Jupiter Came in Like a Wrecking Ball! A New History of Our Home System

It’s difficult to determine the history of the Solar System.  The planets have been in their current orbits for Billions of years, and any signs of prior activity or configuration has to come from leftover geologies of smaller, rocky worlds.  It makes it especially difficult when the Billions of interloper asteroids and comets throughout history have to be accounted for, adding to the already complex task.  But if there is one thing humanity has going for us it’s the ability to theorize, model, simulate, and test scenarios here on Earth.  We can try new ideas and see if they match the observations of our solar system and other planetary systems in space.  If the theory answers all of our tough questions about what we see, then it becomes our most plausible theory of the formation of the solar system.

This snapshot from a new simulation by Caltech and UC Santa Cruz researchers depicts a time early in the solar system’s history when Jupiter likely made a grand inward migration.  As it moved inward, Jupiter picked up primitive planetary building blocks, or planetesimals, and drove them into eccentric orbits (turquoise) that overlapped the unperturbed part of the planetary disk (yellow), setting off a cascade of collisions that would have ushered any interior planets into the sun. Credit: K. Batygin/Caltech

In a new simulation by scientists from UC Santa Cruz and Caltech, the mighty Jupiter is actually a super-Earth killer.  In this scenario, Jupiter migrates into the inner solar system, tug boated in by the massive amounts of material present. At this point it used its massive gravity to kick a population of young super-Earths into the Sun, clearing out the inner solar system and paving the way for the smaller rocky planets present today.  But what stopped it from moving in? Saturn!  Saturn would have pulled it back out through a gravitational resonance.

When we look at other solar systems that we have studied so far, we find a lot of massive gas planets bigger than Jupiter that orbit close to their home star (Hot Jupiters).  If Jupiter formed early and was pulled in, there would have still been enough gaseous material in the outer solar system to form another smaller gas giant like Saturn which would pull it back out while leaving a small amount of material in the middle for the rocky planets.

This image shows a super-Earth exoplanet and its moons. Image credit: Luciano Mendez / CC BY-SA 3.0.

One of the biggest questions of our solar system answered by this theory is how the rocky planets have such small masses compared to the inner planets of other solar systems.  The most beautiful part of this theory is that it explains other solar systems with hot Jupiters.  Reading the article, found here, it’s clear that the simulations can explain a lot of the current properties of multiple planetary systems.

Currently we have found only a relatively small population of solar systems in our local region of the Galaxy.  Statistically we can make generalizations about all stellar systems from looking at a small population, but we also don’t have the best data on those systems.  For example, it naturally is more difficult to see the innermost parts of an exoplanetary system due to the brightness of the host star blocking out any small planetary signatures.  As we gather better data from other planetary systems we will be able to refine theories of how our own planets formed.

This theory shows how our solar system is an outlier, an uncommon configuration built by perfect timing and a wrecking ball gas giant.  But does this mean that life can only form in a solar system where this happens? And if so does this mean life is extremely rare? With the massive population of stars in the Universe, its likely we will someday find another planetary configuration like our own, but will it harbour life?


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