G. J.
Taylor: Research Interests
I use a combination of petrology, geochemistry, field observations, remote
sensing, and theory to address problems in planetary science. Most recent
studies focus on igneous processes, the evolution of planetary crusts, and
the bulk composition of the Moon and Mars. I have become increasingly
interested in understanding how aqueous processes have affected the surface
chemistry of Mars, stemming from my work with the Mars Odyssey Gamma Ray Spectrometer. I also
spend some time planning future space exploration, including the use of teleoperated rovers for remote field work and how to
prospect for resources on the Moon and Mars.
Lunar Science
I am involved in a number of collaborative remote sensing projects with my
colleagues here at the University
of Hawai'i. This
includes understanding the general composition of the crust and mantle of the
Moon, which is crucial to understanding lunar origin and differentiation. We
are using Clementine and Lunar Prospector data to unravel impact dynamics,
the distribution and nature of anorthosites, the composition of the mantle,
and the nature of mare basalts. I recently collaborated with Ross Taylor (Australian National
University) and Larry Taylor
(University of Tennessee) to write a paper about the
composition of the Moon, which summarizes our various views on the subject,
making use of the latest data and interpretations of data on the Moon. I am
also working with our graduate student Sam
Lawrence and Marc Norman
(Australian National University)
on trace element analyses of mineral clasts in
Apollo 17 impact melt breccias.
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Assuming a crust 50 km thick (7.75 wt% of silicate portion of Moon)
containing an average of 28 wt% Al2O3, this plot
shows the variation in Al2O3 in the lunar mantle as
a function of the average Th concentration in the crust, assuming that the
Moon has a chondritic Al/Th ratio. Each solid line represents different
average Th contents of the mantle, assuming that there is no systematic
variation in composition with depth. Dashed lines represent enrichment
factors for refractory elements (Moon/Earth). For the Moon to have the same
refractory element content as the Earth, and assuming that the Th content
of the crust is > 0.6 ppm, the lunar mantle must have substantially less
than 0.05 ppm Th and <2.1 wt% Al2O3. If the Moon
is enriched in refractory elements by 50% (1.5 in the diagram), then the
mantle must contain > 0.5 ppm Th and > 4 wt% Al2O3,
and the crust must contain > 0.6 ppm Th. Rectangle represents the Taylor
et al. (2006) best estimate of mantle Al
and crustal Th. This estimate is consistent with >25% enrichment in
refractory elements in the Moon compared to the Earth. The square labeled W
shows Paul
Warren’s (2005) preferred
value, which suggests that the Moon is not significantly enriched in
refractory elements compared to Earth.
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Pertinent publications:
Taylor,
S. R., Taylor, G.
J., and Taylor,
L. A.
(2006) The Moon: A Taylor
Perspective. Geochim.
Cosmochim. Acta 70,
5904-5918.
Hawke, B. Ray, Giguere, Thomas A., Blewett, D. T., Lucey, Paul G.,
Smith, G. A., Taylor, G. J., and Spudis, P. D.
(2002) Igneous activity in the southern highlands of the Moon. J. Geophys.
Res. 107, 10.1029/2002JE001494, 07 December 2002.
Fagan, T. J., Taylor, G. J., Keil, K., Bunch, T.
E., Wittke, J. H., Korotev,
R. L., Jolliff, B. L., Gillis, J. J., Haskin, L.
A., Jarosewich, E., Clayton, R. N., Mayeda, T. K., Fernandes, V.
A., Burgess, R., Turner, G., Eugster, O., and
Lorenzetti, S. (2002) Northwest Africa 032: Product of lunar volcanism. Met.
Planet. Sci. 37, 371-394.
Giguere, T.
A., Taylor,
G. J.,
Hawke, B. R.,
and Lucey, P. G.
(2000) The titanium content of lunar mare basalts. Meteoritics
and Planetary Science 35, 193-200.
Cushing, J.
A., Taylor,
G. J., Norman, M. D.
and Keil, K. (1999) The granulitic impactite suite: Impact melts and metamorphic breccias of
the early lunar crust. Meteoritics &
Planetary Science 34, 185-195.
Lucey, P. G., Taylor, G. J., Hawke, B. R., and Spudis, P. D. (1998) FeO and TiO2 concentrations in the
South Pole-Aitken basin: Implications for mantle composition and basin
formation. J.
Geophys.
Res. 103, 3701-3708.
Ryder, G., Norman,
M. D.,
and Taylor, G. J.
