Geological Society of America - 2006 G.K. Gilbert Award

GSA Medals & Awards

2006
G.K. Gilbert Award

Michael J. Gaffey
University of North Dakota

Presented to Michael J. Gaffey

Citation by Michael S. Kelley

Bridging interplanetary gaps:
Thirty years of combining laboratory measurements and telescopic observations

The Planetary Geology Division of GSA presents the G. K. Gilbert Award annually “to an individual who has contributed in an outstanding manner to the solution of a fundamental problem of planetary geology.” The Award is presented for either “a single outstanding publication or a series of publications that have had great influence in the field.” Dr. Michael J. Gaffey qualifies on both criteria. His individual papers on the spectroscopy of meteorite chemical groups, the connection between at least four different meteorite classes and their original main-belt asteroid parent body locations, and the surficial mapping of 4 Vesta all qualify as single outstanding contributions. Three decades of fundamentally important contributions further justifies the presentation of this Award to him.

It has been said among Mike Gaffey’s former graduate students that Mike does not publish as often as many of his colleagues, but what he publishes is usually seminal. This has been true since his first publications (e.g., McCord & Gaffey 1974; Gaffey 1976), still referenced today as seminal works in reflectance spectroscopy and their use in relating meteorite compositions to asteroid spectral classes. Mike’s graduate work in meteorite and asteroid spectroscopy was a precursor and an introduction to what has become a Gaffey process trademark: comprehensive data collection, followed by exacting data calibration and reduction, concluded by putting the results of the data analysis into multiple perspectives, large and small, long-term and short-term, as well as an insistence on harnessing the extant geological knowledge of mineralogy, petrology, and thermodynamics to give his extended conclusions a firm basis.

Mike Gaffey’s greatest philosophical contribution to asteroid studies is to treat every asteroid as an individual planet, an object that also has relationships and interactions with other objects, both similar and dissimilar, yet still retains a uniqueness that makes it worthy of study on its own. This philosophy has lead to Mike developing an observational technique that is unique: sub-hemispheric spectral reflectance mapping. The technique is complicated, but not complex, in that it requires long hours, perhaps even many nights, observing a single object at a telescope, along with the necessary observations of calibration standard stars, reducing the raw data to usable, high-quality reflectance spectra, then using extant or deriving new rotational parameters and relating each individual reflectance spectrum to a point on the asteroid’s surface. These data are then used in an analysis of the mineralogical and petrologic relationships on the surface of the asteroid, which are in turn used in a geological and thermodynamic context to draw conclusions regarding the current compositional state of the asteroid as well as its possible provenance.

He has used this technique of rotational spectral variations on a number of asteroids, the first of which to be published was an analysis of 8 Flora (Gaffey 1984). His results indicated that, of all the S-type asteroids known at that time, and thought to be parent bodies of the ordinary chondrites, this particular S-type asteroid could not have been such a parent body. The analysis related the oxidation state of 8 Flora’s composition, through variation in surface modal abundances of olivines, pyroxenes, and Fe-Ni metal, to that of all classes of ordinary chondrites and found that there was no thermodynamic way in which the asteroid could be mineralogically related to any member of those meteorite classes.

Adverse reaction to his conclusions in the 8 Flora paper caused him to investigate more deeply the spectral behavior of the Fe-Ni metal component in ordinary chondrites and found (Gaffey 1986) that the spectral behavior of the metal component in ordinary chondrites meteorites was remarkably different from the spectral behavior of the Fe-Ni metal component in asteroids. This work lead to a complete re-evaluation of the use of terrestrial spectral analogs in trying to analyze asteroid surface compositions from reflectance spectra. Through these results, it is now taken as a given that when terrestrial spectral analogs are used in analyzing and relating asteroid surface compositions through reflectance spectra, great care must be taken to make sure that the analogs used are accurate to the conditions of the body.

