Astronomers have so far discovered over 3,000 exoplanets, or planets that orbit stars outside of the Solar System, but most of these alien worlds are old whose age often range from at least a billion years.
Erik Petigura, from the California Institute of Technology, and colleagues, however, appeared to have found the youngest fully formed exoplanet crossing its host star.
The Neptune-sized planet, located about 500 light-years away from Earth, is estimated to be only 5 to 10 million years old. The planet dubbed K2-33b can be considered an infant when compared to our home planet, which is about 4.5 billion years old.
Petigura and colleagues found the planet, which orbits its star K2-33 every five days using NASA's Kepler Space Telescope and the W. M. Keck Observatory on Mauna Kea, Hawaii.
The "super-Neptune," estimated to be about five times the size of the Earth and almost 10 times closer to its star than Mercury is to the Solar System's sun, is the youngest fully formed planet to be discovered around its star and one of the best characterized.
"The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune," the researchers reported in their study, which was published in the journal Nature on June 20.
Infrared measurements taken by the U.S. space agency's Spitzer Space Telescope revealed that the exoplanet's star K2-33 is surrounded by a thin disk of planetary debris hinting that the planet-formation phase of the star system is wrapping up.
Planets form from thick disks of gas and dust known as protoplanetary disks that surround young stars.
The discovery and existence of the planet likewise show that close-in planets, or those that orbit very close to their star like Mercury, achieve their final orbital distances early on.
Close-in planets may have formed close to their star or formed further out but migrated closer to their sun later on. The process was earlier believed to take hundreds of millions of years.
"With K2-33b, we're getting a glimpse of planet formation as it occurs," Petigura said. "Astronomers have believed for some time that gaseous planets need to form in the first 10 million years of their star's lifetime. K2-33b provides some of the best direct proof of this theory."