I have been learning about the solar system from popular science shows. In these shows they suggest that, after having seeing around 2500 other solar systems, astronomers have concluded that our solar system is not the normal one. They see sun hugging hot jupiters and super earths close to their star. They find most systems have most of their matter closer to their star. They draw conclusions about our system, namely that our system is a freak.
We know that the first exoplanets found were hot jupiters. And they found super earths close to their star. We also know that telescope technology is always improving. With increasing telescope quality, we can find dimmer objects. These would naturally be smaller planets orbiting distant stars at further distances from their stars.
My question is this: how do we know that the apparent rare quality of our system is not an artifact of limited observing power that selects for larger objects close to their star?
Best Answer
The solar system cannot be said (yet) to be "rare" because we lack the ability to examine the planetary systems around other stars in detail. In particular, the census of low-mass planets and planets that are more than an astronomical unit from their star is very incomplete.
Nevertheless, enough is known to say that the solar system is unusual in some respects. The main oddity about the solar system is that it doesn't contain any "super-Earths" or "sub-Neptunes" at all (i.e. planets intermediate in size between Earth and Neptune), despite them being common in other systems, and the close-in planets are all small and rocky. Most ($\sim 70$%) solar-type stars have at least one exoplanet larger than the Earth orbiting with a period of 100 days or less (e.g. Kunimoto & Matthews 2020). Most of these close-in planets are 2-5 times the size of the Earth.
The presence of a Jupiter-sized planet at 3-7 au is also somewhat unusual - occurring in $<10$% of solar-type stars Wittenmyer 2016).
The lack of a hot Jupiter in the solar system is not unusual, since the occurrence rate of these is only of order 1%.
These frequencies are corrected for the known and well-understood biases in detection sensitivity associated with system geometry, signal-to-noise ratio and observing cadence. These factors can easily be accounted for in a forward modelling approach. This is where you simulate your exoplanet population, then "observe" it, in software, including all the observation biases and detection thresholds, and then adjust the characteristics of the simulated population until the simulated observations match the real observations.
Note for those wanting to discuss the anthropic principle. It seems to me that whether the planetary system around our Sun has an unusual architecture has nothing to do with our presence. What the anthropic principle may have a bearing on is explaining why we live in an unusual solar system or why we might expect the solar system to be unusual.