Phyllosilicate Emission from Protoplanetary Disks: Is the Indirect Detection of Extrasolar Water Possible?

TL;DR

This study investigates the potential to detect phyllosilicates, hydrous minerals formed by water-rock interactions, in protoplanetary disks via infrared emission features, which could indicate the presence of liquid water in planetesimals.

Contribution

The paper demonstrates that phyllosilicates at 3% abundance in disks produce detectable infrared spectral features, linking mineral detection to liquid water and planetary system evolution.

Findings

Phyllosilicates cause significant spectral differences at 3% abundance.

Infrared detection of phyllosilicates can indicate liquid water in planetesimals.

Detection supports the waterworlds hypothesis and links to radionuclide content.

Abstract

Phyllosilicates are hydrous minerals formed by interaction between rock and liquid water and are commonly found in meteorites originating in the asteroid belt. Collisions between asteroids contribute to zodiacal dust, which therefore reasonably could include phyllosilicates. Collisions between planetesimals in protoplanetary disks may also produce dust containing phyllosilicates. These minerals possess characteristic emission features in the mid-infrared and could be detectable in extrasolar protoplanetary disks. Here we determine whether phyllosilicates in protoplanetary disks are detectable in the infrared using instruments such as those on board the Spitzer Space Telescope and SOFIA (Stratospheric Observatory for Infrared Astronomy). We calculate opacities for the phyllosilicates most common in meteorites and compute the emission of radiation from a protoplanetary disk using a 2-layer radiative transfer model. We find that phyllosilicates present at the 3% level lead to observationally significant differences in disk spectra, and should therefore be detectable using infrared observations and spectral modeling. Detection of phyllosilicates in a protoplanetary disk would be diagnostic of liquid water in planetesimals in that disk and would demonstrate similarity to our own Solar System. We also discuss use of phyllosilicate emission to test the "waterworlds" hypothesis, which proposes that liquid water in planetesimals should correlate with the inventory of short-lived radionuclides in planetary systems, especially 26Al.