Remembering Tom Gehrels (1925-2011)

The first thing I saw when I entered the University of Arizona office of Tom Gehrels last April was his racing bicycle. Fitting enough for a Dutchman, Gehrels always rode it from his Tucson home to the Lunar and Planetary Laboratory and back again, even at age 86.

The second thing I saw were Indian tapestries and Buddhist artifacts, giving the office a distinct Eastern look and feel. As a lifetime Fellow of the Physical Research Laboratory in Ahmedabad, Gehrels spent a few months each year lecturing in his beloved India. And, yes, he practiced yoga every day, presumably right up to his peaceful death on July 11th.

The third thing I saw was a frail man with light-blue, watery eyes and a friendly smile. When I asked him how he was doing, he replied in Dutch, "Het gaat heel goed!" — "I'm doing very well!" In fact, he said, his health appeared to be improving over the years.

Born February 21, 1925, Gehrels was a unique and wonderful person. Raised in the Dutch Bible-Belt community, he started to wonder about truth, reality, and the existence of God at a very early age. He was only a teenager when he became active in the Dutch Resistance during World War II. Gehrels fled to England, where he carried out secret operations for the Dutch government. One of his brothers was later killed at a Nazi concentration camp.

After the war, Gehrels studied astronomy at Leiden University. In the late 1940s, on a shoestring budget, he hitchhiked from New York to California, where he met famous astronomer Walter Baade at Palomar Observatory. Soon he would make the United States his home.

Gehrels worked with fellow Dutchman Gerard Kuiper, first at the Yerkes Observatory, and later in Tucson, where he would remain for the rest of his life. A pioneer in balloon-borne observations and skilled in polarimetry and photometry, he served as principal investigator for the "cameras" (actually scanning photopolarimeters) on the twin Pioneer spacecraft that obtained the first close-ups of Jupiter and Saturn.

As a young Dutch amateur astronomer in the 1970s, I felt nothing less than awe for this man, who in 1960 had carried out the now-famous Palomar-Leiden asteroid survey with Kees van Houten and Ingrid van Houten-Groeneveld. Together they turned up a whopping 4,177 new asteroids. (It's one of the reasons why so many Dutch people are immortalized in the solar system, by having an asteroid named after them.)

In 1983, together with his Arizona colleague Bob McMillan, Gehrels founded the Spacewatch Project, which still scans the night sky over Kitt Peak National Observatory for threatening near-Earth objects. I remember interviewing Gehrels about this work in the early 1990s. "Suppose an asteroid would be discovered that would hit the Earth," I offered. "What would you do?" His eyes began to twinkle as he replied, "Go out there and have a look, of course!"

On the shelf behind his Tucson desk is perhaps Gehrels' most enduring legacy: the 30-or-so massive volumes of the Space Science Series.

Produced by the University of Arizona Press, these tomes cover almost every topic in our solar system (or in those elsewhere) and represent a kind of collective bible to planetary astronomers. For his tireless involvement as the series' general editor, in 2007 the AAS's Division for Planetary Sciences honored him with the Harold Masursky Award for outstanding service to planetary science and exploration.

My brief visit in April came just two weeks after a luncheon at which Gehrels was honored for his remarkable half century of service to the University of Arizona. But we spoke little of that, or killer asteroids, or the Space Science Series.

Instead, we mainly discussed his latest unconventional ideas about cosmology. Inspired by his University of Chicago teacher Subrahmanyan Chandrasekhar, Gehrels explored an almost mystical equation that appears to numerically connect quantum physics, gravity, and relativity. In his final monograph, Can We Do Without the Big Bang?, he describes his own view of Truth and Reality — a hard-to-grasp, pseudoscientific set of ideas concerning an "interuniversal medium", dark energy as a consequence of "old photons", and an eternal multiverse without need for a Big Bang.

"I've been called a crackpot by cosmologists, and I can't blame them," he said, again with those heavenly, twinkling eyes and that loving smile. "They've built their careers on a wrong idea, and I am an outsider. But I don't care. When I started Spacewatch in the 1980s, the same thing happened: no one would take me seriously."

As I left the small office — which probably would have smelled of incense if Gehrels had been allowed to burn it — I shook his bony hand. Suddenly he frowned and looked wounded, recalling the compulsory church visits in the small Dutch village of Halfweg, where he was raised. But then his face brightened again as he said: "Have you been there recently? They've torn it down! It's torn down!"

In his search for understanding, Tom Gehrels encountered the frailty of humanity — constantly threatened by cosmic impacts — and lost track when he tried to answer the biggest questions science can ask. He was a remarkable fellow, a creative scientist infused with a spirited personality. I feel privileged to have met him less than three months before he died.

Asteroid 10986 Govert, named after contributor Govert Schilling, was discovered as part of the Palomar-Leiden Survey.