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Our Solar System Isn't Normal

300 points by sajid 13y ago

tocomment 13y ago
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.
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- 3JPLW 13y ago
  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 a planet like our Jupiter.
  - schiffern 13y ago
    Kepler uses occlusion, not wobbling.
    - Udo 13y ago
      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).
    - teamonkey 13y ago
      Yes, and it's designed to detect Earth-sized planets as well as larger gas giants.
      - Tuna-Fish 13y ago
        But detection probability is directly correlated to planet size and shortness of the local year. Eventually, Kepler and Kepler-like probes will be able to locate all earth-like planets with orbits that cross the path between the star and us. However, this technique will find the larger planets with shorter orbits first.
        teamonkey 13y ago
        Yes indeed, but the point is that according to current theories Kepler should already be finding more Earth-sized planets than it has and few inner gas giants. The observable evidence does not match the predicted model.
      - Retric 13y ago
        Can detect is one thing, can detect at the same distance is another. Assume you can detect an earth like planet at say 100 light years and a Jupiter sized planet at 1,000 light years and you find 1000x as many Jupiter sized planets that does not mean there are 1,000x as many just that you can detect them in 1,000x as much space. Granted I don't know there search pattern but we are talking about less than 1,000 systems at this point. And I think we have found 2 reasonably earth like planets already which suggests there are at a minimum millions of them in this galaxy.
    - lutorm 13y ago
      True, but occultations are also very biased towards planets with small semimajor axis, because the solid angle that produces an occultation goes roughly as 1/a.
      - schiffern 13y ago
        You use "but" as though you're disputing some statement I made, when I intentionally avoided making any statement outside my knowledge. I said Kepler does use occlusion, and does not use wobbling. I'm not trying to single you out here. I'm just curious what one has to say on HN so as not to be corrected. Is there some "don't assume I've implicitly made a bunch of unsupported remarks" initialism that I can tack on to the end of all my posts? /DAIIMABOUR
        dandelany 13y ago
        No need to get defensive, lutorm was just pointing out that the assumption made by the OP is still supported. His comment was simply a productive, interesting addition to yours, unlike this complaint.
        fusiongyro 13y ago
        I'm glad he brought it up. I have noticed it is getting awfully hard to say anything precisely enough to get it past the cadre of pedants.
        cmccabe 13y ago
        Actually, the correct expression is "cohort of pedants."
        fusiongyro 13y ago
        Are these tears of laughter or rage?
  - sbierwagen 13y ago
    Most exoplanets are discovered by the radial velocity method, (tracking the doppler shifts in the spectrographic lines in the light emitted by the star) but the best data is produced by Kepler, which uses occlusion and thus can tell you how big the planet is, by how much the star dims. Both methods are biased towards finding big planets (which produce clear, easy to detect spikes) that are close to their star. (so you get enough data points) Kepler tends to be a little more biased, simply because it hasn't been running long enough: http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scatter_Discovery_Method_TR.png http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scat... Kepler was launched in 2009. Realistically, you'd have to run it for another three or four centuries if you wanted to detect exoplanets that orbit as far out as Neptune. (orbital period: 165 years) No wonder we're seeing a lot of planets orbiting close in!
    - S4M 13y ago
      That's a very interesting point. I knew about this method but didn't connect it to the article. it would be interesting to have some stats on the number of stars that were probed and that were found to have exoplanets. I have no idea of what the actual numbers are, but if we need to probe 100000 stars to find one that has an exo planet, it means that the radial velocity method might not be that efficient.
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- joshuahedlund 13y ago
  Indeed. Couldn't you just as easily say we used to think our solar system was abnormal because we hadn't discovered any planets around other stars?
- madaxe 13y ago
  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-in things with short periods are the easiest planets to detect by a country mile, as you get a nice big occlusion along with a nice big wobble, all happening on nice short timescales. This entire article is oriented around sample bias due to current instrumentation and techniques. We have little hope of spotting the equivalent of, say, Uranus, with the same orbital period and distance, as we'd need, um, a good few centuries of observations using wobble and occlusion to be certain - and the net effects measured would be tiny, so you'd need a huge pile of data to get a statistically significant measure. Finally, earth-mass planets at an earth-like distance - again, tricky. Less tricky than the above, arguably, particularly if they have atmospheres (spectral changes are a dead giveaway), but still tricky. JWST could serve up the goods.
