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At Nautilus: Were It Not for Cosmic Good Fortune, We Wouldn’t Be Here


Sean Raymond, Beibei Liu & Seth Jacobson offer a solar system model affirming that the “dynamical instability” of our early solar system had to go just right, or we probably wouldn’t be here.

Who doesn’t want the trains to run on time? When stuff runs like clockwork, we’re happy. And thankfully, that’s how the planets orbit the sun: dependable, and always on time. But it wasn’t always like this. 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? 

The idea of a dynamical instability crept into the minds of planetary scientists from the outside, from research on exoplanets. The first exoplanets astronomers discovered around stars like the sun were gas giants on orbits very close to their stars. Call them “hot Jupiters.” They’re exotic, circling about 1 percent of sun-like stars. But once astronomers discovered gas giants on more distant orbits—starting just wider than Mercury’s orbit around the sun—they noticed that the planets’ orbits were often extremely stretched-out.

It’s not immediately obvious, but the stretched out orbit of a gas-giant exoplanet is a massive scar. It’s a remnant of a violent past. When planets’ orbits cross, it leads to close encounters that, due to gravity, deflect the planets’ paths. After a series of encounters, one or more planets get ejected into interstellar space. The survivors have eccentric orbits—a telltale sign of something going seriously out of whack. At least three quarters (and probably 90 to 95 percent) of all giant exoplanet systems must be the survivors of dynamical instabilities.

Which raises the question: 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.

In 2005, researchers took the world of planetary science by storm after coming up with a theory, the Nice model, linking the instability with an apparent spike in the cratering rate on the moon called the “late heavy bombardment.” 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. The Nice model, (pronounced like “niece”) after the city in France where it was developed, has survived 17 years of intense scrutiny, and accounts for the orbits of the asteroid belt, Kuiper belt, Jupiter’s Trojan asteroids, and even the irregular moons of the giant planets.

The orbit of a gas-giant exoplanet is a remnant of a violent past.

But a re-analysis of the moon’s craters suggests that there was no cataclysm or spike. The impact rate declined smoothly instead. So, 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 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. 

See full article at Nautilus.
Just say anything to avoid the obvious. ET
As to: "Who doesn’t want the trains to run on time? When stuff runs like clockwork, we’re happy. And thankfully, that’s how the planets orbit the sun: dependable, and always on time." In regards to just how delicately balanced our 'stable' solar system is,,,
“You might also think that these disparate bodies are scattered across the solar system without rhyme or reason. But move any piece of the solar system today, or try to add anything more, and the whole construction would be thrown fatally out of kilter. So how exactly did this delicate architecture come to be?” - R. Webb - Unknown solar system 1: How was the solar system built? - New Scientist – 2009 Rare Planetary System BY HUGH ROSS - JUNE 12, 2017 Excerpt: Thanks in large part to research on extrasolar planets, astronomers also know that every planet in the solar system fulfills a key role in making advanced life possible on Earth. Two Brazilian astronomers showed that even tiny adjustments in the orbits of Jupiter, Saturn, Uranus, and Neptune would prove catastrophic for life in our solar system.5 Regions beyond the precise orbital positions of Jupiter, Saturn, Uranus, and Neptune abound in destructive mean motion resonances. As it is, Uranus is close to a 7:1 resonance with Jupiter (where Jupiter would make exactly 7 orbits around the Sun for every single orbit of Uranus), a 2:1 resonance with Neptune, and a 3:1 resonance with Saturn. Meanwhile, Jupiter and Saturn are very close to 5:2 resonance. If any of the solar system gas giant planets’ orbital positions were to shift ever so slightly, that shift would destabilize the orbit of one or more of the eight planets in the solar system with catastrophic consequences for a long history of life on Earth. Three Canadian astronomers further demonstrated that the orbital positions of Venus, Earth, and Mars must be fine-tuned so as to break up mean motion resonances that could be damaging for life on Earth. They showed that even the orbital features of the Earth-Moon system must be fine-tuned for this purpose.6 The Earth-Moon system suppresses a resonance in Venus’ orbit that is generated from the orbital patterns of Jupiter, Saturn, Uranus, and Neptune. Unless the Earth-Moon system is configured the way it is, both Venus’ and Mercury’s orbits would destabilize and generate destructive chaos throughout the inner solar system. Every planet in our solar system and Earth’s Moon contribute to making advanced life possible on Earth. The solar system’s array of eight planets must be exactly the way it is. Have you thanked God today for Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune? https://www.reasons.org/explore/blogs/todays-new-reason-to-believe/read/todays-new-reason-to-believe/2017/06/12/rare-planetary-system Is the Solar System Stable? By Scott Tremaine - 2011 Excerpt: So what are the results? Most of the calculations agree that eight billion years from now, just before the Sun swallows the inner planets and incinerates the outer ones, all of the planets will still be in orbits very similar to their present ones. In this limited sense, the solar system is stable. However, a closer look at the orbit histories reveals that the story is more nuanced. After a few tens of millions of years, calculations using slightly different parameters (e.g., different planetary masses or initial positions within the small ranges allowed by current observations) or different numerical algorithms begin to diverge at an alarming rate. More precisely, the growth of small differences changes from linear to exponential:,,, As an example, shifting your pencil from one side of your desk to the other today could change the gravitational forces on Jupiter enough to shift its position from one side of the Sun to the other a billion years from now. The unpredictability of the solar system over very long times is of course ironic since this was the prototypical system that inspired Laplacian determinism.,,, https://www.ias.edu/about/publications/ias-letter/articles/2011-summer/solar-system-tremaine Of Gaps, Fine-Tuning and Newton’s Solar System - Cornelius Hunter - July 2011 Excerpt: The new results indicate that the solar system could become unstable if diminutive Mercury, the inner most planet, enters into a dance with Jupiter, the fifth planet from the Sun and the largest of all. The resulting upheaval could leave several planets in rubble, including our own. Using Newton’s model of gravity, the chances of such a catastrophe were estimated to be greater than 50/50 over the next 5 billion years. But interestingly, accounting for Albert Einstein’s minor adjustments (according to his theory of relativity), reduces the chances to just 1%. http://darwins-god.blogspot.com/2011/07/of-gaps-fine-tuning-and-newtons-solar.html
When you begin to understand just how many things had to go just right at just the right time, you realize it takes a heck of lot of faith to believe the secular origins account! They too have faith. And sometimes, it seems like that faith is blind faith to boot! I mean they will believe any old just so story if it seems needed to keep their worldview in tact. tjguy

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