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Early History

(Based on articles by William K. Hartmann, Donald R. Davis, and Stuart J. Weidenschilling in the PSI Newsletter, Winter 2002 and Summer 2003)

Historical Balcony 1971

In the Beginning

The roots of PSI were established in the late 1960s, when several young PhD’s graduated from the University of Arizona laboratory of the pioneering planetary astronomer, Gerard Kuiper, and ended up working in a space division of a Chicago organization called IITRI - the Illinois Institute of Technology Research Institute. IITRI provided planning and mission analysis support to NASA HQ for post-Apollo exploration of the solar system—both planets and the Moon— and needed guidance from planetary scientists for this endeavor. Toby Owen and Alan Binder were hired by IITRI in Chicago; however, efforts to attract other young scientists were unsuccessful, in part due to IITRI’s location in Chicago. Binder (who later led the Lunar Prospector mission that discovered ice in the polar soil of the moon) agitated successfully to open a Tucson planetary division of IITRI, and by 1971 this division included Binder, Bill Hartmann (who was working on the Mariner 9 Mars mission, Don Davis (U.A. PhD graduate known at that time for participating in saving the Apollo 13 mission), and Clark Chapman (an MIT PhD known for his work on asteroids). We were led by a very capable and clever IITRI manager named Dave Roberts and the first office was in downtown Tucson, at 201 N. Stone Ave.

From the beginning, the philosophy was to develop a group of collaborative scientists in an atmosphere conducive to producing excellent science — a group run by scientists for the benefit of science. The “superstar” model was rejected in favor of a team approach in which individual Principal Investigators would have overlapping but distinct areas of expertise. PSI management sought to attract good young scientists and help them develop proposals that would start their independent careers and fund their work through the group.

Official Founding of PSI

Early PSI in 1976

By late 1971, this group decided to join a fledgling parent company known as Science Applications Incorporated, which had just been formed by a nuclear engineer, Bob Beyster. Hartmann’s employee number at SAI was 224, an irony since SAI grew into the enormous technology firm, Science Applications International Corporation, where employee numbers are now in the high tens of thousands! Beyster allowed us to be a nonprofit center within this larger profit-making company, and was pleased with the prestige of involvement in NASA-funded science. We selected the name Planetary Science Institute.

To make the transition, a few of us at a time left IITRI and joined SAI. Hartmann had been participating in the Mariner 9 Mars mission, and in early 1972 returned to Tucson. The newly formed Planetary Science Institute started as a desk in his living room on Sunray Drive in the Tucson  mountains. While we looked for a real office, the others made the transition to SAI/PSI. For these reasons, we officially date the birth of PSI as February 1972, and celebrate our anniversary open house each year on Ground Hog Day. PSI found office space in Northwest Tucson and remained there for several years.

Initial Work at PSI

Noteworthy research began to flow from PSI immediately. Hartmann and Davis collaborated on a what turned out to be a famous paper, given at a Cornell meeting in 1974 and published in 1975, which first suggested that the Moon formed when a collision with a giant, primordial interplanetary body blew material out of the outer layers of Earth, providing debris to make the Moon. This theory was recognized in 1984 as the leading theory of lunar origin and has kept that place to the present day.

During the 1970s, Chapman carried out observations of asteroids and helped develop the taxonomic system by which asteroids are classified according to different compositions. Hartmann continued work on lunar and Martian cratering. From numbers of craters, he was able to conclude that many lava flows on Mars had ages of “only” a few hundred million years, which is young in planetary terms; this controversial result was confirmed by Martian meteorites in the 1980s and 90s.

Rick Greenberg, an MIT graduate and dynamicist, joined the group in 1976. Stuart Weidenschilling, yet another MIT graduate, who had done postdoctoral work with the famous dynamicist, George Wetherill, joined PSI in 1978. We developed a democratic structure, with decisions made by discussion and consensus. Hartmann served briefly as manager, followed by Davis who retained the position for more than 20 years.

Now, with Greenberg, Weidenschilling, Davis, Chapman, and Hartmann, we had a group with a powerful depth of understanding of collisions and aggregation of the primordial bodies, or “planetesimals”, that orbited the sun and eventually formed the planets. In the mid 1970s, our PSI group collaborated on creating a complex computer model that allowed us to start with innumerable planetesimals and follow their collisions until they grew into planets — a process called accretion. Some of our ideas were inspired by earlier work, not widely recognized at that time, by a Soviet scientist named Victor Safronov, who was later much honored as the father of collisional accretion theory. We were honored when he was able to visit our office in 1979. The PSI model included complex orbital theory and results from new collision experiments that we conducted at NASA’s Ames Research Center to learn how materials absorb energy or fragment during collisions. In the late 1970s we began publishing these results.

In the mid 1970s, the two Viking missions landed on Mars and placed orbiters in position to send back large amounts of data. Viking scientist, Jim Cutts, joined PSI in 1974 and formed a separate office in Pasadena that same year which did notable Mars research with the Viking results. PSI-Pasadena also absorbed various contracts for work farmed out from Cal Tech’s Jet Propulsion Lab, which ran the Viking mission. Unfortunately, as the Viking mission wound down and JPL policies evolved, the Pasadena office ran out of contracts and closed in 1979. Notable researchers such as Karl Blasius (Mars) and Tommy Thompson (lunar radar) worked with us through the Pasadena office at that time. The PSI “planet forming model” has continued to evolve under the leadership of Weidenschilling and Davis, and continues to be the basis for much research on planet formation and collisional evolution of asteroids, both in the main asteroid belt and in the more recently verified “Edgeworth-Kuiper belt” on the outskirts of the solar system.

