An artist’s rendering of a system showing its host star, transiting planet, and erratic protoplanetary disk
NASA/JPL-Caltech/R. Hurt, K. Miller (Caltech/IPAC)
The world seen orbiting a 3-million-year-old star 520 light-years from Earth is one of the youngest known planets, providing a window into early planet formation.
The star is an early-stage dwarf star that is much darker and more massive than our sun. Its age has been calculated by comparing the intensity and wavelengths of the light it emits with other stars.
Madison Barber at the University of North Carolina at Chapel Hill and his colleagues studied the star using NASA’s Transiting Exoplanet Survey Satellite (TESS). They discovered a planet about a third of Jupiter’s mass and 10 times the diameter of Earth by noticing the decrease in starlight as the planet passed in front of it.
The mass and size of the world suggest that it is either a large rocky planet, known as a super-Earth, or a small gas giant, called sub-Neptune, in the process of formation.
The Earth took between 10 million and 20 million years to form, about 4.5 billion years ago, Barber says. “So it was surprising to see anything in 3 million years.”
The system is also notable for having a protoplanetary disk of dust and gas, meaning the star and planets are still in the process of forming, although this disk is aligned out of the plane of the system for reasons that are unclear. . “We’re not really sure what caused the misalignment,” says Barber. “It is likely that the interstellar flight occurred while the system was forming.”
The planet is very close to its star, completing an orbit every nine days, which is also surprising because it is not clear whether planets can form this close. They can move inward over time, as is thought to have happened when some of the giant planets jockeyed for position in our solar system. “It suggests that rapid planetary migration is a thing,” says Barber.
Although we know of other young planets, they tend to be much larger worlds. This can give us a closer representation of how the worlds are in us solar system was created “We try to extrapolate from these other worlds how fast planet formation might have been in the early solar system,” he says. Melinda Soares-Furtado at the University of Wisconsin-Madison.
Some young stars have also seen gaps in their protoplanetary disks after only half a million years, suggesting the existence of planets forming “along with their host stars”.
“Things seem to happen early,” says Soares-Furtado, “so it’s really cool to take pictures of systems like this.”
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