When planet formation begins and how it occurs is still unclear, especially for massive planets. Gas giants like Jupiter could theoretically form through two mechanisms: either like a star through the gravitational collapse of a small part of the protoplanetary disk or like rocky planets through the gradual accretion of dust and gas. According to the models, the latter takes several million years and is only possible in the dense areas of the protoplanetary disk that are not too far away from the star.
The strange thing, however, is that astronomers have already discovered gaps in the protoplanetary disks of some young stars that are only a few hundred thousand years old – that is actually far too early to come from growing planets. Images of massive gas giants only a few million years old that orbit very far out in their protoplanetary disk, such as the stars PDS 70 and WISPIT 2, are also difficult to reconcile with gradual accretion.
Elijah 2-24: View into a stellar nursery
Now another “early” young planet deepens this mystery. Astronomers led by Andrea Bernardi from the University of Diego Portales in Chile evaluated coronagraph images from the Keck Observatory in Hawaii to search for planets in the protoplanetary disks of several young stars. The focus was on the young star Elias 2-24, which is around 450 light-years away from us. This young star is less than a million years old and is still growing. According to some studies, Elias 2-24 could be as young as 200,000 to 400,000 years old.
However, previous images have already shown several gaps in the gas and dust disk around this young star. In one of them, astronomers also discovered a telltale point of light, perhaps coming from a young planet. Bernardi and his team therefore targeted Elias 2-24 and its protoplanetary disk several times at intervals of two years using the powerful Keck telescopes.
A growing gas giant
And indeed: The new images confirm that there must be a young planet around the young star Elias 2-24. They show a point of light moving in an orbit around the star over the course of two years of observation. The young planet, named Elias 2-24 b, orbits in a gap in the protoplanetary disk that is around 55 astronomical units from the star – almost twice as far from the star as Neptune is from the Sun.
Position of the protoplanet Elias 2-24 b in 2018 (left) and 2020 (right). The change reveals that it is following an orbit around the star. — © Bernardi et al./ The Astrophysical Journal Letters 2026, CC by 4.0
The new recordings and previous images from the ALMA radio telescopes also suggest that the young planet Elias 2-24 b has not yet reached its full size: Apparently it continues to attract material from its surroundings: “As the planet grows, it generates a strong increase in pressure that holds millimeter-sized dust particles at the edge of the gap. This leads to the characteristic bright edge that can be seen in the ALMA image,” explain the astronomers. According to their calculations, the growing planet is already between 1.9 and four times the mass of Jupiter.
How could Elijah 2.24 b grow so big so quickly?
“Elias 2-24 b is by far the youngest exoplanet ever directly detected. Its confirmation has far-reaching significance for our ideas about planet formation,” state Bernardi and his colleagues. The young gas giant shows that planets the size of Jupiter can form much faster than previously assumed based on the PDS 70 and WISPIT 2 systems – and at distances of more than 50 astronomical units from their star.
But how? Theoretically, a massive young planet could be formed very quickly and early through the gravitational collapse of a part of the disk, as the astronomers explain. However, this is usually reflected in characteristic spiral gas structures in the protoplanetary disk – which are missing in Elias 2-24. Instead, the rotating cloud of dust and gas around the young star shows a classic structure into denser rings and narrow gaps.
Gaps in planet formation models
“The close agreement of the disk morphology with the core accretion planet formation model suggests that Elias 2-24 b and other protoplanets imaged in the gaps of protoplanetary disks most likely formed through accretion,” the astronomers write. But that means that this young planet must have formed and grown much faster than current models predict – it reached its already large mass in less than a million years.
“Our planet formation models already had explanation problems for the youngest known planets around the five-million-year-old stars PDS 70 and WISPIT 2,” says Bernardi’s colleague Lucas Cieza. “Elias 2-24 b now shows us that even our best models of planet formation are still missing some important processes.”
Novel space telescope could solve the mystery
The astronomers hope that the Roman space telescope, which has just been launched, can provide more information here. Because its coronagraph can create even higher-contrast and higher-resolution images of exoplanets. “Elias 2-24 b is at the limit of what current telescopes can detect,” says Cieza. “But with new instruments like the Roman telescope, this is becoming easier. We are only at the beginning of a new era of discoveries.”
https://science.de/artikel/roman-weltraumteleskop-was-kann-das-neue-auge-im-all
Source: The Astrophysical Journal Letters, 2026; doi: 10.3847/2041-8213/ae9bb6