Dynamics of Hierarchial Two-Planet Systems

Currently, astronomers have identified over 40 multi-planet extrasolar planetary systems. Accurate data on the orbits of the planets in these systems permits researchers to address the following questions:

  1. How do the orbital eccentricities, inclinations, and semi-major axes of the known planets in each system change with respect to time?
  2. What is the timescale for the development of instability in these systems?
  3. Will these systems permit the existence of additional smaller planets?
  4. How will tidal forces, mean motion resonances, and general relativity affect the orbits of the detected (and other possibly existing) planets in the systems?

The answers to these questions also impact the search for other planets capable of sustaining life.

Two astronomers, Dimitri Veras and Eric Ford of the University of Florida, combined published orbital data with a statistical technique known as Markov Chain Monte Carlo analysis on five multi-planet systems: HD 11964, HD 38529, HD 108874, HD 168443, and HD 190360.1 They then used the data and the technique to model the dynamic evolution for each system.

They found that planetary orbits in systems where the gas giant planets manifest large orbital distance ratios will “exhibit complex dynamics and can become highly eccentric and may be significantly inclined.”2 Such outcomes rule out the possibility that an advanced-life-friendly planet could exist in the same system as these gas giants.

Veras and Ford also discovered that over time general relativity alters the inclinations of planets where the planets in any given system display significantly different orbital inclinations. This discovery also rules out the possibility of an advanced-life-friendly planet existing in the same system. However, this outcome may be a moot point since the very existence of gas giant planets with markedly different orbital inclinations in itself rules out the possible existence of a planet hospitable to advanced life in the same planetary system.

The detailed orbital simulations performed by Veras and Ford provide yet more evidence for the rare Earth and rare solar system doctrines. Planetary systems are proving abundant in the Milky Way Galaxy. However, advanced-life-sustaining planets like Earth and ensembles of gas giant planets like Jupiter, Saturn, Uranus, and Neptune ensuring long-term survival of that advanced life are proving either extremely rare or unique to the solar system.

In turn, the rare Earth and rare solar system doctrines provide more support for the supernatural design of Earth and its planetary partners for the specific benefit of advanced life and, in particular, for human beings.


1. Dimitri Veras and Eric B. Ford, “Secular Orbital Dynamics of Hierarchical Two-Planet Systems,” Astrophyiscal Journal 715 (June 1, 2010): 803–22.

2. Ibid., 803.


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