Is there extraterrestrial life of any kind, such as bacterial life? Part of the problem here is to define “life” itself, and there are various points of view on what qualifies for being “alive”.


[CAUTION:–This subject is NOT about people who claim to have been abducted by aliens or whether aliens have landed in Roswell, New Mexico and there has been a massive government cover-up. Science generally rejects such claims, and the weight of present scientific opinion is that there is as yet no convincing evidence for alien visits. Whether or not this should be so is a separate topic which will be offered, but which I have not yet organized. To find out what this subject is about, read on.]

There are really several levels of questions here:

1.) Is there extraterrestrial life of any kind, such as bacterial life? Part of the problem here is to define “life” itself, and there are various points of view on what qualifies for being “alive”. [What is life?] (See Reference #6 below for a possible discovery of alien bacteria.) A subtopic would be, is there life in our own solar system? This subject is discussed in reference #1 below (Kryss Tals’s article). However, he writes from 2004 but the Cassini probe to Saturn has changed the picture and now the most likely candidate for life in the solar system is Enceladus, another moon of Saturn. [Why? What is it about Enceladus that is so promising?]

2.) Is there intelligent life, or are we alone?” (Actually, what we really would like to know is if there is “communicating” life. In other words, are there life forms advanced enough to send signals to us or to receive our signals?)

BEFORE YOU START there are a couple of terms you need to understand well. You must answer the questions in this paragraph. First, you need to know how the large distances between stars are measured. [What is a light year, and how far is it in miles?] (Note that a light year is a distance and not a time.) Second, you need to know how the stars are arranged in galaxies. [What is a galaxy? In particular, you should understand the structure of our own galaxy, the “Milky Way”. How many stars in the Milky Way? What is the distance across it in light years? Where is our sun placed in the galaxy?] You can look these things up on line or in your text.

Here is the basic problem. There are so many stars in the universe, and presumably so many planets, that is almost inconceivable that we should be the only planet where life has arisen. Yet, despite decades of listening for radio signals from “out there”, [what is SETI?] there hasn’t been a peep [was the “WOW!” signal an exception?]. And no real convincing evidence of ET life in any other way either. To quote Carl Sagan in his book “The Demon-Haunted World”:

“I’m frequently asked, ‘Do you believe in extraterrestrial intelligence?’ I give the standard arguments—there are a lot of places out there, the molecules of life are everywhere, I use the word billions, and so on. Then I say it would be astonishing to me if there weren’t extraterrestrial intelligence, but of course there is as yet no compelling evidence for it.”

Or, as the well known physicist Enrico Fermi famously asked, “Where are they?”

(For example, if ET life was really common, one might think that Pennsylvania Avenue in Washington D.C. would be lined with embassies from the stars. One might think that our zoos would be full of alien tourists. One might expect to find the bar scene from Star Wars somewhere near Cape Canaveral. Yet there’s nobody here but us humans.)

For a more sober elaboration on the problem, see reference #3.) below, paragraph #4 (starting with “The rationale…”) and paragraph #5.

The following is a list (not necessarily in order of importance) of web articles you can google that will give you information on these questions. There are a couple of “must reads” listed below but otherwise the choice of exactly which articles you decide to look up and which topics you choose to discuss is up to you. Of course the more research you do on your own the better it will be. Just be sure to always cite your sources.

Note: If you report on any of the references below you must answer the questions in [square brackets]. But if you do not report on that subject you are not required to answer the questions unless you are specifically instructed to answer. (You can if you want.)


1.) Kryss Tal: Extraterrestrial Life
This essay does a good job in presenting a reasonable estimate of the number of stars in the universe and the possible number of habitable planets. (However it is a 2005 essay. For a more up to date estimate on planets in our galaxy suited for life see reference #2 below.) The Tal essay is also good for the chemical basis of life and how these molecules are distributed out there. He gives his own definition of “life”. A must read.

2.) The Milky Way’s 500 Million Potentially Habitable Planets
This is a recent deduction from the findings of the Kepler telescope. They extrapolate to the number of habitable planets in our galaxy and also the universe as a whole.

