common intelligent life. If we were off by a mere thousand light years from a planet with common-intelligent life but we find no signs of intelligent life at that point in space, which direction do we then elect to go in to continue our search? We may head off in a direction taking us 5000 light years in the opposite direction from that planet. Of course, we may go in a direction where life is theorized to possibly exist, but there is no guarantee that life would actually exist there. Or life could exist there, but has not yet evolved beyond that of slugs crawling across rocks. Or we may find evidence that some kind of intelligent life did exist there once, but never evolved beyond a Type 0 civilization and that they ended up destroying themselves and their planet. Or intelligent life did exist there, but has evolved far past our ability to communicate with and, for all intended purposes, does not exist to us -- how often do you communicate with an ant?

If we are lucky, we might discover another common-intelligent species after a half-a-million years of traveling and mapping the galaxy in our star ship. To be able to do this would require that mankind maintain a mapping of the search over a half-a-million year time span, in order to eliminate the waste of time in searching "where some one has searched before". How would this information be maintained over a half-a-million years? Even our most robust data storage methods today cannot retain data for more than a few centuries. Add to this the inevitability of many future tumultuous human social upheavals that endanger the most robustly kept information and data. Remember the Library of Alexandria? It stood only for three hundred years before being burned to the ground. So, if such a map of mankind's search around the galaxy for common-intelligent life were maintained for only 10,000 years before becoming lost, the search would then have to begin anew.

All-in-all, I believe that there are probably millions of common-intelligent worlds in our galaxy alone, but the likelihood of our civilization ever finding more than one of those worlds in the entire history of our human species is virtually non-existent merely because of the vast and incomprehensible size of space.

[Cato]

'incomprehensible size of space', that is what the distance to the Moon seemed to a roman galley. If they knew how far the Moon was. Which they did not. So, he is just like a monkey, swinging from a branch, howling nonsense.

What I am objecting to, is the sense of certitude and righteousness of some of these fellows. To put it bluntly we do not know, and many aspects of what the future may hold, are counter intuitive :-)

[Matt Rhodes]

Dead zones are exactly that - conditions are to inhospitable for life to develop. There may only be a handful of habitable systems in any given galaxy, even if that galaxy has 400 billion stars. The odds are just stacked AGAINST life. The environments are pretty stark and unforgiving.

[radtech]

For starters, assuming you had such a starship, you would probably not want to send it off in some random direction. Rather, you would likely want to send it towards a destination where something of interest (say, a star with a spectral type between F5 and M5) is located, which would significantly reduce the volume that needed to be searched (and, thereby, the time required to search that volume).

Second, though I'm not certain what is meant by "common-intelligent life," though I suspect it refers to life that is as intelligent as modern-day humans on Earth, I don't believe the odds of finding another intelligent species at or near our levels of scientific and/or technological achievement is very likely. Statistically speaking, given that intelligent life may have begun to appear some five billion years ago, most intelligent species that have formed civilizations of some sort or another will either be significantly more advanced or much less advanced than ourselves. If one considers only that life which has not attained sapience, then odds are that it is nearly ubiquitous throughout the Galaxy, with virus-like and single-celled organisms being the most common examples.

Finally, as to the durability of data storage media: Humans have been recording and storing data for many tens of thousands of years (a lunar calendar painted on a cave wall in Lascaux, France has been attributed to the Aurignacian Culture that lived in Europe some 32,000 years ago). Aside from this example, many inscribed clay tablets made by the ancient Sumerians several thousand years ago have been found in what is now Iraq. If there is a need to preserve data for astronomically significant periods of time, then inscribed sheets of lead could be bound into extremely long-lived "books" that could, depending on where and how they were stored, outlive most main-sequence stars. The first "chapter" or so could describe the contents of the tome, its purpose, and a graphic guide to its translation for far-future readers. Such a record would not be as accessible or user-friendly as, say, a compact disk, but it might serve as a "reference standard" much like the standard metric measures kept in Paris.