  - saalweachter 13y ago
    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.
- mturmon 13y ago
  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.
  - lake99 13y ago
    tocomment is right. Watch http://www.youtube.com/watch?v=8JTneTI82nE http://www.youtube.com/watch?v=8JTneTI82nE from 5:00 to 7:00. Yes, scientists may have been quoted in this article, but I have seen how most journalists mangle, ignore, or sensationalize things that were said.
    - scott_s 13y ago
      She also agrees with the main point of the original article, which is that our solar system is probably unusual. (From 6:47 to 7:00.)
      - lake99 13y ago
        Unusual is a subjective term. She says 10%-20% of the planetary systems are like ours. Are you saying that that was the point made in the original article too?
- namuol 13y ago
  Precisely my thoughts. Has this notion been refuted? I would think this is common thought among the community of exoplanet hunters.
- Alex3917 13y ago
  "I would argue the exo-planets we have found so far are a very biased sample." All of science is based on sampling bias, by definition. That's one of the main reasons why science isn't a perfect lens for discovering truth. But just because something is probably wrong doesn't mean it isn't a 'scientific fact.'
ra 13y ago
Kepler has been revolutionary in discovering these 700 odd planetary systems, but we can't even begin to imagine what surprises await for when we point the James Webb Space Telescope at them. One of JWSTs mission objectives is to study the planetary systems discovered by Kepler, and the origins of life. http://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Mission http://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Miss...
- tocomment 13y ago
  What specifically will the telescope tell us about this exo-planets? It surely can't image them directly, right?
  - ra 13y ago
    Not quite, but JWST will be out at the L2 point, beyond the moon in essentially what amounts to an earth-matching solar orbit. It's large aperture infrared sensors will have an unobstructed view of the universe (unlike Hubble which is in low earth orbit, and so only gets 90 minute windows of observation). Basically, using IR spectroscopy we will be able to analyse the atmospheric composition as well as the thermal emissions of exoplanets. Finally, JWST won't be limited to a small, fixed field of view like Kepler.
Filligree 13y ago
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?
- Udo 13y ago
  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.
- IsaacL 13y ago
  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.
  - run4yourlives 13y ago
    There's not much suggesting that there is only one Great Filter. After all, we haven't met anyone else yet, so the likelihood of another filter being in our future is just as real as it is if there was one in our past. Call it the "two neptune filter", to borrow from the article. :-)
  - gwern 13y ago
    I don't think it's a good candidate; certainly it pushes some amount of the Filter into our past, but even if only 1 in 700 solar systems is Sol-like, there are so many we'd still expect to see tons of aliens. For a single-step Filter or for solar systems to even be a majority of the filter, you need a step so unlikely that it can push the presence of interstellar life down from, like, trillions of star systems to ~1.
Gravityloss 13y ago
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.
- vec 13y ago
  Probably not, assuming our current theories about how these systems form are correct. Our best guess is that hot jupiters form about where our jupiter or saturn is and their initial orbit decays inward. If so, that would tend to destroy the orbit of anything vaguely earth-sized on the way in.
unreal37 13y ago
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?
- simonh 13y ago
  http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet
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- johngalt 13y ago
  They are more commonly called rouge planets. http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet
  - MartinCron 13y ago
    I always thought Mars was the rouge planet.
  - rbanffy 13y ago
    I bet johngalt's spell czech is on. ;-)
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- pavel_lishin 13y ago
  Other terms are "orphan planets" and "rogue planets". Naturally, since they don't orbit a star and are usually pretty dark, they're hard to find, though there are candidates: http://www.nbcnews.com/id/49823152/ns/technology_and_science-space/#.UKQa4IZNga8 http://www.nbcnews.com/id/49823152/ns/technology_and_science... http://en.wikipedia.org/wiki/Rogue_planet#Known_or_possible_rogue_planets http://en.wikipedia.org/wiki/Rogue_planet#Known_or_possible_... One could argue that these are proto-stars, or brown dwarves, I guess - but to me, no fusion == planet. http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet
