Having discovered roughly 4,000 exoplanets, we are certain of one thing. There are some truly peculiar worlds out there. The latest one is just 21 light-years away and is an exoplanet five times the mass of the Earth, but with a lower density.
It’s not just its mass that makes this a super-Earth, unlike our planet. Its composition does too. Known as HD219134 b, it is likely to be rich in aluminum oxide, a key component in many gemstones, and for this reason, researchers think that sapphires and rubies might be present on the planet.
This world orbits its star in just three days and is in a very hot region around the star. The team used computer models to establish how such a planet would form and discovered that it would likely be rich in calcium and aluminum, with silicon and magnesium as well, but very little iron.
The research, published in the Monthly Notices of the Royal Astronomical Society, suggests that the planet's potential composition would lead to a different cooling time from other Earth-like planets and different properties in general. The researchers think that this object is part of a new class of super-Earths, and there are other examples that could fit the description too.
"What's exciting is that these objects are completely different from the majority of Earth-like planets, if they actually exist," lead author Dr Caroline Dorn, from the University of Zurich, said in a statement. "In our calculations we found that these planets have 10 to 20 percent lower densities than Earth. We looked at different scenarios to explain the observed densities. We've thus found three candidates that belong to a new class of super-Earths with this exotic composition."
Among the potential candidates is WASP-47 e, a super-Earth in a four-planetary system 652 light-years from Earth. There is also 55 Cancri e, another extremely hot planet that has been popularized in the media as a diamond planet. The team thinks their model suits it better.
"We're turning the supposed diamond planet into a sapphire planet," said Dorn.
The alternative explanation for HD219134 b's low density is the presence of deep oceans. But the team is skeptical about this. The system has a second planet further out and it would make little sense if the inner hotter planet was the water-rich one. More research is clearly needed but a planet of sapphires and rubies is definitely a great image.