[prizm1]

In response to radtech:

I could not imagine how within the evolutionary lifetime of any sentient species that one sexdecillion(10^51) cubic miles could be closely mapped and scrutinized to verify the existence of another sentient civilization. Sure, in the future we will have quantum computers that could analyze an entire universe of data, but the collection of the data must first occur. The process (energy) involved in traveling to, or remotely collecting a galaxy of data to be analyzed and verified, is unimaginable, even with the advent of quantum computing.

By common-intelligent life I mean sentient life that we could actually communicate with, no matter what biological or synthetic form the sentient life may have.

The ancients knew in which direction to point at the moon. But, if I scatter three million “needles” around a one sexdecillion cubic mile galaxy and ask you to point in the direction of where any one of them could be located, in which direction would you know to point to? Just because you may think that a certain location is a likely area where a needle may be located does not mean that one is there, since there would be billions of other likely locations as well. Also, our point of determination is severely limited to our relatively fixed point of observation from the Earth's location at the rim of the galaxy. How within the existence of any sentient species could all these likely locations be journeyed to for up close examination and verification?

Three million sentient civilizations probably exist. We have and will continue to find planets in the goldilock zone, although I predict that the chance of finding one that harbors one of the estimated three million common-intelligent civilizations scattered around the galaxy is extremely unlikely considering the vast size of this galaxy.

I iterate that sci-fi shows have conditioned the public into the false perception that the dimensions of the galaxy are just a few scales of order to that of the dimensions of their video screens (what's the chance that Captain Kirk would randomly encounter Harry Mudd twice in a lifetime of space travel?). This has skewed the perception of the actual size of space and it has unrealistically enhanced the view of the actual probability of discovering other common-intelligent or developing
extraterrestrial civilizations.

There is one possible method of data storage that could maintain integrity over time – DNA data encoding. As long as the human race exists, data encoded into our unused DNA structures would pass from generation to generation, thus ensuring a continuity of maintainable data throughout the existence of the human species.

[starfox]

do you understand what "prove" means?

[Bob Greenwade]

I do doubt that the figures provided in Rare Earth "prove" the Rare Earth Theory. They support it, but they don't "prove" it.

The conditions for life to exist on a planet are fairly simple, but recent developments have shown that conditions needed for complex life (that is, organisms above the microbial level) are quite rare. We need not just an appropriate temperature and the presence of water, but also a strong magnetic field, a moon large enough to generate tides, a gas giant positioned to clear out comets and asteroids that are prone to causing mass extinctions, and many more features.

The vastness of the Milky Way, as pointed out, means that there are plenty of stars to choose from. For any given star, the odds are massively stacked against complex life, but there are enough stars out there that the odds are also massively stacked in favor of it existing in several dozen, if not several hundred, planets in the galaxy. And that's just thinking of complex life that can exist in an environment that we can survive.

The big question, of course, is: among these planets, how common is human-level intelligence? Some think that it's nigh-inevitable. While I tend to agree that it's inevitable given enough time, I think it's an unlikely result in any given ecosystem.

Then again, Dr. Michio Kaku (among others) has pointed out some obstacles that a sapient species must overcome to fully mature as a species. One is ecologic change: will the species pollute its environment to the point that it becomes no longer livable? A second is war, with the development of weapons of mass destruction: will cultural hate, combined with the ability to destroy huge parcels, likewise destroy the species' habitat?

A third obstacle is the galactic environment -- events that are beyond the species' control. What's to say that a sapient species won't be wiped out by anything from a meteor strike to a gamma-ray burst? These things can happen with little to no warning, and can destroy a civilization if it happens before said civilization reaches the stars.

This is why I think we're probably the only sapient species in the Milky Way. There are probably others in other galaxies -- and I think Triangulum is as good a place to look as Andromeda -- but I'd be surprised (though only mildly so) if we were to find another in this one.

But I also think we'll find plenty of planets where we can set down colonies once we've mastered interstellar travel. (And, hopefully, we'll have worked out how to do sustainable, low-impact colonization by then, having learned the lessons of the past.)

[Matt Rhodes]

I've been forming the hypothesis that there is indeed sentient life elsewhere, but it's very rare, very different and very very far away from where we are.

