Our solar system may be unique after all, despite the discovery of at least 120 other systems with planets, astronomers said on Wednesday. All the other solar systems that have been found have big, gassy planets circling too close to their stars to allow them to be anything like Earth or its fellow planets, the British and U.S.-based researchers said. ...it is time to start thinking about the possibility that our system is unique or at least unusual, Livio said. What has been seen up to now does not bode well for the main purpose of seeking other planets -- finding life outside our solar system. "If the orbit is very elliptical then the planet may come very close to its sun at some point and that doesn't appear to be very healthy for life," Livio said.The article also mentions how the new findings have prompted changes in planetary formation theories. One of the predictions from the likes of Reasons to Believe is that research will continue to demonstrate the uniquely fine tuned characteristics Earth has necessary for advanced life to even be possible. You don't have to be a rocket-scientist or an evolutionary biologist to understand the implications. Update - Several of the comments left on this post deserve attention: Were the implications that the earth/solar/system/universe were designed by an intelligent entity for life, as evidenced by the parameters in the respective biomes being compatable with life? No, those are not the implications. The implications of fine tuning come from observing that the laws of physics do not favor a solar system capable of harboring advanced life. Note that this has nothing to do with just blind dumb luck. Low probability must be connected with viable function. For example, the mere fact that you are dealt a hand in poker despite the low probability of getting that exact hand is meaningless unless it is attached to whether or not you can win with that hand. Note also that the processes being analyzed are not of the same random quality as some wolf-like creature deciding to hang-out by the water's edge - and then eventually evolving into a whale. Type III stars (and I'm writing from memory here, so if anyone finds an error, please let me know) happened at a certain time in the Universe's history because of specific physical qualities. The makeup of our Sun was dependent on the prior existence of two different types of supernova eruptions, within precise time and distance ranges. If there had been different physical conditions, the results would have been demonstrably different. In order to enjoy the life essential benefits of our Earth / Moon system, the planetary body that supposedly hit the Earth around 4 1/2 billion years ago had to be the right size, consist of the right material, hit at the right angle, speed, and time. It is analyses like these which are much more difficult to dance around. So, if we continue to discover that independent events are necessary for advanced life to even be possible on Earth, and that the norm for those events, as seen outside our system, is that of chaotic systems (as compared to ours), what conclusions can we infer? Either we sure are impossibly lucky, or the cards were stacked from the beginning. ...I understand the implications, and they have nothing to do with Divine Creation or Intelligent Design. The fact that we, and every other Earthly lifeform that has ever existed, existed here, is proof positive that we could, and did, and nothing more. We are the product of an environment which may or not be unique. Postulate a different environment, and all bets are off. Postulate any change in the specific sequence of potentially mundane events occuring on earth over the past 4.5 billion years and all bets are off. The data is showing us that we are, in fact, in a unique environment. The data is also showing us that the range of environments in which advanced life is possible is narrow (as in, what we find here). Reference Rare Earth - Brownlee & Ward, Nature's Destiny - Denton, Origins - Shapiro. One of the sticky little features of cosmology, as well as continued research into Earth's entire history, is that very few of the "mundane" events are that. Consider, from Rare Earth, the phenomenon in which the Sun's increasing brightness is coincidentally matched by a reduction in greenhouse gases through plate tectonics (thanks to the planetary body that slammed into us early on). Interestingly enough, to claim that all bets are off is a type of myth in and of itself - for how does one show that all bets are, indeed, off? Well you know, there is one way, at least with regards to planetary formation... look at other systems and see what happens when the events causing them are shifted from our own. Ed - I think this is rather disingenuous. The method we're using only detects large, close-in planets, so that's what we find. We have a model for how they form, and that precludes earth-like planets. But that doesn't mean that such a model is the universal one, because we lack the technology to find anything to contradict it. So earth-like planets could be extremely common, or very rare - we haven't found anything to demonstrate that either way. Here are the candidate planets around main sequence stars. Confirming what Paul has stated, the overwhelming majority of planets are large planets orbiting close to their stars. This diagram comparing the mass of the planets with their orbital range may help. Note, however, that there are large planets out beyond 3 AU. Jupiter is about 5 AU from the Sun. The point I am driving is not that we haven't found Earth-sized planets (yet) but that the planets that have been found are not only a-typical to our system but that if our system were like those found so far, advanced life would not be possible. Jupiter sized planets orbiting closer than Mercury would have spelled doom for any Earth-like planet that may have formed in the system. Consider the following diagram which compares the orbital eccentricity (how much the orbit differs from a circle) and distance (the x-axis scale is logarithmic). Earth is shown as point of reference. What should also be stated is that Jupiter has an eccentricity of about 0.05. Highly circular orbits are needed to keep a system stable. Finally, note what is written about Orbital Eccentricities at Exoplanets.org:
The occurrence of circular orbits may require special initial conditions. More common initial conditions may lead to gravitational perturbations of planes by other planets or by the protoplanetary disk, leading to orbital ellipticities or ejection. Perhaps our Solar System, with its coplanar, nearly circular orbits, represents a fortuitous unperturbed, low-entropy state for a planetary system. The circular orbit of Jupiter in our Solar System promotes the stability of circular orbits among the other 8 planets. If our Jupiter were in an eccentric orbit, the Earth and Mars would likely be gravitationally scattered, perhaps out of the Solar System. Thus an anthropic argument can be made for Jupiter's circular orbit, if it affects the onset or the evolution of biology on Earth. It remains a question of molecular and evolutionary biology regarding the necessity of circular orbits and the resulting nearly uniform temperatures for life. Eccentric orbits may occur relatively commonly in extrasolar planetary systems. The second law of thermodynamics suggests that orbits, once scrambled, will remain so. While an eccentric giant planet would certainly induce dynamical dominoes for terrestrial planets, the supposed demise of life may be a circular argument.