Energetic Processing of Astrophysical Solids Daniele Fulvio Pontifícia Universidade Católica do Rio de Janeiro, RJ, Brazil dfu@puc-rio.br
Experimental Astrophysics (new discipline: about 30 years old) A deeper comprehension of the chemical/physical complexity of the Universe: the life cycle of species and materials of astrophysical interest the role played by these species in processes of star and planet formation the chemical pathways leading from simple to pre-biotic species Species and Materials of interest for Astrophysics: A. “ices” (volatile species condensed from gas phase) B. “ dust ” (cosmic dust grains and lab. analogues) C. “rocks” (meteorites and terrestrial rocks with mineralogical composition similar to that of some classes of asteroids or planetary surfaces)
My research activity has been focused on: (1) ion and photon processing experiments of astrophysical ices, cosmic dust, and meteorites; (2) chemical reactions induced by radiation processing at the interface ices/cosmic dust; (3) detection of molecules in space and study of their formation pathways, abundances, and spectral features;
Daniele’s timeline (after the PhD here in OACT) University of Virginia – USA Laboratory for Atomic and Surface Physics 2015 - ….. 2010 - 2013 2013 - 2015 Max Planck Institute for Astronomy – Heidelberg – Germany Laboratory Astrophysics and Cluster Physics Group
Species and Materials of interest for Astrophysics: A. “ices” Interstellar medium B. “ dust ” C. “rocks” Solar System
Species and Materials of interest for Astrophysics: A. “ices” Interstellar medium B. “ dust ” Outer SS C. “rocks” Solar System
A. Interstellar Medium (ISM) Observations and models have established that ISM regions are enormous chemical factories, with over 190 molecules already unambiguously detected. Diffuse clouds: T ̴ 100 K, n ̴ 10 - 100 particles cm -3 Dense clouds: T ̴ 10 - 100 K, n ̴ 10 4 - 10 8 particles cm -3
A. Interstellar Medium (ISM) Observations and models have established that ISM regions are enormous chemical factories, with over 190 molecules already unambiguously detected. Diffuse clouds: T ̴ 100 K, n ̴ 10 - 100 particles cm -3 Dense clouds: T ̴ 10 - 100 K, n ̴ 10 4 - 10 8 particles cm -3
A. Interstellar Medium (ISM)
B. outer Solar System - Trans-Neptunian Objects (TNOs) - comets - icy satellites of external planets
B. outer Solar System Palumbo et al., 2008, JPhys 101, 012002
Improve our understanding of irradiation processes to shade light on: - the composition of ISM dust grains, comets, and TNOs; - the composition of the primitive solar nebula (i.e., the less altered materials of the SS) - prebiotic chemistry (basic chemical building blocks for life) To date: most processing experiments focus only on 1 component: Cosmic ices dust Result: “UNREALISTIC” exp conditions (example: KBr, Si or Au substrates)
Improve our understanding of irradiation processes to shade light on: - the composition of ISM dust grains, comets, and TNOs; - the composition of the primitive solar nebula (i.e., the less altered materials of the SS) - prebiotic chemistry (basic chemical building blocks for life) To date: most processing experiments Do dust grains play any role in driving focus only on 1 component: the evolution of ices in space? Cosmic Cosmic ices ices dust dust Result: “UNREALISTIC” exp conditions Result: “REALISTIC” exp conditions (dust analogues substrates) (example: KBr, Si or Au substrates) This original and interdisciplinary research area has been investigated only occasionally (e.g., Mennella et al. 2004, 2006; Gomis & Strazzulla 2005).
Radiation processing at the interface ices / cosmic dust The case of CO 2 - CO 2 is an important constituent of the icy mantles covering dust grains in molecular clouds (up to about 25% with respect to solid H 2 O). Taurus dark cloud illuminated by Elias 16 (Whittet et al., 1998) Observations in dense clouds show that the abundance of solid CO 2 is much larger than what can be accounted for by accretion from the gas phase.
