The Youngest Confirmed Exoplanet Ever Discovered Is Rewriting Our Understanding of Planet Formation

The question of how planets first form and grow to their full size is one of the most fundamental open inquiries in modern astronomy, and researchers have long sought to answer it by observing still-developing "infant planets" — a task far easier proposed than executed.

Every planet in our solar system is a uniform 4.6 billion years old, so astronomers have to cast their observational nets far beyond our cosmic neighborhood to find far younger, recently formed worlds, making exoplanets a high-priority research target. Even so, the vast majority of the roughly 6,000 confirmed exoplanets identified to date are also billions of years old. This is not because youthful worlds are rare across the galaxy, but a side effect of common detection techniques: the widely used transit method, for example, spots tiny dips in stellar brightness when a planet passes in front of its host star, and this approach is far more sensitive to fully formed, ancient planets than to newly born counterparts.

Newly formed exoplanets are almost always buried deep inside protoplanetary disks: the swirling clouds of leftover gas and dust that act as the raw building materials for growing worlds. The extreme difficulty of locating these faint, hidden young celestial bodies is exactly what makes the recent confirmation of exoplanet Elias 2-24b — now the youngest verified planet on record — such a landmark, exciting discovery.

Led by Andrea Bernardi at Chile’s Diego Portales University, the research team identified the new exoplanet by focusing on seven protoplanetary disks marked by distinct, sizable gaps in their dense dust and gas, as prevailing theory holds that actively growing planets carve out these clear voids as they trace their orbits. They reanalyzed data captured via coronagraphy, an imaging technique that blocks out the blinding light of a system’s central star, allowing the dim reflected glow of surrounding orbiting bodies to stand out clearly.

Astronomers have known about the prominent gap in the protoplanetary disk surrounding star Elias 2-24 for nearly a decade. The European Southern Observatory’s Very Large Telescope (that is its official, delightfully straightforward name) first detected a faint point of light within this gap years ago, sparking a long-running field-wide debate over whether the signal was truly a forming planet, or just an unrelated background object or observational noise.

The researchers used position data of that faint dot collected at Hawaii’s W.M. Keck Observatory across 2018 and 2020 to track its movement over multiple years. They concluded that the bright signal was not a distant unassociated background star or equipment artifact, but a celestial body gravitationally bound to the Elias 2-24 system: in other words, a genuine exoplanet.

Elias 2-24b sits roughly 450 light-years from Earth, and orbits its host star at a distance of ~55 astronomical units (one astronomical unit equals the average distance between Earth and the Sun). Researchers estimate its maximum mass falls between 1.9 and 4 times the mass of Jupiter, though they note its physical volume is likely far smaller than our solar system’s local gas giant. Since its host star is less than 1 million years old, Elias 2-24b shares that extreme youth. Prior to this find, the youngest exoplanets ever confirmed via direct observation were the worlds orbiting stars PDS 70 and WISPIT 2, both of which are more than 5 million years old — meaning this new discovery shatters the previous age record by a massive margin.

Elias 2-24b has a set of properties that is already forcing astronomers to re-evaluate existing planetary formation models. The longstanding core accretion theory, one of the field’s standard frameworks, posits that giant planets form when a dense solid core grows massive enough to pull in large swathes of surrounding gas. The exact timeline of this process shifts based on modeled conditions, but NASA calculations note a Jupiter-sized planet should take roughly 5 million years to fully form, a timeline calibrated for worlds orbiting at ~5 AU, the same distance Jupiter sits from our Sun. For a giant planet with a far more distant orbit like Elias 2-24b, prevailing models predicted accruing its full mass would take even longer. But Elias 2-24b defies all these rules: despite sitting 55 AU from its host star, it has already developed into a full giant planet in a remarkably short 1 million years.

The research team still believes this world formed via core accretion, which would mean the process is capable of churning out giant planets far faster than scientists previously assumed. "Elias 2-24 b shows us that even our best planet-formation models are still missing some important processes," Lucas Siesa, study coauthor and professor at Diego Portales University, pointed out in a press release.

Finding more ultra-young planets to refine these incomplete models is about to become far easier than ever before. NASA’s Nancy Grace Roman Space Telescope, launched this past August, is fitted with a far more powerful coronagraph instrument than the tools the research team used to locate Elias 2-24b. Astronomers expect the new observatory will soon detect a huge cache of hidden young planets, alongside other worlds previously obscured by the blinding light of their host stars.

"This is just the beginning of a new era of discovery," Siesa said. "It’s incredible that with modern technology, we are actually able to see planet formation in action, and Roman will take planet hunting to the next level."

This story is adapted from a piece originally published on WIRED Japan, translated from Japanese.