Astronomers Read Planetary 'Fingerprints' in Protoplanetary Disk Rings to Estimate Exoplanet Mass
Summary: A research team led by the University of Warwick's Farzana Meru, with MIT's Jessica Speedie as co-author, published a study on 28 May in The Astrophysical Journal showing that the bright concentric rings within the dusty "protoplanetary disks" surrounding young stars are essentially "planetary fingerprints." The width of each ring and the radial location of its brightest point correlate with the mass of the planet carving it, independent of observing wavelength and dust grain size. The team validated the method on the well-studied PDS 70 system 370 light-years away, reproducing the existing estimate of about 7.5 Jupiter masses for PDS 70 c. The approach works without requiring detailed prior knowledge of disk dust properties, giving ALMA and future facilities a tool to characterise planets still embedded in their natal disks — including a possible window into how our own solar system formed 4.6 billion years ago.
The first author Faruqi and colleagues first ran computer simulations to map how planets of different masses would shape the rings in protoplanetary disks. They found that ring width and the location of the brightest point in a ring are the key diagnostics of planet mass. The relationship between planet mass and the radial position of peak ring brightness holds across the wavelengths used by ALMA and the JVLA and across dust grain sizes — meaning observers do not need to invert the dust distribution to estimate planet mass.
The team then applied the technique directly to PDS 70, a system about 370 light-years away that hosts at least two directly imaged exoplanets, PDS 70 b and PDS 70 c, and has been a long-running ALMA target. The method delivered an estimated mass of about 7.5 Jupiter masses for PDS 70 c, in line with current estimates, and provided an independent mass constraint for PDS 70 b.
Jessica Speedie of MIT's Department of Earth, Atmospheric and Planetary Sciences said in a University of Warwick release: "One of the strengths of this work is that it doesn't stay in the realm of theory — we've been able to take these simulation results and apply them directly to real observed systems. Using the PDS 70 system, we've shown that this approach works in the real, observable universe." Farzana Meru, of Warwick's Department of Physics, added: "What excites me most is the timing. With ALMA delivering increasingly detailed disk images, and future facilities on the horizon, there has never been a better moment to develop these methods. Combining our detailed simulations with new observations will open a brand-new window on how planetary systems form."
The result also implies the method could be turned on our own solar system's history, since the Sun and its planets condensed from a similar disk about 4.6 billion years ago.
Sources (original pages)
- How do you study an invisible exoplanet? Astronomers discover planetary 'fingerprints' in the rings around stars — space.com
- Hero image: PDS 70 system illustration by Robert Lea (created with Canva), via space.com.