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Our Solar System Isn't Normal

npr.org

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Re: Our Solar System Isn't Normal

#11

Post by Udo »

schiffern wrote: post #6
3JPLW wrote: post #5

Earlier quoted context omitted.

I was very surprised that the article made no mention of such a bias. It was my first thought, too. I'm not terribly up-to-date on how Kepler has been detecting planets, but isn't it due to the 'wobble' of the stars? Surely they'll find planets that orbit faster (and wobble their stars faster) first. It'll take many many years of very consistent observations (or one very lucky day) to see a wobble (or occlusion) from…

Kepler uses occlusion, not wobbling.

Still, a very rare event requiring a precise alignment of the star system that gets more improbable and more rare the further out a planet is. And I imagine we need 2-3 data points of transitions at least to exclude false positives - that simply doesn't happen within a reasonable time (e.g. Neptune has an orbital period of 165 years).

Re: Our Solar System Isn't Normal

#12

Post by Gravityloss »

And how many of those close-to-the-sun planets exclude the existence of earth-like planets a bit further out?

Maybe if they're Jupiter-sized, then they would make some orbits further out unstable, but if they're smaller...

The system can be different than ours but still just as habitable, or even more so.

Re: Our Solar System Isn't Normal

#13

Post by teamonkey »

schiffern wrote: post #6
3JPLW wrote: post #5

Earlier quoted context omitted.

I was very surprised that the article made no mention of such a bias. It was my first thought, too. I'm not terribly up-to-date on how Kepler has been detecting planets, but isn't it due to the 'wobble' of the stars? Surely they'll find planets that orbit faster (and wobble their stars faster) first. It'll take many many years of very consistent observations (or one very lucky day) to see a wobble (or occlusion) from…

Kepler uses occlusion, not wobbling.

Yes, and it's designed to detect Earth-sized planets as well as larger gas giants.

Re: Our Solar System Isn't Normal

#14

Post by Udo »

Filligree wrote: post #10

It's true that this could still turn out to be mostly observational bias, but I feel like everyone is missing the monkey wandering across the corridor. The anthropic principle, that is. Isn't it possible that, while gas planets clustered closely around the star is the normal shape of solar systems, such a configuration is not amenable to complex life?

While it's a big assumption that this is down to observational bias, at least there is some theoretical support for that statement. The further out a planet is, the less likely it becomes we can observe a transition event (which also becomes extremely rare).

Now that only our system's configuration - as special or as common as it may be - is amenable to complex life is completely unrelated and unfounded.

Re: Our Solar System Isn't Normal

#15

Post by mturmon »

tocomment wrote: post #2

I would argue the exo-planets we have found so far are a very biased sample. We don't have great technologies for detecting solar systems like ours. And at least the first few years of planet hunting we'll tend to find a lot of large giants orbiting close to their stars since they're the easiest to find.

Yes, but they quoted both Steve Vogt and Mike Brown, who have devoted most of their careers to planet-finding. And both of them said that our solar system seems unusual. Since they are well aware of the biased sample issue, I would bet there is more to it than this.

For instance, maybe they are able to model the effect of the bias, at least for some range of planetary masses, and the bias is not enough to explain the frequency-vs-mass curve they are getting. Or maybe their use of multiple techniques allows them to characterize the bias.

This excerpt from their recent paper on an Earth-like planet in the habitable zone of a nearby M-class star gives an indication of where they're going with this work:

"Using the relations given by Charbonneau et al. (2007), the reported candidates have non-negligible probabilities of transiting in front of the star (∼2.7%, 1.1%, and 0.6% for planets b, c, and d, respectively). [...] With the new generation of optical and infrared spectrographs, many nearby M dwarfs will be efficiently surveyed for low mass planets. If the detection rate holds, very soon now we may have a real chance of searching for spectroscopic signatures of water and life on one of these worlds."

In other words, detect a bunch of candidates, watch for transits, and use spectroscopic information to detect water.

Re: Our Solar System Isn't Normal

#16

Post by unreal37 »

I had no idea that:

"Or maybe it got ejected — astronomers are finding emigrant planets, lonely orbs that wander the universe with no star, just drifting. Maybe one of those used to live here."

There are planets not orbiting stars? I searched Google for "emigrant planets" and the npr article is the number 1 result for that. I think he invented the term. What are these called if I wanted to find more information about them?

Re: Our Solar System Isn't Normal

#17

Post by saalweachter »

madaxe wrote: post #9
tocomment wrote: post #2

I would argue the exo-planets we have found so far are a very biased sample. We don't have great technologies for detecting solar systems like ours. And at least the first few years of planet hunting we'll tend to find a lot of large giants orbiting close to their stars since they're the easiest to find.

Yeah, that was my first thought too. Sample bias all the way. 1) Things which orbit rapidly are easy to spot as we get lots of observations from occlusion and wobble. You can identify a planet over the course of a few weeks if it has a period measured in days. 2) Things which are massive are easy to detect using wobble methods. The closer in they are, the more wobble there is. GMm/r^2 and all that. 3) Massive close-i…

I think sampling bias is definitely the most likely reason we haven't seen any solar systems like ours, but...

Even with sampling bias, we could still be seeing something legitimately weird. We expect to detect some certain number of exo-planets with a certain range of characteristics with our current technology. We don't think this set of exo-planets is necessarily representative of the average exo-planet in the galaxy, because of the limits of our technology, but we expect to look at X stars, and see Y planets, which look about like Z (where Z is probably Jupiter-sized planets orbiting at Jupiter-like distances). We might also expect to see a few weird planets, where the solar systems are aberrations or we just got lucky and detected something better than we'd expect with our technology.

But what this article seems to be saying (maybe a little poorly) is that the set of planets observed is not the subset of planets we expected to observe. We expected (say) to look at 100,000 stars, see 100 normal Jupiters, fail to see 9,900 other normal Jupiters that were there but we didn't detect, and see 1 aberration, like an Earth-like planet we accidentally detected or a hot Jupiter representing a weirdly captured wandering planet. Instead, we saw 1000 aberrations, hot Jupiters. More than we expected to see based on how we thought solar systems formed.

Just because the unexpected thing is actually extremely easy to detect once you're looking at the universe in the right way doesn't make it any less unexpected. Even if we eventually find millions more solar systems that look like ours than ones with hot Jupiters, we might still have to figure out why there are so many more hot Jupiters than we expected.

Re: Our Solar System Isn't Normal

#19

Post by IsaacL »

Filligree wrote: post #10

It's true that this could still turn out to be mostly observational bias, but I feel like everyone is missing the monkey wandering across the corridor. The anthropic principle, that is. Isn't it possible that, while gas planets clustered closely around the star is the normal shape of solar systems, such a configuration is not amenable to complex life?

It would also be a good candidate for the Great Filter - the hidden factor that has stopped the development of all the other intelligent civilisations that would otherwise be out there. That would mean this is good news - we'd rather the Great Filter lies in our past (because that means we've already survived it) than in our future.

Re: Our Solar System Isn't Normal

#20

Post by simonh »

unreal37 wrote: post #16

I had no idea that: "Or maybe it got ejected — astronomers are finding emigrant planets, lonely orbs that wander the universe with no star, just drifting. Maybe one of those used to live here." There are planets not orbiting stars? I searched Google for "emigrant planets" and the npr article is the number 1 result for that. I think he invented the term. What are these called if I wanted to find more information about…

http://en.wikipedia.org/wiki/Rogue_planet
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