Reasons to Believe

Effect of Distant Orbiters on Habitability

Distant bodies in a planetary system are like some distant in-laws. Even when they live far away and never visit they can still cause lots of problems.

A recent study by an MIT astronomer of a distantly orbiting companion to the nearby planet-hosting star HD 3651 illustrates the problems a distant relative can pose for any possible life-supportable planet.1 The planet orbiting HD 3651 is more than 60 times as massive as Earth and nearly 4 times closer to its star and, therefore, is not a candidate for supporting life.2 But, in addition to the relatively small gas-giant planet orbiting HD 3651 astronomers have discovered a distantly orbiting brown dwarf star.3

The brown dwarf companion to HD 3651 is 30 times less massive than the Sun or 35 times more massive than Jupiter. It orbits HD 3651 sixteen times more distantly than Pluto orbits the Sun. Neglecting the fact that the planet orbiting HD 3651 eliminates the possibility of another planet in the same system possessing the capacity to support life, the MIT astronomer investigated whether the brown dwarf companion by itself would negate any possibility for such a life-supportable planet.

Based on calculations by two other teams of astronomers,4 the MIT astronomer concluded that gravitational perturbations induced by the brown dwarf most likely would inhibit the formation, long-term existence, and/or the habitability of any possible planet orbiting HD 3651 at a distance where surface liquid water might be possible. Of perhaps even greater risk to any possibility of life support in the planetary system, he pointed out, would be the manner in which the brown dwarf’s gravity would scatter small bodies in the outer reaches of the planetary system toward a possible life-support planet. Just as the solar system possesses an enormous cloud of millions of asteroids and comets (the Oort Cloud) up to 2 trillion miles from the Sun, astronomers likewise have strong evidence that other stars in the vicinity of the Sun also possess such distant comet and asteroid clouds.5 Sustained impacting of the possible life-support planet would guarantee that life would never take hold on the planet.

Searches for a distantly orbiting brown dwarf about the solar system have turned up negative.6 However, the situation appears quite different for extrasolar planetary systems. A team of American and British astronomers was surprised to discover that at least 23 percent of the 131 extrasolar planetary systems they observed contain two or more stars.7 Since the team’s instruments lacked the sensitivity to detect very small stars and brown dwarfs, it could well be that “nemesis” stars and dwarfs eliminate the majority of planetary systems as possible candidates for harboring any kind of planet with the possibility for supporting life. The bottom line is that astronomers now have one more reason for concluding that planets like Earth are rare, so exceptionally rare that the conclusion of supernatural design seems inescapable.

Subjects: Extrasolar Planets, Habitable Planets, Life on Other Planets, SETI, Solar System Design, TCM - Cosmic Design

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. Read more about Dr. Hugh Ross.


  1. Adam J. Burgasser, “The Physical Properties of HD 3651B: An Extrasolar Nemesis?” *Astrophysical Journal *658 (2007): 617-21.
  2. Hugh Ross, The Creator and the Cosmos,, 3rd ed. (Colorado Springs: NavPress, 2001), 175-99.
  3. K. L. Luhman et al., “Discovery of Two T Dwarf Companions with the Spitzer Space Telescope,” Astrophysical Journal 654 (2007): 570-79.
  4. Daniel Malmberg, Melvyn B. Davies, and John E. Chambers, “The Instability of Planetary Systems in Binaries: How the Kozai Mechanism Leads to Strong Planet-Planet Interactions,” Monthly Notices of the Royal Astronomical Society Letters *377 (2007): L1-L4; Genya Takeda and Frederic A. Rasio, “High Orbital Eccentricities of Extrasolar Planets Induced by the Kozai Mechanism,” *Astrophysical Journal 627 (2005): 1001-1010.
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  6. Saul Perlmutter, “An Astrometric Search for a Stellar Companion to the Sun,” Ph.D. Thesis, University of California, Berkeley (1986), Dissertation Abstracts International, Volume 48-05, Section B: 1385.
  7. Deepak Raghavan et al., “Two Suns in the Sky: Stellar Multiplicity in Exoplanet Systems,” Astrophysical Journal 646 (2006): 523-542.