namuol 13y ago
Couldn't the techniques we are using be biasing the results? Maybe solar systems like ours are simply harder to detect.
- NicolasBeuzeboc 13y ago
  I agree, I'm speculating that by looking at a star wobble or it's brightness decrease that method of detection would bring up all these systems with close orbiting planets that would be bigger than "normal".
calinet6 13y ago
"We have to figure out why our solar system turned out different from all the others." Not entirely—we have to understand statistics and the anthropic principle, which states "observations of the physical Universe must be compatible with the conscious life that observes it." (Wikipedia: http://en.wikipedia.org/wiki/Anthropic_principle http://en.wikipedia.org/wiki/Anthropic_principle). In other words, our situation appears "perfect" because it was one of the many random combinations available which produced an observer able to look at it. In other words, the fact that our solar system is so stable might just be a random anomaly, but the fact that it was so stable resulted in our existence, and therefore our contemplation of the fact. As an analogy, winning the lottery is extremely rare—if you go and interview the person who won the lottery, they must think themselves very lucky. But on the grand scale, the probability of someone winning the lottery in the entire pool is exactly one. We know that a winner necessarily exists—just as we know that we, as winners of the cosmic lottery, necessarily exist. But that just tells us that someone won the lottery—something we already knew. It may be that the lottery is rigged, and that there are some characteristics of our particular solar system which are amenable to life, and those things are definitely valuable to study and find out, so that we might be able to recognize other solar systems capable of supporting life in some way. But by no means is our solar system special in any light: it's only special in that its particular conditions produced lifeforms able to observe it. "We are a way for the cosmos to understand itself." - Carl Sagan Another random question: are the planetary systems we've discovered similar to each other? If ours is significantly deviant from a significant clustering that would be pretty interesting. And of course, that's surely what the original findings were probably about.
- stephenhuey 13y ago
  Unlike a cash lottery for which we intend there to be a winner, winners of a cosmic lottery do not "necessarily" exist--a winner like us is not guaranteed, I mean.
  - calinet6 13y ago
    Not guaranteed, no, but it has been verified experimentally.
Shivetya 13y ago
Being a long time fan of 4x games, well of space games in general, this article makes me smile. I remember reading game forums where one subject that always arose was galaxy and system formations. So many of our concepts are strictly based on the very little observable data we have. Its great to live in a time when many assumptions are proven to be just that. Now the question that remains is, which configurations are more favorable to life, not just as we know it.
- yolesaber 13y ago
  A bit off-topic, but can you recommend any recent space 4x games to check out? The last one I played was Galactic Civilizations II and I enjoyed it immensely.
  - ekimekim 13y ago
    There's a new-ish one called Endless Space, which I would describe as Gal Civ inspired. It's a little weird in that all players take turns simultaneously (you still have movement restrictions, etc, but it adds a real-time component because you want to wait to react to your opponent's movements, but also there's a time limit). The impression I got was that it was a way to speed up gameplay (less sitting around while others make their moves). But it's a cool little game, lots of race customisation (with a few truly unique race benefits), interesting four-category tech tree (and equivalently, four ways to win), custom ship classes built out of components (like Gal Civ). The combat is a little weird, they have some card-game-like thingy that can significantly influence battle outcomes. EDIT: Not a turn-based game but there's also this: http://triton.ironhelmet.com/ http://triton.ironhelmet.com/ Neptune's Pride is an always-on real time game played over several weeks in matches of up to 12 players. The mechanics are refreshingly simple, and there's a focus on diplomacy and betrayal in order to come out top.
  - icambron 13y ago
    I liked Endless Space. Also Sins of a Solar Empire.
gweinberg 13y ago
I think the author has the "frost zone" theory backwards. It's not that it's too cold for rocky planets to form outside the frost zone (after all, there are some planet-sized moons out there) but rather that inside the frost zone it is too hot for planets to hold on to hydrogen, so you don't get gas giants. I would think that a gassy planet close to a star would have to have a really big solid or liquid core of heavy elements.
- teamonkey 13y ago
