There have been in these last weeks many news discussing aspects of the biggest gas giant of the Solar System, and one of them has caught my attention. This article explains how Jupiter would most likely be the responsible of the shape and the characteristics of our (rather unusual) planetary system. Why is the Solar System so special, for a start? First of all, it lacks planets that orbit closely to the Sun: now we have knowledge of exoplanets with orbits generally more packed than Mercury’s.
According to a study recently published in Proceedings of the National Academy of Sciences and available here, not happy with having prevented the formation of a planet after Mars – whose protoplanets and other components survive scattered in the Asteroid Belt – Jupiter would have also wreaked havoc in the inner orbit when changing its position towards the outer system.
(Credit: K.Batygin/Caltech)
In the simulation presented, “Jupiter migrates inward from a > 5 astronomical units (AU) to a ≈ 1.5 AU before reversing direction, can explain the low overall mass of the Solar System’s terrestrial planets, as well as the absence of planets with a < 0.4 AU. Jupiter’s inward migration entrained s ≳ 10−100 km planetesimals into low-order mean motion resonances, shepherding and exciting their orbits. The resulting collisional cascade generated a planetesimal disk that, evolving under gas drag, would have driven any preexisting short-period planets into the Sun. In this scenario, the Solar System’s terrestrial planets formed from gas-starved mass-depleted debris that remained after the primary period of dynamical evolution.”
Translated in plain English, it means that Jupiter first migrated inward toward the Sun, picking up planetesimals and setting them into eccentric orbits that sent all the forming inner planets directly to collision with our star, with the result of having them destroyed. Then, the successive formation of Saturn caused Jupiter to reverse course and migrate outward again, to assume today’s position.
This scenario is not completely new. It has been originally proposed in 2011 and it’s called “the Grand Tack’s hypothesis”. But what happened before this inward migration, and why? This has been explained in detail in the NASA’s page dedicated to it: “Jupiter formed in a region of space about three-and-a-half times as far from the sun as Earth is (3.5 astronomical units). Because a huge amount of gas still swirled around the sun back then, the giant planet got caught in the currents of flowing gas and started to get pulled toward the sun. Jupiter spiralled slowly inward until it settled at a distance of about 1.5 astronomical units-about where Mars is now.”
The new study published this week, together to offer additional support to this theory, also shows how this double migration has affected Solar System’s inner rocky planets like the Earth, which would have formed later than the outer planets, and from a different supply of components.
This would make sense of Mars’ size, for example, smaller than it would have been otherwise being farther away from the Sun than the Earth or Venus. Finally it might explain why the Asteroid Belt is made up of both dry, rocky objects and icy objects – another long-standing mystery the Dawn mission specifically aims at solving.
All mindboggling to an unscientific mind like mine, but thanks for trying to explain! Seems to underline not only the fluid and evolving state of systems (as opposed to the clockwork model of popular imagination) but also the fluid and evolving nature of theorising as new data and insights present themselves.
You’re certainly true, and this is something that never stopped amazing me. Universe changes as we change the way of looking at it – it’s not just quantum physics, it’s reality, once again, stranger than fiction.