(1997) The complex stratigraphy of the highland
crust in the Serenitatis region of the Moon
inferred from mineral fragment chemistry. Geochim.
Cosmochim. Acta 61,
1083-1105.
Lucey, P.
G., Taylor,
G. J., and Malarete,
E. (1995) Abundance and distribution of iron on the Moon. Science 268,
1150-1154.
Mars
I was selected as a Participating Scientist for the Mars Odyssey Gamma Ray
Spectrometer (GRS) Team. This has been a great experience! We are getting our
first look at the global chemical composition of Mars. The data contain
information about the origin and evolution of the Martian crust, the planet's
bulk composition, and how aqueous processes have affected the composition of
the crust. Besides working with the Odyssey GRS Team, I have been working
with Julie
Stopar (a graduate student here)
on modeling aqueous geochemical processes on Mars. We focused our attention
first on the kinetics of dissolution of olivine (very important for
understanding the geological history of regions rich in olivine on Mars, as
identified by thermal emission spectroscopy on Mars). I also continue to work
on Martian meteorites and to use their compositions for comparison with the
GRS data.
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Mars Odyssey data for Mars shows that most of the surface has Th and K
concentrations larger than found in Martian meteorites (also called SNC
meteorites). This suggests that most of the Martian crust formed from
undepleted (previously unmelted) mantle, whereas
the SNC meteorites formed by partial melting of depleted mantle. Error bar
is typical uncertainty for K and Th. These uncertainties will decrease as
the mission continues because of the larger number of accumulated counts.
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The K/Th ratio is diagnostic of bulk planetary K/Th, an important cosmochemical parameter. It is not affected too much by
igneous processes, but is greatly affected by aqueous processes. I hope we
can use the variations seen in this ratio to understand global aqueous
processes on Mars.
Pertinent publications:
Stopar, J. S., G. J. Taylor, V. E. Hamilton, L. Browning (2006) Kinetic
Model of Olivine Dissolution and Extent of Aqueous Alteration on Mars. Geochem. Cosmochim. Acta 70, 6136-6152.
Taylor, G. J., W. Boynton, J. Brueckner, H. Waenke, G. Dreibus, K. Kerry, J. Keller, R. Reedy, L.
Evans, R. Starr, S. Squyres, S. Karunatillake,
O. Gasnault, S. Maurice, C. d'Uston,
P. Englert, J. Dohm, V.
Baker, D. Hamara, D. Janes,
A. Sprague, K. Kim, and D. Drake (2006), Bulk Composition and Early
Differentiation of Mars, J. Geophys. Res. 111,
E03S10, doi:10.1029/2005JE002645.
Taylor, G. J., J. Stopar, W. Boynton, J. Brueckner,
H. Waenke, G. Dreibus, K. Kerry, J. Keller, R.
Reedy, L. Evans, R. Starr, L. M. V. Martel, S. Squyres,
S. Karunatillake, O. Gasnault,
S. Maurice, C. d'Uston, P. Englert,
J. Dohm, V. Baker, D. Hamara,
D. Janes, A. Sprague, K. Kim, D. Drake, S. M.
McLennan, and B. Hahn (2006), Causes of Variations in K/Th on Mars, J. Geophys. Res. 111, E03S06, doi:10.1029/2006JE002676.
Keller, J., W. V. Boynton, S. Karunatillake, V.
R. Baker, J. M. Dohm, L. G. Evans, M. J. Finch, B.
C. Hahn, D. K. Hamara, D. M. Janes,
K. E. Kerry, H. E. Newsom, R. C. Reedy, A. L. Sprague, S. W. Squyres, R. D. Starr, G. J. Taylor, and R. M. S.
Williams, (2006), Global Distribution of Chlorine Measured by Mars GRS, J.
Geophys. Res. 111, E03S08, doi:10.1029/2006JE002679.
Karunatillake, S. K., S. W. Squyres,
G. J. Taylor, J. Keller, O. Gasnault, L. G. Evans,
R. C. Reedy, R. Starr, W. Boynton, D. M. Janes, K.
E. Kerry, J. M. Dohm, A. L. Sprague, B. Hahn, and
D. Hamara (2006), Mineralogy of Low Albedo Regions
in the Northern Hemisphere of Mars: Implications of Mars Odyssey Gamma Ray
Spectrometer Data, J. Geophys. Res. 111,
E03S05, doi:10.1029/2006JE002675.
Boynton, W. V.
and 24 others, including G.
