Our solar system possesses five belts of asteroids and comets.
- the Main Belt (between Mars and Jupiter)
- the Centaurs (between Jupiter and Neptune)
- the Scattered Belt (extends from just outside Uranus’ orbit, out to twenty billion miles from the Sun)
- the Kuiper Belt (exists just outside Neptune’s orbit, between four and six billion miles out from the Sun)
- the Oort Cloud (extends from about ten billion to two trillion miles out from the Sun).
For advanced life to be possible on a planet, the surrounding planetary system must be extraordinarily fine-tuned—including its asteroids and comets. Belts that are too massive or too close will deliver too many devastating collisions and far too much water. On the other hand, asteroid and comet belts that are insufficiently massive or too far away will fail to provide the water and heavy metals that advanced life and civilization needs.
Terrestrial planets like Mercury, Venus, and Earth form in a dry region of a protoplanetary disk.1 Therefore, for water to exist on such a planet it must be delivered to its surface via comets (which can be as much as 85 percent water) and asteroids (which can be more than 10 percent water). However, too much water delivery can be a problem in that even very aggressive plate tectonic activity will fail to generate enough silicate material to produce exposed continental landmasses. Meanwhile, too little water will result in oceans too small to sustain an adequate water cycle or to efficiently recycle nutrients.
In addition to the just-right amounts of water, Earth also needs just-right amounts of heavy elements to support human civilization. Yet early Earth was molten and its gravity pulled heavy elements into its core, leaving its surface depleted of these elements. Again, it took asteroids and comets to salt Earth’s crust with resources such as iron, copper, nickel, silver, gold, and platinum.
Two NASA astronomers, Rebecca Martin and Mario Livio, referred to computer simulations2 establishing that asteroids form adjacent to a planetary system’s snow line.3 The snow line refers to the distance from a star at which water and other volatiles (such as ammonia and methane) freeze into solid grains. For the present-day solar system the snow line is 40–50 million miles inside the orbit of Jupiter.4 Martin and Livio then tabulated observations of warm dust orbiting 20 solar-type stars.5 This warm dust, the signature of exoasteroid belts, is consistently located at the snow lines of the stars.
The formation of an asteroid belt depends upon the existence of a giant planet orbiting beyond the snow line. However, observations of extrasolar giant planets reveal that more than 94 percent orbit their stars inside the snow line.6 Theoretical models confirm that the vast majority of giant planets, having formed, will continue to interact with planetesimals and undergo substantial inward migration. Such inward migration typically obliterates a planetary system’s asteroid and comet belts.
One team of researchers demonstrated that in only 1–2 percent of planetary systems will the most massive planet linger somewhere near Jupiter’s orbital distance.7 This rarity may explain why warm dust is observed around so few stars.
Martin and Livio point out, however, that a small amount of migration is needed to remove a large enough fraction of asteroids and comets—otherwise, too many impact events will occur on the terrestrial planets and prevent life from existing.
For a giant planet to not migrate it must form at the same time that the gas in the interplanetary disk is depleted completely. As Martin and Livio explain, “There appears to be a very narrow ‘window of opportunity’ of time during which the giant planet should form in order for the correct amount of migration to take place—potentially making our Solar system even more special.”8
Indeed, Martin and Livio provide yet one more example of the evidence accumulating for the supernatural design of the solar system for the specific benefit of human beings and human civilization. Let’s thank God for the exquisite design of our solar system’s five belts of asteroids and comets that make it possible for us to exist.