• Gregory Herzog
  • Professor Emeritus
  • Research Synopsis: Origin and evolution of solar system materials, cosmogenic radionuclides





  • B.A. 1964, Cornell
  • M.A. 1965, Ph.D. 1970, Columbia
  • Visiting Scientist, Max Planck Institute for Kernphysik, Heidelberg 1976-77
  • Visiting Scientist, École Normale Supérieure, Lyon, 2011
  • Visiting Scientist, Technische Universität München, 2011

Research Summary

Cosmochemistry. Origin and evolution of extraterrestrial materials, which include meteorites, micrometeorites, Moon rocks, and particles from comets and asteroids.

Interactions of extraterrestrial materials with cosmic rays

One line of research focuses on the interactions of extraterrestrial materials with cosmic rays. Cosmic rays produce tiny but measurable quantities of various "cosmogenic" radionuclides, which can be measured in extraterrestrial materials. These radionuclides provide information about how long the object was exposed to cosmic rays and about major collisions that the object underwent. In some cases, they help identify the particular parent bodies from which the object came. The cosmogenic radionuclides also have many terrestrial applications. For example, they give clues to the long-term effects of erosion on the Earth’s surface. We use accelerator mass spectrometry, an extremely sensitive technique, to determine the cosmogenic radionuclide contents of extraterrestrial and terrestrial materials.

Thermal histories of extraterrestrial materials

A second line of research is directed toward determining the thermal histories of extraterrestrial materials. When a molten system evaporates, changes in its isotopic composition may occur. We use various forms of mass spectrometry to measure these changes. The results constrain the degree of mass loss experienced by the system and provide information about its composition before heating. Examples of systems studied are micrometeorites, which undergo extensive evaporation as they pass through the Earth’s atmosphere, and chondrules, which formed from molten siliceous droplets about 4.5 billion years ago.

Ar/Ar dating of small extraterrestrial particles

In collaboration with members of the Department of Earth and Planetary Sciences, we measure the Ar/Ar ages of extraterrestrial materials. Ar/Ar ages are especially sensitive to heating, which may be caused by the decay of now-extinct radioactivity, by impacts on asteroids, or even by heating when an orbit brings an object close to the Sun. Examples of systems studied are martian meteorites, rocks thought to have come from the Solar System’s second largest asteroid Vesta, and dust particles collected by the Japanese mission Hayabusa to the asteroid Itokawa 25143. Images below show the asteroid and the grains analyzed, which had a total mass of about 2 µg. The measured age, ~1 Ga, of the particles is much younger than the age of the Solar System, indicating recent heating.

Figure 1. The three particles dated came from sites in a beach-like belt on the asteroid Itokawa. Particle RA was from Landing site 2, and particles RB1 and RB2 from Landing site 1. (Image from website; http://darts.isas.jaxa.jp/planet/project/hayabusa/amica.pl, Phase=Home Position, Date=20051010. For further details, see Park et al., (2015)

asteroid Itokawa v1

Figure 2. Backscattered electron (BSE) images of Itokawa particles RA-QD02-0199 (RA), RB-CV-0002 (RB1) and RB-CV-0051 (RB2). Ol = olivine; Pl = plagioclase; Px = pyroxene; Chr = chromite; K-fsp = potassium-bearing feldspar.

Backscattered electron Itokawa particles v1

Recent Publications

Herzog G.F., Caffee M.W., Faestermann T., Hertenberger R., Korschinek G., Leya I., Reedy R.C., and Sisterson J.M. (2011) Cross sections from 5 to 35 MeV for the reactions natMg(3He,x)26Al, 27Al(3He,x)26Al, natCa(3He,x)41Ca, and natCa(3He,x)36Cl: Implications for early irradiation in the solar system. Meteoritics Planet. Sci., 46, 1427-1446.

