Maybe because of the context of the midterm elections, but it sounds like some sort of an anachronistic political endorsement: the Kepler spacecraft is supporting Michael Denton’s fine-tuning campaign with large contributions of data.
How commonplace is the Earth? Not many decades ago, optimism ran high about alien worlds — earth-like planets inhabited not just by simple organisms, but by advanced civilizations. Carl Sagan proclaimed in his popular Cosmos series, “There may be a million worlds in the Milky Way galaxy alone that are at this moment inhabited by other intelligent beings.” His efforts to create the Voyager record yielded this from President Jimmy Carter: “We hope someday to join a community of galactic civilizations.”
The optimism came after Kepler (the scientist) and before Kepler (the spacecraft). Johannes Kepler (1571-1630) did speculate about life on other worlds, writing one of the first works of science fiction, The Dream, in which he imagined a flight to the moon. He never let his imagination get in the way of his science, though. The Kepler spacecraft, undoubtedly named in part because of the 17th-century scientist’s dreams of extraterrestrial life, launched in 2009 amid high hopes of finding alien worlds like the Earth. Exoplanets. Earth twins.
Kepler’s launch represented the pinnacle of optimism that we are not alone. Hints of extrasolar planets, proposed by Peter Van den Kamp in the mid to late 20th century, remained unconfirmed until his death in 1995. That very year, instruments had become precise enough to confirm his search for the faint wobble of a star tugged on by its planets. Astronomers could then plot the motions over time, detecting a sine wave that allowed calculation of mass and orbital radius. For the next decade, large Jupiter-sized planets dominated the exoplanet count largely due to selection effects: large, close-orbiting planets were easier to detect.
The transit method, developed around the turn of the millennium, requires an eclipsing planet (one whose orbit as seen from Earth is aligned with the star), but provides more data. Changes in the light curve and spectrum of the star offer clues about the planet’s atmosphere, as well as its mass, density, and period. This is the method the Kepler spacecraft used. So successful has it been till its demise on October 19, it has catalogued some 2,327 planets so far, according to NASA’s Exoplanet Archive, bringing the overall total of exoplanets to 3,826. Enough data have been collected to catalog most of them by mass, radial distance, density and parental star type, so that comparisons with our solar system can be made.
The Pendulum Swings
The Kepler data started deflating the optimism. Most exoplanetary systems looked nothing like ours. So-called “hot Jupiters” dominated the counts, and many with wildly eccentric orbits suggested that our solar system might be the exception rather than the rule. Only 23 “candidate” earth-like planets met criteria for mass and orbital radius, although several hundred candidates still await precise determination. Even among these, it has been difficult to argue for a true “Earth twin” out there. Astrobiologists can still argue that we’ve only sampled a very tiny fraction of stars, but if the trend continues, the statistics indicate Earth might be exceptional.
Recently, pessimists have scored again. They have effectively swept a large number of candidate Earth-like planets off the chart by considering the types of stars they orbit. News from NASA Exoplanet Exploration says, “Superflares from young red dwarf stars imperil planets.” superflares, that are orders of magnitude more energetic than those produced by our sun. Moreover, they occur every day or several times a day. Any candidate planet orbiting such a star would likely be burned to a crisp after its atmosphere were blown off by regular and repeated blasts. After that, the planet would quickly become tidally locked to the star, vastly reducing habitable surface area.
More bad news came just days ago. Early results from the Gaia spacecraft, the European Space Agency’s contribution to planet-hunting, have not been encouraging. Mike Wall explains this in his article on Space.com, “Number of Habitable Exoplanets Found by NASA’s Kepler May Not Be So High After All.”
To date, NASA’s prolific Kepler space telescope has discovered about 30 roughly Earth-size exoplanets in their host stars’ “habitable zone” — the range of orbital distances at which liquid water can likely exist on a world’s surface.
Or so researchers had thought. New observations by the European Space Agency’s (ESA) Gaia spacecraft suggest that the actual number is probably significantly smaller — perhaps between two and 12, NASA officials said today (Oct 26). [Emphasis added.]
The problem this time is not cool red stars with superflares, but hot, bright stars.
Gaia’s observations suggest that some of the Kepler host stars are brighter and bigger than previously believed, the officials added. Planets orbiting such stars are therefore likely larger and hotter than previously thought.
They Should Have Known
Years before the Kepler mission, in 2000, Peter Ward and Donald Brownlee campaigned against astrobiological optimism with their book, Rare Earth: Why Complex Life Is Uncommon in the Universe. Their thesis considered the number of factors necessary for a planet to host complex life, although they thought simple bacterial life might be common (as if bacteria are simple). These factors had to be so finely tuned as to render their simultaneous occurrence highly improbable. Illustra Media interviewed Brownlee about this book in their film, The Privileged Planet.
An even more astonishing book about fine-tuning appeared in 2016. In their book, A Fortunate Universe: Life in a Finely Tuned Cosmos, Geraint F. Lewis and Luke A. Barnes looked in detail at the laws of physics and constants of nature that if varied by the most infinitesimal amounts would rule out matter, stars and planets altogether.
Denton the Polling Favorite
Michael Denton, author of The Wonder of Water, now has a companion book, Children of the Light: The Astonishing Properties of Sunlight that Make Us Possible. These books make a new argument: independent factors for habitability actually seem to “conspire” to allow for large, complex beings like humans.
The “coincidences” are truly remarkable. The type of star we orbit, for instance, emits its primary radiation in “one tiny, infinitesimally small band” of possible wavelengths: the range we call the “visual spectrum,” plus some of the infrared. Our atmosphere, next in line, allows these bands through, but blocks most of the dangerous high-energy frequencies that would harm organisms. Finally, the molecules in plants are finely tuned to utilize sunlight for photosynthesis, allowing us “light eaters” to exist. That’s for starters. In his recent podcast for ID the Future, Denton is almost at a loss for the right words to express how remarkable this all is.
We exist because of an extraordinary degree of fine-tuning in nature…. It looks like things have been arranged for the end [purpose] of life on Earth…. One thing is for sure: science has discovered the fine tuning. Fine tuning is a fact…. It’s very, very remarkable indeed. Descriptive terms fail me when I think about it. I’m blown away by this evidence. I mean, it’s not just the evidence of the fine tuning of sunlight, the atmosphere and so forth for photosynthesis…
He discusses multiple independent instances of fine tuning, then continues:
The important thing is that this fine tuning is a discovery of science. So the fine tuning is not really in doubt. It’s totally bewildering. The fine tuning cannot be got rid of. It’s there now; it’s been discovered by science. And the common-sense interpretation of it is that it looks as if some intelligence has ordered things for the existence of beings like ourselves on a planet like the Earth.
Image: Kepler spacecraft, by NASA [Public domain], via Wikimedia Commons.