Gliese 367b, also known as Tahay, is quite an odd planet. In fact, it is considered a USP (Ultrashort Period) Planet as it only takes 7.7 hours to orbit its star.
Odd Planet Gliese 367b
The planet belongs to a small exoplanet class known as super-Mercuries. Its composition is similar to Mercury. However, it is denser and larger.
Gliese 367b was found by astronomers through 2021 Transiting Exoplanet Survey Satellite (TESS) data. It was found when the TESS picked up a weak signal from the Gliese 367 red dwarf star. This signal was detected at TESS' detection capability limits. Because of this, astronomers knew that the planet was tiny like the Earth.
In scientists' catalog of over 5,000 planets, there are nearly 200 other USP planets. This means that in such aspects, this planet is not entirely unique.
However, it still remains an outlier in certain aspects, most especially because it is an extremely dense planet. Its density is equivalent to nearly double the Earth's.
In the 2021 study, researchers made use of the HARPS (High-Accuracy Radial Velocity Planet Searcher) spectrograph in the European Southern Observatory. They did so in order to know the density and mass of the planet. Doing so enabled them to identify that the planet's mass was 55% that of Earth's and its radius was 72% that of Earth's. These findings showed that the planet was most likely made of iron.
In the recent study, astronomers were refining the radius and mass of the planet with better measurements. Interestingly, the study also found two of Gliese 367b's planetary siblings, G 367 c and d.
Gliese 367b Is Denser Than Expected
The researchers still used HARPS for examining the tiny planet. This time, they utilized 371 HARPS observations. However, their findings revealed that the density of the planet was even greater than what was previously discovered in 2021. This recent research reveals that the mass of Gliese 367b is 63% that of Earth's, while its radius is 70% that of Earth's.
This means that the density of G367b is equivalent to twice the Earth's.
Mysterious Density
How the planet ended up this way remains a mystery, as it is unlikely that it remained the same since its formation. There is a possibility that its core was stripped off a rocky mantle.
Elisa Goffo, a PhD student from the University of Turin's Physics department and the lead author of the study, explains that they think that the iron planet had a similar formation with Earth. Its core could primarily contain iron that is surrounded by a mantle rich in silicate.
Goffo explains that something incredible could have taken place for the odd planet to lose its own mantle. This may have left its dense core naked, while internal and inter-protoplanet collisions could have shed off the planet's outer layer.
There is also a possibility that the planet was born in a protoplanetary disc region that is unusually rich in iron. This hypothesis, however, seems unlikely.
Another hypothesis holds that the planet could be a remnant of a gigantic gas world. For this possibility to work, it would have been necessary for the planet to form far from the star before migrating inside. Currently, Gliese 367b is extremely close to its star to the point where its atmosphere may have been boiled due to its star's strong irradiation.
Overall, there are three possible ways to explain Gliese 367b's oddness. While all of them remain possibilities, it may not be necessary to just settle with just one of them. The researchers conclude the planet is an extraordinary focus for knowing more about the migration and formation of USPs.
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