New observations show that planets forming in protoplanetary disks like that around PDS 70 can trigger the formation of subsequent planets.
This finding, based on high-resolution images from ALMA, supports the domino effect in the sequential formation of planetary systems.
Discoveries in Multi-Planet Systems
New radio astronomy observations of a forming planetary system reveal that once the first planets emerge near a star, they can influence the surrounding material, guiding it to form additional planets farther out. In this process, each planet plays a role in creating the next, much like falling dominos triggering one another.
So far, astronomers have identified over 5,500 planetary systems, with more than 1,000 confirmed to have multiple planets. Planets form in protoplanetary disks — massive clouds of gas and dust surrounding young stars. Despite this knowledge, the exact process of how multi-planet systems like our Solar System develop remains unclear.
Case Study: PDS 70
A key system for studying planet formation is PDS 70, a young star located 367 light-years away in the constellation Centaurus. It’s the only known star where fully formed planets have been directly observed within a protoplanetary disk using optical and infrared imaging. (First Confirmed Image of Newborn Planet Caught with ESO’s VLT.)
Earlier radio wave observations from the Atacama Large Millimeter/submillimeter Array (ALMA) detected a ring of dust grains beyond the orbits of PDS 70’s two known planets. However, these initial observations lacked the resolution needed to explore the ring’s detailed structure.
Advancements in Observation Techniques
In this research, an international team led by Kiyoaki Doi, formerly a Ph.D. student at the National Astronomical Observatory of Japan (NAOJ)/the Graduate University for Advanced Studies, SOKENDAI and currently a postdoctoral fellow at the Max Planck Institute for Astronomy, performed high-resolution observations of the protoplanetary disk around PDS 70. The team again used ALMA, but observed at a longer wavelength of radio waves. This is because longer wavelengths are better for peering into the dusty cloud of the protoplanetary disk.
Findings from ALMA’s Latest Observations
The new ALMA observations clearly show a concentration of dust grains to the northwest (upper right) in the ring outside the orbits of the two existing planets. The location of this dust clump suggests that the already-formed planets interact with the surrounding disk, concentrating dust grains into a narrow region at the outer edge of their orbits. These clumped dust grains are thought to grow into a new planet.
This work observationally shows that the formation of planetary systems, like the Solar System, can be explained by the sequential formation of the planets from inside to outside by the repetition of this process; like a line of falling dominos, each one triggering the next.
Reference: “Asymmetric Dust Accumulation of the PDS 70 Disk Revealed by ALMA Band 3 Observations” by Kiyoaki Doi, Akimasa Kataoka, Hauyu Baobab Liu, Tomohiro C. Yoshida, Myriam Benisty, Ruobing Dong, Yoshihide Yamato and Jun Hashimoto, 14 October 2024, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ad7f51
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