Small Extrasolar Water World Discovered

Extrasolar planets frequently make news; in particular, a recent discovery by a team of 19 American and European astronomers is attracting attention. The newly detected planet is now the second smallest known extrasolar planet that orbits a hydrogen-burning star and is also water rich.1 In the words of Geoffrey Marcy, an astronomer who has probably discovered more extrasolar planets than any other, this team has provided “the most watertight evidence so far for a planet that is something like our own Earth, outside our Solar System.”2

Does this discovery mean that astronomers are on the verge of discovering Earth-like planets with the capacity to support life? Does the discovery imply our home planet is rather ordinary and, therefore, not supernaturally designed for humanity’s benefit?

Ironically, the discovery does just the opposite. The measured characteristics of this newly discovered planet and its host star add to the already overwhelming case for the supernatural, super-intelligent design of the entire solar system for the specific benefit of the human race.

The “new” planet stands out among known extrasolar planets because astronomers know so much about its features. This knowledge results from, (1) the planet being so close by (the planet’s host star, GJ 1214, is just 42 light-years away), and (2) from astronomers measuring the planet’s characteristics by two very different techniques. The researchers used the transit method, where they measured the dimming of the host star’s light as the planet passed in front of the star, and also used the radial velocity method, where they measured how much the gravity of the planet pulls the host star’s position away from or toward Earth as it orbits about the star.

GJ 1214’s planet has a mass of 6.55 Earth masses and a diameter 2.68 times greater than Earth’s. These measurements imply a density of 1.9 grams per cubic centimeter, which is about three times less than Earth’s density. The planet orbits just 2,153,000 kilometers (1,138,000 miles) away from GJ 1214. However, because GJ 1214 is such a small star (0.157 solar masses) and consequently very dim (0.00328 as luminous as the Sun), the planetary equilibrium temperature falls between 120°–280° Centigrade (250°–530° Fahrenheit).

To keep GJ 1214’s planet at such a low density requires that it contain an enormous amount of water—about fifty percent by mass. The determination that the planet is extremely water rich generated the expectation that humanity was the brink of discovering many habitable planets. However, as I discussed in the January 12, 2009 release of Today’s New Reason to Believe (TNRTB), too much water on a planet is just as detrimental to advanced life as not enough water.

With too much water continents will never appear on the planet’s surface. Earth has continents, and thus nutrient recycling and advanced life-habitable environments, because the planet’s water content makes up less than 0.05 percent of its total mass. In the January 12, 2009 TNRTB, I described an analysis by MIT planetary scientists demonstrating that planets ranging in size from one to several times the mass of Earth located at distances from their host stars which yield planetary equilibrium temperatures under about 150° C would end up with a water content equivalent to at least five percent of the planet’s mass.

The new measurements on GJ 1214’s planet confirm the accuracy of the planetary scientists’ analysis. They also confirm that Earth is truly exceptional in being so extremely water poor. It was only thanks to exquisitely designed collision events early in Earth’s history that our home lost just the right amounts of water.3


1. David Charbonneau et al., “A Super-Earth Transiting a Nearby Low-Mass Star,” Nature 462 (December 17, 2009): 891–94.

2. Geoffrey Marcy, “Water World Larger Than Earth,” Nature 462 (December 17, 2009): 853.

3. Hugh Ross, More Than a Theory (Grand Rapids: Baker, 2009), 135–40.