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Bullies are everywhere and the universe is no exception. In our own solar system, Jupiter’s mass is second only to that of the Sun. Its gravitational effects tug around a set of asteroids known as the Trojans and may prevent the asteroid belt from becoming anything more substantial. Fortunately, our humble planet gets along with this gravitational monstrosity, but it didn’t have to be so. What could such massive menaces do to planets like Earth in newly forming solar systems?
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At present, over 400 known extra solar planets scattered across over 300 different solar systems. In decades past, before astronomers had such numerous examples, it was believed that other solar systems would be much like our own. But as astronomers discovered more and more systems, that belief was all but demolished.
Now it seems our own solar system is, at the very best, an oddity. Most discovered systems feature planets far larger than our own Jupiter, and many of those are in very tight orbits around their parent stars. Of course, most of these planets are detected by the “stellar wobble” method, which detects such systems more readily, and as such there is an inherent bias. But the point remains; Earths are rare. If Earth like planets were out there, we would have to do better to find them.
In 2005, a team lead by astronomer Eugenio Rivera at Lick Observatory, announced the discovery of a planet seven and a half times as massive as Earth and became the first “super-Earth” around a main sequence star. This category of exoplanets is generally defined to be planets less massive than 10 times Earth mass.
Since then, several more have been discovered. Again, most of these systems were very different than our own, although at least one was reported in the habitable zone. But as astronomers do, some where not content with simply looking to see what might be found. A recent paper by E. Podlewska, from the University of Szczecin in Poland, looked at what other configurations might be physically possible.
In general, planets can not simply exist in any configuration. For example, studies of forming planetary systems have shown that planets cannot exist in orbits too close to one another. If two such planets were similar in mass their gravity will tug each other out of stable orbits, often sending one from the solar system all together and likely sending the other spiraling into the parent star. If one is significantly larger than the other, its orbit may not be greatly disturbed, but the smaller planet would still not fare well.
The paper by Podlewska attempted to answer the question of where a super-Earth could exist in relation to a more massive planet? To answer this, they simulated systems with a massive “hot-Jupiter” (a massive, Jupiter-like planet with a tight orbit around its parent star, thus making it hot) and a super-Earth still embedded in a gaseous disk similar to what would be expected for a newly formed system. They analyzed the case of a system with both a super-Earth inside the orbit of the hot-Jupiter and exterior to it for many different separations.
Surprisingly for some ratios of distances from the parent stars, resonances formed, stabilizing the orbits for the duration of the 2500 orbit simulation. However, when they repeated the simulation for super-Earths outside of the massive planets orbit, they discovered that no matter the initial separation, the super-Earth would always be ejected from the system.
The implication for this is that, if such hot-Jupiters were to exist in the habitable zone, “then a terrestrial planet … can also be located in the habitable zone.” Podlewska also points out that, “Some of the known extrasolar gas giants as well as the recently discovered super-Earth in the Gliese 581 system are in the habitable zone.
So while living with these planetary antagonists may be difficult, it may still be possible… if you get in on the right side.