The newly discovered exoplanet exhibits so unusual properties that astronomers believe it must have undergone a giant impact some time ago. Although TOI-1853b is an exoplanet just slightly smaller than Neptune, it has nearly twice the density of Earth, suggesting a rock-rich composition that is difficult to explain by normal planetary formation and evolutionary pathways. Rather, a team of researchers led by physicist Luca Naponiello at the University of Rome tor Vergata in Italy and the University of Bristol in the UK found that the planet was once losing its atmosphere due to extreme violence, and is much more vast and gas-rich. I thought it was the center of the world. “This planet is so amazing! We normally think of planets made of so much rock that they become gas giants like Jupiter with densities similar to water,” said the University of Bristol. physicist Jinyao Dou explains. “TOI-1853b is about the size of Neptune, but denser than steel. Our study shows that this can happen when planets undergo highly energetic interplanetary collisions during their formation. These collisions removed some of the light atmosphere and water, leaving behind a dense and inherently rocky planet. An artist rendering of an exoplanet in the Neptune desert. (Ricardo Ramirez/University of Warwick) TOI-1853b is a rarity among exoplanets. It is trapped in a crevice known as the Neptune Desert. This world is about the same size as Neptune, which revolves around a star.
Of the more than 5,500 known exoplanets to date, only a handful of worlds have been discovered that fit this description. Understanding why the Neptune desert is so devoid of exoplanets will help us better understand how planets formed and evolved. TOI-1853b is 3.46 times her radius of Earth. Neptune’s Earth radius is 3.88. But the similarities end there. This exoplanet orbits her parent star, an orange dwarf star about 80 percent the size of the Sun, once every 1.24 days. Its radius doesn’t stretch the imagination much, but its mass is truly astonishing, at 73.2 times the mass of Earth. Neptune has only 17.15 times the mass of Earth. At this size and mass, the research team calculates the density of TOI-1853b to be 9.7 grams per cubic centimeter. this is wild. Neptune’s average density is 1.64 grams per cubic centimeter. While the Earth averages 5.15 grams, iron has a density of 7.87 grams per cubic centimeter, and steel has about the same density. Neptune has a very low density because it has a dense and extensive atmosphere. The density of TOI-1853b indicates that its composition is rich in denser material and not much in the atmosphere. (Also, the density of the Earth’s core is up to 13 grams. Matter inside a massive body is compressed by all the mass above it, increasing its density.)
Naponiero and his team ran simulations to figure out how planets in the galaxy form this way. They find that the most likely explanation is a high-velocity collision between two giant, still-forming exoplanets that collided and ejected them out of the atmosphere. His two different formation scenarios for TOI-1853b. (Napionello et al., Nature, 2023) “Our contribution to this study potentially removes the light atmosphere and water/ice from the originally larger planet to produce the extreme densities measured. It was to model a possible extreme mega-collision,” says physicist Phil Carter of the University of Bristol. “To produce TOI-1853b as observed, the original planetary body was probably rich in water and would have had to undergo an extreme giant impact at velocities in excess of 75 kilometers per second. got it.” The research team will conduct follow-up observations to look for traces in the atmosphere around TOI-1853b and analyze its composition to determine whether it is a possible collision scenario. Interestingly, another similar exoplanet has just been discovered by another group of scientists. TOI-332b has an Earth radius of 3.2 and an Earth mass of 57.2, orbits the orange dwarf star in 18.72 hours, and has a density of 9.6 grams per cubic centimeter. Perhaps two separate teams could combine their efforts.
source: https://www.nature.com/articles/s41586-023-06499-2