A Puffed-Up Extrasolar Planet

Maggie McKee writes, "New Scientist Space reports astronomers have found a planet less dense than a wine cork and 38% larger than Jupiter. It circles a star about 450 light years from Earth. A similarly bloated planet has been found before (HD 209458b), so these puffed-up planets may be quite common. But no one knows how they got so swollen. One possibility is 'that some poorly understood mechanism has separated hydrogen and helium in each planet.'"

Comments

Re:Astronomers...

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Nope. If you take a small number of samples from a very large and diverse population, the odds are actually very high that several of the very uncommon results (e.g. planet types) will be highly overrepresented. It's a variation on "there are so many extremely unlikely things which can happen that it's extremely likely that a few of them will happen."

Re:Another possibility

[merlin_jim]

Maybe these bloated planets are the only large enough for us to be able to see at this point.

There are certainly limits to the lower range of sizes of planets we can detect - and since most detection methods work based on gravitational influence, it is apparent that a large worlds close in to its sun will be easier to detect than a small one far away.

Many of the first planets we found were very large with very close orbits, however recently we've been able to detect terrestrial - "rocky" that is as opposed to gas giant (none earth sized or smaller yet, alas) - planets around other stars

So while these planets may in fact be common (and I would suspect internal heating more than some esoteric mechanism that we don't understand to explain their densities), we also know of many other types of planets - the most common being dense hot giants with very close orbits to their primaries...