Elias 2-24b: Astronomers confirm discovery of youngest ever exoplanet

Astronomers have confirmed the discovery of the youngest exoplanet ever found, a giant world orbiting a baby star some 450 light-years from Earth.

The planet, named Elias 2-24b, is less than one million years old. It is so young that its existence challenges the core theories of planetary formation, showing that gas giants can grow far quicker, and much further from their stars, than scientists previously thought possible.

A record-breaking infant

Until now, the youngest directly observed exoplanets were those orbiting the stars PDS 70 and WISPIT 2. Both of those are ancient by comparison, at over five million years old. Elias 2-24b breaks those records by a significant margin.

The newborn planet is massive. Researchers estimate its mass is between 1.9 and 4.0 times that of Jupiter, though it is likely much more compact. It orbits its host star at a distance of 55 astronomical units (AU) — 55 times the distance from Earth to the Sun. For comparison, Neptune, the outermost planet in our solar system, orbits at about 30 AU.

It is this combination of extreme youth, massive size, and vast distance from its star that has stunned astronomers.

Proving it exists

The discovery, published by a research team led by Andrea Bernardi at Chile's Diego Portales University, was made by looking closely at the dust and gas swirling around the star Elias 2-24.

This disk of raw material, known as a protoplanetary disk, is where planets are born. Nearly a decade ago, astronomers noticed a wide gap in this disk, and the European Southern Observatory’s Very Large Telescope picked up a tiny point of light inside it. For years, scientists debated whether the light was a real planet, a trick of the light, or an unrelated background star.

To settle the argument, Bernardi's team reanalysed coronagraph data from the W.M. Keck Observatory in Hawaii taken in 2018 and 2020. By blocking out the blinding light of the central star and comparing the bright spot's position over those years, they proved it was moving in tandem with Elias 2-24. It was not background noise, but a planet gravitationally bound to its host.

Challenging the models

The existence of Elias 2-24b upends the standard blueprint for building gas giants, known as the core accretion model. Under this theory, a solid rocky core forms first and slowly pulls in surrounding gas.

According to NASA, this process should take about five million years to build a Jupiter-sized planet at a distance of just 5 AU. To build a planet up to four times more massive than Jupiter, at 11 times that distance, should theoretically take much longer.

Yet Elias 2-24b has done it in less than a million years. The research team believes the planet did form through core accretion, meaning the process can work vastly quicker than previously assumed.

"Elias 2-24b shows us that even our best planet-formation models are still missing some important processes," Lucas Siesa, a professor at Diego Portales University and co-author of the research, said in a press release.

Finding more baby planets could help rewrite those models. Astronomers hope NASA’s Nancy Grace Roman Space Telescope, equipped with a highly advanced coronagraph, will soon reveal more of these hidden infant worlds.

"It’s incredible that with modern technology, we are actually able to see planet formation in action," Siesa said.