Who ‘Created’ Planetary Science?

Recently, two interesting news stories grabbed my attention, not only for their newsworthiness, but also for their underlying historical narrative. One story was an interview with the author of a new history of the University of Arizona’s Lunar and Planetary Laboratory that describes the founding and early years of one of the nation’s premier institutions for planetary science. The other story promotes an upcoming appearance by an early participant in America’s unmanned space exploration efforts, my former colleague at the Applied Physics Laboratory, Tom Krimigis. Both of these articles make statements about the origins of modern planetary science—attributing not merely crucial, early efforts to these groups and individuals, but foundational roles as well.

The Lunar and Planetary Laboratory (LPL) in Tucson was one of the first university departments in the nation to host a group devoted to the study of the Moon and planets. Founded in 1961 by astronomer Gerard P. Kuiper, the LPL began by collecting the best images of the Moon (taken from telescopes on Earth) to create an atlas for a rapidly growing cadre of scientists drawn to lunar studies by the advent of the Space Age. The new history of the LPL is a welcome contribution in that it collects the specific memories and recollections of the early members of that group. The other news story covers a scheduled appearance by Tom Krimigis at Flagstaff’s Lowell Observatory to recall his almost 60-year involvement with various robotic space missions. Tom was a student of the famous James Van Allen, discoverer of the radiation belts that surround the Earth (discovered by America’s first orbiting satellite, Explorer 1).

Both stories suggest that these efforts “created” modern planetary science (by this term, I mean the analysis and interpretation of images and data collected by spacecraft missions). However, is this accurate in the sense that they founded the discipline and that others followed the path thereby blazed? Or is the story more complicated?

After World War II and decades of neglect, scientific interest in the Moon and planets began to be reignited, in part through the publications of people interested in the process of high-velocity impact, such as geologists Reginald Daly and Robert Dietz. But renewed interest in the Moon was led (nearly single-handedly) by Ralph Baldwin, a physicist and astronomer by training and an executive of the family business, the Oliver Machinery Corporation of Grand Rapids, Michigan. While giving public lectures at Chicago’s Adler Planetarium, Baldwin marveled at the magnificent enlargements of telescopic pictures of the Moon. Studying them, he noticed the pattern of radial lineaments and scoring that pointed back to the center of Mare Imbrium on the Moon. From investigating the literature, he was surprised to find that no one had described these lunar surface features before (at that time, Baldwin was unaware that geologist G.K. Gilbert had first described these features from telescopic observations in the 1890s). In 1949, Baldwin wrote up his findings and conjectures in a book, The Face of the Moon, published by the University of Chicago Press.

Though not a best seller, Baldwin’s book was read by some key people who would significantly influence the development of planetary science. Harold Urey, Nobel-prize winning chemist and Manhattan Project scientist, read it and was captivated by the idea that samples of the Moon could unlock the secrets of Solar System formation. Eugene Shoemaker of the U.S. Geological Survey read both Gilbert and Baldwin, and as a young geology student, he became convinced that a geological approach—using images, field study and sample collection—was the appropriate methodology for the study of a rocky object such as the Moon. Although this seems obvious today, it was not obvious at the beginning of the Space Age, which brings us to the other thread in this history.

Geophysicists had long studied the magnetic field of the Earth. Our new ventures into space gave them the opportunity to directly measure the magnetic fields of the Earth and other planets, and their interaction with the environment of space. These studies, dubbed “sky science” by one observer, measured electromagnetic fields and cosmic particles of widely varying energies—measurements that not only do not require the presence of people, but where the presence of humans actually interferes with the phenomena to be studied. Thus, early in the history of planetary exploration, a dichotomy of space scientists developed, one having outright antipathy to the human spaceflight program and the other intent on developing plans for the direct human exploration of other worlds. James Van Allen and his students (one of whom was Tom Krimigis) designed and built the experiment on Explorer I that discovered the radiation belts that surround the Earth and now bear his name (as well as flying similar experiments to all of the planets in the following decades). It was a major discovery—one that led to our current understanding that the “vacuum” of space is actually permeated with strange radiation, electromagnetic fields and energetic, colliding particles.

I bring these two articles up because both claim significant roles for these two separate groups in the “founding” of modern planetary science, yet in fact, it is better to understand that they are actually pieces in the larger mosaic of shared discovery, serendipity and insight. Interestingly, these two groups are examples of a philosophical divide that led to a division in planetary science that persists to this day—the divide between “sky” scientists and geoscientists and their endless debate on the claimed superiority of robotic missions to human missions. The great contribution of people like Gerard Kuiper was to value images as a source of scientific information. As Gene Shoemaker showed, geological sequence could be determined from such images. In addition, being an experienced field geologist himself, Gene made sure that astronauts sent to the Moon were trained in the rudiments of this science, even taking the lead himself with some of the initial field tutorials for the first two astronaut groups. While many sky scientists expressed skepticism about this approach, no credible or informed observer can seriously argue that simple robotic missions could have accomplished the level of work that the Apollo astronauts did in their field explorations of the Moon. The geological approach taken during lunar exploration has led to our current understanding of “impact” and the formation and evolution of the planets.

So who “founded” planetary science? With due respect to both Kuiper and his LPL, and to Tom Krimigis and his mentor James Van Allen, I believe, as is the case with most scientific disciplines, planetary science grew from several disparate threads (some parallel and others intersecting) over the last 60 years. The sky scientists made important discoveries about interplanetary space and the internal structures of the planets. The geoscientists uncovered the early accretion and subsequent evolution of the bodies, especially the rocky objects of the Solar System. Together, both groups “founded” planetary science. And like robots and humans, both are necessary to explore space.

Paul D. Spudis | READ MORE

Paul D. Spudis (1952-2018) was a senior staff scientist at the Lunar and Planetary Institute in Houston, Texas, and a prolific author on the subject of the moon. His books include The Value of the Moon: How to Explore, Live, and Prosper in Space Using the Moon's Resources.