Impact with comet changed understanding
Michael A’Hearn, the chief architect and director of an intentional space collision of a comet and spacecraft to advance the eternal human search for the secrets of the solar system, died May 29 at his home in University Park, Md. He was 76.
The cause was pancreatic cancer, said his wife, Maxine A’Hearn.
An astronomer and professor emeritus at the University of Maryland, Dr. A’Hearn was the chief scientist for the NASA mission known as “Deep Impact,” in which an impactor spacecraft was launched directly into the path of a speeding comet.
“Nothing like it had ever been attempted before,” Jim Green, NASA’s director of planetary science, said in an interview. What A’Hearn was proposing, Green said, was to “blow a hole” in the comet to see what was inside.
At 1:52 a.m. on July 4, 2005, the 23,000-mph collision occurred 83 million miles from Earth. It made headlines and led news broadcasts around the world.
The machinery consisted of two parts: a “flyby” craft equipped with sophisticated recording equipment, and a detachable “impactor,” an 820-pound, refrigerator-sized craft for the comet to strike. The comet, known as Tempel 1, was about 9 miles long and 3.7 miles wide and moved around the Sun in an elliptical orbit between Jupiter and Mars.
There was a blinding shower of light and a giant plume of gas and icy debris when the comet and impactor spacecraft collided with the force of what was said to have been the equivalent of 4½ tons of dynamite.
Scientists had long believed that comets contain remnants of matter left over from the formation of the solar system. They wanted to look inside Tempel 1 to see if an interior view might yield more information.
From the Tempel 1 collision and later flyby observations of other comets, the scientific community gained “a complete rethinking of our understanding of the formation of comets and of how they work,” A’Hearn said in a 2013 announcement of the formal end of the “Deep Impact” mission.
“These small, icy remnants of the formation of our solar system are much more varied, both one from another and even from one part to another of a single comet, than we ever had anticipated,” he said.
Michael Francis A’Hearn was born in Wilmington, Del., on Nov. 17, 1940, and grew up in Boston. He graduated from Boston College and then received a doctorate in astronomy from the University of Wisconsin in 1966. That year he joined the faculty at the University of Maryland.