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Retrospections Search for Life in the Universe II
Search for Life in the Universe II
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Alien Life
Posted:   06/25/03
Author:    Neil deGrasse Tyson

Summary: In this two-part essay, Director of the Hayden Planetarium, Neil deGrasse Tyson, reflects on the scientific and cultural implications of finding life elsewhere in the cosmos.

The Search for Life in the Universe II

Reflections on the scientific and cultural implications of finding life in the cosmos

Search for Life in the Universe: Part I

How about intelligence? Since there is still debate on how to define it and measure it in people, I wonder what the question even means when applied to extraterrestrials. Hollywood has tried, but I give them mixed reviews. I know of some aliens that should have been embarrassed at their stupidity. What about all those aliens that manage to traverse thousands of light years through interstellar space, yet bungle their arrival by crash-landing on Earth?

V-ger, Spock investigates ancient probe
Credit: Paramount

Then there were the aliens in the 1977 film Close Encounters of the Third Kind, who, in advance of their arrival, beamed to Earth a mysterious sequence of repeated digits that were eventually decoded to be the latitude and longitude of their upcoming landing site. But Earth longitude has a completely arbitrary starting point -- the prime meridian -- which passes through Greenwich, England by international agreement. And both longitude and latitude are measured in peculiar unnatural units we call degrees, 360 of which are in a circle. Armed with this much knowledge of human culture, it seems to me that the aliens could have just learned English and beamed the message, "We're going to land a little bit to the side of Devil's Tower National Monument in Wyoming. And since we're coming in a flying saucer we won't need the runway lights."

The award for dumbest creature of all time must go to the alien from the original 1983 film Star Trek, The Motion Picture. V-ger, as it called itself (pronounced vee-jer) was an ancient mechanical space probe that was on a mission to explore and discover and report back its findings. The probe was "rescued" from the depths of space by a civilization of mechanical aliens and reconfigured so that it could actually accomplish this mission for the entire universe. Eventually, the probe did acquire all knowledge and, in so doing, achieved consciousness. The Star Trek crew come upon this now-sprawling monstrous collection of cosmic information at a time when the alien was searching for its original creator and the meaning of life. The stenciled letters on the side of the original probe revealed the characters V and ger. Shortly thereafter, Captain Kirk discovers that the probe was Voyager 6, which had been launched by humans on Earth in the late twentieth century. Apparently, the oya that fits between the V and the ger had been badly tarnished and was unreadable. Okay. But I have always wondered how V-ger could have acquired all knowledge of the universe and achieve consciousness yet not know that its real name was Voyager.

Remarkable frozen texture on Jupiter's moon, Europa.
Credit: NASA/JPL

Regardless of how Hollywood aliens are portrayed, or how good or bad the films are, we must not stand in denial of the public's interest in the subject. Let us assume, for the sake of argument, that humans are the only species in the history of life on Earth to evolve high-level intelligence. (I mean no disrespect to other big-brained mammals. While most of them cannot do astrophysics, my conclusions are not substantially altered if you wish to include them.) If life on Earth offers any measure of life elsewhere in the universe, then intelligence must be rare. By some estimates, there have been more than ten billion species in the history of life on Earth. It follows that among all extraterrestrial life forms we might expect no better than about one in ten billion to be as intelligent as we are, not to mention the odds against the intelligent life having an advanced technology and a desire to communicate through the vast distances of interstellar space.

On the chance that such a civilization exists, radio waves would be the communication band of choice because of their ability to traverse the galaxy unimpeded by interstellar gas and dust clouds. But humans on Earth have only understood the electromagnetic spectrum for less than a century. More depressingly put, for most of human history, had aliens tried to send radio signals to earthlings we would have been incapable of receiving them. For all we know, the aliens have already done this and unwittingly concluded that there was no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility would be if aliens had become aware of the technologically proficient species that now inhabits Earth, yet they had drawn the same conclusion.

In 1998, NASA's Associate Administrator Wesley Huntress, Jr., stated, "Wherever liquid water and chemical energy are found, there is life. There is no exception.".
Credit: NGS

Our life-on-Earth bias, intelligent or otherwise, requires us to hold the existence of liquid water as a prerequisite to life elsewhere. A planet's orbit should not be too close to its host star, otherwise the temperature would be too high and the planet's water content would vaporize. The orbit should not be too far away either, or else the temperature would be too low and the planet's water content would freeze. In other words, conditions on the planet must allow the temperature to stay within the range for liquid water. As in the three-bowls-of-food scene in the fairy tale Goldilocks and the Three Bears, the temperature has to be just right. When I was interviewed about this subject recently on a syndicated radio talk show, the host commented, "Clearly, what you should be looking for is a planet made of porridge!"

While distance from the host planet is an important factor for the existence of life as we know it, other factors matter too, such as a planet's ability to trap stellar radiation. Venus is a textbook example of this "greenhouse" phenomenon. Visible sunlight that manages to pass through its thick atmosphere of carbon dioxide gets absorbed by Venus's surface and then re-radiated in the infrared part of the spectrum. The infrared, in turn, gets trapped by the atmosphere. The unpleasant consequence is an air temperature that hovers at about 900 degrees Fahrenheit, which is much hotter than we would expect knowing Venus's distance to the Sun. At this temperature, zinc would swiftly become molten and a 16" pepperoni pizza will cook in nine seconds.

The discovery of simple, unintelligent life forms elsewhere in the universe (or evidence that they once existed) would be far more likely and, for me, only slightly less exciting than the discovery of intelligent life. Two excellent nearby places to look are the dried riverbeds of Mars, were there may be fossil evidence of life from when waters once flowed, and the subsurface oceans that are theorized to exist under the frozen ice layers of Jupiter's moon Europa. Once again, the promise of liquid water defines our targets of search.

If we consider the possibility that we may rank as primitive among the universe's technologically competent life forms however rare they may be then the best we can do is keep alert for signals sent by others because it is far more expensive to send rather than receive them. Presumably, an advanced civilization would have easy-access to an abundant source of energy such as its host star. These are the civilizations that would be more likely to send rather than receive. The search for extraterrestrial intelligence (affectionately known by its acronym "SETI") has taken many forms. The most advanced efforts today uses a cleverly designed electronic detector that monitors, in its latest version, billions of radio channels in search of a signal that might rise above the cosmic noise.

The discovery of extraterrestrial intelligence, if and when it happens, will impart a change in human self-perception that may be impossible to anticipate. If we don't soon find life elsewhere, what will matter most is that we had not stopped looking. Our species demands that we keep looking. Deep in our soul of curiosity we are intellectual nomads in search of other places, in search of other life forms because we derive almost as much fulfillment from the search as we do from the discovery.

Neil De Grasse Tyson is Frederick P. Rose Director, Hayden Planetarium, American Museum of Natural History (since 1996); Visiting Research Scientist, Department of Astrophysics, Princeton University (since 1994).

Related Web Pages

Search for Life in the Universe: Part I
A Perfect World I: Tyson
Tyson and Planetary Society
Tyson Testimony to Congress on Astrobiology
Edward Weiller: Are We Alone?
Chris Chyba: The Search for Life
Table Talk

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