When talking about the prospect of life in outer space, we are actually referring to three separate issues: the prospect of permanent human life away from Earth, the prospect of extraterrestrial life of any kind (i.e. primitive and non-intelligent species), and the prospect of intelligent alien civilizations similar to or far more advanced than our own. It is, naturally, the third of these which tends to attract the most public attention.
– The Prospect of Human Life in Outer Space –
Regardless of what other life lies in wait for us in the galaxy, it’s unlikely we will find it before venturing into outer space on a more permanent basis ourselves. Today, there have been no substantive efforts to build self-supporting, permanent human settlements off the Earth. The closest we have come are a pair of space stations, the former Mir and the current International Space Station, were astronauts engage in “long-term” missions lasting for several months. These, moreover, remain wholly dependent on a regular schedule of supply ships sent from the surface, which deliver food, oxygen, and water, and offload waste products.
Still, it is generally acknowledged that a permanent and at least semi-self-supporting base could be built on the Moon. Indeed, the U.S. Army and U.S. Air Force drew up plans for just such a base around 1960, and until the Vision for Space Exploration was all but cancelled in 2010 by the Obama administration, NASA’s official mission list called for the erection of a lunar base in the 2020s. From there we would move on to Mars and probably to near-Earth asteroids, although the most speculative and far-reaching studies have analyzed how we might build floating colonies on Venus and over Jupiter, colonize the moons of Saturn and Jupiter, and so on.
All such projects would rely on a technological capacity well in advance of our current one, of course, but few doubt that these missions would be possible in most respects. Some important questions do remain – in particular, about the threat posed by solar radiation. Nevertheless, the prospects for human life in outer space do still seem high, even if the most optimistic writers of the 1950s and 1960s have died with their dreams unrealized, and we will likely not see more than a further succession of orbital and lunar experiments in our lifetimes either.
– The Prospect of Life in Outer Space –
If intelligent life exists on multiple planets in the galaxy, then logically, non-intelligent life probably exists on far more planets. So far as we can tell, in order for life to emerge, several basic conditions must be established, including the presence of water, organic compounds, and a range of climate which is neither excessively cold nor excessively hot (i.e. Mercury is probably too hot, and Pluto is probably too cold; most analysts believe the habitable zone lies roughly between Venus at its innermost and Mars at its outermost.
On the one hand, a look at our nearest neighbours shows that location isn’t the only factor that makes a planet habitable. Venus may be too hot: a runaway greenhouse effect means that its wind-swept surface is permanently hundreds of degrees above freezing, and Soviet probes which landed on the surface during the Cold War tended to last only a few minutes before succumbing to the intense heat. Mars is probably unsuitable now for other reasons: its atmosphere is too thin and its surface is too exposed to solar radiation and micrometeorites to be a friendly place for life.
Nevertheless, the abundant presence of the basic building blocks of life in our solar system, and what we know about the history of the planets, suggests that if our solar system is anything like average, the stage is set for life all over the galaxy. Mars and possibly Venus once had water oceans on their surface, before their climates became too hostile. Comets are rich sources of water and organic compounds. We may still find evidence of primitive microorganisms in our analysis of the Martian soil. Saturn’s moon Titan has a methane atmosphere rich with organic compounds, and Jupiter’s moon Europa has a massive under-the-surface ocean. (Other moons are believed to have subterranean oceans as well, but Europa actually is a water world, blanketed with a thick layer of ice.) To date we have not found evidence of life at any of these locations, but if other solar systems are like ours, the probability that at least primitive life forms have evolved in many locations seems very high.
– The Prospect of Intelligent Alien Life in Outer Space –
Ultimately, of course, when most people discuss the prospect of life in outer space, what really interests them is the question of whether intelligent alien civilizations exist in outer space, which might make contact with us or with whom we might one day make contact ourselves. On this question there is much more uncertainty (although, of course, there continues to be a minority who not only believe that alien civilizations exist in large numbers, but that one or several of these civilizations are currently engaged in active operations on Earth).
Two basic scientific principles describe the problem of intelligent life in outer space. The first, known as the Drake Equation, is a pseudo-mathematical formula intended to estimate the prospect of life in outer space. The Drake Equation is essentially a list of all of the variables believed necessary for intelligent life to emerge: a suitable star, orbited by suitable planets at suitable distances, containing suitable chemical precursors for life, which then go on to form increasingly complicated forms of life, which then goes on to develop complex and technological societies.
A relatively moderate use of the Drake Equation suggests there could be a dozen or more intelligent civilizations in the Milky Way Galaxy at any given time; more optimistic beginning assumptions yield higher numbers, while more pessimistic assumptions lead to lower numbers, perhaps even just one (ourselves). Still, overall the Drake Equation does indicate that what we suspect about the odds of life in a galaxy containing hundreds of billions of stars is accurate: there should be a number of intelligent alien civilizations among the stars.
This, however, leads to the second principle: the Fermi Paradox. Essentially, the Fermi Paradox states: if the odds show that there are a lot of alien civilizations, why haven’t we seen them? Given the rate of technological progress humanity has made since industrialization, even a few centuries’ extra progress could lead to technology we would find indistinguishable from magic. In a galaxy which is billions of years old, it is quite believable that there are civilizations thousands of years older than ours. If they do exist, and survive to spread among the stars, they ought to be virtually everywhere by now. At the very least we should be able to see them.
It is possible, of course, that for various reasons alien civilizations do exist in large numbers and simply do not wish to make themselves known to us. Perhaps there is no solution to the greatest problem in space flight: the vast distances between the stars, which science fiction eliminates through means of fanciful warp drives and hyperdrives. Perhaps highly advanced civilizations simply switch from radio to some more advanced communications technology, so that we can’t hear what they are transmitting and they are no longer listening to our broadcasts, either. Perhaps they have even walled off Earth, and other similar planets, as the interstellar equivalent of nature reserves.
All of these are comforting thoughts for those who do not want humanity to be alone in the universe, but the chilling and disturbing fact is that the most logical resolution of the Fermi Paradox is that, for some reason, we cannot see advanced alien civilizations in our galaxy because there are none there – or at least, there are none close enough to be seen from Earth. Perhaps humanity is more of an evolutionary fluke than we supposed. Or perhaps (most frightening of all), the Drake Equation missed an important stage at which intelligent life forms tend to destroy themselves. We have certainly come close ourselves, with nuclear war, and may yet come close again through environmental destruction.