STRW local: Colloquia


Tracing the building blocks of life from "star stuff" to terrestrial planets

Date: 28-03-2019
Time: 15:30 h
Author: Melissa McClure

Should we expect life to arise on the terrestrial members of the confirmed exoplanet population? The probability of finding life depends largely on the availability in solids of four key elements: Carbon, hydrogen, oxygen, and nitrogen (CHONs). With the exception of oxygen, these CHON elements are strongly depleted on Earth. Cometary impacts are thought to have delivered these icy elements, and possibly pre-biotic complex molecules (COMs), to Earth early in its history. Ices and COMs are formed early in the star formation process, in cold molecular clouds, and should be dispersed to all stars forming from these clouds. If we can understand how abundant icy molecules are in the solid state, and whether they survive infall onto protoplanetary disks to form comets or planets, then we can assess the probability of life evolving elsewhere in the universe. I present my research program to answer this question, tracing the icy solids from the cloud to the outer regions of protoplanetary disks. Through observations with the Spitzer Infrared Spectrograph, I have shown that icy grains have grown substantially already in molecular clouds. These grains become enhanced in CO ice in the outer regions of protoplanetary disks. Direct observations of midplane ices indicate less water ice than expected. By 2 Myr, there is evidence for collisions between icy planetesimals, or exo-comets. Using a novel technique to measure the leftover gas accreted onto the star, I confirm for the first time the presence of exo-comets in a primordial disk, suggesting that the mechanisms for CHON delivery are already in place early in the system's lifetime. Upcoming programs with the James Webb Space Telescope (e.g. IceAge, PI McClure) and ALMA (PI McClure), and future opportunities with SOFIA HIRMES, VLT CRIRES+ and MATISSE, and ELT METIS will enable my group to determine how much of this icy material is available to form life on terrestrial planets.