Patrick Thaddeus

Patrick ("Pat") Thaddeus, one of the founders of the field of astrochemistry, who was largely responsible for recognizing that our galaxy is filled with a vast number of molecular clouds, died peacefully at home in Cambridge, Massachusetts, on April 28, 2017. He was 85 years old.

Pat was born in the utopian village of Arden, Delaware, on June 6, 1932. He was a curious, high spirited and mischievous youngster, often suspended from school for truancy. His home life was difficult. His parents divorced when he was seven and his mother took him to Buffalo. Missing his "native land," he later returned to Arden to live with his father. He fondly recalled befriending German prisoners of war as they worked in nearby fields.

Pat graduated from the University of Delaware in 1953 with a degree in physics, then studied theoretical physics as a Fulbright Scholar at Oxford. In 1955 he enrolled in a PhD program at Columbia. For his thesis under the supervision of Nobel laurate Charles Townes, Pat measured the transition frequencies of a number of molecules with a maser beam spectrometer that he built.

In 1960, he took a research post at Columbia, and stayed for the next 26 years, rising to adjunct full professor, while also working as a research physicist at the NASA Goddard Institute for Space Studies. In 1986, he was recruited by Irwin Shapiro to move to the Center for Astrophysics in Cambridge, Massachusetts. He was appointed Professor of Astronomy and of Applied Physics at Harvard, and Senior Space Scientist at the Smithsonian Astrophysical Observatory, where he continued to work unabatedly until his retirement in 2014.

The discovery of the cosmic microwave background (CMB) in 1965 piqued his interest. With his optical experience limited to having built a reflecting telescope as a youth, Pat and students John Clauser and Victor Bortolot set out to see whether a pair of optical transitions of CN in the interstellar medium could act as a reliable thermometer for the CMB. Using the Lick 120-inch telescope they established the temperature of the CMB to be 2.7 Kelvin. For a long time their measurement remained the short wavelength anchor in the spectrum, proving the CMB to be black body in nature. He later mused "my excursion into optical astronomy [with] the thrill of holding up a developed photographic plate ... and seeing the faint, barely perceptible absorption lines of excited CN, knowing that it was a fingerprint of the universal radiation field filling all space, once as brilliant as the surface of the Sun, was an aesthetic and intellectual pleasure that I have never again experienced in research." The idea for a space measurement of the CMB at wavelengths shorter than a millimeter was hatched in his office with his post-doctoral fellow, John Mather. This ultimately led to the Cosmic Background Explorer (COBE) satellite and a Nobel Prize for Mather.

With the surprising detection around 1970 of millimeter-wave emission from several simple molecules in space, Pat sensed another field ripe for investigation. Using one of the few radio telescopes capable of observing at such high frequencies, Pat and his students Marc Kutner, Ken Tucker and Gordon Chin set out to map the distribution of such molecules around the Orion Nebula. What they found was the first example of a so-called giant molecular cloud (GMC), vast regions of dense gas that we now know are the main sites of star formation. Realizing that mapping such objects throughout the Galaxy would take decades with existing telescopes, he and his group, which included students Gordon Chin, Richard Cohen, and Hong-Ih Cong, decided to build their own, a small radio dish that they placed in the most unlikely of spots for astronomical observations, the center of Manhattan on the Columbia campus. Asked by a reporter how observations could be done there, he responded that at the frequency of their observations, "New York was as quiet as the day Henry Hudson came sailing up the river." The so-called "mini" telescope was set to work day and night mapping the vast GMCs that hung like invisible thunderclouds over the New York skyline. Soon a second mini was constructed and sent to Chile to map the southern sky. Ultimately the two telescopes provided the data for 24 of Pat's PhD students and produced what is still the only complete map of the distribution of molecular clouds in the Milky Way, which was published in 2001. The mini continues its survey work to this day, more than 40 years after its commissioning.

At the same time the molecular cloud work was beginning, Pat realized that his spectroscopy lab would enable him to search for many more exotic molecules in space by first precisely measuring their spectral lines in the lab. He would often proclaim proudly that his "ironclad" identifications of molecules in space far exceeded the specificity of a human fingerprint. To date over 200 molecules have been identified in the interstellar medium, a substantial fraction of them discovered by Pat's group, his students, and his collaborators. The molecules range from simple organics to large carbon rings and chains, the largest having twice the molecular weight of the simplest amino acid glycine. Pat's more spectacular discoveries include the first interstellar organic ring, C3H2, and the first detections of negatively charged molecules, or anions, in the interstellar medium.

Pat had broad intellectual interests and was a raconteur par excellence. He held dinner audiences in rapt attention discussing topics as varied as the aerodynamics of the wandering albatross, the Greco-Persian wars, and the foundational issues of quantum mechanics. He taught himself Italian and read an Italian newspaper every day. He was a member of the National Academy of Sciences and his many other honors include the Herschel Medal of the Royal Astronomical Society and an honorary degree from the University of Chicago.

Pat's first wife, Janice (Farrar) Thaddeus, died in 2001. She was a scholar, poet, and Lecturer at Harvard. They were married for 44 years and had two children, Eva, an editor, and Michael, a professor of mathematics at Columbia. In 2003, Pat married Valerie McCollom, who survives him.

The years took their toll on Pat physically, but they never diminished his zest for life. Just a few days before he died, bedridden in his Cambridge home, his wife raised his curtains to a sunny morning. Pat's face brightened as he exclaimed "Ah spring!"

[This memoir was adapted from the "Memorial Minute" presented to the Faculty of Arts and Sciences, Harvard University, and published in the Harvard Gazette, May 19, 2019.]