Astronomers have spotted a newborn planet orbiting a young star, forming in just 3 million years—a swift pace in cosmic terms that challenges current understanding of how quickly planets can emerge.
This infant world, estimated to be 10 to 20 times the mass of Earth, is one of the youngest exoplanets ever discovered. It resides within the remnants of the dense gas and dust disk—known as a protoplanetary disk—that encircles its host star and provided the building blocks for its formation.
The host star, destined to become an orange dwarf less hot and less massive than our sun, has about 70% of the sun’s mass and is approximately half as luminous. Located about 520 light-years away in our Milky Way galaxy, the star offers a unique window into early planetary development.
“This discovery confirms that planets can attain a cohesive form within 3 million years, which was previously unclear as Earth took 10 to 20 million years to form,” said Madyson Barber, a graduate student at the University of North Carolina at Chapel Hill and lead author of the study published in Nature.
Co-author Andrew Mann, an astrophysicist at the same institution, added, “We don’t really know how long it takes for planets to form. We know that giant planets must form faster than their disk dissipates because they need a lot of gas from the disk. But disks take 5 to 10 million years to dissipate. So do planets form in 1 million years? 5? 10?”
The newly discovered planet, named IRAS 04125+2902 b or TIDYE-1b, completes an orbit around its star every 8.8 days at a distance about one-fifth that between Mercury and the sun in our solar system. With a mass between that of Earth and Neptune, it is less dense than Earth and has a diameter about 11 times greater. Its exact chemical composition remains unknown.
Researchers suspect the planet formed farther from its star before migrating inward. “Forming large planets close to the star is difficult because the protoplanetary disk dissipates from the inner region near the star the fastest, meaning there’s not enough material to form a large planet that close that quickly,” Barber explained.
The planet was detected using the transit method, observing dips in the host star’s brightness as the planet passes in front of it from Earth’s perspective. It was found using data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
“This is the youngest-known transiting planet. It is on par with the youngest planets known,” Barber noted.
While exoplanets are sometimes directly imaged using telescopes, these are typically massive worlds, about ten times the size of Jupiter. This discovery showcases the potential of the transit method in detecting younger and smaller planets.
Stars and planets form from clouds of interstellar gas and dust. “To form a star-planet system, the cloud of gas and dust will collapse and spin into a flat environment, with the star at the center and the disk surrounding it. Planets will form in that disk. The disk will then dissipate starting from the inner region near the star,” Barber said.
She added, “It was previously thought that we wouldn’t be able to find a transiting planet this young because the disk would be in the way. But for some reason that we aren’t sure of, the outer disk is warped, leaving a perfect window to the star and allowing us to detect the transit.”
This discovery not only provides insight into the early stages of planet formation but also raises new questions about how quickly planets can form and migrate within their stellar systems. As astronomers continue to study young planetary systems, they hope to better understand the processes that shaped our own solar system.
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