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View Full Version : Fascinating Caltech Study: Jupiter Likely Responsible for Today's Solar System Makeup



Fiery Phoenix
2015-Mar-25, 11:23 PM
Here (http://www.caltech.edu/news/new-research-suggests-solar-system-may-have-once-harbored-super-earths-46017)

The story has been circling the web for the past few days, but I didn't see it here so I thought I'd go ahead and share. Essentially, it explains why our Solar System looks the way it does today, with terrestrial, low-mass planets in the inner region and more massive gas giants in the outer region. It also sheds some significant light on why other star systems tend to have close-orbiting Hot Jupiters and/or massive terrestrial planets.

If you're looking for the meaty details, the actual paper itself can be read here:

http://authors.library.caltech.edu/55970/2/1423252112.full.pdf

It should be emphasized, however, that this is more like a proposal at this point and has not been taken as 'official'. Nonetheless, it seems to have captured so much attention I won't be surprised if it ends up being an officially accepted explanation for this phenomenon.

Amazing study.

Ken G
2015-Mar-26, 05:16 AM
I agree it is an interesting model, but I can take issue with some of the logic. For example, Batygin says: "Indeed, it appears that the solar system today is not the common representative of the galactic planetary census. Instead we are something of an outlier. But there is no reason to think that the dominant mode of planet formation throughout the galaxy should not have occurred here. It is more likely that subsequent changes have altered its original makeup."

In fact there is an excellent reason to think that the dominant mode of planet formation might not have happened here: we have life here, and those other systems do not (the half that have large planets close to the Sun and nothing else). In other words, Batygin's logic is that if our system is different from the rest, yet we had a generic formation, then whatever was unusual for us must have happened after formation, and Jupiter might be the culprit. But no matter how you slice it, something different happened here, so there is no logical basis for assuming that the difference happened after formation rather than during formation. All one can really say is that we have both alternatives, and he has chosen to look at the former alternative. Others might choose to look at the latter alternative. But good science never rules out an alternative without a solid logical basis, a basis that is lacking here. He has a nice model, there's no need to oversell it and claim it has to be true, ignoring other possibilities.

What's more, it's not clear that the observational biases have been properly accounted for. The article says that about half of sun-like stars have very different planetary configurations from our own, but it implies the other half don't have planets at all. But the dataset would be hard pressed to detect the planets we have in our solar system, it is better at finding planets closer to the Sun. It's possible that Kepler data would by now be capable of detecting planets like in our solar system, but there may still be room for many systems that are more like ours than like the ones described in the article, and we might not know it from Kepler data. If those systems were later discovered, it might tempt us to look at contrasting formation scenarios that distinguish the two basic types, rather than look for similar formation with different later evolution. Those are just always going to be the two cases to consider.