Archival NASA-funded data confirm youngest known planet at under a million years old

A gap in a dust disk only hints at a planet. ALMA mapped the gap around Elias 2-24 about a decade ago, and the Very Large Telescope later found a faint point of light sitting inside it ^[11]. Astronomers then argued about what the dot was, because formation theory said such gaps appear too early and too far from their stars for a planet to have carved them ^[12]. "The planets should be found within the gaps, since they are carving them," Bernardi said ^[6].

The Keck Observatory Archive, a NASA-funded partnership between the observatory and the NASA Exoplanet Science Institute at Caltech/IPAC, held the same point of light in coronagraph images from 2018 and 2020, and the team stitched those together to follow its motion over time ^[15]. The search covered archival coronagraph data on seven stars, each hosting a disk whose structures and gaps hint at planets forming ^[3]. Two other telescopes had already flagged this candidate.

Separation is what pushes on the models. The dot sits 55 times farther from its star than Earth is from the Sun ^[14]. Jupiter orbits at just over five times the Earth-Sun distance, which puts Elias 2-24 b roughly ten times farther out than Jupiter ^[2]. Models put about 5 million years on assembling a Jupiter-size planet at Jupiter's distance, and longer than that farther out ^[13]. An object of about Jupiter's mass and under a million years old, at ten times that radius, has to come together at least five times faster than the models allow at the easier distance ^[1].

The planets it displaces were already awkward. Lucas Cieza, a co-author and professor at the Instituto de Estudios Astrofisicos in Chile, said the previous record was a four-way tie between two planets at PDS 70 and two at WISPIT 2, all more than 5 million years old, and that the models already struggled with those ^[5]. "Elias 2-24 b shows us that even our best planet-formation models are still missing some important processes," he said ^[4].

By construction, the comparison sample is thin. Transits, which found most known exoplanets, work poorly on a planet buried in dust or orbiting far from its star, so the overwhelming majority of the 6,000 confirmed exoplanets are billions of years old and close in ^[8]. Otherwise the models lean on theory, simulation, and observations of young disks where no planet has been detected at all ^[9]. "We are mostly blind to these baby planets right now," Cieza said ^[10].

The record rests on the age, and NASA did not say how the age was derived ^[16]. A revision of that number would leave the detection in the gap untouched, and would move Elias 2-24 b back toward the PDS 70 and WISPIT 2 group without changing what the coronagraph saw. The star is about 450 light-years from Earth ^[7].