Energetic Processing of Astrophysical Solids Daniele Fulvio - - PowerPoint PPT Presentation

Energetic Processing of Astrophysical Solids

Daniele Fulvio

Pontifícia Universidade Católica do Rio de Janeiro, RJ, Brazil dfu@puc-rio.br

A deeper comprehension of the chemical/physical complexity of the Universe:

Experimental Astrophysics

(new discipline: about 30 years old)

• 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
• 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

• f asteroids or planetary surfaces)

Species and Materials of interest for Astrophysics:

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)

2010 - 2013 2013 - 2015 2015 - ….. Max Planck Institute for Astronomy – Heidelberg – Germany Laboratory Astrophysics and Cluster Physics Group University of Virginia – USA Laboratory for Atomic and Surface Physics

• A. “ices”
• B. “dust”
• C. “rocks”

Interstellar medium Solar System

Species and Materials of interest for Astrophysics:

• A. “ices”
• B. “dust”
• C. “rocks”

Interstellar medium Solar System

Species and Materials of interest for Astrophysics:

Outer SS

• 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 ̴ 104 - 108 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 ̴ 104 - 108 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

To date: most processing experiments focus only on 1 component:

ices

Cosmic dust

Result: “UNREALISTIC” exp conditions (example: KBr, Si or Au substrates)

• 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)

Improve our understanding of irradiation processes to shade light on:

To date: most processing experiments focus only on 1 component:

ices

Cosmic dust

Result: “UNREALISTIC” exp conditions (example: KBr, Si or Au substrates) Do dust grains play any role in driving the evolution of ices in space?

ices

Cosmic dust

Result: “REALISTIC” exp conditions (dust analogues substrates)

• 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)

Improve our understanding of irradiation processes to shade light on:

This original and interdisciplinary research area has been investigated only

• ccasionally (e.g., Mennella et al. 2004, 2006; Gomis & Strazzulla 2005).

• CO2 is an important constituent of the icy mantles covering dust grains in

molecular clouds (up to about 25% with respect to solid H2O). Observations in dense clouds show that the abundance of solid CO2 is much larger than what can be accounted for by accretion from the gas phase.

The case of CO2

Taurus dark cloud illuminated by Elias 16 (Whittet et al., 1998)

Radiation processing at the interface ices / cosmic dust

• CO2 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)
• TNOs, comets
• …...

On Galilean Satellites

Ganymede and Callisto (Hibbitts et al., 2003)

Radiation processing at the interface ices / cosmic dust

The case of CO2

• CO2 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)
• TNOs, comets
• …...

On Saturnian Satellites

a - Phoebe b - Hyperion c - Dione d - Iapetus (Cruikshank et al., 2010)

Radiation processing at the interface ices / cosmic dust

The case of CO2

CO2 can be synthesized directly on grains by irradiation of photons and ions of condensed CO or mixtures CO:H2O or CO:O2, or by radiation-less surface chemical reactions, such as oxidation of CO by atomic O.

CO2 synthesized by ion and photon irradiation at the interface ice – cosmic dust

What is the origin of solid CO2?

Alternative synthesis route: active role of carbonaceous cosmic dust!

CO2 production from 100 keV H+ irradiation

• f H2O onto amorphous-C
• oxidation of C at the interface by OH radicals

produces CO2.

• higher initial creation yield (CO2/proton) and ηsat

at 120 K are due to increased mobility of the OH radicals inside the ice.

Au-coated QCM

protons

H2O ice film (100 nm thick)

13C foil

(50 nm thick)

• Reaction pathways involve ion induced

H2O dissociation (ionization; excitation; breaking of HO - H bond; Dissociative Electron Attachment).

• CO2 production has an initial linear

growth and approaches steady-state value at ~ 30×1015 H+ cm-2, when CO2 formation and dissociation become comparable.

(Raut, Fulvio, Loeffler, and Baragiola 2012, ApJ 752, 159)

IR spectroscopy

a)

3 ML 1 ML

Ion irradiation of H2O 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 CO2 (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.

CO2 production from 100 keV H+ irradiation

• f H2O onto amorphous-C

a)

(Raut, Fulvio, Loeffler, and Baragiola 2012, ApJ 752, 159)

CO2 and O3 synthesized by UV irradiation

• f solid O2 onto amorphous-C (21 K).

Au-coated QCM

UV photons

O2 ice film

13C foil

(50 nm thick)

Oxygen is the third most abundant element in the universe. Flux of ≈ 7 × 1014 photons cm−2 pulse−1 from an ArF excimer laser at 193 nm (6.41 eV). IR spectroscopy No thermal desorption of oxygen was induced by laser irradiation (checked with QCM technique). The bottom spectrum (dotted line) is from experiments where H2O was deposited at 25 K on top of 13C and irradiated up to 1019 photons cm−2.

