Krulwich Wonders: “Our Very Normal Solar System isn't Normal Anymore”

We are now beginning to understand that nature seems to overwhelmingly prefer [planetary] systems that have multiple planets with orbits of less than 100 days, says Steve Vogt, astronomer at the University of California, Santa Cruz. This is quite unlike our own solar system, where there is nothing with an orbit inside that of Mercury. So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up.

Robert Krulwich

Hmm, 700 known planetary systems out of an estimated 100 billion planets in the entire galaxy? I wouldn’t start drawing conclusions as to whether our own system is typical or not. They might be just as wrong as when we knew only one and assumed it was “the norm”.

But speaking of that, why assume we live in a ‘standard’ system in the first place? Look at the chart below: you might think these are four (very different) planetary systems: the first solitary gas giant, the next with a couple of Neptune-sized giants and a small rocky planet, the third a mixture of several planetary types and the last with four big Jovian planets.

Well, you would be wrong, because it’s a diagram of the biggest satellites (radius larger than 100km) of the gas giants in our solar system, from Neptune at the top to Jupiter at the bottom. Each a mini-system of its own but completely unlike each other, also not similar to the larger system they all belong to. Our solar system is far from being a quiet place – just check out the possible scenarios for the birth of the Moon – and its history probably much more violent than we suspect. Assuming the setup we see today is some sort of gold standard was always just that: an assumption with little scientific evidence.