On June 12, at the Goddard Space Flight Center in Greenbelt, Maryland, NASA posthumously awarded the Exceptional Public Service Medal to University of Maryland Distinguished University Professor Michael F. A'Hearn, one of the world's leading cometary scientists. The NASA Medal is for “fundamental work on comets and small bodies of the solar system, leadership in space missions, and ensuring public access to data from NASA missions and related projects.”
A'Hearn, who died on May 29 at his home in University Park, Maryland at the age of 76, was most widely known as the principal investigator (PI) of the NASA Deep Impact mission. On July 4, 2005, the spacecraft released a washing-machine-sized probe that collided spectacularly with comet Tempel 1, while the main spacecraft observed the results. The powerful impact gave scientists their first-ever view of pristine material inside a comet and garnered massive public attention for planetary science, solar system exploration, NASA and the University of Maryland.
The impact was also observed by NASA and other space telescopes and from Earth by many professional groundbased telescopes and thousands of amateur astronomers. The event set a then NASA record for webpage hits (more than 1 million) and drew front-page news coverage by broadcast, print and web media outlets around the world.
“Mike A’Hearn devoted his life to exploration, and his work has transformed our understanding of what comets are made of and how they interact within our corner of the universe,” said Jim Green, director of NASA’s Planetary Science Division. “This is a great loss for the small bodies community and for me personally.”
After Deep Impact’s original mission ended, A'Hearn and his science team convinced NASA to use the surviving primary spacecraft for continued cometary studies. With A'Hearn as PI, the project embarked on an extended mission, designated EPOXI, with dual purposes-- studying extrasolar planets and comet Hartley 2. On the way to Hartley 2, the Deep Impact spacecraft flew between the Earth and the Moon. Its instruments were able to confirm the surprising presence of water on the Moon’s surface. The Deep Impact spacecraft later imaged two other comets-- C/2009 P1 Garradd (in 2012), which had a surprisingly high carbon monoxide content, and C/2012 S1 ISON (in 2013), a comet that disintegrated as it grazed past the Sun. The images and findings of these later missions further advanced comet science and attracted more media and public attention.
When NASA lost contact with the Deep Impact spacecraft in September 2013, A’Hearn said: “Deep Impact has been a principal focus of my astronomy work for more than a decade and I’m saddened by its functional loss. But, I’m very proud of the many contributions to our evolving understanding of comets that it has made possible.”
Illuminating the Primordial Dust
He looked at comets across the range of light (electromagnetic radiation) wavelengths from extreme ultraviolet radiation to visible light to radio waves. In particular, in the 1970’s he pioneered the study of comets in the ultraviolet, using the International Ultraviolet Explorer space telescope, coordinated the world’s ground-based observations of comet Halley in the 80’s, and in the 90’s compiled the most comprehensive set of compositional data of comets to date.
A’Hearn’s post-Deep Impact work included being co-investigator on the Stardust-NExT mission to re-visit comet Tempel 1, which documented changes on the comet’s surface since Deep Impact, and a co-investigator on two instrument teams (the OSIRIS camera and the NASA Alice ultraviolet spectrograph), on the European Space Agency’s Rosetta mission, which co-orbited and landed on comet Churyumov–Gerasimenko.
In addition to being a pillar of cometary science, another major contribution to planetary science was A'Hearn’s nearly three decades as principal investigator for the Small Bodies Node, which is the part of NASA's Planetary Data System that specializes in the archiving, cataloging, and distributing scientific data sets relevant to asteroids, comets and interplanetary dust. A founder and advocate for the Planetary Data System, A’Hearn championed its mission to preserve data of planets and make it publically accessible for use by future generations as they seek answers to questions that current researchers don’t even know to ask. Under his leadership, the Small Bodies Node developed from a two-person group to a strong, UMD-based, organization of 18 scientists and programmers.
Together with colleagues, many of whom he had mentored, A’Hearn used observational and exploratory tools, computer models (numerical simulations), and experiments (biggest was the Tempel 1 impact) to help us better understand comet chemistry and comet components (body, or nuclei, and surrounding gas and dust called the coma). This work was done with the goal of gaining new insights into how the dense disc of gas and dust that had rotated around our newly formed Sun, formed into our solar system’s planets, comets and asteroids, and thus, ultimately, into us.
“Everything about Mike was genuine-- his love of comets and the secrets they hold to our origin and his concern for individuals,” said University of Maryland Professor Jessica M. Sunshine, director of the UMD Small Bodies Group. “Mike inspired thousands of UMD undergrads to appreciate science, formally and informally guided generations of young cometary scientists all over the world and he advocated for future solar system exploration, open and long-term access to planetary data, and the protection of our planet from the hazards of cometary and asteroidal impacts.”
Defending Planet Earth
He was vice-chair of a 2010 National Academy of Sciences/National Research Council report entitled “Defending Planet Earth: Near-Earth-Object Surveys and Hazard Mitigation Strategies (2010) Chapter: 2 Risk Analysis.” He also chaired the mitigation sub-panel that wrote the section of the report devoted to protecting our planet from dangerous “near-Earth objects” and to mitigating the damage of unavoidable impacts. A brief interview, A'Hearn: Protecting Earth: Four Recommendations, can be seen here.
A Deep and Lasting Impact on Comet Science and Colleagues
Other recognitions of his work include an Exceptional Public Service Medal from NASA and the Gerard P. Kuiper Prize from American Astronomical Society Division for Planetary Sciences. The NASA Medal was approved shortly before his death in recognition of his “fundamental work on comets and small bodies of the solar system, leadership in space missions, and ensuring public access to data from NASA missions and related projects.” The Kuiper Prize “recognizes and honors outstanding contributors to planetary science.”
A’Hearn’s tremendous impacts on his field and university were personal as well as professional. Colleagues universally say he was a great and thoughtful friend as well as a terrific teacher and mentor for younger scientists, many of whom now will continue his legacy by further advancing the understanding of comets and asteroids and the early history of our solar system.
"Mike was a wonderful friend, mentor, and colleague to so many in our astronomy department and everywhere,” said UMD Astronomy Department Chair Stuart Vogel. “He was the founder of the department's Small Bodies Group and one of the most respected and admired planetary scientists in the world. He will be deeply missed."
In 2011 A’Hearn became a professor emeritus, but, even in “retirement” he continued to produce important work and to mentor younger scientists. He authored a review article, Comets: Looking Ahead that was published the day of his death. He is a coauthor of at least one other forthcoming paper.
“Dr. Mike A’Hearn was one-of-a-kind in a group of unique individuals – the hand full of planetary scientists who have led a mission of exploration through our solar system,” said Lindley N. Johnson, NASA’s planetary defense officer and program executive for Deep Impact/EPOXI. “Mike was a joy to work with. Not only was he a treasured advisor to so many graduate students, he was a valued mentor to us all. I’d like to now think of him as having grabbed a comet by its vibrant tail – and forever riding it around the solar system.”
Born in Wilmington, Delaware in 1940, A’Hearn grew up in Boston, graduated from Boston College High School and from Boston College (’62) and received his Ph.D. from the University of Wisconsin (’66), studying polarization of the atmosphere of Venus.
Michael A’Hearn passed away at his home on May 29, 2017. He is survived by his wife Maxine, sons Brian J. A’Hearn (Zlata) of Oxford, UK, Kevin P. A’Hearn (Kanlayane) of Vienna, VA, and Patrick N. A’Hearn of Seattle, WA; and grandchildren Sean, Brendan, Marie, Eliane, and Gabriel.
June 13, 2017