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Paper: Jupiter doesn’t shield Earth, comets kickstarted life


From ScienceDaily:

Not only is the ‘Jupiter as shield’ concept, implying that the planet shields Earth from comet impacts, not true, but perhaps Jupiter’s most important role in fostering the development of life on Earth was just the opposite — delivering the volatile materials from the outer Solar System needed for life to form. This new simulation study, and the previously underestimated role that Saturn may have also played in the evolution of life on Earth.

In “Jupiter: Cosmic Jekyll and Hyde”), Kevin Grazier, PhD, at the NASA Jet Propulsion Laboratory in Pasadena, describes the study in which he simulated the evolution of tens of thousands of particles in the gaps between the jovian planets for up to 100 million years. Based on the results, Dr. Grazier concludes that the widely reported shield role attributed to Jupiter is incorrect. The simulations showed that Jupiter teams with Saturn to kick a significant fraction of the particles into the inner Solar System and into orbits that cross Earth’s path. He proposes that a Solar System with one or more planets similar to Jupiter located beyond the region of potential terrestrial planets is beneficial for the development of life. More.

Fine-tuning?: Same fine, different tuning (?)

See also: Forbes: Our solar system is like waterfront property: It’s scarce, and they’re not making any more of it.

Copernicus, you are not going to believe who is using your name. Or how.


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Here’s the abstract:

It has been widely reported that Jupiter has a profound role in shielding the terrestrial planets from comet impacts in the Solar System, and that a jovian planet is a requirement for the evolution of life on Earth. To evaluate whether jovians, in fact, shield habitable planets from impacts (a phenomenon often referred to as the “Jupiter as shield” concept), this study simulated the evolution of 10,000 particles in each of the jovian inter-planet gaps for the cases of full-mass and embryo planets for up to 100 My. The results of these simulations predict a number of phenomena that not only discount the “Jupiter as shield” concept, they also predict that in a Solar System like ours, large gas giants like Saturn and Jupiter had a different, and potentially even more important, role in the evolution of life on our planet by delivering the volatile-laden material required for the formation of life.

The simulations illustrate that, although all particles occupied “non-life threatening” orbits at their onset of the simulations, a significant fraction of the 30,000 particles evolved into Earth-crossing orbits. A comparison of multiple runs with different planetary configurations revealed that Jupiter was responsible for the vast majority of the encounters that “kicked” outer planet material into the terrestrial planet region, and that Saturn assisted in the process far more than has previously been acknowledged. Jupiter also tends to “fix” the aphelion of planetesimals at its orbit irrespective of their initial starting zones, which has the effect of slowing their passages through the inner Solar System, and thus potentially improving the odds of accretion of cometary material by terrestrial planets. As expected, the simulations indicate that the full-mass planets perturb many objects into the deep outer Solar System, or eject them entirely; however, planetary embryos also did this with surprising efficiency. Finally, the simulations predict that Jupiter’s capacity to shield or intercept Earth-bound comets originating in the outer Solar System is poor, and that the importance of jovian planets on the formation of life is not that they act as shields, but rather that they deliver life-enabling volatiles to the terrestrial planets. Key Words: Asteroid—Comets—Interstellar meteorites—Extrasolar terrestrial planets—Simulation. Astrobiology 16, 23–38. (Public access) – Grazier Kevin R.. Astrobiology. January 2016, 16(1): 23-38. doi:10.1089/ast.2015.1321.

This stands in for the Fri Nite Frite unless something scarier comes along (not likely):

Um, isn't the most likely result of perturbing a body's orbit to loop SHARPLY toward the center of the solar system to be that body getting sucked into the Sun? The study also ignores ALL of bodies (comets and asteroids) with elliptical orbits that cause them to spend most of their time outside the orbit of Pluto. The study would also seem to suggest that the Moon is also not a shield but in fact attracts additional objects toward Earth and that once close to the Earth-Moon system, the Moon then nudges the objects into collisions with Earth. Haven't people already run models WITHOUT Jupiter and WITHOUT the Moon? And didn't those studies conclude that we NEED Jupiter (and his comrades) to shield the inner planets? mahuna

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