Physicists from the Leiden Observatory carried out a study that revealed unexpected details about protoplanetary disks. As widely reported, their findings show that these disks might not be quite as museums-fillingly typical as we used to think. Authors Osmar M. Guerra-Alvarado, Mariana B. Sanchez, and Nienke van der Marel were the study’s leaders. They found that most of the young stars they observed are surrounded by relatively small disks of gas and dust, some with radii measuring only 1.2 astronomical units (AU). This new, emerging view defies decades of accepted wisdom on these cosmic structures.
Their observations, carried out with the Atacama Large Millimeter/submillimeter Array (ALMA), looked at 73 protoplanetary disks in the Lupus star forming region. The results showed that two-thirds of these disks have an average radius of six AU. To put this measurement into context, it is similar to the entire orbit of Jupiter. The smallest disk we observed was only 0.6 AU in radius, which is even smaller than the radius of Earth’s orbit around the Sun! These miniature disks primarily link up with low-mass stars. These stars are only 10 to 50 percent the mass of the Sun.
This research has shown that previous estimates of the size of protoplanetary disks were wrong. While scientists had historically assumed that larger disks were the norm, the study showed that most are much tinier. This incredible piece of information has tremendous implications for grasping planet formation and the makeup of exoplanets.
The high-resolution observations necessary for this study were particularly challenging owing to the tenuous nature of these disks. Using ALMA's highest possible resolution of 0.030 arcseconds, observations were made in 2023 and 2024 to capture the necessary details. This technological feat made it possible for researchers to make a crucial connection between directly imaged protoplanetary disks and exoplanets.
This research shows that our solar system formed from an enormous protoplanetary disk. Over the course of this process, they created giant gaseous planets, such as Jupiter and Saturn, but did not end up forming any super-Earths. This is in stark contrast to the much smaller disks seen around other stars, suggesting a variety of planetary formation processes.