  The frost line is the point at which ice crystals can form of the major planetary gasses. The theory was that outside the frost line these crystals would add to the density of particulates in the region, therefore larger planets would form outside the frost line and they would have a greater proportion of gasses than the inner planets.
qdog 13y ago
I think everyone here concentrating on sampling bias is missing the point. The evidence in solar systems so far does NOT fit the theory involving a frost line, and giants like Jupiter are unexpectedly observed tightly orbiting suns. Whether our solar system is normal is conjecture, but our model for how solar systems are(were?) formed is obviously flawed. Pretty interesting find, imho.
- chc 13y ago
  I don't see how the fact that gas planets are capable of migrating inward shows that our model for planetary formation is deeply flawed. I didn't think the current model said that it was impossible for planets to migrate inward. The point about sampling bias is that our current techniques are bad at spotting systems like ours. If this is true (I think it is, but I'm not qualified to say), we wouldn't expect the evidence to fit our theory even if our theory were true because we are nearly incapable of finding evidence that does fit our theory no matter how much of it there is out there.
  - qdog 13y ago
    Perhaps I mangled that a bit, instead of frost line I should have just said the seemingly most popular theory of how the solar system formed. From the article the bit that caught my eye: Mike Brown, an astronomer at Caltech, wrote me that while everybody is busy hunting for an Earth-like planet, they missed this story. "Before we ever discovered any [planets outside the solar system] we thought we understood the formation of planetary systems pretty deeply." We had our frost line. We knew how solar systems formed. "It was a really beautiful theory," he says. "And, clearly, thoroughly wrong."
- rjd 13y ago
  I did some reading into this last year while I was stuck in bed sick and what I came across was it was to do more with light pressure than a frost line. The frostline has more to do with where water is likely to form than how a come to exist. Light has trouble pushing heavy materials outwards, so theres a denser percentage of them in close to a star, the lighter the material the more it gets pushed out, high percentage of hydrocarbons in outer planets. Like a giant centrifuge. So our system should be fairly standard unless the rules of physics are different elsewhere. That doesn't exclude random formations as you are dealing with super heated eddies, explosions etc... during formation. Or even stars pulling there planets in. Both our planet set up, and hot Jupiters are to be expected because its a giant chaotic exploding mess.
transfire 13y ago
Oh Heaven for Betsy. Every time some nitwit looks at new data with results they did not expect, suddenly every thing we have ever known is wrong. Give me a break. Here's a "lightbulb" for you: A large gas giant near a star is created in the same fashion as a binary star system (a formation that is quite common) with the simple difference that the planet did not get enough material to actually become a star.
peter303 13y ago
All the conventional planet hunting methods are biased towards fast, large, close-in planets. If we could run Kepler for 20 years we might see systems more like ours.
tenpoundhammer 13y ago
This is a grand example of our infinite hubris.
CyberDroiD 13y ago
Goof balls can't even see most of the solar systems, and they are saying what is and what is not normal? Hubris alert!
jksmith 13y ago
What is normal in the context of the universe? What is context in the context of the universe?
bitwize 13y ago
That is AWESOME. The fact that there is so much diversity of planets and solar systems out there flabbergasts me. I don't even care about what kind or whether there's life out there -- just thinking about how there are so many different worlds with prevailing conditions that I never even dreamed of gives me the chills. Space... space... so much space... gotta see it all...
jammi 13y ago
Regarding no gassy planets near our sun: The rocky ones, including earth, [are supposedly the cores of old gassy ones](http://www.astrobio.net/exclusive/4220/rocky-planets-could-have-been-born-as-gas-giants http://www.astrobio.net/exclusive/4220/rocky-planets-could-h...).
mrab 13y ago
If space is infinite, it is entirely possible that we are ridiculously close to the norm.
- mrab 13y ago
  Or that there isn't a norm at all!
pm 13y ago
Does anyone know how far away we are from being able to confirm the presence of planets as we might on a photograph? Or the obstacles we face getting to a high enough resolution?
- grkvlt 13y ago
  Minus five years? See this HST image from 2008: http://hubblesite.org/newscenter/archive/releases/2008/39/image/e/format/xlarge_web/ http://hubblesite.org/newscenter/archive/releases/2008/39/im...
Allower 13y ago
When I read "nature prefers" and the author admits the data's sample size is less than a drop in an ocean (we found < 1000 solar systems), I just have to stop reading.

