Summary
Astronomers have confirmed Elias 2-24 b, a Jupiter-mass exoplanet less than a million years old and still forming inside its star’s gas-and-dust disk. Its confirmation came from combining archival observations from the Keck Observatory with earlier observations from ALMA and the Very Large Telescope.
Astronomers have confirmed the youngest known exoplanet: Elias 2-24 b, a world less than a million years old that is still forming inside the disk of gas and dust surrounding its young star. The planet is about as massive as Jupiter and lies roughly 450 light-years from Earth.
The result, reported by NASA from a study published in The Astrophysical Journal Letters, came from combining observations made with several telescopes. The team led by Andrea Bernardi of Chile’s Universidad Diego Portales identified the planet in archival data from the W. M. Keck Observatory in Hawaii, confirming that a faint object previously seen in a gap in the star’s disk was moving like a planet rather than being an imaging defect or a background star.
A planet caught inside its birth disk
Stars and planets form from clouds of gas and dust. Around a young star, the leftover material spreads into a rotating disk. Over time, dust, ice and rock clump together, while larger bodies can clear gaps in the disk as they orbit.
Elias 2-24 b was found inside one of those gaps. The system had already attracted attention about a decade ago, when observations from the Atacama Large Millimeter/submillimeter Array, or ALMA, revealed the gap. The European Southern Observatory’s Very Large Telescope later detected a faint point of light in the same location.
The object was difficult to interpret because planet-formation models predicted that a Jupiter-sized planet should take about 5 million years to form at a distance comparable to Jupiter’s orbit around the Sun, and longer at greater distances. Elias 2-24 b is about 55 times farther from its star than Earth is from the Sun, yet it appears to be forming while the star and its disk are less than a million years old.
The Keck observations supplied the motion needed to resolve the question. The research team searched the observatory’s archive and found the object in images from 2018 and 2020. By combining those observations with earlier data, the researchers tracked its position over time and confirmed its planetary behaviour.
A coronagraph was important to the search. This instrument blocks most of the much brighter light from the host star, allowing astronomers to look for the faint glow of a nearby planet. Directly imaging a young planet is especially challenging because the planet is embedded in dusty material and can be overwhelmed by starlight.
Why this young world matters
Most of the roughly 6,000 confirmed exoplanets described by NASA are billions of years old and orbit relatively close to their stars. Many were discovered through transits, when a planet passes in front of its star and causes a small, temporary drop in brightness. Transits are difficult to detect for planets buried in dusty disks or orbiting far from their stars.
Elias 2-24 b therefore offers a rare view of a planetary system during its construction. Its wide orbit and apparent growth inside a disk provide a way to test theories of giant-planet formation against a system much younger than the Solar System.
The discovery also shows why observations from different facilities can be more powerful together than isolated measurements. ALMA revealed the disk structure, the Very Large Telescope detected the faint source, and the Keck archive provided observations of its motion. NASA says the planet is close to the limit of what current telescopes can detect.
The finding points to a challenge for existing models: they do not yet account for how a Jupiter-mass planet could form so early and so far from its star. NASA’s Nancy Grace Roman Space Telescope, which the agency says launched on Aug. 30, is designed with a more powerful coronagraph. Using a similar imaging technique, Roman could make it easier to find young planets and search for worlds in smaller orbits, including Jupiter analogues that are currently difficult to observe through the glare of their stars.