What If There Was A Super Earth Sandwiched Between Mars And Jupiter?


Ever wondered what our solar system might be like with an earthlike planet —- or one even five or six times larger —- orbiting between Mars and Jupiter?

Conventional theory has long held that the gravitational influence of Jupiter would have ripped any terrestrial mass planet to shreds or never allowed it to form there at all. But a new paper just accepted for publication in The Planetary Science Journal argues that a “hypothetical planet” ranging from one to ten earth masses located between the orbits of Mars and Jupiter would wreak havoc on our inner solar system within a timeframe of only a few million years.

There’s been much speculation about whether the solar system could safely harbor an additional planet between Mars and Jupiter where most of our asteroids are located, Stephen Kane, a planetary astrophysicist at the University of California in Riverside and the paper’s lead author, told me via email. This study shows how such a planet would destabilize planetary orbits, he says.

As Kane notes in his paper, there would be gradual increases in the orbital eccentricities of both Earth and Venus. This would lead to catastrophic close encounters between the two planets within a time frame of only eight to nine million years.

I conducted several thousand dynamical simulations that placed the additional planet at locations in the range 2 to 4 astronomical units (one A.U. is equal to one Earth-Sun distance), says Kane. Each simulation was run from the present time until 10 million years into the future, and the changes in the orbits for all the planets were carefully monitored, he says.

Kane’s paper reveals that after only some 3.5 million years, a super-earth inserted between the present orbits of mars and Jupiter would begin to vacillate wildly. Its hypothetical orbit would range roughly between the present orbits of Saturn and Neptune. Kane writes that this period of instability would persist for the next several hundred thousand years. That is, until the super-Earth is ejected from the system. From start to finish such a super earth would be expected to be ejected from our solar system within about 4.2 million years, Kane notes.

All this just adds fuel to the fire that our own solar system is both dynamically fragile and architecturally unique.

As for whether our own solar system ever harbored a super-earth that orbited between Mars and Jupiter?

There does not appear to be evidence of a previous super-Earth, at least not interior to the orbit of Neptune, says Kane. Such a planet ejection would result in a much higher eccentricity for some or all of the planets due to conservation of angular momentum, he says. The dwarf planet Ceres is currently the largest object in the asteroid belt and has a radius that is only some 27 percent the radius of our Moon, Kane notes. But it’s possible there were larger objects in that region when the solar system was very young, he says.

Jupiter may be the real culprit behind all this orbital instability, however.

Our own Jupiter is more massive than all the other planets in the solar system, says Kane. My simulations show that a consequence of that is even a minor perturbation of Jupiter’s orbit can have far reaching consequences, he says.

Theory has it that Jupiter and Saturn migrated inward from their present location due to interactions with the disk from which they formed, and then back out again due to interactions with each other, says Kane. The inward migration of Jupiter and the orbital gravitational resonances of Jupiter (that affect the whole of what we term the Main Asteroid Belt) had a profound effect on the formation of the terrestrial planets, he says. This would include truncating the size of Mars and the prevention of planet formation in the region between Mars and Jupiter, says Kane.

As for the stability of our current inner solar system?

The present orbital eccentricities of Venus and Earth are extremely low, says Kane. But the gravitational influence of a super-earth in certain locations and the resulting perturbations of Jupiter’s orbit could cause both Venus and Earth to have a close encounter, he says. As a result, they could even be ejected from the solar system, says Kane.

Are solar systems without Jupiter analogs ultimately more stable?

Kane’s paper supports the idea that planetary systems without Jupiter analogs would in fact be best for a given solar system to harbor multiple, stable earthlike planets in its inner solar system.

“Without a giant planet, multiple terrestrial planets can fit in the Habitable Zone of a star,” said Kane.

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