300 points by sajid 13y ago

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.

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3JPLW 13y ago
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 a planet like our Jupiter.
- schiffern 13y ago
  Kepler uses occlusion, not wobbling.
  - Udo 13y ago
    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).
  - teamonkey 13y ago
    Yes, and it's designed to detect Earth-sized planets as well as larger gas giants.
    - Tuna-Fish 13y ago
      But detection probability is directly correlated to planet size and shortness of the local year. Eventually, Kepler and Kepler-like probes will be able to locate all earth-like planets with orbits that cross the path between the star and us. However, this technique will find the larger planets with shorter orbits first.
      - teamonkey 13y ago
        Yes indeed, but the point is that according to current theories Kepler should already be finding more Earth-sized planets than it has and few inner gas giants. The observable evidence does not match the predicted model.
    - Retric 13y ago
      Can detect is one thing, can detect at the same distance is another. Assume you can detect an earth like planet at say 100 light years and a Jupiter sized planet at 1,000 light years and you find 1000x as many Jupiter sized planets that does not mean there are 1,000x as many just that you can detect them in 1,000x as much space. Granted I don't know there search pattern but we are talking about less than 1,000 systems at this point. And I think we have found 2 reasonably earth like planets already which suggests there are at a minimum millions of them in this galaxy.
  - lutorm 13y ago
    True, but occultations are also very biased towards planets with small semimajor axis, because the solid angle that produces an occultation goes roughly as 1/a.
    - schiffern 13y ago
      You use "but" as though you're disputing some statement I made, when I intentionally avoided making any statement outside my knowledge. I said Kepler does use occlusion, and does not use wobbling. I'm not trying to single you out here. I'm just curious what one has to say on HN so as not to be corrected. Is there some "don't assume I've implicitly made a bunch of unsupported remarks" initialism that I can tack on to the end of all my posts? /DAIIMABOUR
      - dandelany 13y ago
        No need to get defensive, lutorm was just pointing out that the assumption made by the OP is still supported. His comment was simply a productive, interesting addition to yours, unlike this complaint.
        fusiongyro 13y ago
        I'm glad he brought it up. I have noticed it is getting awfully hard to say anything precisely enough to get it past the cadre of pedants.
        cmccabe 13y ago
        Actually, the correct expression is "cohort of pedants."
        fusiongyro 13y ago
        Are these tears of laughter or rage?
- sbierwagen 13y ago
  Most exoplanets are discovered by the radial velocity method, (tracking the doppler shifts in the spectrographic lines in the light emitted by the star) but the best data is produced by Kepler, which uses occlusion and thus can tell you how big the planet is, by how much the star dims. Both methods are biased towards finding big planets (which produce clear, easy to detect spikes) that are close to their star. (so you get enough data points) Kepler tends to be a little more biased, simply because it hasn't been running long enough: http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scatter_Discovery_Method_TR.png http://en.wikipedia.org/wiki/File:Exoplanet_Period-Mass_Scat... Kepler was launched in 2009. Realistically, you'd have to run it for another three or four centuries if you wanted to detect exoplanets that orbit as far out as Neptune. (orbital period: 165 years) No wonder we're seeing a lot of planets orbiting close in!
  - S4M 13y ago
    That's a very interesting point. I knew about this method but didn't connect it to the article. it would be interesting to have some stats on the number of stars that were probed and that were found to have exoplanets. I have no idea of what the actual numbers are, but if we need to probe 100000 stars to find one that has an exo planet, it means that the radial velocity method might not be that efficient.
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joshuahedlund 13y ago
Indeed. Couldn't you just as easily say we used to think our solar system was abnormal because we hadn't discovered any planets around other stars?
madaxe 13y ago
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-in things with short periods are the easiest planets to detect by a country mile, as you get a nice big occlusion along with a nice big wobble, all happening on nice short timescales. This entire article is oriented around sample bias due to current instrumentation and techniques. We have little hope of spotting the equivalent of, say, Uranus, with the same orbital period and distance, as we'd need, um, a good few centuries of observations using wobble and occlusion to be certain - and the net effects measured would be tiny, so you'd need a huge pile of data to get a statistically significant measure. Finally, earth-mass planets at an earth-like distance - again, tricky. Less tricky than the above, arguably, particularly if they have atmospheres (spectral changes are a dead giveaway), but still tricky. JWST could serve up the goods.
- saalweachter 13y ago
  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.
mturmon 13y ago
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.
- lake99 13y ago
  tocomment is right. Watch http://www.youtube.com/watch?v=8JTneTI82nE http://www.youtube.com/watch?v=8JTneTI82nE from 5:00 to 7:00. Yes, scientists may have been quoted in this article, but I have seen how most journalists mangle, ignore, or sensationalize things that were said.
  - scott_s 13y ago
    She also agrees with the main point of the original article, which is that our solar system is probably unusual. (From 6:47 to 7:00.)
    - lake99 13y ago
      Unusual is a subjective term. She says 10%-20% of the planetary systems are like ours. Are you saying that that was the point made in the original article too?
namuol 13y ago
Precisely my thoughts. Has this notion been refuted? I would think this is common thought among the community of exoplanet hunters.
Alex3917 13y ago
"I would argue the exo-planets we have found so far are a very biased sample." All of science is based on sampling bias, by definition. That's one of the main reasons why science isn't a perfect lens for discovering truth. But just because something is probably wrong doesn't mean it isn't a 'scientific fact.'

