Cosmologic philosophy: chaotic beginning (Introduction)

by David Turell , Friday, May 27, 2022, 18:11 (911 days ago) @ David Turell

Our solar system was chaotic in the beginning in arranging planet arrangements:

https://nautil.us/were-it-not-for-cosmic-good-fortune-we-wouldnt-be-here-18446/

"Scientists suspect the solar system, some time in its early years, underwent a violent seismic shift. The orbits of the gas giants—Jupiter and Saturn—got tweaked big time, and the aftershocks affected all the planets, including Earth and Mars, as well as the asteroid and Kuiper belts.

"In our new study, published in Nature, we rewrite the origins of this massive shift—called a “dynamical instability”—and explain how everything in the solar system today found its place. What’s more, our idea is broadly applicable and may explain the orbits of exoplanets.

***

"Did our solar system get lucky? Our planets have near-circular orbits—did we somehow avoid instability? Several signs point to no. The most compelling is that the giant planets’ orbits appear to have been re-shuffled since they grew out of the sun’s gaseous, planet-forming disk. Simulations show that the giant planets’ orbits should have been near-circular and much more compact. Jupiter’s orbit would be about the same as today, but the orbits of the other giant planets would be shrunk-down, putting Saturn much closer to Jupiter, Uranus close to Saturn’s present-day orbit, and Neptune just a bit farther from the sun. Clearly, the orbits of the giants shifted a lot between their birth and today.

***

"An analysis of the rocks Apollo astronauts brought back from the moon suggested there was a delayed burst of impacts on the rocky planets about 500 million years after they formed, around 4.1 to 3.8 billion years ago. By that time, the oceans were already around, potentially harboring life.

***

"our only hint is that the seismic shift in the early solar system must have happened within the first 100 million years—although this doesn’t tell us whether it happened before Earth and the other rocky planets finished forming or afterward. What triggered the big shift? We show, in our new paper, that it was likely the dispersal of the sun’s planet-forming disk.

***

"The sun’s disappearing donut is what shook the orbits of the already-formed planets. As the outward-sweeping inner edge of the gaseous disk passes by each planet in turn, it drags the planet outward with it. (Jupiter is an exception, as its large mass clears out a gap in the disk near its orbit, blocking the “push” from the sweeping inner edge.) In our simulations, we saw that as Saturn is pushed outward, it approaches the orbits of ice giants Uranus and Neptune. The net effect is to squeeze the planets’ orbits closer together. The stability of planets’ orbits depends on the spacing: More widely-separated orbits are far more stable. The squeezing of the system eventually triggers dynamical instability by causing one ice giant’s orbit to cross that of another, or of Saturn’s.

"The gravitational effects of the instability would have stunted Mars’ growth, potentially explaining why it’s so much less massive than Earth. What’s more, the instability would have led asteroids and comets to bombard the growing Earth, rather than one potentially already hosting primitive life. All of this means that planetary systems are bitten by the hand that feeds them, as instabilities among planets are triggered by the disks that spawned them.

"The instability was a big deal for our solar system but, compared to those in other exoplanet systems, it was far weaker. Fortunately, Jupiter and Saturn must have avoided any close encounters, because if they had scattered off of each other, Jupiter’s present-day eccentricity would be 5 to 10 times greater—similar to many giant exoplanets. In that case, there would be no Earth. Its building blocks would have been scattered into the sun."

Comment: Planned chaos or plain luck? We are here and there is so much contingency in chance events, it is easily seen as planned by the designer.