By Harry Keller
Editor, Science Education
“Superhabitable” worlds may be common in our galaxy, making ideal homes for extraterrestrial life — Scientific American cover, January 20151.
Years ago, Carl Sagan famously wrote about a scientist’s “baloney detection kit” in The Demon-Haunted World (1995). You can learn all about this storied chapter by searching on the Internet for “baloney detection kit.” His point was that scientists obtain this mental tool kit as a side effect of their training and that we should similarly train everyone.
Scientific American magazine just published an article, “Better than Earth,” which shows us that scientists are not immune from broadcasting baloney themselves at times. The article is really quite good and interesting. Its statements are, as far as we can tell, accurate. Where is the baloney then?
At one point, the article states, “[T]he more closely we scientists study our own planet’s habitability, the less ideal our world appears to be.” The article also faults our own star’s “short” lifetime of about 10 billion years. “By some 1.75 billion years from how, the steadily brightening star will make our world hot enough for the oceans to evaporate, exterminating any simple life lingering on the surface.”
Looks as though we evolved just in time to enjoy our planet for a billion years or so before we are all steamed to death. Slower evolution may not have left enough time for us to exist here.
We circle a G-class star. According to the author, the next step down in star size, “K dwarfs[,] appear to reside in the sweet spot of stellar superhabitability.” K dwarf stars will shine for tens of billions of years, many times longer than our star. However, the author cautions that our planet is too small for conditions suitable for life to exist for that long period of time. Our core would have cooled too much to sustain our magnetic field and plate tectonics, both necessary to life.
Planetary magnetic fields shield them from destructive cosmic rays and solar flare radiation. Plate tectonics maintain volcanic activity that keeps recycling carbon dioxide (CO2) without which the planet may freeze. The so-called greenhouse effect keeps planets from losing their warmth through thermal radiation to space. CO2 is an important greenhouse gas and is produced even without biological activity.
A rocky planet, placed at the right distance from a K dwarf star so that water is mostly liquid, would have lots more time to evolve life than our own Earth. Therefore, these superhabitable planets should be looked for if we are to locate planets most likely to host life, according to the author.
He is probably correct, but does not add an important caution. Upon reading this article, you may well consider that superhabitable planets will have trees growing and birds flying over fields of flowers. It is by leaving you with this impression that the author is disbursing baloney. He makes no statement, pro or con, about complex life. His superhabitable planets may have lots of life that you will see as slimes and oozes — nothing more.
The superhabitable planets speculated upon in this article have one important feature, which is stability. They will reach and remain in a fairly stable state for a very long time — tens of billions of years. There may be some out there already that are ten- or twenty-billion years old, much older than our 4.5 billion year history here on Earth. The implication is that more time means more evolution and therefore more advanced life forms.
Our own planet has had a rather chaotic history with at least five major extinction events since becoming home to multicellular life around 550 million years ago. We don’t know how many such events preceded those during its previous roughly 3 billion years of harboring life because that life was single-celled and left nearly no record of its existence. We do know that major extinction events were a key part of evolution as we know it. Life moves ahead slowly when things are stable. Small improvements take place in existing life forms when no stress has been imposed. Instead of finding new and innovative ways of expressing life, evolution merely finds an occasional enhancement that slowly wends its way into the mainstream of life. New species are rare, and new genera even more unusual.
We don’t really know that a somewhat larger planet circling a somewhat smaller star at the right distance would not have major extinction events, but the evidence suggests that it would have fewer of them. Without recent extinctions, our planet may still be covered with trilobyte descendants. Some of them may have moved onto dry land and covered it with shell-bearing multi-legged tiny creatures. More distant extreme events may have triggered the enormous step to multicellular life. In our even deeper past, the step from prokaryotic to eukaryotic life may have come not from evolution in a stable environment but from environmental stresses caused by our planet’s size and location plus the size of our star.
Certainly, the dinosaurs showed no propensity toward evolving in the direction of tool-making intelligence or of any intelligence at all. Without the last extinction, this planet would most likely be home to dinosaurs, and the mammals would have remained small shrew-like creatures existing mostly in burrows well out of the reach of the rapacious reptile spawn. There would be no technology here at all.
The Scientific American article has great information in it and is exciting in itself. Its baloney is hidden beneath its surface through omission and its author’s desire to transmit his excitement to his readers. He concludes, “With considerable luck, we may all soon be able to point to a place in the sky where a more perfect world exists.” It would seem that perfection, like beauty, is in the eye of the beholder. With all of its faults, I’ll take our planet no matter how imperfect those astrobiologists may make it out to be. For me, it’s perfect — unless we destroy it ourselves.
1 See René Heller’s “Planets More Habitable Than Earth May Be Common in Our Galaxy,” Scientific American, 1 Jan. 2015. Also see Mariette DiChristina’s “From the World Economic Forum to the World Library of Science to Superhabitable Worlds,” Scientific American, 16 Dec. 2014; and Michael Moyer’s “Twin Earth May Be Better Than Earth for Life,” Scientific American, 17 Apr. 2014.