Astronomers using the Keck Observatory on Mauna Kea have found the youngest fully formed planet around another star.

The discovery could offer important clues to the process of planetary formation, given that our solar system is “middle-aged” at 4.5 billion years, the scientists say.

The planet, dubbed K2-33b, is only 5 million to 10 million years old. K2-33b is about six times as big as Earth, or 50 percent larger than Neptune. It races around its star once every five days and is too close to it — about 5 percent of the distance from Earth to the sun — to have liquid water.

“This discovery is a remarkable milestone in exoplanet science,” said Erik Peti­gura, a postdoctoral scholar in planetary science at Caltech, in a statement this week. “The newborn planet K2-33b will help us understand how planets form, which is important for understanding the processes that led to the formation of the Earth and eventually the origin of life.”

Petigura is a co-author of the research paper on the planet published tomorrow in the journal Nature.

The planet was detected using the Kepler space telescope during its secondary or “K2” mission, and studied further by high-resolution instruments at the twin Keck observatories on Mauna Kea. As of Sunday, the planet was not listed in the K2 catalog.

The space telescope detected a periodic dimming in the light emitted by the planet’s host star, K2-33, that hinted at the existence of an orbiting planet. That was confirmed using the HIRES instrument on Keck I and the second-generation Near-Infrared Camera or NIRC2 on the Keck II.

“HIRES was used to measure the Doppler shift (radial velocity) of the star over time, and confirm that the orbiting companion is a planet,” said Trevor David, first author on the paper and a Caltech graduate student working with professor of astronomy Lynne Hillenbrand. “The high resolution spectra were also used to confirm the youth of the star, measure its temperature and how fast it is rotating, and rule out the presence of any additional stars in the system.”

He added, “At 4.5 billion years old, the Earth is a middle-aged planet — about 45 in human years. The planet K2-33b would be an infant of only a few weeks old.”

When stars form they are encircled by dense regions of gas and dust called protoplanetary disks. By the time a star is a few million years old, the planetary formation is nearly complete, and the disk has mostly dissipated.

NASA’s Spitzer space telescope found that the star K2-33 has a small amount of disk material left, indicating that it is in the final stages of dissipating.

In our solar system giant planets like K2-33b are all far from the sun.

K2-33b’s proximity to its star means it formed there or formed far away and then migrated in, the scientists said. Since it is so young, if it migrated, it did so very quickly, they added.

“In the last 20 years, we have learned that nature can produce a staggering diversity of planets — from planets that orbit two stars to planets that complete a full orbit every few hours,” Petigura said. “We have much to learn, and K2-33b is giving us new clues.”