3.) Fermi Paradox
This is a comprehensive Wikipedia article. [What is the Fermi Paradox? You should answer this question even if you don’t discuss this article in detail in your essay.] Much of the article deals with possible explanations (“solutions”) of the Fermi Paradox. Generally speaking, these are either ideas to suggest why intelligent life is rare, or ideas to explain why we haven’t detected it even if it is common. The sheer number of these ideas (although many of them are fascinating) may startle and even overwhelm you. But some of them may also appeal to you or even “turn you on”. You may champion any of these ideas that appeal to you (you can either explain why you think so, or simply say that the idea sounds right to you), or you may just throw up your hands and say that all of this is just useless speculation because we have no actual evidence. Or, you may have a different take of your own. Another must read.

4.) Search for Extraterrestrial Intelligence (SETI)
Another Wikipedia article. About the first two thirds of this article is just enormous detail about the search (a little boring!) . However, the part that starts with the “Fermi paradox” is quite to the point and includes suggestions not mentioned in Reference #3.).
Perhaps some of this will “turn you on”.

5.) The Fate of Noospheres
(the noosphere is the “sphere” of all human thought, which grows as human minds interact—don’t be discouraged by this strange word as much of the article is independent of it) This essay is John J. Reilly’s arguments against some of the solutions to the Fermi paradox, such as the idea that intelligent races will inevitably destroy themselves by “atomic suicide”, etc. Reilly frequently bases his arguments on actual human history, a refreshing change from all the Astronomer based viewpoints. If you read the Fermi Paradox (reference #2.) you will have noticed that many of the ideas were stated without a lot of discussion. So an in-depth criticism is useful. Reilly’s views may not be the last word (one can always argue against them) but the essay is quite intelligent. (And by the way, if you want to understand about the “omega” point, where humanity supposedly ultimately disappears from the universe, you might watch the science fiction classic movie “Forbidden Planet”.)

6.) Alien Bacteria Fossils Found in Meteorite by NASA scientist
Well…maybe. [What is a Meteorite?]

7.) Self-Replicating Spacecraft
This subject could be considered the most critical one in the discussion of extraterrestrial life. If extraterrestrial life is common and if it is true (as theory indicates) that the galaxy could be completely (and relatively cheaply!) explored by automated probes in as little as half a million years, then why is our solar system not just chock full of Von Neumann Probes? [What is a Von Neumann Probe?] After all, we ourselves are exploring Mars and the other planets by automated probes and not by astronauts (which would be much more difficult and expensive). Not only that, but the present weight of opinion at NASA (if not for us more romantic science fiction fans) is that by far the best and most economical way to carry out space exploration would be by automated probes. So wouldn’t other life forms come to the same conclusion? For an important counter argument, check Carl Sagan’s response, now known as “Sagan’s Response” (to the problem of the missing Von Neumann Probes).

8.) Rare Earth Hypothesis
About an important 2000 book by Peter Ward and Donald Brownlee, which argues that life on Earth is a freak, unlikely to be reproduced elsewhere. This is the argument against extraterrestrial life. Basically, it departs from the Copernican Principle which most arguments automatically assume when asserting that life in the universe should be common. Many reasons to support this view, both astronomical and biological are given in the book. [What is the Copernican Principle, or the Principle of Mediocrity?]. The article summarizes the book, but also regularly mentions objections to assertions in the book, based on more recent research. While this criticism is generally welcome, one gets the impression that the author of the article does not agree with the Rare Earth Hypothesis, and therefore that the article may be slanted (biased against the book).

9.) Extraterrestrial Life
An overall Wikipedia article on the subject. Everything is covered, at least in outline form. In particular, it has a tremendous number of links to almost everything that bears on the subject of ET life. Not a bad place to start. And if you want to branch out on your own, lots of trailheads start here.


If you wish to, you may come to your own conclusion about the existence of extraterrestrial life. Here are some of the opinions that others have come to:

a) Intelligent life in the universe should be common.

b) Intelligent life is common but it will be very difficult (for various reasons) or even forever impossible to communicate with them.

c) There is intelligent life out there, but it is rare.

d) We are the first. (We are alone.)

e) We are the only planet with life that we know about, and it is impossible to make statistical predictions about the prevalence of life in the universe based on a statistical sample of only one. (In other words, there is just not yet enough evidence available to settle the question one way or the other.)

BUT whatever point of view you come to, you must explain your attitude to the Fermi Paradox (discussed above).

IN CONCLUSION: This is a fascinating topic. If ET life is discovered it could well be the most important discovery ever made. I hope you enjoy reading about it. But it is also very seductive. One could go on reading about it forever. So go into it as deeply as you can, but be careful not to bury yourself in it! You undoubtedly have lots of other commitments in life, not to mention that I don’t want this to distract you from all of your other school work. Good luck.

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