NASA / Dana Berry
Mystery: Is our solar system normal?
ON THE face of it, it’s a biggie: fully 1.4 times the diameter of Jupiter, the largest planet in our solar system. But it is nothing unusual in itself. Discovered in 2016, KELT-11b at first seemed to be just one of many large “hot Jupiters” orbiting close to their star, causing a large drop in light whenever they cross its face.
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But when astronomers calculated KELT-11b’s mass, they found it was a minnow, with just 20 per cent of Jupiter’s mass. Combine that figure with its size, and the average density of the planet is little more than that of polystyrene packaging.
We now have a growing roster of these puffy planets: just this year we found WASP-127b, which has very similar vital statistics to KELT-11b. The problem is that they fly in the face of everything we thought we knew about planet formation, based on our solar system. “We don’t really understand how they get so inflated,” says Joshua Pepper of Lehigh University in Pennsylvania, who led the KELT-11b team.
Our solar system makes sense to us. There are the small rocky planets including Earth close in, and gas giants such as Jupiter further out. When the planets were forming, the heat near the sun chased off most gas, but greater quantities of volatile substances condensed in the cooler, outlying regions, providing bigger solid cores around which vast balls…