There are trillions of galaxies out there, but only each one (or one galaxy out of a dozen) may only have a single planet where life hyper-evolved and broke free from environmental constraints and achieved the evolutionary epoch of intelligence.

[Jack Butler]

At this stage in human development, the internet either is or is rapidly becoming the substratum of the conscious mind of the species. That is to be distinguished from our individual awarenesses in the way that our brains are different from their cells. The species will become a thinking individual, and we will be comparable to nodes or cells. We will not know what the species is thinking any more than our cells know what we are thinking. Too bad for the Tea Partiers, because just as our liver cells do not fight our heart cells, we will quit fighting each other and settle into roles. It will look like morality at first.

If no way to travel faster than light is ever found, then the vast distances between stars--prizm is right about that--mean that no significant travel can be made in a human lifetime. But in the lifetime of a species?

How can a single intelligent species keep from being lonely? Only be finding other intelligent species.

It's conceivable that the universe is suited for exploration, but not by individuals--instead, by individually conscious species.

[Matt Rhodes]

"It's conceivable that the universe is suited for exploration, but not by individuals--instead, by individually conscious species."

I like Jack Butler's thoughts in his comments above.

I too think that travel through the universe is conceivable, but not by anything BIOLOGICAL. Machines and/or artificial lifeforms last virtually forever, and I think short of a gamma ray burst, meteorite collision, disease or self destruction that is where humans are headed.

To be one with the machine. Cybernetic organisms that need not worry about the distances in space, they have information on their side, their bodies and conscious minds are encased in alloys which defy the laws of time and mortals.

We may be among the first species in the universe to reach such a mark.

[John George Imhotep]

Which direction should we steer our starship? ALL OF THEM.
Watch this excellent presentation.
http://www.youtube.com/watch?v=zQTfuI-9jIo

[Justin Cooney]

Fascinating article, I didn't know there were so many vast dead zones in the Universe. At the very least I expect that life would be very rare and possibly incredibly different from what we know here on Earth.

[Olga Altstatt]

Common-intelligence? Is HUMANITY of that kind?I do hope We'll go beyond this catergory one day, if we stop poisoning our BRAIN; and RELIGION and MEDIA stop BRAINWASHING young GENERATION.
So far we only speculate about many things in the COSMOS! One day that will be changed when we find right PLANETS and right INTELLIGENT BEINGS!

[7LeagueBoots]

The Rare Earth hypothesis is an interesting idea, but is difficult to take seriously when it is supported by creationist/intelligent design proponents like Guillermo Gonzalez and his ilk.

Also, not sure why so many commentators are talking about physically going out and surveying extra-solar planets. That's slow, inefficient, expensive, and would be nearly impossible even with the appropriate technology. You have to do all the survey work remotely, then maybe, if you have found a likely place to go, you have to be fortunate enough to have that place be close enough that the civilization is still there by the time you get there.

[Matthew]

Exactly i seriously doubt any advanced civilization would send spaceships to explore the universe at random. With the technology needed to make exploration of space possible it would also require advanced long range macro detection of possible life bearing worlds. They would not be looking for a needle in a haystack. They would search the entire haystack and find the needle easily. More than likely sending advanced artificial intelligence drone probes to scout for potential planets to explore.

[smartypants]

Out of curiosity, what makes you so sure they would be looking for life? Why not hunting for resources? Especially if they were a race that needed, say gold for their electronics, or a salty water to drink (if they maybe came from a place with only salt water). Maybe they need something that powers our magnetic belts that we havent realized yet. Or even our dilithium crystals! According to this post most of the galaxy is low on metals, why not go for them? Especially once life has been found plentiful, if that ever happens, would we go 2,000 light years to find new life or go to pay bills?

[Ez]

"Dead zones are exactly that - conditions are to inhospitable for life to develop. There may only be a handful of habitable systems in any given galaxy, even if that galaxy has 400 billion stars. The odds are just stacked AGAINST life. The environments are pretty stark and unforgiving."

so is a street corner for a baby.

we've yet to leave this womb of a planet\solar system :\

this is a kind of shitty time to exist in tbh, world getting smaller, universe getting bigger, and were still throwing rocks at anything we dont agree with.

roll on computerised life, sign me up.