(Fulvio et al., 2012, ApJ Letters 752, L33)

b)

Numbers adjacent to the spectra are fluences (x1016 photons cm−2).

• CO2 production is linear with photon fluence.

The photosynthesis yield is: Y= 3.3 ± 0.3 × 10-5 CO2 photon-1

• CO2 production does not decrease at high

fluences since CO2 does not absorb radiation below 7 eV (Warren 1986).

10

1

10

2

10

3

0.01 0.1 1 10 100

 (10

15 mol cm

• 2)

Fluence (10

16 photons cm

• 2)

O3

13CO2

• CO2 formation requires oxidation of the C-atoms
• f the substrate by O atoms produced by photolysis

in the O2 film.

• Neither CO2 nor O3 are formed when irradiating

H2O on top of the 13C-substrate. This is consistent with the fact that H2O is transparent to 6.41 eV radiation (starts to absorb above 7 eV; Kobayashi 1983; Warren & Brandt 2008).

• This is the first study on CO2 production which

does not require H2O or CO.

CO2 and O3 synthesized by UV irradiation

• f solid O2 onto amorphous-C (21 K).

b)

(Fulvio et al., 2012, ApJ Letters 752, L33)

• C. Planetary Sciences: Small Solar System Bodies (SSSBs)

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. 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

• f the processes that led to the genesis and evolution of the Solar System.

Understand the mechanisms and processes induced by space weathering on planetary and asteroid surfaces and the way space weathering alters the observed spectra.

• C. Planetary Sciences: space weathering

Only way for a correct interpretation of planetary and asteroid spectra! Unique contribution from experiments: ion and photon irradiation

• f meteorites and terrestrial analogues, to simulate the space

weathering processes!

Several tens of MBAs (“V-types”) have been found to exhibit basaltic surface composition similar to asteroid Vesta (Bus & Binzel 2002). Vesta is the only known differentiated asteroid (Dawn Mission!). Many of these objects belong to the Vesta dynamical family (“Vestoids”) and they are believed to derive from the large craters near the South pole of Vesta (Thomas et al. 1997).

Vesta

Space weathering of V-type asteroids

However, Vis-NIR spectra of V-types cover an huge range of spectral slopes (red lines) while Vesta shows a flat spectrum.

Vesta

Space weathering of V-type asteroids

Can space weathering effects explain it? What does determine such colour spread?

Several tens of MBAs (“V-types”) have been found to exhibit basaltic surface composition similar to asteroid Vesta (Bus & Binzel 2002). Vesta is the only known differentiated asteroid (Dawn Mission!). Many of these objects belong to the Vesta dynamical family (“Vestoids”) and they are believed to derive from the large craters near the South pole of Vesta (Thomas et al. 1997).

A combined observational/experimental program was granted in 2009 - 2010 at the Telescopio Nazionale Galileo (Canary Islands) to obtain NIR spectroscopic

• bservations of non-Vestoid asteroids (P.I.: D. Fulvio).
• to extend the available sample of NIR spectra of non-Vestoids
• to investigate the differences between the spectra of non-Vestoids and Vestoids,

to highlight possible spectral differences and get clues on the existence of other basaltic parent bodies other than Vesta.

• to investigate the effects of space weathering on V-types belonging to different

dynamical classes About 50 V-types do not belong to the Vesta family (“non-Vestoids”) and they could be fragments of distinct differentiated parent bodies. The main goals of this research are:

Space weathering of V-type asteroids

Observations carried at the TNG-INAF, to extend the available sample of NIR spectra

• f non-Vestoids

(Fulvio et al. 2016, MNRAS 455, 584-595)

• fugitives: escaped from the vestoid family via mean motion and secular

resonances and/or Yarkovsky effect

• low-i: inner main belt V-types with low inclination (i < 6 ͦ and 2.3<a<2.5 AU),

that cannot be linked to a dynamical origin from Vesta

• inner others: non-vestoids in the inner main belt not belonging to any of the

previous subclasses.

Among the “non-Vestoids” we separate:

• Finally, we also have V-type NEAs

(Fulvio et al. 2016, MNRAS 455, 584-595)

(Fulvio et al. 2016, MNRAS 455, 584-595)

The reflectance spectra of asteroid Vesta also show spectral features and brightness similar to those of the basaltic Howardite, Eucrite, and Diogenite achondrite meteorites (HEDs).

This agreement is considered the main proof of the relationship between Vesta, the V-types and these

• meteorites. However, Vesta and the

HEDs are spectroscopically flatter than most V-types.