ra 13y ago

Kepler has been revolutionary in discovering these 700 odd planetary systems, but we can't even begin to imagine what surprises await for when we point the James Webb Space Telescope at them. One of JWSTs mission objectives is to study the planetary systems discovered by Kepler, and the origins of life. http://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Mission http://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Miss...

tocomment 13y ago
What specifically will the telescope tell us about this exo-planets? It surely can't image them directly, right?
- ra 13y ago
  Not quite, but JWST will be out at the L2 point, beyond the moon in essentially what amounts to an earth-matching solar orbit. It's large aperture infrared sensors will have an unobstructed view of the universe (unlike Hubble which is in low earth orbit, and so only gets 90 minute windows of observation). Basically, using IR spectroscopy we will be able to analyse the atmospheric composition as well as the thermal emissions of exoplanets. Finally, JWST won't be limited to a small, fixed field of view like Kepler.

Filligree 13y ago

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?

Udo 13y ago
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.
IsaacL 13y ago
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.
- run4yourlives 13y ago
  There's not much suggesting that there is only one Great Filter. After all, we haven't met anyone else yet, so the likelihood of another filter being in our future is just as real as it is if there was one in our past. Call it the "two neptune filter", to borrow from the article. :-)
- gwern 13y ago
  I don't think it's a good candidate; certainly it pushes some amount of the Filter into our past, but even if only 1 in 700 solar systems is Sol-like, there are so many we'd still expect to see tons of aliens. For a single-step Filter or for solar systems to even be a majority of the filter, you need a step so unlikely that it can push the presence of interstellar life down from, like, trillions of star systems to ~1.

Gravityloss 13y ago

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.

vec 13y ago
Probably not, assuming our current theories about how these systems form are correct. Our best guess is that hot jupiters form about where our jupiter or saturn is and their initial orbit decays inward. If so, that would tend to destroy the orbit of anything vaguely earth-sized on the way in.

unreal37 13y ago

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?

simonh 13y ago
http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet
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johngalt 13y ago
They are more commonly called rouge planets. http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet
- MartinCron 13y ago
  I always thought Mars was the rouge planet.
- rbanffy 13y ago
  I bet johngalt's spell czech is on. ;-)
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pavel_lishin 13y ago
Other terms are "orphan planets" and "rogue planets". Naturally, since they don't orbit a star and are usually pretty dark, they're hard to find, though there are candidates: http://www.nbcnews.com/id/49823152/ns/technology_and_science-space/#.UKQa4IZNga8 http://www.nbcnews.com/id/49823152/ns/technology_and_science... http://en.wikipedia.org/wiki/Rogue_planet#Known_or_possible_rogue_planets http://en.wikipedia.org/wiki/Rogue_planet#Known_or_possible_... One could argue that these are proto-stars, or brown dwarves, I guess - but to me, no fusion == planet. http://en.wikipedia.org/wiki/Rogue_planet http://en.wikipedia.org/wiki/Rogue_planet

namuol 13y ago

Couldn't the techniques we are using be biasing the results? Maybe solar systems like ours are simply harder to detect.

