Earth is very different from any other planet we have discovered inside or outside of our solar system. One key factor that makes our planet habitable is our Moon. The Moon serves several important roles, including holding Earth in a stable rotation. The Moon can be a stabilizer for Earth because of its relatively large size. Other planets have moons that are much smaller in comparison to the planets they orbit. Also, other planets in our solar system have multiple moons which make conditions less stable.
Many of the planets discovered outside of our solar system are huge and located incredibly close to their stars with highly eccentric orbits. A solar system in the constellation Serpens was found with a planet seventeen times as massive as Jupiter. Someone might respond with the observation that we can only see the big planets because those systems are so far away. That observation misses the point. These huge, Jupiter-sized and larger planets are located as close to their stars as we are to our Sun or closer. If there is a small planet in the vicinity, it would be twisted and wrenched about by the influences of the large planet. The problem with highly elliptical orbits and life is that there would be too much variation in the amount of energy that the planet receives from its star. Earth’s orbit is only slightly elliptical giving us stable temperatures. If we had only one planet in our solar system with a radically elliptical orbit, there would be a danger of it crashing into our planet. Circular orbits are important for stability. The instability produced by highly eccentric orbits of large planets would make the area sterile and void as far as life is concerned. Everything we see indicates that our solar system is a cosmic oddball.
There are many properties of our planet, Sun, solar system, and the galaxy in which we live that have to be exactly as they are for any kind of life, not just intelligent life, to exist. The galaxy has to be the right type of galaxy, we must be in the right position in the galaxy, and our Sun has to be the right type of star and at the right age in its life process. Our planet must have the right size, mass, tilt, magnetic field, distribution of land masses, chemical makeup, atmosphere, distance from the Sun, and much, much more.
To calculate the overall probability, you must multiply the probability of each of the dependent variables. Every time scientists find a new variable that has to be precisely determined for a life-sustaining planet to exist, that probability is multiplied by all the other probabilities. Considering all of the required factors and the probability of each and multiplying them all together, the total probability of another planet like Earth is exceedingly small. “In the beginning, God created the heaven and the earth” takes on a whole new level of meaning as we continue to gain knowledge about the cosmos.
–John N. Clayton and Roland Earnst © 2017