Reasons to Believe

Pervasive Eccentricity

When I was fulltime as a Caltech researcher, I blended in with my peers. I cut my own hair, maybe three times a year. I purchased my clothes and shoes at the Lucky supermarket. I bought pants three inches short so the cuffs wouldn’t get caught in my bicycle chain. I paid no attention to matching colors or patterns, only to comfort. I bought shirts with two chest pockets to hold all my pens, pencils, and a protractor. Because I eschewed pocket protectors (they were too uncomfortable), all my shirts sported ink stains. However, with scientific calculators horribly expensive in those days, I did hang a leather calculator holster from my belt.

I later learned that, while I saw myself as commonplace, people in the church and Bible studies I attended saw me as “eccentric.”

Recently, three astronomers from Northwestern University found that eccentricity (of a slightly different kind) is as commonplace for planets outside of our solar system as my eccentricity appeared at Caltech. Their findings reveal previously unnoticed or underappreciated design features belonging to Earth and Earth’s planetary partners.1 In other words, they’ve discovered more evidence for fine-tuning, the work of the Creator.

When used by astronomers, eccentricity refers to the shape of a planet’s orbit around a star. An eccentricity number between zero and one is used to indicate the degree of deviation from an exactly circular orbit, with 0 representing a perfect circle and 0.9 representing an extremely stretched ellipse. An eccentricity of 1.0 represents a parabola, and greater than 1.0 applies to a hyperbola, both of which are not closed orbits (see figure 1).

The three astronomers first examined the challenges a planet’s eccentricity poses for life. A high eccentricity would mean freezing conditions (for such compounds as H2O) in one part of a planet’s orbit and evaporation conditions in another part. The greater a planet’s eccentricity, the greater the variation in its exposure to radiation from its host star, thus the more likely that these extremes will render the planet’s climate unsuitable for life, any kind of life.

Figure 1: Orbits With Different Eccentricities (e)
Point F is the focal point. In a planetary system, the host star resides
very near the focal point. (Diagram released into the public domain by
the author, Scott Alan Hill)

The situation is most severe for advanced life. An eccentricity as small as 0.05 would generate such extreme climate differences as to challenge the survival of warm-blooded animals. It would also significantly reduce the quantity of vegetation. In the words of the three astronomers, any such disturbance  to long-term climatic stability “could disturb the possible origin, evolution, and prevalence of life on the planet.”2

The highlight of this recent study is the astronomers’ demonstration of how many—and how readily —celestial mechanisms disturb planetary orbits and heighten eccentricities. Such mechanisms include these:

1. a distant stellar companion to the host star

2. a distant brown dwarf companion to the host star

3. a star that passes near the planetary system one or more gas giant planets within the planetary system

The three astronomers point out that these mechanisms are ubiquitous throughout the Milky Way Galaxy. So any Earth-type planet found anywhere beyond our particular solar system “is likely to experience a broad range of orbital evolution.”3 In other words, orbital eccentricity and variability is the norm for extrasolar “earths.” This finding severely diminishes the possibility of life’s prevalence or long-term survival on planets outside our solar system. If any kind of life were ever to exist there, it would be insufficient in both abundance and longevity to sustain advanced life.

Planets of similar size, mass, and distance from their host stars as Earth may indeed prove abundant. However, Earth-type planets with nearly circular and highly stable orbits will likely prove extremely rare or non-existent. And to find such planets amid a suite of planetary partners all manifesting low orbital eccentricities would appear even less likely. This conclusion is consistent with the Bible’s message that God supernaturally designed Earth, Sun, Moon, and its planetary partners, for the specific benefit of life, especially life as complex and as sensitive to climatic variation as human beings.


1. Ryosuke Kita, Frederic Rasio, and Genya Takeda, “Pervasive Orbital Eccentricities Dictate the Habitability of Extrasolar Earths,” Astrobiology 10, no. 7 (September 2010):733–41.

2. Ibid., 733.

3. Ibid.

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.