The Spectacular Death of Stars --Planetary Nebula NGC 2392
Supermassive Black Holes --"Did They Form Inside Galaxies or Create Them?"

"Dead Zones of the Universe" --A Challenge to the Search for Extraterrestrial Life





While the Kepler Space Telescope has discovered more than 3,000 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.

Kepler has discovered exoplanets in alien star systems  in an area that represents around 1/400th of the Milky Way. By extrapolating the 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.

In stark contrast to the optimism 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. The image at the top of the page shows NGC 4631 (the Whale Galaxy or Caldwell 32) is a spiral galaxy, 30 million ly away in Canes Venatici. It has a central starburst, and is interacting with dwarf elliptical galaxy NGC 4627.

Globular Clusters: Although they contain millions 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."

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.

The Daily Galaxy via


and let`s not forget the Titan or Europa satellites like, that may harbor life if they revolve a giant gaseous planet like Jupiter only this time much closer to the star (which seems to be more often than what we have in our solar system) . In my opinion that should double the life expectancy overall.

The constant mantra is, "life as we know it" syndrome, where given our limited knowledge of the universe we become know it all's. The belief that we are the template for all life in the cosmos is narcissistic and self serving. I thought science was about being open minded to all the possibilities that may lay outside of our limited experiences. We still cling to the illusion that we are the center of the universe, and if they do exist out they why haven't they called to invite us over for tea and crumpets? The universe is a hostile place and how could life exist outside 'The Garden of Eden'(Earth). The world is flat. Earth is the center of the universe. Nothing existed before the Big Bang. This is the only universe that exist. We are the only species that exists and will exist, and we are destined to go forth and propagate the universe. Go forth add, subtract, divide, and multiply.

Today, we know of only one planet with life. We also know a lot about how certain molecules, very common and crucial for life on Earth, are formed naturally. But still, we cannot start from inorganic ingredients and produce life.

That is why we always speak about life as we know it, because that is the only case of life we know. It is not a self-restriction in our research, but rather the normal scientific stance of not assuming anything we do not know.

Actually, in our effort to understand all the possible forms that life may take, life forms in extreme conditions here on Earth become important in the search for extraterrestrial life.

Such cases of life in extreme conditions could be microbia or other microorganisms living in deep caves, or under kilometers of ice in Antarctica, where they can't possibly be receiving their energy from the sun. Or, microorganisms living in volcanoes under the ocean.


Given the massive number of planets in our universe the probability of life on other planets must be very high, even if only one in a million or one in a billion planets can support life.

We are also looking at life simply from a human perspective. There could well be a possibility that life comes in a variety of different forms.

The question I see sometimes is why we have not made contact. There are several reasons for this, as listed below:
1. The distances in the universe are so vast that any attempt at contact is going to take a long time to reach its destination.
2. Our technology may not be advanced enough.
3. There is a strong possibility that any signal we send out simply breaks down.
4. Any life on other planets, would they recognise where the signal came from?
5. It is possible, even allowing for highly intelligent civilisations, our means of communicating may not be recognised.
6. There are possibly civilisations that are aware of us, but they choose to ignore us instead.
7. We are probably only covering only a tiny segment of the universe.

this article is still very superficial because "earthlike" must still include 20+ other improbable circumstances which preclude other advanced civilizations existing in space: such as, a)tectonic plates which recycle chemical elements needed for life; b)a Moon to stabilize nutation and prevent the planet from wobbling so that evolution can proceed uninterrupted; c)no major impacts during early phase of civilization development- which may require a nearly unique physical location without much debris in its path around its galaxy; d)long term stellar stability, orbital stability- no double star systems, yellow stars only!; e)DNA development open to high intelligence...which we have no idea now what this may can go on and ON! Face it. We are the first. We are alone. We must hatch out of this fertilized egg and explore space.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)