Around 1975, PSI moved to an office on North First Avenue, and moved again in 1978 to the Sun Building at 2030 E. Speedway, to be closer to the University of Arizona. We were quite happy at this location; however, the University of Arizona administration expanded and took over neighboring office space, including the Sun building. Despite appeals from University planetary scientists that PSI be allowed to stay, we were evicted in 1988 and moved to nearby quarters at 2421 E. Sixth St, several blocks further from the university. After a few years, this location proved unsuitable and we had to move again, relocating in 1993 to 620 N. Sixth Ave., about a mile west of the university.

Our work during the 1980s featured a continued series of papers about planet formation using the PSI planet-growing model, as well as  observational work on asteroids and comets from Rick Binzel, Humberto Campins, Clark Chapman, and William K. Hartmann. Hartmann collaborated with Dale Cruikshank and Dave Tholen (U. Hawaii) to use the Mauna Kea telescopes in observations which were the first to show that outer solar system asteroids and comets all have similar, very dark colors, and are closely related to each other. One discovery successfully predicted that Halley’s Comet would be a black body with only 4% reflectivity (as confirmed by the European Giotto probe), when the prevailing wisdom was that it would look like a dirty iceberg with about 26% reflectivity.

Courtyard of Sun BuildingDuring this period, Clark Chapman landed a plum assignment as a team member on NASA’s Galileo Mission to Jupiter. He spent several years planning the mission and then analyzing photos of Jupiter’s satellites, as well as editing the Journal of Geophysical Research–Planets for a short period from our office. Hartmann was selected to be on the Mars Observer mission, which failed as it approached Mars, and then was appointed to the Mars Global Surveyor (MGS) imaging team. MGS successfully sent back close to 100,000 images from 1997 to 2002.

PSI continued to evolve as some members left and others arrived. Among notable staff were the well-known asteroid researcher Rick Binzel, who came in 1985, and the comet observer Humberto Campins, who came in 1986. Alan Binder departed in 1976 to work in Germany; Greenberg went back to the University of Arizona in 1985; Binzel went to MIT in 1991; Campins to the University of Florida in 1994; and Chapman to the Southwest Research Institute in 1997.

Steve Howell joined the group in 1988, first on an appointment split between computer systems administration and science. He broadened our coverage into astrophysics and quickly succeeded in attracting grants and developing a full-time program emphasizing observations and interpretation of cataclysmic variable stars. Steve left for a few years to go to the University of Wyoming, but returned in 1997, staying until 2002 when he moved to the University of California at Riverside.


In 1995, after much debate, we elected to pull out of SAIC and merged with a fledgling group in San Juan Capistrano, established by former JPL scientist Doug Nash who became director. The merger of the two groups greatly strengthened the California group, and gave PSI Tucson non-profit status. The Tucson group retained its identity at PSI, while administrative and financial management was located in the San Juan Capistrano office. The San Juan Capistrano office included not only Doug Nash and his lab, but Bruce Betts, who had worked on various problems in Mars research, and a very active community outreach education program.

However, Nash retired in 1998, shortly after our merger, and Bruce Betts took a three-year leave to work at NASA HQ in Washington, DC, so maintaining the California home office (in a refurbished bank building in San Juan Capistrano) became untenable. The California office relocated to a series of smaller facilities ending up in Laguna Niguel, CA, until its closure in 2005. Donald Davis his position of Institute Director following the retirement of Doug Nash, and remained as director until handing the reins of the Institute to Mark Sykes in 2004.

Into the 21st Century

1978 An early experiment in planetary collisions

The late 1990s saw a prosperous period of expansion for PSI. Steve Howell worked with several graduate students and post docs, and oversaw PSI’s involvement with a consortium of four other institutions, led by the Western Kentucky University, to refurbish the old 50-inch telescope on Kitt Peak for remote control and robotic operation. Part of our support for this program came from The Planetary Society founded some years earlier in  Pasadena by Carl Sagan and former JPL director Bruce Murray.

As Mars work geared up for the Mars Global Surveyor mission in 1997-2002, we attempted to attract new, younger staff by offering opportunities for recent PhD’s to develop proposals through PSI, to be submitted to NASA. The first case was Dr. Jennifer Grier who wrote a proposal with Hartmann and was funded as PI for a three year project to study a volcanic province of Mars. Grier pursued this work off site from a base in Boston, where her husband took a position with MIT.

Dr. Cathy Weitz, at NASA HQ, affiliated with PSI in 2000 from the Washington, DC area. Next was a successful proposal from Dr. Melissa Lane to study unexpected mineral deposits on Mars, and she pursued this from Tempe, AZ. Then came a funded proposal with Dr. Elizabeth Turtle as PI in a study of ice flow processes on Mars.

These developments not only added a significant number of lower cost operations off site, but also created, in part, a 21st century virtual institute.

Dramatic developments occurred in 2001-2002 in the Tucson office, too, as numerous new staff appeared. Dr. Elizabetta Pierazzo joined PSI from the University of Arizona to work on cratering and impact theory. Dr. David Crown joined PSI from the University of Pittsburgh to work on Martian geological processes. And Dr. Steve Kortenkamp joined PSI from the University of Maryland to work on PSI’s continuing interest in the origin of planetary systems by modeling of accretion processes. These additions to the staff led to growth strains as well as opportunities, resulting in a move to a new building.

In 2004 the institute moved to their current location at 1700 E. Fort Lowell in Tucson and in 2016 opened a small office in Denver, Colorado.  By 2022 there are scientists working remotely from 30 states and 10 other countries.

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