Hot Jupiters Bully Super Earths
Written by Jon Voisey
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?
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.
Filed under: Extrasolar Planets, Planetary Formation, Solar System
Tags: Extrasolar Planets, hot jupiter, super earthRelated stories on Universe Today
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November 23rd, 2009 at 12:50 pm
What this really suggests to me is that planets could be ejected from their parent starts in numerous scenarios and just be floating out there. Have we yet observed a parent-less "planet"? A super earth just floating around in interstellar space would be an interesting discovery to say the least.
November 23rd, 2009 at 2:39 pm
@ Jon,
One possible candidate is Cha 110913-773444, but there is no consensus among astronomers as to whether to classify the object as a sub-brown dwarf (with planets) or a rogue planet (with moons).
November 25th, 2009 at 4:15 pm
Jon, as Ivan pointed out, tentative discoveries have been made. There should be quite a few out there, but the trick is finding them. Planets around stars are dim enough as it is, and they have a light source RIGHT THERE to reflect. One out in interstellar space would be even dimmer. So direct detection that way isn't going to happen.
The best bet of finding them is by waiting for one to pass in front of another star and then detecting the gravitational lens it creates as the background star brightens and dims in a characteristic manner. The trouble is, it's a one shot deal. Even if you see it happen, you're not going to see it pass in front of another star. So it's hard enough to find these things in the first place, but even harder to confirm them.
Long story short, we know they have to be out there (models of forming systems tell us), but detecting them is easier said than done.
November 27th, 2009 at 12:34 pm
Apparently such a planet exists and is on its way to Earth to wreak havoc upon our world in a couple of years. Didn't you guys see the movie?!!
November 28th, 2009 at 10:12 am
I'm more worried about the Sun burning out and us having to restart it with some nukes!