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My scientific research has general involved the origin and evolution of the planetary system and planetary surfaces. Special interests have included of evolution of surface features, craters, and interplanetary bodies. Career highlights:

In 1962, I was lead author, with G. P. Kuiper, in the first recognition of multi-ring impact basins with concentric and radial structure on the moon, including the discovery of the Orientale basin bullseye on the east limb of the moon. Such basins have since been recognized on most cratered planets and satellites. This was first recognized on "rectified photos" in which telescopic photos of the moon were projected on a globe.

In 1965 I used crater counts on the moon and Earth to predict successfully that the lunar lava plains have an age of "about 3.6 x 10 9 years" (Icarus, 4:164). The date was confirmed five years later with Apollo samples from the moon. This work helped pioneer the usefulness of craters for interpreting planet surface ages; the 1966 Nininger Meteorite Award was shared for this work.

Discover of the Orientale Impact Basin Discovery of the Orientale Impact Basin. Drawing by William K. Hartmann from Earth-based photos showing multi-ring basin on the limb of the moon, as it appears from Earth. From Hartmann and Kuiper, 1962, Comm. Lunar and Planetary Lab. 1:51-66.

Discover photo of the Orientale multi-ring impact basin on the moon.
Discovery photo of the Orientale multi-ring impact basin on the moon. This photo was made by projecting an Earth-based photo onto a white globe, and re-photographing the globe, in a pre-Apollo mapping program designed by G. P. Kuiper. During this program, we discovered multi-ring impact basins. From Hartmann and Kuiper, 1962, Comm. Luner and Planetary Lab. 1:51-66.

In 1971-72 I was a co-I on the Mariner 9 mission which first mapped Mars in detail. With Bruce Murray, Carl Sagan, and others on the imaging team, we discovered Mars' dry river channels, volcanoes, and other features.

Mariner 9 photo of a martian channel, Nirgal Vallis
Mariner 9 photo of a martian channel, Nirgal Vallis.

In 1974-5, I was lead author, with D. R. Davis, of what has become the most widely accepted theory of the origin of the moon, by impact of giant planetesimal at the close of the planet-forming period. See PSI's Origin of the Moon page.  At a lunar origin conference in 1984, this idea was rated as the leading hypothesis for lunar origin, and is still rated that way as of today (2018). An interesting “isotope crisis” contested the hypothesis in 2009-13, based on the assumption that primordial Earth would have been hit by an impactor with different isotope chemistry. However, it survived an “isotope crisis” conference in 2013, which pointed that enstatite chondrite meteorites (likely formed alongside Earth) have virtually the same isotope chemistry as Earth, so that such an impactor apparently could have produced the moon. See Hartmann, W. K. 2014 The Giant Impact Hypothesis: Past, Present, (and Future?), Philosophical Transactions of the Royal Society (A), 372, 20132049 (no pagination in this journal).    


Diagram from Hartmann and Davis (Icarus, 1975) Diagram from Hartmann and Davis (Icarus, 1975) showing schematic history of growth of planetesimals near Earth's orbit. Our suggestion was that the 2nd-largest body grew to large size before hitting Earth, ejecting mantle material that formed the moon.

My work in 1973-1980 focused on effects of the high impact-cratering rates what we were deducing from studies of dated sample-return sites, from the U.S. Apollo and Russian Luna lander programs. Apollo landings had established that meteorite “sandblasting” impacts in the last 3.2-3.5 billion years created about 5 to 20 meter-deep layers of pulverized dust and gravel on the moon, called “regolith.” My results indicated that intense cratering rates before about 3.5-3.9 billion years ago would have created much deeper layers in the older regions of the moon. The 1973 paper listed below coined the term “mega-regolith” for this phenomenon, and noted that if the high early impact rate-vs.-time curves could be slightly extrapolated back before 3.8 to 4.0, 4.1, or 4.2 billion years ago, the depths of megaregolith could easily reach a few kilometers in depth. See my papers “Ancient Lunar Mega-Regolith and Subsurface Structure,” Icarus, 18, 634-636 (1973); “Dropping Stones in Magma Oceans: Effects of Early Lunar Cratering. In Proc. Conf. Lunar Highlands Crust, ed. J. Papike and R. Merrill. (N.Y.: Pergamon Press). Pp. 155-171 (1980).


