Planet Earth: The Largest Possible Habitat?

Planet Earth: The Largest Possible Habitat?

When I first moved to California the enormity of peoples’ homes surprised me. It seemed to me that “California dreamin’” was the quest to own a home with as many square feet as possible.

On a larger scale, another form of California dreamin’ is the desire of modern-day humans for a bigger planetary home. In fact, the latest justification for an atheistic worldview is the charge that an all-loving, all-powerful God would never confine his creatures to such a tiny pale blue dot of a planet.1 However, thanks to the discovery and research of “super-earths,” a response to this latest charge from atheists is beginning to develop.

Super-earths are planets weighing in at 1–10 times the mass of Earth. To date, astronomers have discovered 23 super-earths outside the solar system. Previously, most astronomers presumed super-earths to be like our own planet—composed almost entirely of rocks and metals with only miniscule accompanying oceans and atmospheres.

As I described in two previous Today’s New Reason to Believe articles  (January 12, 2009, and January 18, 2010), emerging observational and theoretical research on super-earths reveals that such planets possess densities considerably lower than Earth’s, which measures at 5.52 times the density of liquid water. The densities of super-earths are so low as to imply that such planets must be loaded with at least a hundred times as much water per unit of mass as Earth. That much water would rule out the possibility of both continents and oceans existing on the surfaces of those planets and, thus, the possibility of advanced life.

Now a new set of planetary atmosphere models shows that super-earths also possess atmospheres far thicker than Earth’s.2 Two astronomers, Eliza Müller-Ricci and Jonathan Fortney, at the University of California, Santa Cruz, took advantage of transit measurements (where astronomers measure the dimming of the host star’s light as the planet passes in front of the star) of the super-earth GJ 1214b to determine the mass, radius, and structure of the planet. They then explored the possible range of atmospheres that the planet could manifest.

Müller-Ricci and Fortney concluded that GJ 1214b possesses an atmosphere that is dominated either by hydrogen and helium, by carbon dioxide, by water vapor, or by all of these gases plus methane and ammonia. In every possible event, however, the atmosphere of GJ 1214b must be at least 4,000 times more massive than Earth’s. This means that all of these potential atmosphere scenarios definitively rule out the possibility of advanced life. These scenarios also call into question the identification of such planets as super-earths. It may be more accurate to refer to super-earths as small gas giants, rather than as large terrestrial planets. Perhaps “mini-Neptune” would be a more appropriate moniker for planets in this group (Neptune’s mass = 17.6 Earth masses and Uranus’ = 14.5).

The study performed by Müller-Ricci and Fortney provides yet more evidence that a planet capable of sustaining advanced life must be fine-tuned or designed to an extreme degree. It also provides more evidence that Earth’s size is in fact compatible with the all-loving, all-powerful nature of the God of the Bible. It seems God indeed has blessed humanity with the largest possible home planet permitted by the laws of physics he chose to govern the universe.3

  1. Victor Stenger, God: The Failed Hypothesis (Amherst, NY: Prometheus Press, 2007): 160-161.
  2. Eiza Müller-Ricci and Jonathan J. Fortney, “The Nature of the Atmosphere of the Transiting Super-Earth GJ1214b,” Astrophysical Journal Letters 716 (June 10, 2010): L74-L79.
  3. For a dozen different reasons why God chose the specific laws of the universe see my book Why the Universe Is the Way It Is.