Organic materials in planetary and protoplanetary systems: nature or nurture?

Abstract

Aims. The objective of this work is to summarize the discussion of a workshop aimed at investigating the properties, origins, and evolution of the materials that are responsible for the red coloration of the small objects in the outer parts of the solar system. Because of limitations or inconsistencies in the observations and, until recently, the limited availability of laboratory data, there are still many questions on the subject. Our goal is to approach two of the main questions in a systematic way: -Is coloring an original signature of materials that are presolar in origin ("nature") or stems from post-formational chemical alteration, or weathering ("nurture")? -What is the chemical signature of the material that causes spectra to be sloped towards the red in the visible? We examine evidence available both from the laboratory and from observations sampling different parts of the solar system and circumstellar regions (disks). Methods. We present a compilation of brief summaries gathered during the workshop and describe the evidence towards a primordial vs. evolutionary origin for the material that reddens the small objects in the outer parts of our, as well as in other, planetary systems. We proceed by first summarizing laboratory results followed by observational data collected at various distances from the Sun. Results. While laboratory experiments show clear evidence of irradiation effects, particularly from ion bombardment, the first obstacle often resides in the ability to unequivocally identify the organic material in the observations. The lack of extended spectral data of good quality and resolution is at the base of this problem. Furthermore, that both mechanisms, weathering and presolar, act on the icy materials in a spectroscopically indistinguishable way makes our goal of defining the impact of each mechanism challenging. Conclusions. Through a review of some of the workshop presentations and discussions, encompassing laboratory experiments as well as observational data, we infer that both "nature" and "nurture" are instrumental in the coloration of small objects in the outer parts Article published by EDP Sciences A98, page 1 of 14 A&A 533, A98 (2011) of the solar system. While in the case of some observations it is clear that the organic reddening material originated before the solar nebula (i.e. presolar grains found in meteorites), for many other cases pointers are not as clear and indicate a concurrence of both processes.

The global dust modelling framework THEMIS

“…and with the likely irradiation effects and the associated aliphatic to aromatic transformation in the ISM (e.g., Jones 1990; Dartois et al 2004a,b;Pino et al 2008;Mennella 2008;Godard et al 2011), in circumstellar regions (e.g., Goto et al 2003Goto et al , 2007Sloan et al 2007;Pino et al 2008), in interplanetary dust particles (IDPs, Muñoz Caro et al 2006) and solar system organics (Dalle Ore et al 2011). Thus, the most physically-realistic carbonaceous grain materials, albeit inherently rather complex, would appear to be the extensive family of (hydrogenated) amorphous carbons, a-C(:H) 4 .…”

The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point

“…Further, they appear to undergo rather complex, sizedependent evolution arising, principally, from ultraviolet (UV) photon absorption leading to photo-or thermal-processing (e.g., Jones 2009Jones , 2012a and incident ion and electron collisions in shock waves and in a hot gas (e.g., Micelotta et al 2010a,b;Bocchio et al 2012). The evolution of their properties have received quite some interest as a model for the solid carbonaceous matter in the interstellar medium (ISM, e.g., Jones et al 1990;Duley 1995;Duley et al 1997;Dartois et al 2004aDartois et al ,b, 2005Pino et al 2008;Serra Díaz-Cano & Jones 2008;Jones 2009;Godard & Dartois 2010;Godard et al 2011;Compiègne et al 2011), in circumstellar media (e.g., Goto et al 2003;Sloan et al 2007) and in the Solar System (e.g., Dalle Ore et al 2011).…”

Variations on a theme – the evolution of hydrocarbon solids

“…The evolution of hydrocarbon solids is a key issue in astrophysical studies and these materials have received considerable interest as a model for the properties of the solid carbonaceous matter in the interstellar medium (ISM, e.g., Jones et al 1990;Duley 1995;Duley et al 1997;Dartois et al 2004aDartois et al ,b, 2005Pino et al 2008;Serra Díaz-Cano & Jones 2008;Jones 2009;Godard & Dartois 2010;Godard et al 2011;Compiègne et al 2011), in circumstellar media (e.g., Goto et al 2003;Sloan et al 2007) and in the Solar System (e.g., Dalle Ore et al 2011).…”