NicolasBeuzeboc 13y ago
I agree, I'm speculating that by looking at a star wobble or it's brightness decrease that method of detection would bring up all these systems with close orbiting planets that would be bigger than "normal".

calinet6 13y ago

"We have to figure out why our solar system turned out different from all the others." Not entirely—we have to understand statistics and the anthropic principle, which states "observations of the physical Universe must be compatible with the conscious life that observes it." (Wikipedia: http://en.wikipedia.org/wiki/Anthropic_principle http://en.wikipedia.org/wiki/Anthropic_principle). In other words, our situation appears "perfect" because it was one of the many random combinations available which produced an observer able to look at it. In other words, the fact that our solar system is so stable might just be a random anomaly, but the fact that it was so stable resulted in our existence, and therefore our contemplation of the fact. As an analogy, winning the lottery is extremely rare—if you go and interview the person who won the lottery, they must think themselves very lucky. But on the grand scale, the probability of someone winning the lottery in the entire pool is exactly one. We know that a winner necessarily exists—just as we know that we, as winners of the cosmic lottery, necessarily exist. But that just tells us that someone won the lottery—something we already knew. It may be that the lottery is rigged, and that there are some characteristics of our particular solar system which are amenable to life, and those things are definitely valuable to study and find out, so that we might be able to recognize other solar systems capable of supporting life in some way. But by no means is our solar system special in any light: it's only special in that its particular conditions produced lifeforms able to observe it. "We are a way for the cosmos to understand itself." - Carl Sagan Another random question: are the planetary systems we've discovered similar to each other? If ours is significantly deviant from a significant clustering that would be pretty interesting. And of course, that's surely what the original findings were probably about.

stephenhuey 13y ago
Unlike a cash lottery for which we intend there to be a winner, winners of a cosmic lottery do not "necessarily" exist--a winner like us is not guaranteed, I mean.
- calinet6 13y ago
  Not guaranteed, no, but it has been verified experimentally.

Shivetya 13y ago

Being a long time fan of 4x games, well of space games in general, this article makes me smile. I remember reading game forums where one subject that always arose was galaxy and system formations. So many of our concepts are strictly based on the very little observable data we have. Its great to live in a time when many assumptions are proven to be just that. Now the question that remains is, which configurations are more favorable to life, not just as we know it.

yolesaber 13y ago
A bit off-topic, but can you recommend any recent space 4x games to check out? The last one I played was Galactic Civilizations II and I enjoyed it immensely.
- ekimekim 13y ago
  There's a new-ish one called Endless Space, which I would describe as Gal Civ inspired. It's a little weird in that all players take turns simultaneously (you still have movement restrictions, etc, but it adds a real-time component because you want to wait to react to your opponent's movements, but also there's a time limit). The impression I got was that it was a way to speed up gameplay (less sitting around while others make their moves). But it's a cool little game, lots of race customisation (with a few truly unique race benefits), interesting four-category tech tree (and equivalently, four ways to win), custom ship classes built out of components (like Gal Civ). The combat is a little weird, they have some card-game-like thingy that can significantly influence battle outcomes. EDIT: Not a turn-based game but there's also this: http://triton.ironhelmet.com/ http://triton.ironhelmet.com/ Neptune's Pride is an always-on real time game played over several weeks in matches of up to 12 players. The mechanics are refreshingly simple, and there's a focus on diplomacy and betrayal in order to come out top.
- icambron 13y ago
  I liked Endless Space. Also Sins of a Solar Empire.

gweinberg 13y ago

I think the author has the "frost zone" theory backwards. It's not that it's too cold for rocky planets to form outside the frost zone (after all, there are some planet-sized moons out there) but rather that inside the frost zone it is too hot for planets to hold on to hydrogen, so you don't get gas giants. I would think that a gassy planet close to a star would have to have a really big solid or liquid core of heavy elements.

teamonkey 13y ago
The frost line is the point at which ice crystals can form of the major planetary gasses. The theory was that outside the frost line these crystals would add to the density of particulates in the region, therefore larger planets would form outside the frost line and they would have a greater proportion of gasses than the inner planets.