J. Taylor
(2002) Distribution of hydrogen in the near surface of Mars: Evidence for
subsurface ice deposits. Science 297, 81-85.
Lentz, R. C. F., Taylor, G. J., and Treiman, A.
H. (1999) Formation of a martian
pyroxenite: A comparative study of the nakhlite
meteorites and Theo’s flow. Meteoritics and Planetary Science 34,
919-932.
Magmatic processes in asteroids
Some asteroids melted soon after they formed. Understanding how magmas
migrated, fractionated, and erupted on these small bodies may help us
understand magmatic processes in general. My colleagues and I have examined
the nature of partial melting residues, aspects of metal segregation to form
cores, the nature of the core-mantle boundary, processes that might have
operated inside asteroidal magma oceans, and the
dynamics of lava flows. Most recently, I have been concentrating on the
nature of basaltic volcanism on the parent body of the eucrite
meteorites, which many scientists believe is asteroid 4 Vesta. I have been working with Rachel Lentz
(U. Tennessee) to use the textures of Hawaiian basalts to shed light on the
eruptive and lava flow emplacement mechanisms on Vesta.
Pertinent publications:
Rushmer, T., Minarik,
W. G., and Taylor, G. J.
(2000) Physical processes of core formation. In Origin of the Earth and
Moon (R.
Canup
and K. Righter, eds.), 227-243. Univ.
of Arizona Press, Tucson.
Yamaguchi, A., Taylor, G. J.,
and Keil, K. (1997) Metamorphic history of the eucritic crust of 4 Vesta.
J.
Geophys.
Research 102, 13,381-13,386.
Yamaguchi, A., Taylor, G. Jeffrey,
and Keil, K. (1996) Global crustal metamorphism of
the eucrite parent body. Icarus
124, 97-112.
Taylor,
G.J., Keil,
K., McCoy, T., Haack, H. and Scott,
E.R.D. (1993) Asteroid differentiation: Pyroclastic
volcanism to magma oceans. <I.METEORITICS< i>28,
34-52.
Taylor,
G.J. (1992) Core formation in asteroids. J. Geophys.
Res. 97, 14,717-14,726.
Planetary Rovers and Resource
Exploration
A long time ago, Paul
Spudis
(Applied Physics Lab, The Johns Hopkins University) and I were devising ways
to explore the Moon effectively. One interesting extension of humans was to
use robots. However, geological observations are too difficult for any
autonomous robot to make, so we pounced on the idea of doing it through teleoperation. We were especially interested in
experiments using telepresence, the sense of
actually being at the remote site. Since then, some experiments have been
carried out, involving quite a few organizations. The most extensive and
successful so far took place in February of 1995 at Kilauea Volcano. Teams of
geologists operated a rover from Ames
Research Center
in California,
and made maps of the area explored. These were compared to observations made
directly, and the results were promising. It is still better to be there in
person.
Large space settlements on the Moon or Mars will require use of indigenous
resources to build and maintain the infrastructure and generate products for
export. Prospecting for these resources on the Moon is a crucial step in
human migration to space and needs to begin before the establishment of
industrial complexes. We are devising a multi-faceted approach to prospect
for resources that involves planetary research, technology development, human
workforce training, and education. One of the chief aspects of this work is to
develop a theoretical and practical framework for exploring for resources on
the Moon and Mars, the two most likely places for human settlements. We can
begin prospecting immediately, using remote sensing and sample data to search
for places that are good candidates for closer inspection in the future. I
hope this approach will lead to interesting insights into the petrologic
evolution of the Moon and Mars, just because of its unique perspective--it's
a whole new way of looking at the two bodies.
Pertinent publications:
Taylor, G. J.
(2001) Manufacturing a substrate for solar cells by the in situ melting of
the lunar surface: analysis of the concept. AIAA Space 2001--Conference
and Exposition, paper number 2001-4577, CD-ROM. American Institute of
Aeronautics and Astronautics.
Spudis, P.D.
and Taylor, G.J.
(1992) The roles of humans and robots as field geologists on the Moon. The
Second Conference on Lunar Bases and Space Activities of the 21st Century
(W.W. Mendell, ed.), NASA Conf. Pub.
3166, 307-313.
Taylor,
G.J. and Spudis,
P.D. (1990) A teleoperated,
robotic field geologist. Engineering, Construction, and Operations in
Space II (S.W. Johnson
and J. P. Wetzel,
eds.), 246-255. ASCE, New York.
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