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Earth-Sized Exoplanet ‘Made Mainly of Iron’ Likely Remnant Core of Much Larger World
Earth-Sized Exoplanet ‘Made Mainly of Iron’ Likely Remnant Core of Much Larger World
Sputnik International
Successive missions scrutinizing nearby stars for signs of exoplanets have yielded knowledge of a bewildering array of worlds. The latest entry into that catalog of the bizarre is Tahay, which seems to be made of almost pure iron.
2023-09-21T21:02+0000
2023-09-21T21:02+0000
2023-09-22T05:13+0000
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The discovery was explained in detail in an article published recently in the Astrophysical Journal Letters by a team led by Elisa Goffo, a Ph.D. student at the Physics Department of the University of Turin.The planet was first spotted in data collected in 2021 by the Transiting Exoplanet Survey Satellite (TESS), which replaced NASA’s Kepler mission in conducting all-sky surveys to look for exoplanets. It is an ultrashort-period planet that orbits its host star, a red dwarf named Añañuca, in just 7.7 hours, indicating it is extremely close to the star’s surface.That’s not unusual when it comes to red dwarf stars, which are smaller than sun-sized stars, but when the astronomers looked closer using the High-Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory, they saw something strange about the planet’s size and mass - it's actually more dense than previously thought.Tahay was found to have a radius of about 70% that of Earth’s, while its mass is 63% that of Earth’s, indicating a much higher density, on par with that of iron, not rock. Earlier findings placed Tahay's mass and radius at 55% and 72% of Earth's, respectively."This could have important implications for the formation of GJ 367b,” she said. “We believe that the planet might have formed like the Earth, with a dense core made mainly of iron, surrounded by a silicate-rich mantle."So how did it arrive in its present state, with nothing left but a big ball of iron? A collision with another protoplanet during the star system’s formation, when things are more chaotic, might have been the cause.Two other possibilities also exist: Tahay could be the remnant core not of an Earth-like rocky world, but of a large gas giant like Neptune, the atmosphere of which was long blasted away by Añañuca’s radiation. It could also have simply formed that way, in an unusually iron-rich part of the protostar’s nebula - however, the scientists consider that the least likely explanation.Indeed, a 2020 study couldn’t explain the amount of iron in the planet Mercury, which is approximately 70% metallic and only slightly less dense than the Earth, but has just 5% of the mass of the Earth. Like Tahay, Mercury its the closest planet to its host star, although Tahay is 100 times closer to Añañuca than Mercury is to the sun.
https://sputnikglobe.com/20230908/massive-neptune-sized-exoplanet-denser-than-steel-believed-result-of-planetary-collisions-1113216932.html
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exoplanet; transiting exoplanet sky survey; astronomy; gliese 367b
exoplanet; transiting exoplanet sky survey; astronomy; gliese 367b
Earth-Sized Exoplanet ‘Made Mainly of Iron’ Likely Remnant Core of Much Larger World
21:02 GMT 21.09.2023 (Updated: 05:13 GMT 22.09.2023) Several successive missions aimed at scrutinizing nearby stars for signs of exoplanets orbiting them have yielded knowledge of a bewildering array of worlds. The latest entry into that catalog of the bizarre is Tahay, also known as Gliese 367b, which seems to be made of almost pure iron.
The discovery was explained in detail in
an article published recently in the Astrophysical Journal Letters by a team led by Elisa Goffo, a Ph.D. student at the Physics Department of the University of Turin.
The planet was
first spotted in data collected in 2021 by the Transiting Exoplanet Survey Satellite (TESS), which replaced NASA’s Kepler mission in conducting all-sky surveys to look for exoplanets. It is an ultrashort-period planet that orbits its host star, a red dwarf named Añañuca, in just 7.7 hours, indicating it is extremely close to the star’s surface.
That’s not unusual when it comes to red dwarf stars, which are smaller than sun-sized stars, but when the astronomers looked closer using the High-Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory, they saw something strange about the planet’s size and mass - it's actually more dense than previously thought.
Tahay was found to have a radius of about 70% that of Earth’s, while its mass is 63% that of Earth’s, indicating a
much higher density, on par with that of iron, not rock. Earlier findings placed Tahay's mass and radius at 55% and 72% of Earth's, respectively.
"You could compare GJ 367b to an Earth-like planet with its rocky mantle stripped away,” Goffo said in a news release.
"This could have important implications for the formation of GJ 367b,” she said. “We believe that the planet might have formed like the Earth, with a dense core made mainly of iron, surrounded by a silicate-rich mantle."
8 September 2023, 20:22 GMT
So how did it arrive in its present state, with nothing left but a big ball of iron? A collision with another protoplanet during the star system’s formation, when things are more chaotic, might have been the cause.
"A catastrophic event could have stripped away its rocky mantle, leaving the dense core of the planet naked," Goffo explained.
Two other possibilities also exist: Tahay could be the remnant core not of an Earth-like rocky world, but of a large gas giant like Neptune, the atmosphere of which was long blasted away by Añañuca’s radiation. It could also have simply formed that way, in an unusually iron-rich part of the protostar’s nebula - however, the scientists consider that the least likely explanation.
"Possible pathways may include the formation out of material significantly more iron-rich than thought to be normally present in protoplanetary disks. Although it is not clear if disks with such a large relative iron content specifically near the inner edge (where most of the material might be obtained from) exist," they wrote in the paper.
Indeed,
a 2020 study couldn’t explain the amount of iron in the planet Mercury, which is approximately 70% metallic and only slightly less dense than the Earth, but has just 5% of the mass of the Earth. Like Tahay, Mercury its the closest planet to its host star, although Tahay is 100 times closer to Añañuca than Mercury is to the sun.
