Astronomers believe that a recently discovered exoplanet may have experienced a massive collision in the past because of its unusual properties.
Just slightly bigger than Neptune but almost twice as dense as Earth, TOI-1853b is an exoplanet that is difficult to explain through the usual avenues for planet formation and evolution.
The heart of a much larger, gassier globe that lost its atmosphere through great violence, according to a team led by physicist Luca Naponiello of the University of Bristol in the UK and the University of Rome Tor Vergata in Italy.
“This planet is incredibly unexpected!” According to physicist Jingyao Dou of the University of Bristol, “Normally we expect planets developing with this much rock to become gas giants like Jupiter with densities equal to water.”
Despite being larger than Neptune, TOI-1853b has a density greater than that of steel. Our research suggests that this is a possibility if the planet formed as a result of extraordinarily powerful planet-planet collisions. These collisions removed some of the lighter atmosphere and water, leaving a planet with a high density and significant rock enrichment.
Exoplanet TOI-1853b is unusual among them. It is a globe the size of Neptune that is in close orbit to its star, and it rests firmly in the region known as the Neptunian desert.
Of the more than 5,500 verified exoplanets to date, only a few worlds that match this description have been discovered. We would better understand planetary creation and evolution if we could determine why there are so few exoplanets in the Neptunian desert.
Neptune is 3.88 Earth radii away from Earth, while TOI-1853b is 3.46 Earth radii away. The similarities, though, essentially stop there. Every 1.24 days, the exoplanet completes one orbit around its home star, an orange dwarf that is 80% the size of the Sun. While its radius isn’t very amazing, its mass, which is 73.2 times that of Earth, is absolutely perplexing. Just 17.15 Earth masses make up Neptune.
The team determines that TOI-1853b has a density of 9.7 grams per cubic centimeter at that size and mass. That’s crazy. The density of Neptune is 1.64 grams per cubic centimeter on average. The standard on Earth is 5.15 grams. Steel and iron both have a density of around 7.87 grams per cubic centimeter.
Neptune has a thick, extensive atmosphere, which accounts for its extremely low density. The density of TOI-1853b indicates that it must contain a significant amount of denser components and little atmosphere. (Earth’s core has a density of up to 13 grams; material inside a big body is crushed by the mass above it, increasing its density.)
To find out how a planet may have ended up this way in the galaxy, Naponiello and his team ran simulations. They discovered that a high-speed collision between two enormous, still-forming exoplanets that squashed them together and ejected the atmosphere is the most plausible cause of the phenomenon.
The University of Bristol’s Phil Carter is a physicist. “Our contribution to the study was to model extreme giant impacts that could potentially remove the lighter atmosphere and water/ice from the original larger planet in order to produce the extreme density measured,” he adds.
“We found that in order to produce TOI-1853b as it is observed, the initial planetary body would have likely needed to be water-rich and experience an extreme giant impact at a speed of greater than 75 kilometers per second.”
To ascertain whether their crash scenario is feasible, the team intends to carry out follow-up observations to search for signs of an atmosphere surrounding TOI-1853b and examine its composition.
It’s interesting to note that a different team of researchers has just discovered another, comparable exoplanet. With a density of 9.6 grams per cubic centimeter, TOI-332b has a radius of 3.2 Earth radii, a mass of 57.2 Earths, and an orbital period of 18.72 hours around an orange dwarf. Maybe the two independent teams might work together.
“We had not previously investigated such extreme giant impacts as they are not something we had expected,” explains physicist Zo Leinhardt of the University of Bristol.
The material models that underpin our simulations need to be improved, and the range of extreme gigantic impacts needs to be expanded.
The research has been published in Nature.