Moynier F., Blichert-Toft J., Wang K., Herzog G.F., and Albarède F. (2011) The elusive 60Fe in the Solar Nebula. Astrophys. J. 741, 71 http://dx.doi.org/10.1088/0004-637X/741/2/71

Park J., Bogard D.D., Nyquist L.E., and Herzog G.F. (2014) Issues in dating young rocks from another planet: Martian shergottites. In: Advances in 40Ar/39Ar Dating: from Archaeology to Planetary Sciences.(Eds.:Jourdan F., Mark D. and Verati C.) Geological Society, London, Special Publications 2014, 378, 297-316. http://dx.doi.org/10.1144/SP378.10.

Herzog G.F. and Caffee M.W. (2014) Cosmic-ray exposure ages of meteorites. In: Treatise on Geochemistry, Second Edition, Vol. 1 (Eds.: Holland H.D. and Turekian K.K.) Oxford: Elsevier. 419-453.

Lindsay F.N., Herzog G.F., Park J., and Delaney J.S. (2014) 40Ar/39Ar dating of microgram feldspar grains from the paired feldspathic achondrites GRA 06128 and 06129. Geochim. Cosmochim. Acta 129, 96-110.

Herzog G.F., Caffee M.W., and Jull A.J.T. (2014) Cosmogenic nuclides in Antarctic meteorites. In: Thirty-five Seasons of U.S. Antarctic Meteorites (1976-2010): A Pictorial Guide to the Collection (Eds. T. McCoy, R. Harvey, C. Corrigan and K. Righter). AGU Books, 153-172.

Herzog G.F., Cook D., Cosarinsky M., Huber L., Leya I., and Park J. (2014) Cosmic-ray exposure ages of pallasites. Meteoritics Planet. Sci., 50, 86-111.

Lindsay F.N., Delaney J.S., Herzog G.F., Turrin B.D., Park J., and Swisher III, C.C. (2014) Rheasilvia provenance of the Kapoeta howardite inferred from ~1 Ga 40Ar/39Ar feldspar ages. Earth Planet. Sci. Lett. 413, 208-213.

Park J.P., Turrin B.D., Herzog G.F., Lindsay F.N., Delaney J.S., Swisher III, C.C., Uesugi M., Karouji Y., Yada T., Abe M., Okada T., and Ishibashi Y. (2015). Argon/argon age of grains returned from asteroid Itokawa. Meteoritics Planet. Sci., DOI 10.1111/maps.12564.

Righter K., Abell P., Agresti D., Berger E.L., Burton A.S., Delaney J.S., Fries M.D., Gibson E.K., Harrington R., Herzog G.F., Keller L.P., Locke D., Lindsay F., McCoy T.J., Morris R.V., Nagao K., Nakamura-Messenger K., Niles P.B., Nyquist L., Park J., Peng Z.X., Shih C.-Y., Simon J.L., Swisher, III C.C., Tappa M., Turrin B., and Zeigler R.A. (2015) Mineralogy, petrology, chronology and exposure history of the Chelyabinsk meteorite and parent body. Meteoritics Planet. Sci. 50, 1790-1819.

Fimiani L., Cook D.L., Faestermann T., Gómez-Guzmán J., Hain K., Herzog G., Knie K., Korschinek G., Ludwig P., Park J., Reedy R.C., and Rugel G. (2015) Interstellar 60Fe on the surface of the Moon. Phys. Rev. Lett., 116, 151104-1-5.

Westphal A., Herzog G.F., and Flynn G.J. (2016) Cosmic dust toolbox: Microanalytical instruments and methods. Elements 12, 197-202.

Park J., Nagao K., Nyquist L.E., Herzog G.F., Mikouchi T., and Kusakabe M. (2017) The Dhofar 378 Martian shergottite: Noble gas, oxygen, and mineralogical studies and implications for Martian atmospheric neon. Geochim. Cosmochim. Acta, submitted.


Tuniz C., Bird J. Roger, Fink D. and Herzog G.F. (1998) Accelerator Mass Spectrometry: Ultrasensitive Analysis for Global Science. CRC Press, 371 pp.