In the picture of planet formation developed to explain the solar system, giant planets like Jupiter form around rocky cores (like the Earth), which use their gravity to pull in large quantities of gas from their surroundings in the cool outer reaches of a vast disc of material. The rocky cores closer to the parent star cannot acquire gas because it is too hot there and so remain Earth-like.
The most popular alternative theory is that giant planets can form directly through gravitational collapse. In this scenario, rocky cores – potential Earth-like planets – do not form at all. If this theory applies to all the extrasolar planet systems detected so far, then none of them can be expected to contain an Earth-like planet that is habitable by life of the kind we are familiar with.
However, the team are cautious about jumping to a definite conclusion too soon and warn about the second possible explanation for the apparent disparity between the solar system and the known extrasolar systems. Techniques currently in use are not yet capable of detecting a solar-system look-alike around a distant star, so a selection effect might be distorting the statistics – like a fisherman deciding that all fish are larger than 5 inches because that is the size of the holes in his net.
It will be another 5 years or so before astronomers have the observing power to resolve the question of which explanation is correct. Meanwhile, the current data leave open the possibility that the solar system is indeed different from other planetary systems.
Does this seem a bit, well, strange, to anyone else? The conclusion is really reaching…As the article says, it’s not yet possible to detect Earth-like planets, let alone anything smaller, so the exact properties of other systems can’t really be known. Also the selection effect must be enormous given the size of planet that can be detected. The detection of extrasolar planets is still really in its infancy. Even the team themselves admit this, so when the evidence is so ambiguous is it worth issuing a press release? Couldn’t we just as easily draw the conclusion that our solar system has a 1/100 chance of occurring? While the Copernican principle isn’t a rule, it does goes against the grain to decide that the solar system is unique when there are so many things we don’t know yet.
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My suspicions were raised when the words “two ways in which planets could form” appeared. Is this “paper” — which was accepted for publication with no publication date set — merely an attempt to be published (as academians are wont to do) or an attempt to fit the research into a mold to support the theory?
The press release on which this article is based is like a political speech where ideas are tossed out to see what the responses will be. Notwithstanding, I think the article is interesting and worthy of “Front Page” status.