By Ray Jayawardhana
April 21, 2017 5:35 p.m. ET
We live in a “me, me, me” world. Interest in the self, and its assorted extensions, appears to trump all else. Smug politicians and overhyped celebrities are not the only ones to suffer from this common affliction. Astronomers, who might be expected to develop a broader—humbler?—perspective on account of their majestic subject matter, tend to be self-centered in their own way.
I am speaking here of our predilection to judge all other worlds by how closely they resemble ours.
Over the past quarter-century, scientists have identified thousands of planets orbiting stars other than the sun, confirming that our solar system is merely one among tens of billions or more in the Milky Way galaxy alone. The diversity of planets and planetary systems they have uncovered is truly astounding: speedy gas giants in star-hugging orbits, Tatooine-like worlds with double sunsets, rocky globes both scorched and frozen.
Yet we continue to obsess over finding an identical twin of our planet circling an identical twin of our sun. The reasoning is that such a setting would offer the best odds of harboring life. Some have called this idealized world Earth 2.0; others have dubbed it Mirror Earth.
Last August, when evidence of a planet around Proxima Centauri, the sun’s nearest stellar neighbor, came to light, both the researchers themselves and the media reports emphasized its “Earthlike” characteristics. Some glossed over glaring differences between that world and ours. Proxima b, as the planet was dubbed, orbits an active red dwarf star, much less massive than the sun and much more prone to releasing hazardous flares. With a year that is only 11 Earth-days long, Proxima b is almost certainly tidally locked, with one hemisphere baked in constant heat while the other remains in eternal darkness. What’s more, the planet may have lost much of its water and other volatile substances long ago.
In February, when astronomers reported the discovery of a remarkable retinue of seven planets around the nearby star Trappist-1, again the headlines highlighted that they are “Earth-size,” roughly speaking, and that at least three may possess “temperate” climates, like that of the Earth. Trappist-1 is so puny that it barely qualifies as a star, though it may emit lethal doses of ultraviolet radiation. Its planetary orbits are so squashed that all seven would fit well inside Mercury’s orbit around the sun. Does that sound remotely like a replica of our solar system? Obviously not.
But I would argue that we have more to learn from the Trappist-1 planetary system precisely because it is so starkly different from ours. Its mere existence—a prosaic star with a rich entourage of potentially rocky planets—speaks to the ubiquity of such worlds in the galaxy.
It is tempting to believe that there is something extraordinary, or special, about our cosmic circumstances. In fact, some have argued that complex life on Earth emerged through a series of improbable events that are unlikely to be repeated elsewhere, despite the vastness of space and the immensity of cosmic time.
But the real reason for our preoccupation with finding a carbon copy of the Earth is that we don’t know any better. So far, we are aware of only one planet with life—ours—so we are inclined to believe that it must represent the platonic ideal, just as Gottfried Leibniz argued three centuries ago.
In fact, there are good reasons to think that in some cases planets somewhat bigger than ours, so called super-Earths, would provide more-stable conditions. What’s more, planets around red dwarfs, with lifetimes much longer than the sun’s, would offer much more time for the emergence and evolution of life. As a practical matter, it is easier to search for signs of life from afar on a super-Earth around a red dwarf than on a smaller, Earth-size world orbiting a bigger, sun-like star. That’s why the exoplanet announced this week will be a prime target for the James Webb Space Telescope, to be launched next year.
If the plethora of exoplanet discoveries to date has taught us anything, it is to expect the unexpected. Thus, focusing narrowly on “Earthlike” planets in our search for habitable abodes seems unwise. Five centuries after Copernicus, it is about time that we cast aside our geocentric perspective of other worlds and life in the universe.
Mr. Jayawardhana, an astrophysicist and the dean of science at York University in Toronto, is author of “Strange New Worlds” (Princeton University Press, 2011).