In the 1980s, I worked with D. P. Cruikshank, David Tholen, and others to carry out observations at Mauna Kea Observatory on the relationships of asteroids and comets, with D. P. Cruikshank, D. Tholen, and others. Our 2-color diagram of visual and infrared colors (right) showed the close spectroscopic relation of comets and outer solar system asteroids. Bright, icy satellites are in the lower left corner (bluish-white colors), while comets and carbonaceous types of asteroids ("C, P, and D" taxonomic types with brownish-black colors) fall in the upper right corner. We were probably the first to recognize that comets have similar black surface materials (4% reflectivity) to those on outer solar system asteroids. This proposal was controversial at the time, but confirmed a few years later by the Giotto probe at Halley's comet.

2-color diagram relating comets to the sequence of colors
2-color diagram relating comets to the sequence of colors of icy bodies and asteroid taxonomy of outer solar system. From this diagram we correctly predicted in 1985, prior to Halley's comet's arrival, that its nucleus has an albedo of 0.04. Cruikshank, Hartmann, and Tolen, Nature, 315 : 122-124, 1985

Our program also yielded proof that Trojan asteroid 624 Hektor was one of the largest highly elongated bodies in the solar system, and the discovery that "asteroid" 2060 Chiron had erupted and turned into a comet. Generally, our work aided the recognition that comets and asteroids could no longer be considered as independently as had been traditional. Asteroid 3341 was named "Hartmann" in recognition of the research on small bodies.

In 1997, I was named the first winner of the Carl Sagan Medal of the American Astronomical Society's Division of Planetary Sciences, for communication of science to the public.

From 1975 until today, I’ve contributed various papers questioning the overwhelmingly accepted paradigm that a “terminal cataclysm,” aka “late heavy bombardment,” occurred on the moon (and other planets), forming

most of the giant multi-ring impact basins in a ~150 Myr interval at about 3.9 billion years ago. See:

  • Hartmann, W. K. 1975.   Lunar Cataclysm: A misconception? Icarus, 24: 181-187.
  • Hartmann, W. K., G. Ryder, L. Dones, and D. Grinspoon 2000 The Time-Dependent Intense Bombardment of the Primordial Earth/Moon System. In Origin of the Earth and Moon, ed. R. M. Canup and K. Righter (Tucson: Univ. Arizona Press), pp. 493-512.
  • Hartmann, W. K. 2003.   Megaregolith evolution and cratering cataclysm models — Lunar cataclysm as a misconception (28 years later). Meteoritics and Planet. Sci. 38, 579-593.
  • Hartmann, W. K. 2015. “Reviewing “terminal cataclysm:” What does it mean?,” Workshop on Early Solar System Bombardment III; Houston, Feb. Abstract #3003.


I'm concentrating my current (2018) scientific research efforts in two areas. First, applications and implications of the detection of new small craters, in the 1-40 meter size range, on Mars during the ongoing Mars Reconnaissance Orbiter mission, and on the reasons for the failure of the still-widely accepted “terminal cataclysm” paradigm. Roughly half of the fresh Martian impacts produced clusters of small craters, indicating fragmentation of the meteoroid --- indicating in turn information about the very low bulk strengths many interplanetary bodies hitting Mars (a result found also in terrestrial data by Popova, Borovicka, Hartmann, Spurný, Gnos, Nemtchinov, and Trigo-Rodriquez. (2011) “Very low strengths of interplanetary meteoroids and small asteroids, Meteoritics and Planetary Science,” 46: 1525-1550.  

My second current research area is an epistemological review of the origins and evolution of the terminal cataclysm paradigm, and why it was (probably?) wrong.

Models of 624 Hector
Models of 624 Hector. Is it an elongated single body (top), two strong rocky spearheaded bodies in contact (middle), or two weak rubble-pile objects elongated by rotationaly forces (bottom)?
Copyright William K. Hartmann

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