The Planets That Aren’t What They Seem
WHEN ASTRONOMERS STARTED scouring space for signs of planets around other stars, they thought they’d be looking in the mirror. Everyone expected to see ourselves reflected back at us — after all, there’s supposed to be nothing special about us or our place in the cosmos. It should have been a tick-box exercise to find copy after copy of home.
Yet the more worlds we found, the more we realised that, when it comes to exoplanets, the universe is more like a deceptive hall of mirrors — it’s hard to distinguish between truth and illusion.
We’ve found entire classes of planets that simply don’t exist in our own backyard. Hot Jupiters that buzz around their stars in days, worlds where iron rain whips about on ferocious winds. Yet perhaps the most jarring revelation is that there are entire planetary systems without any planets that look like ours. The Sun’s planets can be neatly pigeonholed as either small, rocky worlds or large gas and ice giants. There’s nothing in between to muddy the waters. Yet time and again we’re finding stars that only have planets with sizes betwixt those of Earth and Neptune.
“According to our traditional models of planet formation, they shouldn’t even exist,” says Björn Benneke (University of Montreal).
Yet of the 4,438 confirmed exoplanets, 2,422 have radii between Earth’s and Neptune’s (1 to about 4 Earth radii). The fact that they appear