Skeptics have said that Mike Gaffey “looks too deeply into the data,” meaning that his interpretations go far beyond what can reasonably be determined from the data. I’d like to briefly point out two examples that show this is not the case. Mike has used his rotational spectral variation study technique on a number of asteroids since 8 Flora, including 15 Eunomia (Gaffey and Ostro 1987), 3103 Eger (then known as 1982BB in Gaffey et al. 1992), 9 Metis and 113 Amalthea (Kelley and Gaffey 2000; Gaffey 2002). Perhaps his two most famous efforts are for asteroids 4 Vesta and 6 Hebe (Gaffey 1983; Gaffey 1997; Gaffey and Gilbert 1997).

His early analysis of Vesta indicated the likely presence of large impact craters as well as large basaltic flows that probably were relatively pristine. These conclusions were confirmed when the Hubble Space Telescope acquired imagery of 4 Vesta in late 1994 and showed an extraordinarily large impact crater near Vesta’s south pole (e.g., Thomas et al. 1997, Binzel et al. 1997) and large areas covered in basalt. It is still considered amazing that such surface features could be found through careful and comprehensive analysis of ground-based, non-imagery data.

One Mike’s most valuable and initially controversial contributions using this technique has been in relating the asteroid 6 Hebe to the H-type ordinary chondrites and Type IIE metal meteorites through mineralogical and petrologic analyses of rotational variations in spectral reflectance. Putting his spectral data into a 3-dimensional context allowed him to hypothesize the presence of a new type of ordinary chondrite, one not in any of the collections at the time. This hypothesis opened Mike up to some vehement attacks from both the meteorite community and the asteroid observing community. Due to a deep streak of Irish luck, however, Mike was vindicated when a new type of ordinary chondrite was found, Portales Valley, which had just the composition and petrology suggested in the paper (McHone et al. 1999). Whether Portales Valley actually comes from 6 Hebe remains to be seen, but it was a vindication of Mike’s spectral technique that a meteorite could actually have the “impossible” composition of his hypothesis. It is now appears likely that 6 Hebe is the probable source for at least some of the H-type ordinary chondrites and Type IIE irons.

When Mike Gaffey wants to step back and look at asteroids in general, as apart from these looks at specific bodies, he also produces seminal scientific work. In generalizing about S-type asteroids (Gaffey et al. 1993a) and the spectral reflectance observations produced, he found that it would be mineralogically and petrologically impossible for many of the S-types to be the parents of any of the ordinary chondrites. Through deft use of compositional information from spectroscopy related to geologic thermodynamic knowledge he was able to deduce that only a small number of S-types are mineralogically “least unlike” (his terms) any ordinary chondrite class. As it turns out, 6 Hebe belongs to this group and thus Mike Gaffey is able to place his detailed observations of Hebe into a broader context using his own work, built upon his comprehensive knowledge of geology, mineralogy, and petrology.

All of these successes were born from an insistence upon using the extant data in a comprehensive and collaborative way with an emphasis on not over-interpreting any particular piece of data. In this insistence, Mike Gaffey has become a vociferous advocate of the proper and careful use of spectral reflectance observations. His occasional reviews on the subject (Gaffey et al. 1989; Gaffey et al. 1993b; Gaffey et al. 2002) have provided increasingly detailed knowledge regarding the use and avoidance of the abuse of spectral reflectance data, both for asteroids and other solar system bodies. He has successfully passed on this knowledge and its concomitant philosophy to a number of graduate students, each of whom have gone on to careers in planetary science and industry effectively utilizing these skills.

Mike Gaffey views his life in science and education not as a job or career, but rather a calling. He has only one true goal in his work, to produce the best science possible. He has proven superbly capable of this goal, both in his past achievements and his ongoing work. He has never shirked responsibility for errors he has produced and has always been gracious in his acceptance of his scientific successes. He has always maintained a philosophical attitude that the data should be the basis for all conclusions and all speculation should be obviously marked as such.

