The artist’s illustration depicts a planet’s likely view toward its low-mass host star. The planet, called LHS 3154b, likely has a Neptune-like composition.
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Astronomers are casting doubt on planet formation theories after discovering an exoplanet that technically shouldn’t exist.
The planet, which has about the mass of Neptune and more than 13 times the mass of Earth, was discovered orbiting an ultra-cool M dwarf star called LHS 3154, which is nine times less massive than our Sun. An M dwarf star is the smallest and most massive type of star.
The planet – called LHS 3154b – orbits closely around the star, completing one orbit every 3.7 Earth days, making it the most massive planet known in close orbit around one of the coldest low-mass stars in the universe, according to a new study. A study published Thursday in the journal Sciences. It upends the way scientists understand the formation of planetary systems.
This graphic compares the size of our Sun and Earth with the smaller, cooler star LHS 3154 and the planet it orbits, LHS 3154b.
“This discovery brings home the point of how little we know about the universe,” study co-author Suvrath Mahadevan, a professor of astronomy and astrophysics at Penn State, said in a statement. “We did not expect a planet this massive around a low-mass star.”
Star shape From large clouds of gas and dust, the remaining material forms a disk around the star where planets are later born. The amount of material inside the discs surrounding stars determines how massive the planets that form around them are. The material of the disk depends largely on the mass of the star.
For example, small M-type dwarf stars are most common throughout the Milky Way, and are usually orbited by small, rocky planets, rather than giant gas planets.
“The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to form this planet,” Mahadevan said. “But it exists, so now we need to reconsider our understanding of how planets and stars form.”
The planet orbits a star about 51 light-years from the Sun, and was discovered using the Habitable Zone Planet Finder, or HPF, mounted on the Hobby-Eberly Telescope at the McDonald Observatory in Texas.
A team of scientists led by Mahadevan built the HPF, which is designed to detect planets orbiting within the habitable zone of young, cool stars. The habitable zone is the appropriate distance from a star where a planet is warm enough to support the presence of liquid water on its surface and possibly support life.
The lower surface temperature of young stars means that planets can orbit much more closely and still retain fragile elements like water on their surfaces. As the planets orbit close to their stars, the gravitational force between both objects creates a noticeable wobble that HPF can detect in infrared light.
“Think of it like a star is a campfire. The cooler the fire gets, the closer you are to that fire to stay warm,” Mahadevan said. “The same is true for the planets. If the star is cooler, the planet will need to be closer to that star if it is to be warm enough to contain liquid water. If a planet has an orbit close enough to its ultracool star, we can detect it by seeing a very slight change in the color or light of the star’s spectra as it is dragged by an orbiting planet.
Based on modeling and analysis, the research team believes the planet has a heavy core that would require more solid material in the planet-forming disk than there was around the star, according to study co-author Megan Delamere, an astronomy graduate student. In Pennsylvania.
The researchers estimate that the amount of dust in the disk must be at least ten times greater than what is normally found in disks around low-mass stars.
“Our current theories about planetary formation have difficulty explaining what we see,” Delamere said in a statement. “Based on current survey work using HPF and other instruments, an object like the one we discovered is likely to be extremely rare, so discovering it was really exciting.”
A few massive planets have been found orbiting low-mass stars, like our planet The planet GJ 3512 b was discovered in 2019But their orbital periods are much longer, and the planets do not orbit their stars so closely.
“What we discovered provides an extreme test case for all existing planet formation theories,” Mahadevan said. “This is exactly what we built the HPF to do, to discover how the most common stars in our galaxy form planets — and to find those planets.”
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