qdog 13y ago

I think everyone here concentrating on sampling bias is missing the point. The evidence in solar systems so far does NOT fit the theory involving a frost line, and giants like Jupiter are unexpectedly observed tightly orbiting suns. Whether our solar system is normal is conjecture, but our model for how solar systems are(were?) formed is obviously flawed. Pretty interesting find, imho.

chc 13y ago
I don't see how the fact that gas planets are capable of migrating inward shows that our model for planetary formation is deeply flawed. I didn't think the current model said that it was impossible for planets to migrate inward. The point about sampling bias is that our current techniques are bad at spotting systems like ours. If this is true (I think it is, but I'm not qualified to say), we wouldn't expect the evidence to fit our theory even if our theory were true because we are nearly incapable of finding evidence that does fit our theory no matter how much of it there is out there.
- qdog 13y ago
  Perhaps I mangled that a bit, instead of frost line I should have just said the seemingly most popular theory of how the solar system formed. From the article the bit that caught my eye: Mike Brown, an astronomer at Caltech, wrote me that while everybody is busy hunting for an Earth-like planet, they missed this story. "Before we ever discovered any [planets outside the solar system] we thought we understood the formation of planetary systems pretty deeply." We had our frost line. We knew how solar systems formed. "It was a really beautiful theory," he says. "And, clearly, thoroughly wrong."
rjd 13y ago
I did some reading into this last year while I was stuck in bed sick and what I came across was it was to do more with light pressure than a frost line. The frostline has more to do with where water is likely to form than how a come to exist. Light has trouble pushing heavy materials outwards, so theres a denser percentage of them in close to a star, the lighter the material the more it gets pushed out, high percentage of hydrocarbons in outer planets. Like a giant centrifuge. So our system should be fairly standard unless the rules of physics are different elsewhere. That doesn't exclude random formations as you are dealing with super heated eddies, explosions etc... during formation. Or even stars pulling there planets in. Both our planet set up, and hot Jupiters are to be expected because its a giant chaotic exploding mess.

transfire 13y ago

Oh Heaven for Betsy. Every time some nitwit looks at new data with results they did not expect, suddenly every thing we have ever known is wrong. Give me a break. Here's a "lightbulb" for you: A large gas giant near a star is created in the same fashion as a binary star system (a formation that is quite common) with the simple difference that the planet did not get enough material to actually become a star.

peter303 13y ago

All the conventional planet hunting methods are biased towards fast, large, close-in planets. If we could run Kepler for 20 years we might see systems more like ours.

tenpoundhammer 13y ago

This is a grand example of our infinite hubris.

CyberDroiD 13y ago

Goof balls can't even see most of the solar systems, and they are saying what is and what is not normal? Hubris alert!

jksmith 13y ago

What is normal in the context of the universe? What is context in the context of the universe?

bitwize 13y ago

That is AWESOME. The fact that there is so much diversity of planets and solar systems out there flabbergasts me. I don't even care about what kind or whether there's life out there -- just thinking about how there are so many different worlds with prevailing conditions that I never even dreamed of gives me the chills. Space... space... so much space... gotta see it all...

jammi 13y ago

Regarding no gassy planets near our sun: The rocky ones, including earth, [are supposedly the cores of old gassy ones](http://www.astrobio.net/exclusive/4220/rocky-planets-could-have-been-born-as-gas-giants http://www.astrobio.net/exclusive/4220/rocky-planets-could-h...).

mrab 13y ago

If space is infinite, it is entirely possible that we are ridiculously close to the norm.

mrab 13y ago
Or that there isn't a norm at all!

pm 13y ago

Does anyone know how far away we are from being able to confirm the presence of planets as we might on a photograph? Or the obstacles we face getting to a high enough resolution?

grkvlt 13y ago
Minus five years? See this HST image from 2008: http://hubblesite.org/newscenter/archive/releases/2008/39/image/e/format/xlarge_web/ http://hubblesite.org/newscenter/archive/releases/2008/39/im...

Allower 13y ago

When I read "nature prefers" and the author admits the data's sample size is less than a drop in an ocean (we found < 1000 solar systems), I just have to stop reading.