Earth is about 4.5 billion years old. Elias 2-24 b, a giant planet about 450 light-years away, is less than 1 million years old, which makes it at least 4,500 times younger. In a study published Sept. 16 in The Astrophysical Journal Letters, astronomers confirmed it as the youngest known planet. It is still growing inside the disk of gas and dust around its star.

The previous record holders were a four-way tie between two planets orbiting the star PDS 70 and two orbiting WISPIT 2, all more than 5 million years old. Elias 2-24 b beats them by a wide margin, and its age creates a puzzle.

Current models predict that a Jupiter-size planet at Jupiter's distance from the Sun, just over five times Earth's distance, takes about 5 million years to form, and even longer farther out. Elias 2-24 b orbits about 55 times Earth's distance from the Sun, roughly 11 times Jupiter's distance, and it is already a giant. "Elias 2-24 b shows us that even our best planet-formation models are still missing some important processes," co-author Lucas Cieza of Chile's Instituto de Estudios Astrofísicos said, according to NASA's release on the record-breaking baby planet.

A Gap in the Dust and a Decade-Old Question

The mystery began with a gap. About a decade ago, the ALMA observatory in Chile imaged a prominent gap in the dusty disk around the young star Elias 2-24. Growing planets sweep material from their paths, so a gap strongly suggested a planet. The European Southern Observatory's Very Large Telescope later detected a faint point of light inside it.

Astronomers debated what that dot was. Planet formation theory said gaps like this appeared too early and too far from the star for a planet to have formed there. The dot could also have been an imaging defect or a background star.

A team led by Andrea Bernardi, a doctoral candidate at Universidad Diego Portales in Chile, went back to older data. The researchers analyzed archival coronagraph observations of seven young stars, including Elias 2-24, in the Keck Observatory Archive, a NASA-funded partnership between the observatory and the NASA Exoplanet Science Institute at Caltech/IPAC. A coronagraph blocks a star's glare so fainter objects nearby can be seen. They found the same point of light in Keck observations from 2018 and 2020.

Comparing the images settled the question. The object moved the way a planet orbiting the star would, not like a camera artifact or an unrelated star in the background. "The planets should be found within the gaps, since they are carving them," Bernardi said in NASA's release. "And that's exactly where we found Elias 2-24 b."

How Young and How Big

The planet's age comes from its star. Earlier studies estimated that Elias 2-24 is only about 200,000 to 400,000 years old, and the star is still accreting material at a high rate, Gizmodo reported. To model the planet, the researchers assumed an age of 1 million years, an upper limit.

Its mass is less certain. NASA describes the planet as about as massive as Jupiter, while Gizmodo reported that the study's modeling allows two to 14 times Jupiter's mass. The spread exists because astronomers estimate a young planet's mass from its brightness, and that conversion depends on models that are least reliable at this earliest stage, when the planet is still wrapped in gas and dust.

Co-author Alice Zurlo of Universidad Diego Portales, who conducted the initial 2018 Keck observations of the system, described the challenge in a statement from the W. M. Keck Observatory. "This planet is a rare gem, as it is currently undergoing a stage of its evolution for which theoretical models still struggle to reliably predict its mass, entropy, and, consequently, its expected luminosity," she said. She added that constraining its dynamical mass could help researchers refine and recalibrate evolutionary models for young planets.

The evidence is strong but has limits. The finding is peer-reviewed and based on direct images from two epochs, supported by independent VLT and ALMA observations. The planet's mass has not been measured from its gravitational pull, and its age is inferred from its host star.

Roman Joins the Search

Finding planets this young is hard. Most of the roughly 6,000 confirmed exoplanets are billions of years old and orbit close to their stars, largely because most were found by watching stars dim as planets pass in front of them. Newborn planets hidden in dust and orbiting far out are much harder to detect. "We are mostly blind to these baby planets right now," Cieza said.

That may change soon. NASA's Nancy Grace Roman Space Telescope launched Aug. 30, and Gizmodo reported that Roman has already captured its first starlight in space. Its Roman Coronagraph Instrument is designed to image faint planets near bright stars, and NASA said it could find planets in much tighter orbits, including true Jupiter analogs. Elias 2-24 b sits about 10 times farther from its star than those targets.

For readers on Earth, the payoff is a view into our own past. Our solar system formed from the same kind of disk about 4.6 billion years ago, and planets like Elias 2-24 b let astronomers watch that process as it happens. If giant planets can form this fast and this far out, models of how giant planets form may need revision.

The bottom line: a planet less than 1 million years old has broken the age record, and its size and distance challenge formation models. Its exact mass is still uncertain. Roman's observations should help show whether such fast-growing giants are rare or common.

What Readers Want to Know

What is Elias 2-24 b?

It is a giant planet about 450 light-years from Earth that is less than 1 million years old. It is the youngest known planet and is still forming inside its star's disk.

How much younger is it than Earth?

Earth is about 4.5 billion years old, so Elias 2-24 b is at least 4,500 times younger.

Why does its age surprise scientists?

Models predict that a Jupiter-size planet at Jupiter's distance takes about 5 million years to form, and longer farther out. Elias 2-24 b is already a giant at about 55 times Earth's distance from its star.

How was it confirmed?

Researchers found the planet in archived Keck Observatory coronagraph images from 2018 and 2020. Tracking its motion across those images showed it was a planet, not an artifact or background star.

How big is it?

NASA describes it as about as massive as Jupiter, and the study's modeling allows up to about 14 times Jupiter's mass. The planet is still growing and wrapped in dust, so its exact mass is uncertain.

What were the previous record holders?

Two planets orbiting PDS 70 and two orbiting WISPIT 2 shared the record. All of them are more than 5 million years old.

Will more baby planets be found?

Astronomers expect so. NASA's Roman Space Telescope carries a powerful coronagraph designed to spot faint planets near bright stars.