Reflectance Spectra of Ureilites: First Studies C.A. Goodrich 1 , J. - - PowerPoint PPT Presentation

Effects of Space Weathering on Reflectance Spectra of Ureilites: First Studies

C.A. Goodrich1, J. Gillis-Davis2, E. Cloutis3, D. Applin3,

• D. Takir4, C. Hibbitts5, R. Christoffersen6, M. Fries7,
• R. Klima5 and S. Decker8

1Lunar and Planetary Institute, USRA, Houston, TX 77058 USA (goodrich@lpi.usra.edu); 2HIGP, Univ. HI Manoa, Honolulu HI USA (gillis@higp.hawaii.edu);

• 3Univ. Winnipeg, Winnipeg, MB Canada;

4SETI, Mountain View CA USA; 5JHU/APL, Laurel, MD USA; 6Jacobs, NASA JSC, Houston TX USA; 7ARES, NASA JSC, Houston TX USA; 8Oberwesel Germany.

Space Weathering of Ureilite Meteorites: Motivation

• Dark asteroids are of interest as primitive, volatile-rich,

based on spectral resemblence to carbonaceous chondrites.

• However, not all dark asteroids are primitive!

OSIRIS-REx Hayabusa 2 Lucy

• livine

pyroxene

Optical photomicrograph

1 mm graphite

1 2 3 4 5 6 7 8 9

CB RC

carbon content (wt.%)

CK CO CV CM CR CI Tagish Lake Ungrouped Chondrites OC EC

Ureilites

• Ureilites are differentiated meteorites with very high carbon contents:
• avg. 4.5 wt% C

Ureilites

Space Weathering of Ureilite Meteorites: Motivation

0.4 0.8 1.2 1.6 2.0 2.4 0.00 0.05 0.10 0.15 0.20 0.25 CO

reflectance wavelength (m)

CV Data Sources: Main group ureilites: Cloutis et al. (2010) AhS: Hiroi et al. (2010); Goodrich et al. (2018) CC: Cloutis et al. (2011, 2012a,b) 2008 TC3: Jenniskens et al. (2009)

VNIR reflectance spectra of ureilites (some similarities to CC):

Main group ureilites: exhumed mantle rocks

• Mg-rich olivine and pyroxene (various ratios)
• various amounts metal, sulfide, graphite
• various degrees of shock
• spectral similarities to CO, CV

2008 TC3

CM

Almahata Sitta (2008 TC3): ureilitic regolith*

• AhS ureilites = clasts in regolith
• highly shocked, fine-grained, porous
• some have spectral similarities to CM
• spectral similarities to C-complex asteroids
• 2008 TC3 = F (Tholen)

C-complex asteroids (DeMeo et al. 2009) F asteroids (Tholen 1984)

How to distinguish differentiated dark asteroids from primitive dark asteroids?

*Herrin et al. (2010); Goodrich et al. (2015)

Space Weathering of Ureilite Meteorites: First Studies

3 ureilitic samples from Almahata Sitta (2008 fall):

• liv
• liv

graphite

• liv

MS-MU-038

• livine-rich,

low-shock, abundant graphite

MS-MU-022

• livine + orthopyroxene

medium-shock, low abundance graphite, metal

MS-MU-025

very fine-grained highly-shocked, dispersed graphite, metal, sulfide

interior mantle regolith

• Space weathering of ureilites has not previously been studied.
• Based on space weathering studies of CC* significant effects expected.

*Hiroi & Pieters (1991); Gillis-Davis et al. (2013, 2015); Keller et al. (2015)

Laser pulse heating, with mass spectrometer

▪

1064 nm, 20-Hz, 6 ns pulse, 30 mJ, 0.25 mm spot

▪

Simulate micrometeorite impacts ~ 20 mm in size

▪

Vacuum 10e-7 torr, residual gas analyzer 100 amu

Laser Heating Experiments: (HIGP, U. HI)

References: Gillis-Davis et al. (2015, 2017) Yamada et al. (1999)

• Samples powdered and sieved to <75 m grain size
• Micrometeorite bombardment simulated with pulsed laser irradiation
• Reflectance spectra measured at 6000 12000, 24000, 36000, 48000 laser shots

0.5 1.0 1.5 2.0 2.5 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

reflectance wavelength (m)

MS-MU-038 fresh MS-MU-022 fresh MS-MU-025 fresh

Space Weathering of Ureilite Meteorites: Results

regolith interior mantle

MS-MU-038, 48000 laser shots MS-MU-022, 48000 laser shots MS-MU-025, 48000 laser shots

increasing irradiation  darker, redder, decreased spectral contrast

0.02 0.04 0.06 0.08 0.10 0.12 48,000 shots

reflectance

MS-MU-038 fresh MS-MU-038, 48000 laser shots

fresh 0.02 0.04 0.06 0.08 0.10 0.12 48,000 shots fresh

reflectance

MS-MU-022 fresh MS-MU-022, 48000 laser shots

0.5 1.0 1.5 2.0 2.5 0.02 0.04 0.06 0.08 0.10 0.12

wavelength (m) reflectance

MS-MU-025 fresh MS-MU-025, 48000 laser shots

fresh 48,000 shots

Space Weathering of Ureilite Meteorites: Results

• Raman spectrum of fresh -038 shows olivine and

highly crystalline graphite.

