Getting to Know Vesta
• Based on its spectral similarities to HED achondrite meteorites, Vesta’s
surface is expected to be a mixture of three rock types: diogenites,
basaltic eucrites, and cumulate eucrites.
www.psrd.hawaii.edu/Nov07/HEDs-Vesta.html
Getting to Know Vesta
• The Gamma Ray and Neutron
Detector (GRaND), on Dawn,
will measure elemental
compositions of Vesta’s surface.
• Usui and McSween developed a
way to evaluate the proportion
of different HED rock types
represented in the GRaND
spectral data.
• Their HED-based mixing model
uses molar ratios of Mg, Fe, Al,
and Si (see plot), which show
the compositional differences
between the HED rock types.
Plot of (Mg+Fe)/Si abbreviated as [M/Si]mol
versus Al/Si abbreviated as [Al/Si]mol
www.psrd.hawaii.edu/Nov07/HEDs-Vesta.html
Getting to Know Vesta
• The plot of concentrations of
oxides of Si, Fe, Ti, Mg, Al, Ca,
Cr, Mn, Na, and K measured in
HED meteorites versus their
concentrations calculated from
the mixing model by Usui and
McSween shows excellent
agreement.
• A logarithmic scale is used to
easily show all the elements on
one diagram (K is lowest and Si
is highest).
www.psrd.hawaii.edu/Nov07/HEDs-Vesta.html
Getting to Know Vesta
• Usui and McSween’s HEDbased mixing model can:
– accurately estimate the
abundances of major
elements measured by
GRaND
– predict abundances of minor
elements (Na, Cr, and Mn)
not analyzed by the
instrument.
• Shows the value of an
integrated approach using:
– laboratory data on HED
meteorites (Cosmochemistry)
– remote sensing data from a
spacecraft orbiting Vesta
(Missions)
Neutron Activation Analysis
www.psrd.hawaii.edu/Nov07/HEDs-Vesta.html