Astronomers have confirmed the youngest known planet yet, a world less than 1 million years old that is still surrounded by the gas and dust from which it formed.
The planet, called Elias 2-24 b, was identified using observations preserved in NASA-funded archives. It is still orbiting within its young star’s dusty disk, giving scientists a rare opportunity to study planet formation while it is still happening.
“Our planet-formation models already struggled to explain the previous record holders for the youngest known planet — a four-way tie between two planets orbiting the star PDS 70 and two planets orbiting the star WISPIT 2 — which are all more than 5 million years old,” said Lucas Cieza, a professor at the Instituto de Estudios Astrofísicos in Chile and co-author of a paper detailing the results. “Elias 2-24 b shows us that even our best planet-formation models are still missing some important processes.”
Youngest Known Planet Confirmed
In a study published September 16 in The Astrophysical Journal Letters, researchers led by Andrea Bernardi, a doctoral candidate at the Universidad Diego Portales in Chile, examined archived observations of seven young stars.
Those stars had been observed with the coronagraph at the W. M. Keck Observatory in Hawaii, which works with NASA through a cooperative agreement. Each star is surrounded by a debris disk filled with dust, gas, and pieces of ice and rock. Gaps and other structures in those disks can be signs that planets are forming.
A coronagraph blocks much of a star’s bright light, making it easier to search for much fainter objects nearby. Using that technique, astronomers looked for planets hidden inside the dusty disks. Planets orbiting stars beyond our solar system are known as exoplanets.
“The planets should be found within the gaps, since they are carving them,” Bernardi said. “And that’s exactly where we found Elias 2-24 b.”
Elias 2-24 b is roughly as massive as Jupiter and orbits a star about 450 light-years from Earth. Because the system is so young, studying it gives astronomers a glimpse of what our own solar system may have looked like billions of years ago.
Watching a Planet Take Shape
Stars form inside vast clouds of gas and dust. Planets can then grow from material left over around the newborn star, gradually gathering matter and shaping paths through the surrounding disk.
But observing planets during these earliest stages is extremely difficult because thick dust can hide them from view.
Most confirmed exoplanets have instead been found through transits. A transit occurs when a planet passes in front of its star and causes a small temporary drop in the starlight seen from Earth.
That method becomes much harder to use when planets are still buried in dust or orbit very far from their stars. As a result, most of the roughly 6,000 confirmed exoplanets are billions of years old and orbit relatively close to their stars.
Scientists currently build planet formation models using theories, computer simulations, and observations of young stars surrounded by disks where forming planets are often too difficult to detect directly. Discoveries such as Elias 2-24 b can provide crucial real-world tests for those models.
“The galaxy churns out new stars and planets continuously, so there are many in every stage of evolution,” Cieza said. “That means we can see the entire process in theory, but there is a large gap in what most telescopes can detect. We are mostly blind to these baby planets right now.”
A Decade-Old Mystery Comes Into Focus
The new confirmation also resolves a question astronomers have been debating for about 10 years.
Earlier observations from ALMA (Atacama Large Millimeter/submillimeter Array) in Chile revealed a gap in the dusty disk surrounding the young star Elias 2-24. Later, the European Southern Observatory’s Very Large Telescope in Chile spotted a faint point of light inside that gap.
Scientists wondered whether the object could be a planet. The problem was that existing planet formation theories suggested a large planet should not have been able to form so quickly, especially at such a great distance from its star.
Current models suggest that forming a Jupiter-size planet at Jupiter’s distance from the Sun (which is just over five times larger than the distance of Earth to the Sun) takes about 5 million years. A giant planet much farther out should take even longer.
Yet the faint object in the Elias 2-24 system sits about 55 times farther from its star than Earth is from the Sun and was already showing signs of being a forming planet.
Archival Data Confirms Elias 2-24 b
To investigate further, Bernardi and colleagues searched the Keck Observatory Archive, a NASA-funded collaboration between Keck Observatory and the NASA Exoplanet Science Institute at Caltech/IPAC.
They found the same faint object in observations collected in 2018 and 2020. By combining the observations and tracking how the object moved over time, the team determined that it behaved much more like a planet orbiting the star than an imaging artifact or a distant background star.
That analysis ultimately confirmed the object as Elias 2-24 b.
“We usually hear about telescopes working separately, but this confirmation was possible only by using multiple telescopes together,” Bernardi said. “Elias 2-24 b is at the limit of what current telescopes can detect, but with new instruments like NASA’s Nancy Grace Roman Space Telescope, such detections should become easier.”
Roman Could Reveal More Baby Planets
Roman, which just launched Aug. 30, carries an even more advanced coronagraph designed to detect planets that are much harder to see with existing telescopes.
Using similar observing methods, Roman could identify planets in tighter orbits, including true Jupiter analogs that are currently hidden by the glare of their stars. Elias 2-24 b, by comparison, orbits about 10 times farther from its star.
That added sensitivity could help astronomers discover more planets during their earliest stages of formation and close one of the biggest observational gaps in exoplanet science.
“This is just the beginning of a new era of discovery,” Cieza 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.”
