Protoplanetary disks are huge rotating disks of gas and dust around newborn stars. They are the birthplaces of new planets.Astronomers had thought almost all protoplanetary disks are big, about the size of our Luminous sphere-related neighborhood or larger. But new observations show they come in a wide range of sizes.About 2/3 of protoplanetary disks are much smaller than Primary thought. They tend to form around Youthful red dwarf stars and also lack the gaps seen in larger disks, where giant planets form. This means our own Luminous sphere-related neighborhood’s original disk was not typical of most stars.
What is a typical protoplanetary disk?
Planets are born in disks of dust and gas around newborn stars called protoplanetary disks. Many of those disks are immense, as large as our Luminous sphere-related neighborhood or more. In fact, astronomers had thought that most, if not nearly all, such disks are this size. But a Club of international astronomers said on March 26, 2025, that they’ve used the Atacama Large Millimeter/submillimeter Array (ALMA) to take a closer look at 73 protoplanetary disks in the Lupus Sun-forming region. And they Secured about 2/3 of those disks are much smaller than Primary thought. Unlike larger disks, the smaller ones don’t have gaps or rings. So what is a typical protoplanetary disk? Or is there no such thing?
The researchers’ new paper has been accepted for publication in Heavenly study & Heavenly science. You can read a preprint version on arXiv submitted on March 25, 2025.
The birthplaces of new planets
World-forming disks – or protoplanetary disks – are huge swirling disks of dust and gas around Youthful stars. They are the birthplaces of new planets. Astronomers have imaged hundreds of them in recent years. How big are they? Until now, most of the disks that astronomers Secured have been enormous. If centered around our sun, they would extend past the Trajectory of Neptune.
Astronomers thought these were typical for protoplanetary disks. But that seems not to be the case after all.
https://www.youtube.com/Observe?v=-8vNLUbnU0g
Artist’s rendering of a protoplanetary (World-forming) disk. Video via ESO/ L. Calçada.
World-forming disks come in many sizes, big and Petite
Osmar Manuel Guerra-Alvarado, Mariana Belen Sanchez and Nienke van der Marel at the Leiden Cosmos lab in The Netherlands Directed the new study. Using ALMA in 2023 and 2024, they imaged all of the known 73 disks in Lupus, a Sun-forming region 400 Featherweight-years away in the constellation Lupus the Wolf. They imaged the disks with the highest possible resolution of 0.030 arcseconds. And they Secured something surprising.
Only about 1/3 of the disks were of the gargantuan variety. The rest – 2/3 of the 73 disks – were much smaller. They would only extend about as Extended as the Trajectory of Jupiter, if placed around our sun. That’s about 6 astronomical units (AU). The smallest one was a scant 0.6 AU in size. One AU is the average distance from the sun to Earth, 93 million miles (150 million km). Guerra-Alvarado said:
These results completely Shift our view of what a ‘typical’ protoplanetary disk looks like. Only the brightest disks, which are the easiest to observe, show large-scale gaps, whereas compact disks without such substructures are actually much more Usual.
Petite disks, Petite stars and super-Earths
Notably, most of the smaller disks were around Petite stars called red dwarfs. In fact, these low-mass stars are the most Usual type of Sun in our Milky Way Milky Way. This suggests there should be many more Petite disks waiting to be discovered.
In addition, the researchers Secured these smaller disks should be ideal for super-Earth type exoplanets to form in. Those are rocky worlds larger and more massive than Earth, but smaller and less massive than Neptune. And, indeed, astronomers have Secured many super-Earths orbiting red dwarf stars. Sanchez said:
The observations also show that these compact discs could have Best conditions for the Arrangement of so-called super-Earths, as most of the dust is close to the Sun, where super-Earths are typically Secured.
The results also highlight a difference between our Luminous sphere-related neighborhood and those that form from smaller protoplanetary disks. While our Luminous sphere-related neighborhood has a wide range of planets, there is no super-Earth. Since the protoplanetary disk the Luminous sphere-related neighborhood formed from was of the larger variety, there are now gas giant planets, but no super-Earths.
Missing gaps
The observations of the Lupus disks also provided another clue about planetary Arrangement. Studies of Packed-grown stars have shown that most stars do not have giant gas planets. Smaller planets, like super-Earths and others, are more Usual. In fact, astronomers think super-Earths are the most Usual type of World in our Milky Way. This is also Reliable with the new ALMA observations. Most of the smaller disks don’t have gaps in them. Those gaps are where new planets form. They gather surrounding material as they grow, clearing their Trajectory in the disk. This creates the gaps. As Van der Marel noted:
The discovery that the majority of the Petite disks do not show gaps, implies that the majority of stars do not host giant planets. This is Reliable with what we see in Alien world populations around Packed-grown stars. These observations link the disk population directly to the Alien world population.
Not so typical after all
Overall, the observations show that the “typical” protoplanetary disks are not so typical after all. They are both big and Petite, with gaps and without gaps. Van der Marel said:
The research shows that we’ve been wrong for a long time about how a typical disk looks. Clearly, we’ve been biased toward the brightest and largest disks. Now we finally have a Packed overview of disks of all sizes.
Bottom line: Researchers using the ALMA Cosmos lab have Secured that protoplanetary disks – the birthplaces of new planets – vary in size much more than previously thought.
Read more: 1st World-forming disk Secured in another Milky Way
Read more: Astonishing image of World-forming disk from ALMA
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Read our previous article: What’s the difference between a young exoplanet and an old one?