Radiation processing at the interface ices / cosmic dust The case of CO 2 - CO 2 is also present in many objects of the Solar System: surface of icy satellites Ganymede, Callisto, and Europa (Jupiter) Phoebe, Hyperion, Dione, and Iapetus (Saturn) Ariel, Umbriel, and Titania (Uranus) Triton (Neptune) On Galilean Satellites TNOs, comets … ... Ganymede and Callisto (Hibbitts et al., 2003)
Radiation processing at the interface ices / cosmic dust The case of CO 2 - CO 2 is also present in many objects of the Solar System: surface of icy satellites Ganymede, Callisto, and Europa (Jupiter) Phoebe, Hyperion, Dione, and Iapetus (Saturn) Ariel, Umbriel, and Titania (Uranus) Triton (Neptune) On Saturnian Satellites TNOs, comets … ... a - Phoebe b - Hyperion c - Dione d - Iapetus (Cruikshank et al., 2010)
What is the origin of solid CO 2 ? CO 2 can be synthesized directly on grains by irradiation of photons and ions of condensed CO or mixtures CO:H 2 O or CO:O 2 , or by radiation-less surface chemical reactions, such as oxidation of CO by atomic O. Alternative synthesis route: active role of carbonaceous cosmic dust! CO 2 synthesized by ion and photon irradiation at the interface ice – cosmic dust
CO 2 production from 100 keV H + irradiation a) of H 2 O onto amorphous-C protons - CO 2 production has an initial linear growth and approaches steady-state value H 2 O ice film at ~ 30×10 15 H + cm -2 , when CO 2 formation (100 nm thick) and dissociation become comparable. IR spectroscopy - Reaction pathways involve ion induced H 2 O dissociation (ionization; excitation; 13 C foil breaking of HO - H bond; Dissociative (50 nm thick) Au-coated QCM Electron Attachment). 3 ML - oxidation of C at the interface by OH radicals 1 ML produces CO 2 . - higher initial creation yield (CO 2 / proton) and η sat at 120 K are due to increased mobility of the OH radicals inside the ice. (Raut, Fulvio, Loeffler, and Baragiola 2012, ApJ 752, 159)
CO 2 production from 100 keV H + irradiation a) of H 2 O onto amorphous-C Ion irradiation of H 2 O gives different results when performed on amorphous carbon rather than hydrogenated-carbon. The presence of H in the carbon substrate requires less fluence to produce CO 2 (Mennella et al. 2004 and Gomis & Strazzulla 2005). This could be due to the weakening of the carbon bonds upon hydrogenation. Moreover, these authors obtained higher saturation values, from 3 to 15 ML. Higher saturation values are likely due to a much larger surface area in the grains they considered. (Raut, Fulvio, Loeffler, and Baragiola 2012, ApJ 752, 159)
CO 2 and O 3 synthesized by UV irradiation b) of solid O 2 onto amorphous-C (21 K). UV photons Oxygen is the third most abundant element in the universe. O 2 ice film Flux of ≈ 7 × 10 14 photons cm − 2 pulse − 1 from IR spectroscopy an ArF excimer laser at 193 nm (6.41 eV). 13 C foil (50 nm thick) Au-coated QCM No thermal desorption of oxygen was induced by laser irradiation (checked with QCM technique). The bottom spectrum (dotted line) is from experiments where H 2 O was deposited at 25 K on top of 13 C and irradiated up to 10 19 photons cm − 2 . Numbers adjacent to the spectra are fluences (x10 16 photons cm − 2 ). (Fulvio et al., 2012, ApJ Letters 752, L33)
CO 2 and O 3 synthesized by UV irradiation b) of solid O 2 onto amorphous-C (21 K). - CO 2 production is linear with photon fluence. The photosynthesis yield is: 100 O 3 Y= 3.3 ± 0.3 × 10 -5 CO 2 photon -1 -2 ) 10 15 mol cm - CO 2 production does not decrease at high fluences since CO 2 does not absorb radiation 1 13 CO 2 below 7 eV (Warren 1986). ( 10 0.1 - CO 2 formation requires oxidation of the C-atoms of the substrate by O atoms produced by photolysis 0.01 in the O 2 film. 1 2 3 10 10 10 16 photons cm -2 ) - Neither CO 2 nor O 3 are formed when irradiating Fluence ( 10 H 2 O on top of the 13 C-substrate. This is consistent with the fact that H 2 O is transparent to 6.41 eV radiation (starts to absorb above 7 eV; Kobayashi 1983; Warren & Brandt 2008). - This is the first study on CO 2 production which does not require H 2 O or CO. (Fulvio et al., 2012, ApJ Letters 752, L33)
C. Planetary Sciences: Small Solar System Bodies (SSSBs) The study of the physical and mineralogical properties of asteroids, comets, TNOs, and planets’ satellites (overall: “SSSBs”) contributes in a unique way to the understanding of the processes that led to the genesis and evolution of the Solar System. Most SSSBs are not (or are only weakly) protected by an atmosphere or a magnetic field. This interaction, collectively known as “space weathering” , may cause a remarkable surface processing, such as structural and compositional variations, sputtering, and changes in the surface spectral properties.
C. Planetary Sciences: space weathering Understand the mechanisms and processes induced by space weathering on planetary and asteroid surfaces and the way space weathering alters the observed spectra. Only way for a correct interpretation of planetary and asteroid spectra! Unique contribution from experiments: ion and photon irradiation of meteorites and terrestrial analogues, to simulate the space weathering processes!
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