The Pentagon has debriefed three more senators on alleged naval encounters with UFOs, POLITICO reported recently. The existence of both simple and intelligent life beyond Earth has been a subject of conjecture for centuries. Scientifically speaking, what are the odds?
Most people are likely to have seen a fictionalized depiction of alien life by the time they reach adulthood, and these depictions are often caricatured. Science fiction novels and films, cartoons, video games, television series, and other media have told stories for quite some time of “little green men” visiting our planet for benevolent or malicious purposes. However, with the Pentagon ramping up its release of classified information about alleged naval encounters with UFOs to various government officials, the question of life on other planets may warrant new examination from a scientific perspective.
Optimistic View for Existence of Simple Life Forms
When we discuss life on other planets, microbial life may be more probable than it is exciting, but it’s a valid point of discussion. “There are possibly as many as about one Earth-like planet [orbiting] around every three Sun-like stars,” said Dr. Laird Close, Professor of Astronomy and Astrophysics at The University of Arizona. “We know that there are about 74 such Sun-like stars out to some 32 light years. That means if we optimistically keep the ratio of about 30 percent, there should be on the order of 20-some, Earth-like planets within 32 light years of the Earth.”
Dr. Close said that some planets in nearby star systems are near enough that we can use scientific instruments and methodology to detect whether or not they currently have or have ever had living microorganisms on them. Should we find that they do, it would be a good indicator that much of the universe is brimming with simple life.
“It’s a very exciting quest for science and if we discover this it will be a hallmark occasion for humanity,” he added.
The Rare Earth Theory and Intelligent Life
On the other hand, the odds of intelligent life on other planets could be significantly lower than those of simple life. This is partly because of the amount of time it took for single-celled organisms to evolve into intelligent creatures. The corresponding likelihood—or lack, thereof—of other planets maintaining stable environmental conditions for that long isn’t very optimistic.
Dr. Close cited a book called Rare Earth by two University of Washington scientists—geologist Peter Ward and astronomer Don Brownlee—that details the factors needed for intelligent life to spring up on Earth, according to the “Rare Earth Hypothesis.” “First of all, our Sun is in the right part of the galaxy,” Dr. Close said. “It is not too close to the crowded center, nor does it exist way out on the element-poor fringe of our galaxy. This seems to be an important factor.”
He also said that Sol isn’t just in the right part of the Milky Way, but is also the right size and kind of star. “It is not too big or hot and it is not too small or cold,” he said. Very few stars—he estimated 5 percent in the galaxy—have approximal masses to ours. Another factor is the Earth’s combination of a hot core and plate tectonics. “These, as we have seen, have been key to keeping the Earth stable for life for so long,” Dr. Close said.
There are two final factors that have helped Earth maintain a long-term stable environment. The first is our moon, which Dr. Close said “helps stabilize the spin axis of the Earth and also helps make tide pools.” The second is Jupiter, which effectively serves as a shield protecting the innermost planets in our solar system from incoming impacts.
Some Astronomical Odds
So what are the odds? Dr. Close said one educated guess puts Earth-like planets with similar moons to ours at a ratio of one in 10,000. Large Jupiter-like planets with circular orbits protecting inner Earth-like planets are about one in 100. This means Earth is literally one in a million planets to have both a stabilizing moon and a Jupiter-like protector. “We have also got to take into account that only 5 percent of stars in our galaxy are Sun-like, and of those, only three to 30 percent have [Earth-like] mass planets in the habitable zone,” Dr. Close said. “Therefore, if we have 100 billion stars in our galaxy that leaves us with about 1.5 billion Earth-like planets in our Milky Way.”
And 1.5 billion planets combined with the one-in-a-million odds mentioned earlier means somewhere between 150 and 1,500 planets in the galaxy likely fit the bill. Further qualifications like Earth’s hot core, tectonic plates, proper placement in the galaxy, and so on greatly reduce that number. “According to a strict interpretation of the Rare Earth hypothesis, you would probably only expect there to be three to 30 truly Earth-like photocopy planets in our galaxy right now,” Dr. Close said.
It is, however, still a chance.
Dr. Laird Close contributed to this article. Dr. Close is Professor of Astronomy and Astrophysics at The University of Arizona. Awarded a Canadian (study abroad) Natural Sciences and Engineering Research Council scholarship while attending The University of British Columbia, he then earned his Ph.D. in Adaptive Optics from University of Arizona’s Astronomy Department.