Title: Prelude to Dawn: Vesta and its Relationship to the Vestoids Tom Burbine Mount Holyoke College tburbi
1Prelude to DawnVesta and its Relationship to
the VestoidsTom BurbineMount Holyoke
Collegetburbine_at_mtholyoke.edu
2Number of Collaborators
- Paul Buchanan
- Rick Binzel (MIT)
- Tim McCoy (Smithsonian)
3- The DAWN spacecraft will hopefully be launched in
2007 to spectrally and chemically map the
surface of 4 Vesta. - Arrive at Vesta in 2011
Zellner et al. (1997)
http//www.jpl.nasa.gov/images/dawn/dawn_vesta_cer
es-browse.jpg
4(No Transcript)
5- My cost 20,000
- Dawns cost 450,000,000
6Why do people study meteorites and asteroids?
- Meteorites can be studied in detail in the
laboratory - Isotopic ratios
- Ages
- Minerals
- Elemental abundances
- Asteroids can currently only be studied by remote
sensing - Asteroids give you locations where things formed
7Rocks give you War and Peace, but the first 100
pages are missing. You know how it comes out, but
youre missing the formative stages.
8If you can link meteorites with asteroids?
- You can possibly map the surface and interior
of an asteroid if you can get high-resolution
spectra of the surface - You can possibly determine what are the isotopic,
mineralogical, and chemical gradients in the
solar nebula
9Meteorites
- HEDs howardites, eucrites, and diogenites
- basaltic meteorites that appear genetically
related to each other - Eucrites pigeonite and plagioclase
- Diogenites orthopyroxene
- Howardites mixture of eucritic and diogenitic
material - Mesosiderites stony-iron meteorites that are a
mixture of HED-like material and metallic iron
10eucrite
diogenite
howardite
11eucrite 7 cm long
howardite 1.9 cm long
diogenite 13 cm long
12mesosiderite
NWA 2932
http//i1.ebayimg.com/02/i/06/df/a1/3f_1.JPG
13http//www4.nau.edu/meteorite/Meteorite/Images/Ves
taStratigraphy.jpg
14Eucrites have band positions at longer
wavelengths than howardites Howardites have band
positions at longer wavelengths than diogenites
eucrite (Bouvante)
Band II
Band I
How light is reflected from a sample.
howardite (EET 87503)
Normalized Reflectance
visible
near-infrared
diogenite (LAP 91900)
Wavelength (µm)
15Absorption features due to the presence of Fe2
Splitting due to the application of a
non-spherical electrostatic field from
surrounding atoms
3d
16Electrons
- Electrons can absorb photons at specific energies
to go from one energy level to another - The energies of these photons correspond to
visible and near-infrared wavelengths
17Ca and Mg
- Ca and Mg do not have incompletely filled 3d
orbitals - Do not have absorption features in the visible
and near-infrared - Pure enstatite has no absorption features
- But their presence affects the position of the
absorption features due to Fe
18Ibitira
(Weichert et al. 2004)
Greenwood et al. (2005)
19Yamaguchi et al. (2002)
20eucrite fractionation line
Greenwood et al. (2006)
21What do the Meteorites tell us?
- Most HEDs appear to come from the same parent
body - 4 Vesta?
- A few HEDs have distinctly different oxygen
isotopic values, implying that they come from
different parent bodies - Iron meteorites imply the formation of a large
number of differentiated bodies - Mesosiderites have indistinguishable oxygen
isotopes from most HEDs - Did an iron asteroid impact Vesta and form
mesosiderites?
22Asteroids
- 4 Vesta - 500 km diameter asteroid
- reflectance spectrum similar to the HEDs
- Vesta family asteroids with similar orbital
elements to Vesta - Over 4,500 known members
- Vestoids asteroids with reflectance spectra
(visible and/or near-infrared) similar to HEDs - found inside and outside the Vesta family and
among the near-Earth asteroids - Usually have estimated diameters less than 10 km
23V-type 4 Vesta
Normalized Reflectance
Band I
Band II
howardite (EET 87503) (Hiroi et al. 1995)
Wavelength (µm)
24Vesta and the HEDs
- Vesta seems to be the best spectral match to a
group of meteorites
25Most asteroids do not match
25143 Itokawa (Binzel et al., 2001)
Greenwell Springs (LL4)
26D
A
T
Classes Defined By David Tholen (1984)
X
S
B
Q
C
F
R
G
V
2725143 Itokawa Picture from Hayabusa Spacecraft
535 294 209 m
28Vestoid
V-type 1929 Kollaa
Normalized Reflectance
eucrite (Bouvante) (Burbine et al. 2001)
Wavelength (µm)
29Normalized Reflectance
Wavelength (µm)
3031 resonance
1459 Magnya
1468 Zomba
21238 1995 WV7
4731 Monicagrady (not a Vestoid)
3131 resonance
1459 Magnya
1468 Zomba
Fragments of Vesta?
