William Hartmann

Professional History

INTRODUCTION: 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 onto a globe. In 1965, I used crater counts on the moon and Earth to successfully predict that the lunar lava plains have an age of “about 3.6 × 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. In 1971-72, I was a Co-Investigator 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. 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 out 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]. My work in 1973-1980 focused on effects of the high impact-cratering rates that 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, eds. 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 two-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. 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, eds. 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.