• After irradiation the carbon peaks have broadened

and the D band is as intense as the G band, both indicators of disordered carbon.

Raman

D G

MS-MU-022 MS-MU-025

100 nm 100 nm

SEI

Comparisons with Asteroid Classes

0.80 0.84 0.88 0.92 0.96 1.00 1.04 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 fresh Xe Xk X K T D L R S Cg Cgh Ch Cg Cb

AhS ureilite MS-MU-038 AhS ureilite MS-MU-022 AhS ureilite MS-MU-025 AhS ureilites (Hiroi et al. 2010; Goodrich et al. 2018)

750/550 nm ratio 450/550 nm ratio

B Xc

SMASS II means: DeMeo et al. (2009) Albedo data: Mainzer et al. (2011)

0.9 1.0 1.1 1.2 1.3

0.04 0.08 0.12 0.16 0.20 0.24

Xe

Xk

L Q

AhS ureilite MS-MU-038 AhS ureilite MS-MU-022 AhS ureilite MS-MU-025 Other AhS ureilites Asteroid 2008 TC3

albedo 750/550 nm ratio

S A K D T Xc B Ch X Cgh Cg C Cb fresh

Increasing irradiation  move away from C-complex, toward D, T, some X. Asteroid 2008 TC3 may not have been significantly space weathered.*

*Consistent with Hiroi et al. (2010) and absence of solar gases in AhS (Ott et al. 2010; Downes et al. 2015; Riebe et al., this meeting).

Comparisons with Asteroid Classes

No exact spectral matches with asteroid class means for fresh or laser-weathered ureilites

0.4 0.8 1.2 1.6 2.0 2.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

MS-MU-025 fresh MS-MU-025, 48000 laster shots

T Cgh Xk XC D

550 nm-normalized reflectance wavelength (m)

X 0.4 0.8 1.2 1.6 2.0 2.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

MS-MU-038 fresh MS-MU-038, 48000 laser shots

T Cgh Xk XC D

550 nm-normalized reflectance wavelength (m)

K X 0.4 0.8 1.2 1.6 2.0 2.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

MS-MU-022 fresh MS-MU-022, 48000 laster shots

T Cgh Xk XC D

550 nm-normalized reflectance wavelength (m)

X

But, none of these samples individually represents bulk properties of ureilitic regolith.

interior mantle regolith

Conclusions (So Far)

• Space weathering results in significant changes in the reflectance spectra
• f ureiltes.
• Results suggest that non-space weathered ureilitic regolith may resemble

C-complex asteroids, whereas space weathered ureilitic material may resemble D, T, or some X type asteroids.

• Space weathering experiments on a series of ureilite samples with

controlled variations in petrologic properties are essential to understand the range of spectral signatures of ureilitic asteroids.

• Especially need to study fine-grained, highly-shocked AhS ureilites most

likely to represent the bulk of asteroid 2008 TC3 (ureilitic regolith).

Future Work

• Space weathering experiments on a series of ureilite samples with

controlled variations in petrologic properties.

• Space weathering experiments on fine-grained, highly-shocked

Almahata Sitta ureilites most likely to represent the bulk of asteroid 2008 TC3 (ureilitic regolith).

• Include UV (to 140 nm) and Raman, to examine changes in carbon

phases.

• TEM of space weathered powdered to understand microstructural

changes that affect optical properties.

Extra Slide (see Goodrich et al. this meeting)

2.7 mm band

0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 0.02 0.04 0.06 0.08 0.10 0.12 2008 TC3 F

CM

Cgh Ch

CM

reflectance wavelength (m)

AhS 91A chips and powders AhS ureilites [27] Asteroid 2008 TC3 [2], albedo estimated C-complex asteroid types [28,29] CM - Nogoya and Murchison (RELAB) C

• Almahata Sitta sample UOK 91A is a friable breccia of hydrated CC

material with clasts of ureilitic minerals and other chondrites (OC, EC).

• Suggested to represent significant fraction of the mass of 2008 TC3.
• Spectra of 91A show 2.7 m band!

2.7 m band water of hydration

• n a ureilitic asteroid!

R EL EH CC

Ang

L LL EL

CC H

Development of Diverse Regolith on Ureilitic Asteroid many impacts Recent Breakup. Fragments drift into Earth-crossing orbits Typical Polymict Ureilites 2008 TC3 Main Group Ureilites Goodrich et al. (2015) (deep regolith) (shallow regolith)