21238 1995 WV7
minimum
?
32What do the Asteroids tell us?
- Most Vestoids appear to be fragments of Vesta
- What is their mineralogy?
- Some Vestoids are relatively far from Vesta
- Do they have different mineralogies?
33My Work
- Our group (headed by Rick Binzel at MIT) has
near-infrared spectra of 17 main-belt
Vestoids - I am trying to determine the mineralogy of these
objects - Use HEDs as a guide
34Deriving Formulas for Determining Pyroxene
Mineralogies
- Used high-resolution spectra of 13 HEDs (Hiroi)
and high-quality analyses of the same HEDs
(primarily from Buchanan) - Band I center fitted Band I minimum with
continuum slope removed - Band II minimum fitted Band II minimum (not
sure what continuum slope is over this wavelength
region) - average pyroxene mineralogy average of a number
of grains
35Ca-content Mg-content Fe-content
36Takeda (1997)
37R2 0.9253
diogenites
eucrites
howardite
38En
En
39Wo
Wo
40Fs
Fs
41Mg
Mg
42Gaffey et al. (2002) also has formulas
- Fs (5) 268.2Band II center (µm) - 483.7
(Wolt11) - Fs (5) 57.5Band II center (µm) - 72.7
(Wo11-30 Fslt25 excluded) - Fs (4) -12.9Band II center (µm) 45.9
(Wo30-45) - Fs (5) -118.0Band II center (µm) 278.5
(Wogt45) -
- Wo (3) 347.9Band I center (µm) - 313.6
(Fslt10 Wo?5-35 excluded) - Wo (3) 456.2Band I center (µm) - 416.9
(Fs10-25 Wo?10-25 excluded) - Wo (4) 418.9Band I center (µm) - 380.9
(Fs25-50)
43With all these formulas
- Should be able to predict the mineralogy of
Vestoids - One complication
- HED band positions move to shorter wavelengths as
the temperature decreases - Meteorites are measured at room temperature (300
K) - Vestoids have temperatures of 160-200 K
- Band I moves 0.00 to -0.01 µm for asteroid
temperatures - Band II moves -0.02 to -0.03 µm for asteroid
temperatures
44Some Preliminary Fits of Some Vestoids
- Most of the fits were done using polynomials to
fit Band I and Band II, respectively - I am checking to see how much the calculated band
position depends on the fitting routine - Did not divide out the continuum slope to
determine the Band I center for the asteroids - some asteroids did not have visible spectra
- Error bars are just estimates
- I need to fit with a variety of methods and
determine uncertainties - Did not calculate temperatures for the asteroids
(just made the same estimated temperature
correction for all the asteroid band positions)
45eucrites
3155
2851
howardite
21238
diogenites
(minima for asteroids)
4621238 1995 WV7
1929 Kollaa
Wavelength (µm)
47Mesosiderites
Pinnaroo metal
Estherville
Vaca Muerta
Normalized Reflectance
Lamont
Pinnaroo
0.5
1.0
1.5
2.0
2.5
Wavelength (µm)
48added mesosiderites
Lamont
Estherville
(minima for asteroids)
491468 Zomba
1459 Magnya
(average of the results from the Band I and Band
II formulas)
21238 1995 WV7
501468 Zomba
1459 Magnya
2851 Harbin
21238 1995 WV7
511468 Zomba
1459 Magnya
3155 Lee
2851 Harbin
21238 1995 WV7
521468 Zomba
1459 Magnya
2851 Harbin
21238 1995 WV7
5321238 1995 WV7
diogenites
2851 Harbin
3155 Lee
1459 Magnya
1468 Zomba
eucrites
54Conclusions
- Most of the Vestoids have inferred compositions
consistent with eucrites/howardites - The Vestoids that do not appear to be related
to Vesta have a range of compositions - Further work needs to be done to see how well we
can map Vesta using these fragments
55Any questions?