Planet for heavy metal fans? A Earth-sized globe made entirely of iron has been discovered.

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4 min readSep 28

This is one of the strangest planets we’ve learned about in recent years. It orbits remarkably close to its star and is ultra-dense. Scientists suspect it is composed entirely of iron.

[Image by pizar almaulidina from Pixabay]

In recent years, we’ve become accustomed to the idea that there are many exoplanets in space. We’ve also learned that they can vary significantly from the planets in our Solar System. In our system, there are rocky inner planets (with Earth being one of them) close to the star, and farther out, there are gas and ice giants.

However, Earth’s neighbors in space are relatively unvaried. If you were to venture beyond the Solar System, you would encounter some of the strangest planets imaginable. This year, we wrote about the discovery of planets, one of which was denser than steel and another that was heavier than lead. We also wrote about a planet that reflects light like a mirror and one that is as fluffy as marshmallow.

Now, another unique globe has joined the ranks of cosmic oddities. It’s essentially a massive ball of pure iron. It’s called Gliese 367 b, or Tahay.

Exoplanet named after a flower

The second word is the local name for Calydorea xiphioides, a flower endemic to Chile. It has a particular feature — it blooms for only 7–8 hours a year. Exoplanet Gliese 367 b was named after it because its orbital period is only 7.7 hours. That’s how long it takes to orbit its star, a red dwarf.

As such, Gliese 367 b belongs to a special class of exoplanets with ultra-short orbital periods (Ultra-short-period planets, USP). Currently, we know of over 5,000 exoplanets, but only 200 of them are classified as USP planets. For this reason alone, Gliese 367 b is exceptional. However, it has one more distinct feature.

When it was discovered two years ago (as part of the Transiting Exoplanet Survey Satellite or TESS sky survey), it was observed to be small but relatively massive. At that time, it was estimated to have a radius of 72% of Earth’s radius. Its mass was estimated to be 55% of Earth’s mass. This suggested that the planet is dense and likely composed mostly of iron.

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