Fortunately, for the Planetary Science community, Mike Gaffey shows little sign of slowing down in his research pursuits. He is an active participant in many ongoing projects in addition to his own research. These include rotational studies of M-class asteroids with Paul Hardersen, laboratory calibration and analysis with Ed Cloutis, near-Earth asteroid studies with Paul Abell, asteroid family studies with me, and a variety of projects with his present graduate students, just to name a few.

I am pleased to point out that Gilbert Award Recipient Mike Gaffey is receiving double honors this year. At the annual meeting of the Meteoritical Society in Zurich in early August Mike was presented with that society’s highest honor, The Leonard Medal. It is only the second time in the history of the two awards that the same person received both in the same year. So we should take this as confirmation that Dr. Michael J. Gaffey successfully bridges the gaps between geology and astronomy, and between laboratory meteoritics and asteroid spectroscopic remote sensing.

When his paper entitled “The Early Solar System” was published, it was rumored that Mike was asked to write it because he had actually been around to witness the early solar system. However, I have it on good authority that Mike was born well after the formation of the asteroids. He did begin his critical observations of planetary bodies at a much earlier age than most of his colleagues. When I met Mike’s mother a number of years ago, she told me that Mike’s very first word was “shiny.” She said that he was looking up at the Moon at the time. So maybe it’s not too surprising that we’re honoring him today as a leading contributor to the field of Planetary Science.

I would like to thank Dr. Kevin L Reed, another former Gaffey student, for his help in writing this citation.
[ click here for references ]

2006 G.K. Gilbert Award - Response by Michael J. Gaffey

I am very honored to have been selected for the Gilbert Award by the Planetary Geology Division of GSA. Reading the list of previous recipients is a humbling experience. And it leaves me with a more than passing concern that some administrative error has resulted in my inclusion in such an august company. And that pretty soon I’ll get an “Opps, our mistake …” memo from the Division.

Any such honor is seldom the result of work solely by the recipient. In my case it is the result of contributions from many people: mentors, teachers and students. I have been exceptionally fortunate with respect to mentors and teachers. I received an excellent start from Miss Grace McKenna who taught in the one-room country school house where I attended kindergarten through eighth grade. She encouraged curiosity and a love of learning. I was similarly fortunate in High School with several teachers who encouraged innovative and supportive learning environments for “sports allergic” nerds such as myself. In college my mentor was Dr. James Van Allen who exemplified what it meant to be both a world-class scientist and an outstanding human being. To all of them I owe a vast debt of gratitude.

But perhaps even above those individuals, I owe an almost immeasurable debt to my students. More than anything that I can think of, having a steady cadre of highly intelligent and motivated students has contributed to the success that the Gilbert Award signifies. Especially when they have the self confidence to require that you to prove your case rather than simply accepting is as the word from on high. I’ve been lucky in having many “old hairy” students who haven’t been shy about challenging my ideas and pronouncements. Those interactions have often been more colleague-to-colleague collaborations than advisor-to-student instruction. And I’ve often gained at least as much as I’ve given in those efforts. I owe a great debt to past and present students such as Jeff Bell, Lucy McFadden, Trudie King, Chuck Farrall, Ed Cloutis, Ted Roush, Andy Lazarewicz, Pete Holden, Kevin Reed, Mike Kelley, Cathleen Donovan, John Hancher, Paul Hardersen, Paul Abell, Vishnu Reddy, and Sherry Fieber-Beyer — just to name a few.

I must also thank my colleagues in planetary science for putting up with my ignorance. Being cross-disciplinary necessitates that my knowledge in any given discipline is less than that of the specialists in those disciplines. I’ve often said that “I tell the geologists that I’m an astronomer and the astronomers that I’m a geologist and they leave me alone”. That’s not entirely a joke, and I thank my professional colleagues for their understanding and corrections and for not calling my bluff too often.

