While it's one among nearly 200 other USP planets in a catalog of over 5,500 exoplanets, what sets Tahay apart is its extraordinary density — it's about twice as dense as Earth.
When it comes to understanding nature, outliers can often be the most revealing. Such is the case for exoplanet science, where planets like Gliese 367 b — known also as Tahay — are compelling researchers to reconsider established theories on planetary formation.
Tahay is an Ultra-Short Period (USP) planet that completes an orbit around its star in a mere 7.7 hours. While it’s one among nearly 200 other USP planets in a catalog of over 5,500 exoplanets, what sets Tahay apart is its extraordinary density — it’s about twice as dense as Earth.
Unveiling a Pure Iron World
So, what could be the reason for such extraordinary density? Astronomers speculate that the planet must be almost entirely composed of iron.
Astronomers first located Tahay using data from NASA’s TESS (Transiting Exoplanet Survey Satellite) back in 2021. A recent study in The Astrophysical Journal Letters has now sharpened our understanding of the planet’s mass and radius. Authored by Elisa Goffo, a Ph.D. student at the University of Turin, the study also identifies two other planets sharing its cosmic neighborhood.
The 2021 Milestone: Initial Mass and Density Estimates
The 2021 findings, obtained using the HARPS (High-Accuracy Radial Velocity Planet Searcher) spectrograph, revealed that Tahay’s radius is 72% that of Earth and its mass is 55% that of Earth, strongly suggesting an iron composition.
However, Goffo’s new research, based on an additional 371 HARPS observations, shows that Tahay is even denser than initially thought. Its mass has been revised to 63% of Earth’s, and its radius has shrunk to 70% of Earth’s size.
How did Tahay become so extraordinarily dense? It’s unlikely that the planet originated this way. Goffo posits that the planet is likely the exposed core of what was once a much larger planet, stripped of its rocky mantle.
Beyond the Standard Theories: Goffo’s Insights
According to Goffo, one scenario could be that a catastrophic event or multiple collisions with other protoplanets stripped away Tahay’s mantle. Another less likely possibility is that the planet was born in an area unusually rich in iron.
Adding another layer of complexity, Goffo’s study also revealed two other planets in the system. Given that USP planets usually exist in multi-planet systems, this discovery further reinforces the notion.
The co-author of the study, Professor Davide Gandolfi, points out that the presence of these lower-mass sibling planets challenges but doesn’t rule out the theory that the planets formed in an iron-rich environment.
Multiple Theories, More Questions
There are three leading theories: Tahay either formed in an iron-rich area, lost its outer layers through collisions, or is the stripped-down core of a gas giant that migrated too close to its star. The researchers suggest that all these processes could have played a role in its current form.
While all we have now are theories, Tahay’s unique characteristics make it a compelling subject for further investigation. As a dense, ultra-short-period planet, it offers an ideal laboratory for understanding similar systems.
In conclusion, the researchers emphasize that this multi-planet system hosting Tahay offers a unique chance to explore the formation and migration patterns of such dense, ultra-short-period planets.
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