To simulate the effects of space weathering on Vesta and V-types by solar wind ions, ion irradiation experiments were performed on HED meteorites: the eucrites Bereba and Dar Al Gani 684 (DaG).

• spectral “darkening” (decreasing of reflectance)
• spectral “reddening” (i.e., increasing of the slope)
• reduction of absorption bands with progressive irradiation

Space weathering of V-type asteroids

(Fulvio et al. 2012, A&A 537, L11)

(Fulvio et al. 2016, MNRAS 455, 584-595)

Space weathering time-scales of 106–107 yr are long enough for V-types to experience strong reddening able to alter their surface and reproduce the whole range of observed spectral slopes, with no significant differences among V-types subclasses except the one of NEAs; NEAs’ reflectance spectra should be much redder than they actually appear, in accordance to all other subclasses and possibly even more weathered due to the fact that the solar wind flux at NEAs’ location is higher than for asteroids in the main belt;

Astrophysical Implications and Conclusions

Astrophysical Implications and Conclusions

V-types are not the only taxonomic class

• f NEAs showing surprisingly pristine

surfaces: un-weathered surfaces are also shown by Q-type NEAs with respect to S- type asteroids. Comparing the collisional, dynamical and weathering time-scales, in the case of Q-type NEAs, results that: (1) their surface must experience some kind of frequent rejuvenative process; (2) collisions cannot be the mechanism responsible for un-weathered Q-type NEAs;

Astrophysical Implications and Conclusions

Analyzing the spectral and orbital properties of Q-type and S-type NEAs (Binzel et al., 2010) it was found that:

S-type NEAs  ∼0.7 au (median value ∼0.1 au) (weathered)

MOID: distance between the closest points of the orbits of two bodies.

Q-type NEAs  ∼0.17 au (median value ∼0.05 au) (less-weathered)

Minimum Orbit Intersection Distance (MOID) Close encounters of Q-type NEAs with the terrestrial planets have been proposed* as the responsible process for producing tidal perturbations to their surface that may remove and/or mix up the upper and weathered layers

• f the asteroid surface, therefore exposing

“fresh” un-weathered material from lower subsurface layers.

*Nesvorny et al. 2005, 2010; Marchi et al. 2006; Vernazza et al. 2009

Astrophysical Implications and Conclusions

Analyzing the spectral and orbital properties of Q-type and S-type NEAs (Binzel et al., 2010) it was found that:

S-type NEAs  ∼0.7 au (median value ∼0.1 au) (weathered) Q-type NEAs  ∼0.17 au (median value ∼0.05 au) (less-weathered)

Minimum Orbit Intersection Distance (MOID) Close encounters of Q-type NEAs with the terrestrial planets have been proposed* as the responsible process for producing tidal perturbations to their surface that may remove and/or mix up the upper and weathered layers

• f the asteroid surface, therefore exposing

“fresh” un-weathered material from lower subsurface layers.

*Nesvorny et al. 2005, 2010; Marchi et al. 2006; Vernazza et al. 2009

Itokawa asteroid

Astrophysical Implications and Conclusions

V-type NEAs  ∼0.17 au (median value ∼0.035 au) (less-weathered) Q-type NEAs  ∼0.17 au (median value ∼0.05 au) (less-weathered)

Minimum Orbit Intersection Distance (MOID) We note that, 18 out of 21 V-type NEAs in our sample present MOID < 0.17 au Hence, we propose that the less-weathered surfaces clearly shown by V-type NEAs may be due to close orbital intersections among these asteroids and the Earth, similarly to what experienced by Q-type NEAs. Further observational and theoretical work to investigate in detail the orbital evolution, collisional properties, and planetary encounters experienced by V-type NEAs. Itokawa asteroid

LEMM

Facilities and equipment available at the Accelerator Laboratory and at the Mass Spectrometry Laboratory (LEMM): 4MV accelerator, UV pulsed laser, electron beam, UHV conditions, cryostats with operational temperature down to 10 K, a broad range of analysis techniques (FTIR, TOF, RBS, RGA, …); Accelerator Lab.

My Plans of Future Research at PUC-Rio:

• 2. Radiation processing of ice/dust complexes
• 1. Space weathering of Small Solar System Bodies

The equipment available at the Laboratory of Protective Coatings and Nanostructured Materials and at the Nanoscopy Laboratory provide a unique opportunity to have an “in-house” facility for the production of cosmic dust analogues and their characterization before and after irradiation experiments by means of the multiple experimental techniques available (Raman spectroscopy, FTIR, AFM ….);

Laboratory of Protective Coatings and Nanostructured Materials Nanoscopy Laboratory

My Plans of Future Research at PUC-Rio:

• 2. Radiation processing of ice/dust complexes
• 1. Space weathering of Small Solar System Bodies

THANKS