I am most grateful to the Planetary Geology Division of the Geological Society of America for this honor. And when you finally discover that it was all a clerical error, you’re going to have to come all the way to North Dakota to wrest it from my hands.

References (not comprehensive, in publication order)

T. B. McCord, and M. J. Gaffey (1974), Asteroids: Surface Composition from Reflection Spectroscopy, Science, 186:352-355

Gaffey M. J. (1976) Spectral reflectance characteristics of the meteorite classes. J. Geophys. Res., 81, 905–920.

Gaffey M.J. (1983) The asteroid (4) Vesta: Rotational spectral variations, surface material heterogeneity, and implications for the origin of the basaltic achondrites. Lunar Planet. Sci. XIV pp. 231-232.

Gaffey M.J. (1984) Rotational spectral variations of asteroid (8) Flora: Implications for the nature of the S-type asteroids and for the parent bodies of the ordinary chondrites. Icarus 60: 83-114.

Gaffey M. J. (1986) The spectral and physical properties of metal in meteoritic assemblages: Implications for asteroid surface materials. Icarus, 66, 468–486.

Gaffey M.J., S.J. Ostro (1987) Surface lithologic heterogeneity and body shape for asteroid (15) Eunomia: Evidence from rotational spectral variations and multi-color lightcurve inversions. Lunar Planet. Sci. XVIII, pp. 310-311 (abstract).

Gaffey M.J., J.F. Bell, D.P. Cruikshank (1989) Reflectance spectroscopy and asteroid surface mineralogy. In Asteroids II, (eds. R.P. Binzel, T. Gehrels, M.S. Matthews), University of Arizona Press, Tucson, pp. 98-127.

Gaffey M.J., K.L. Reed, M.S. Kelley (1992) Relationship of E-Type Apollo Asteroid 3103 (1982BB) to the Enstatite Achondrite Meteorites and the Hungaria Asteroids. Icarus 100: 95-109.

Gaffey M.J., J.F. Bell, R.H. Brown, T.H. Burbine, J.L. Piatek, K.L. Reed, D.A. Chaky (1993a) Mineralogical Variations Within the S-Type Asteroid Class. Icarus 106: 573-602.

Gaffey M.J., Burbine T. H., and Binzel R. P. (1993b) Asteroid spectroscopy and the meteorite connection: Progress and perspectives. Meteoritics, 28, 161–187.

Gaffey M. J. (1997) Surface lithologic heterogeneity of asteroid 4 Vesta. Icarus, 127, 130–157.

Gaffey M. J. and Gilbert S. L. (1998) Asteroid 6 Hebe: The probable parent body of the H-type ordinary chondrites and the IIE iron meteorites. Meteoritics & Planet. Sci., 33, 1281–1295.

Kelley M.S.; M.J.Gaffey (2000), 9 Metis and 113 Amalthea: A Genetic Asteroid Pair, Icarus, 144(1): 27-38.

Gaffey M. J. (2002) Asteroid 113 Amalthea: Nature, origin and meteorite affinities of an S(I) assemblage. Icarus, submitted.

Gaffey M.J., E.A. Cloutis, M.S. Kelley, K.L. Reed (2002) Mineralogy of Asteroids. In Asteroids III, University of Arizona Press, Tucson, AZ.

Binzel, R. P., M. J. Gaffey, P. C. Thomas, B. H. Zellner, A. D. Storrs, and E. N. Wells 1997. Geologic mapping of Vesta from 1994 Hubble Space Telescope images. Icarus 128, 95–103.

McHone J.F., M. Killgore, and E. Killgore (1999) Portales Valley, New Mexico Fall of 13 June 1998: Anomolous Fragment Distribution and Composition, Lunar and Planetary Science Conference XXX, paper 1964.

Thomas, P.C., Binzel, R.P., Gaffey, M.J., Storrs, A.D., Wells, E.N., Zellner, B.H., 1997. Impact excavation on Asteroid 4 Vesta: Hubble Space Telescope results. Science 277, 1492–1495.