> <i>To test whether the peas-in-a-pod pattern was real, I concocted (on my laptop) imaginary planetary systems in which the sizes of planets orbiting a given star were random. Could some sort of bias in Kepler’s method of finding planets—which favors the detection of large planets close to their stars—contrive to make the planets in each of my imaginary systems appear to fit the pattern?</i><p>> <i>The answer was no: in more 1000 trials with randomly assigned planet sizes put through a virtual Kepler’s detection scheme, a pattern of similarly-sized planets in the same systems never emerged. This computational experiment did not reproduce what we observe in the Kepler planetary systems. Thus, the regular sizes of planets is a real astrophysical pattern.</i><p>This is actually a really cool use of computer simulations that I haven't noticed before (but I'm sure has been done in the past): simulating expected output for a known bias.<p>I wonder if it would be feasible to do the reverse too for a kind of parameter fitting to fix our model:<p>1. Create a reasonable approximate model for both Kepler's expected detection bias and for planet size distribution.<p>2. Constrain parameter space for these models as much as possible, to minimize the search space.<p>3. Using these models, generate a set different planetary sets for different parameters.<p>4. Find the outputs with the closest match in statistical "shape" of the actually measured data.<p>5. generate new input parameters based on these output that lead to set outputs to refine shape until certain level of matching has been found<p>If done naively this would probably take a lot of computation and result in large a solution space: the more parameters, the higher the conditionality of this space. So the models should be approximations with as few parameters to produce reasonable results, and with constraints on said parameter values based on known physics. This would narrow down both the parameter space to search the possibly valid outputs of this space.<p>Based on these parameters differ from the output we had expected before, we might then get a direction of where to look for the physics that <i>does</i> explain the distribution.
So, the Kepler method of detecting planets only works if the orbital plane (maybe not the right term) of the star we are looking at is such that the planets are between us and the star, right? So if we are looking down at the "top" of the star then no planets will obscure the star, right? Also the planets need to be passing in front of the star at precisely the right time that the planet and star and our telescope are all lined up more or less. Someone looking at our solar system would need to wait quite awhile to see Pluto pass by. If all of that is correct, how are we able to see any exoplanets? My layman's guess would be that it would be incredibly unlikely that everything would line up so that we could see anything. What am I missing in this picture?
I don't stay up on the latest developments in this field day to day, but my understanding is that most of the extrasolar systems that we can observe are a little on the wonky side to begin with, otherwise we wouldn't be able to detect that there are planets in them at all. Super-Jupiters orbiting close enough to make their stars wobble, binary star systems, all kinds of stuff. I'm not sure I'd hazard a guess at any kind of definite conclusion at the makeup of the universe and our overall specialness in it, with tools of observation as crude and limited as we've still got; there's a long way to go just to survey what is out there.
That's pretty comforting. As the solar system we live in seems more unusual it seems more credible that planets with advanced life might be rare. In which case the emptiness of the galaxy seems more explicable.
So to test for unknown bias and sensor anomalies, they put raw modelled data through the statistical machinery looking for homogenized outputs.<p>This strikes me as wrong. If you want to know if your filter is bad, you plug in ground truth and add known noise models. If you want to know if your noise models are wrong, you cant do the same thing, you need to point your sensor at a known object (e.g. calibrate).<p>They seemed to have done a cursory analysis of the former type, which is not the same as saying "our pea-pod hyoothesis is correct".
As a side note, the drawing attached to this article is of Edward Tufte's quality, so much information condensed into a simple-looking drawing and it's so easy to get the idea from a single glance.
My first thought is this should call into question the method(s) we are using to measure and observe planets in other solar systems.<p>Think on this, the one solar system we can empirically confirm with multiple observation techniques, i.e. we've sent satellites to other planets in, is way different than solar systems we are observing by measuring light differences from light years away.
> The answer was no: in more 1000 trials with randomly assigned planet sizes put through a virtual Kepler’s detection scheme, a pattern of similarly-sized planets in the same systems never emerged. This computational experiment did not reproduce what we observe in the Kepler planetary systems. Thus, the regular sizes of planets is a real astrophysical pattern.<p>Any explanation to this? I'd assume small planets are just harder to detect. Large planets could be gas giants that react differently to our observation technique. Also they tend to form further away from the star, leading to a longer orbital period and fewer observations. Could these contribute to an observation bias and does the simulation include these factors?
Random question.. If they are looking for transits, doesn't that presuppose the data will find close in planets? I believe that's not the only method, but wouldn't that push more close planets than distant ones? Would it find transits of things like Neptune or Uranus that take hundreds of years?
This result says that random sizes and orbits are not consistent with observations. But there is a huge gap between "random" and "uniform", even ignoring all the possible different distributions.<p>We know that our solar system is not random -- e.g., we have the "platonic solids" spacing, for our inner planets. So, our solar system is also not described by the disallowed model.<p>It's great that some subset of random distributions are ruled out for systems that happen to have planets packed close to their star, but that says nothing at all about how we compare to the the overwhelming majority of other systems systematically excluded from the sample.<p>As with most results that hit the popular press, any actual significance is garbled to the point of meaninglessness.<p>But a good graphic can be worth a lot if you ignore the headline.
Stranger? We already knew our solar system was strange. At least compared to the other solar systems we observed ( admittedly a tiny fraction - a couple hundred out of 200 billion solar systems ).<p>We already knew gas giants ( a major cause of our peculiarity ) are rare. And we knew that most solar systems had uniform sized planets ( within a particular range ) orbiting very close to their suns.<p>The article doesn't offer anything new that would make us think the solar system is stranger. It just reaffirms everything we knew and why we thought it was strange to begin with.
I am fascinated about how less we know overall about the earth, and the solar system. I would not be surprised if we found life in the solar system. May not be advanced, but multi cellular life. I mean life as it was on earth some 10,000 years ago, with early humans and all.<p>Edit: Sorry I shared my fictitious fascination. It would probably make a good movie, humans finding pre-historic humans on Titan or Europa.
Not convincing.<p>We know Kepler results are heavily biased for (1) systems edge-on to us (2) with big planets (3) very close to their star.<p>The only conclusion to draw is that planets that are all clustered close to their star tend to similar sizes. Then only Mercury is unusual. Even there, it's not unique.<p>Stars with planets distributed more widely, like ours, have been systematically filtered out of the results. We have no idea how common they are. It might be that they are rare, and that would make us unusual. In that case, distribution would be interesting and relative sizes would be unremarkable.<p>If in fact they are common, there is no reason to expect sizes in those cases to be uniform.<p>A system that condensed from a cloud with less intrinsic rotation seems more likely to have its planets clustered close. Less intrinsic rotation could also result in more uniformity.