The Future of Evolved Planetary Systems

TL;DR

The paper addresses how to study the formation, evolution, and chemical diversity of exoplanets by using white dwarfs as fossils of evolved planetary systems. It argues that Gaia, the Vera C. Rubin Observatory, and next-generation spectroscopy will enable an industrial-scale census of evolved planetary systems and precise measurements of thousands of disrupted planetesimals, linked to Galactic populations. It outlines key science opportunities for the 2040s and the technological requirements for future ESO facilities, including broad coverage from 3000 to 10000 Å, blue sensitivity, multi-resolution modes, multiplexing, and time-domain reactivity. This framework aims to produce an unbiased demographic and chemical map of planetary debris, advancing our understanding of planetary formation and fate across the Galaxy.

Abstract

Understanding the formation, evolution, and chemical diversity of exoplanets are now central areas of astrophysics research. White dwarfs provide a uniquely sensitive laboratory for studying the end stages of planetary-system evolution and for probing the bulk composition of both rocky and volatile-rich exoplanetary material. In the 2030s new facilities will transform our ability to carry out \textit{``industrial-scale''} astrophysics, leading to fundamental results and new challenges for the next decade. By combining the volume of data surveyed by the ESA {\em Gaia} mission and Vera C. Rubin Observatory with the next-generation of spectroscopic facilities, the European Southern Observatory (ESO) community will be in a position to obtain an unbiased census of evolved planetary systems, constrain the composition of thousands of disrupted planetesimals, and connect these signatures to Galactic populations and stellar birth environments. Thus, it is now the time for assessing those challenges and preparing for the future. This white paper outlines key science opportunities arising in the next decade and the technological requirements of future ESO facilities in enabling transformative discoveries in the 2040s. These future facilities will have to combine a number of features that are crucial for studying evolved planetary systems at white dwarfs, such as broad optical to near-infrared coverage, a high sensitivity at blue wavelengths, multi-resolution capability, massive multi-plexing, and time-domain reactivity.

Figures (2)

• Figure 1: Four examples of metal detections in optical-blue spectra of white dwarfs. From top to bottom: H-atmosphere accreting a gaseous planet gaensicke2019; He-atmosphere accreting hydrated debris raddi2015; two He-atmospheres (the top one is magnetic) accreting dry debris hollands2017. Spectral types, effective temperatures, and cooling ages are noted in figure.
• Figure 2: Minimum accreted masses inferred from the five most commonly detected elements (O, Mg, Si, Ca, Fe) as a function of white-dwarf cooling ages (i.e., the time since the white dwarf formed), for a subsample in williams2024. Triangles and squares label white dwarfs with H- and He-dominated atmospheres, respectively. Dashed lines compare with the masses of Solar-system objects. The colored bands roughly define the cooling-age boundaries for a 0.6 M$_\odot$ white dwarf at a distance of 100 pc when it possesses an apparent magnitude of Gaia$G = 18$, 20, and 23 mag; its $\sim 2$ M$_\odot$ progenitor would have a $\sim 2$ Gyr pre-white dwarf age. The considered magnitude limits could be respectively reached by existing instruments on the 8-m Very Large Telescope (VLT), like UVES ($R = 20\,000)$, X-shooter ($R = 10\,000)$, and FORS2 ($R = 1000$), delivering a signal-to-noise ratio of $\mathrm{S/N} \approx 10$/pixel in optimal observing conditions with 2-hr exposures.