is there a magnetic field on asteroid (4) vesta? · mcfadden et al. (2008) • second largest...
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Is there a magnetic field on asteroid (4) Vesta?
by Benoıt Carry1,2
in collaboration with:P. Vernazza (ESA/ESTEC), C. Dumas (ESO) & M. Fulchignoni(Obs. Paris)
1European Southern Observatory2LESIA,Observatoire de Paris
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Outline
1. Why is (4) Vesta a highly interesting body ?
2. Observations with SINFONI
3. Mineralogy analysis
4. Distribution of spectral slope
5. Magnetic field?
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Asteroid (4) Vesta
McFadden et al.
(2008)
• Second largest asteroid
⊲ Large crater at south pole⊲ Parent body of Vestoids
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Asteroid (4) Vesta
Vernazza et al.
(2006)
• Second largest asteroid
⊲ Large crater at south pole⊲ Parent body of Vestoids
• Composition
⊲ Mostly similar to HED meteorites⊲ Unweathered???
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Asteroid (4) Vesta
Binzel et al. (1997)
• Second largest asteroid
⊲ Large crater at south pole⊲ Parent body of Vestoids
• Composition
⊲ Mostly similar to HED meteorites⊲ Unweathered???
• Albedo
⊲ Strong variations⊲ Lava flow?⊲ Composition?⊲ Space weathering?
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
0.2 0.4 0.6 0.8Reflectance at 0.55 µm
-0.3
-0.2
-0.1
-0.0
0.1
0.2
0.3
0.4
Slo
pe (
0.4-
2.4
µm) Strong SW signature on Vesta
Slope: 0.145
SW
HowarditeEucriteDiogenite
V
4038
B0
B1
Grainsize
◦ V: Vesta
◦ 4038: Vestoid (4038) Kristina
◦ B0: Bereba before irradiation
◦ B0: Bereba after irradiation
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observations
• Aug. & Oct. 2004
⊲ Science Verification⊲ Reduction’s a pain⊲ J & H+K: 1.1-2.4 µm
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observations
• Aug. & Oct. 2004
⊲ Science Verification⊲ Reduction’s a pain⊲ J & H+K: 1.1-2.4 µm
• Observing conditions
⊲ φ ∼ 0.55′′
⊲ Southern hemisphere⊲ 14% surface
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observations
• Aug. & Oct. 2004
⊲ Science Verification⊲ Reduction’s a pain⊲ J & H+K: 1.1-2.4 µm
• Observing conditions
⊲ φ ∼ 0.55′′
⊲ Southern hemisphere⊲ 14% surface
• Spatial resolution
⊲ Smallest spaxel (0.025′′)⊲ FoV: 0.8×0.8 arcsec⊲ Θ 92, 144, 371 km !!
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observations
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Mineralogy
• Compare to laboratory
⊲ HED meteorites⊲ Fit band wings
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Mineralogy
• Compare to laboratory
⊲ HED meteorites⊲ Fit band wings
• Composition
⊲ Howardite-like⊲ Steady over longitude⊲ N-S trend⊲ Diogenite spot at (180◦, -25◦)
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No⊲ Mineral - Topo: No
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No⊲ Mineral - Topo: No⊲ Albedo - Topo: No
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No⊲ Mineral - Topo: No⊲ Albedo - Topo: No⊲ Albedo - Slope: so so
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No⊲ Mineral - Topo: No⊲ Albedo - Topo: No⊲ Albedo - Slope: so so⊲ Slope - Topo: so so
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Spectral slope distribution
• Slope distribution
⊲ E-W trend⊲ Consistent with HST
• Relationship
⊲ Mineral - Slope: No⊲ Mineral - Albedo: No⊲ Mineral - Topo: No⊲ Albedo - Topo: No⊲ Albedo - Slope: so so⊲ Slope - Topo: so so
• Resume
a. Unweatheredb. Strong albedo variationsc. Correlation Slope-Albedo
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Several scenarios
1. Composition or grain size inhomogeneity
⊕ Albedo variations⊖ Unweathered aspect
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Several scenarios
1. Composition or grain size inhomogeneity
⊕ Albedo variations⊖ Unweathered aspect
2. Continuous bombardment by small meteorites
⊲ Ejected during big impact & stayed inside Hill sphere⊕ Unweathered aspect⊖ Albedo variations
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Several scenarios
1. Composition or grain size inhomogeneity
⊕ Albedo variations⊖ Unweathered aspect
2. Continuous bombardment by small meteorites
⊲ Ejected during big impact & stayed inside Hill sphere⊕ Unweathered aspect⊖ Albedo variations
3. Vestaquake from large crater relaxation
⊕ Unweathered aspect⊖ Lack of correlation between topography & spectral slope⊖ Albedo variations
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Magnetic field scenario
Blewett et al. (2007)
• Surface magnetism
⊲ Crustal / Localized⊲ Remnant⊲ 0.2 nT⊲ 10−3 Moon’s & 10−5 Earth’s
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Magnetic field scenario
Blewett et al. (2007)
• Surface magnetism
⊲ Crustal / Localized⊲ Remnant⊲ 0.2 nT⊲ 10−3 Moon’s & 10−5 Earth’s
• Like on the Moon
⊲ CUPS / Swirls⊲ Albedo variation⊲ Unweathered
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Magnetic field scenario
Blewett et al. (2007)
• Surface magnetism
⊲ Crustal / Localized⊲ Remnant⊲ 0.2 nT⊲ 10−3 Moon’s & 10−5 Earth’s
• Like on the Moon
⊲ CUPS / Swirls⊲ Albedo variation⊲ Unweathered
• Detection
⊲ Slope-Albedo⊲ w/o Topography⊲ w/o Mineralogy
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observing limitations
1. Spectral range
⊲ Slope: J= 1.17-1.32 µm⊲ Mineral: H+K= 1.5-2.4 µm⊲ Limited to pyroxexes⊲ Other compounds?
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observing limitations
1. Spectral range
⊲ Slope: J= 1.17-1.32 µm⊲ Mineral: H+K= 1.5-2.4 µm⊲ Limited to pyroxexes⊲ Other compounds?
2. Spatial resolution
⊲ Θ ≥ 90 km⊲ Largest swirl on Moon: RGF = 100 km⊲ Fine structure unobservable
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Observing limitations
1. Spectral range
⊲ Slope: J= 1.17-1.32 µm⊲ Mineral: H+K= 1.5-2.4 µm⊲ Limited to pyroxexes⊲ Other compounds?
2. Spatial resolution
⊲ Θ ≥ 90 km⊲ Largest swirl on Moon: RGF = 100 km⊲ Fine structure unobservable
3. Spatial coverage
⊲ 14% of total surface⊲ Dark hemisphere
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Asteroid (4) Vesta SINFONI Mineralogy Spectral slope Magnetic field Conclusion
Conclusions
• Fist disk-resolved spectroscopy of an asteroid ever!
⊲ Spatial resolution is the key⊲ Deconvolution algorithm ?
• Magnetic field scenario
⊲ Explain both albedo and spectral slope⊲ Suggested by current data⊲ Require more observations
• NASA Dawn mission
⊲ Arrival 2011⊲ No magnetometer⊲ Spatial resolution ∼100 m⊲ Spectral range 1-5 µm