Impact simulation. Credit: Jingyao Dou

TOI-1853b: Astronomers find a planet with a density exceeding that of steel

. Named TOI-1853b, this Neptune-sized celestial body boasts a density exceeding that of steel, rendering its composition notably unique in contrast to its peers.


An international consortium of astronomers recently unveiled the existence of a planet with an unusually dense composition, reminiscent of the aftermath of a colossal planetary encounter. Named TOI-1853b, this Neptune-sized celestial body boasts a density exceeding that of steel, rendering its composition notably unique in contrast to its peers.

TOI-1853b, not your typical world

The planet’s mass, almost double the magnitude of any comparable planet known to date, and its superlative density, signify that TOI-1853b consists of a significant proportion of rock, much more than is typically anticipated for a planet of its size.

Published in Nature, on August 30, the research was spearheaded by Luca Naponiello from both the University of Rome Tor Vergata and the University of Bristol. The team postulates that such an extraordinary composition may have arisen due to massive planetary collisions. Such intense confrontations could potentially obliterate some of the lighter atmospheric elements and water, subsequently leaving a predominant concentration of rock.

Dr. Phil Carter, a Senior Research Associate at Bristol’s School of Physics and co-contributor to the study, explained, “Past instances provide compelling evidence of monumental collisions between celestial entities within our solar system, exemplified by phenomena like Earth’s moon. Additionally, certain exoplanets have also presented evidence pointing in a similar direction.”


He further elaborated, “A myriad of diverse planets inhabit exoplanetary systems, with many not having any parallels in our solar system. They often occupy the spectrum between rocky planets and the ice giants, Neptune and Uranus. The team’s main contribution was to simulate the catastrophic impacts capable of stripping away the lighter elements and water/ice from a sizable planet, resulting in the heightened density observed.”

Evidence of cataclysmic collisions?

The findings underscore that the precursor planetary body would likely have had a water-abundant composition and would have undergone a cataclysmic collision, with speeds exceeding 75 km/s, to eventually shape TOI-1853b in its current state.

TOI-1853b serves as a pivotal evidence piece underlining the widespread occurrence of such gargantuan collisions in the genesis of planets across the universe. This significant discovery bridges existing planetary formation theories rooted in our solar system with those related to exoplanets. This unusual planet paves the way for deeper insights into the origination and evolution of planetary systems.

Jingyao Dou, a postgraduate scholar and co-contributor to the study, expressed astonishment at the discovery. “It’s intriguing to see a planet, which in its inception had such an extensive rocky composition, not evolve into gas giants akin to Jupiter. Instead, TOI-1853b, comparable in size to Neptune, has a density that surpasses steel. Such a phenomenon can transpire if the celestial body undergoes high-energy collisions during its formative stages, leading to the elimination of some of its lighter atmosphere and water, culminating in a predominantly rocky, high-density planet.”

Future endeavors for the team include meticulous follow-up examinations of TOI-1853b, with aspirations to discern any residual atmosphere and probe its composition further.


Dr. Zoë Leinhardt, an Associate Professor and co-contributor, wrapped up the discussion, stating, “The realm of extreme giant impacts was previously unchartered territory, as they weren’t anticipated. There’s a substantial scope to refine the material models fundamental to our simulations, and also to widen the spectrum of such extreme collisions being modeled.”

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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