Reasons to Believe

Compositions of Extrasolar Planets

When extrasolar gas giant planets were first discovered in 1995,1 many astronomers presumed these planets would prove close analogues to the gas giants in our solar system. The list of known extrasolar gas giants now stands above four hundred. Yet none of these four hundred is even remotely similar to Jupiter, Saturn, Uranus, or Neptune.

Today astronomers stand at the verge of discovering rocky terrestrial-type planets the size of Venus and Earth. Already they’ve found several only a few times the mass of Earth.

In anticipation of this forthcoming discovery, a number of theoreticians have generated detailed computer simulations of extrasolar terrestrial planet formation based on the measured physical properties of known extrasolar planetary systems. So far, however, these simulations have considered only the dynamics of terrestrial planet formation and not the detailed chemical compositions of the final terrestrial planets produced.

In the June 1, 2010 issue of the Astrophysical Journal three astronomers from the Lunar and Planetary Laboratory (LPL) and the Planetary Science Institute (PSI) in Tucson, Arizona, responded to this deficiency.2 As the three astronomers discovered, the presumption that extrasolar terrestrial planets will consistently manifest Earth-like chemical compositions is incorrect. Instead, the simulations revealed “a wide variety of resulting planetary compositions.”3

The LPL/PSI team noted that many of the host stars of known extrasolar planetary systems possess much higher ratios of carbon-to-oxygen than does the Sun. Consequently, any terrestrial planets existing in these systems would possess enormous quantities of graphite, silicon carbide, and titanium carbide—all minerals that, thankfully for advanced life, are relatively rare on Earth. The team concluded that terrestrial planets in these systems would have “compositions and mineralogies unlike any body observed within our solar system.”4

These conclusions pile up yet more evidence for the rare Earth doctrine. This doctrine states that while planets the size and mass of Earth may prove abundant, planets with the just-right characteristics and physical and chemical composition to support advanced life will prove either rare or unique to our solar system.

Such a concept is consistent with the Bible’s message that God supernaturally designed Earth for the specific benefit of human beings.  


Dr. Hugh Ross


2. Jade C. Bond, David P. O’Brien, and Dante S. Lauretta, “The Compositional Diversity of Extrasolar Terrestrial Planets. I. In Situ Simulations,” Astrophysical Journal 715 (June 1, 2010): 1050–70.
3. Ibid., 1050.
4. Ibid.