Until his death this month at the age of 91, James Van Allen continued to do work that had fascinated him since childhood and made him a leading figure of America's Space Age.
Van Allen spent a lifetime exploring the universe, and is most famous for discovering the radiation belts circling Earth which now bear his name.
In what would be his last paper, he explored a subject that hits somewhat closer to home: The likelihood of an asteroid colliding with Earth.
The research, published in this month's American Journal of Physics, details how the likelihood of such an event is enhanced by the gravitational pull between the two bodies.
The research shouldn't raise concern about possible collisions though, said Dave Tholen, an astronomer at the University of Hawaii. "It can happen, but I wouldn't worry about it. We are actively discovering near-Earth asteroids and computing their orbits to monitor the situation."
Tholen said astronomers are intensely focused these days on an asteroid called Apophis, which is set to pass less than 24,000 miles from Earth on April 13, 2029. Van Allen's paper, which details how scientists estimating the probability of a collision should take Earth's gravitational pull into account, could help researchers calculate whether the asteroid will become a threat.
Colleagues say this and other examples of Van Allen's work are remarkable not only for what he found, but also because of the simple experimental designs he employed.
"He really showed that by focusing on the fundamental question and designing simple instruments, you could reveal things about nature you wouldn't have imagined," said Ed Stone, a physics professor at the California Institute of Technology.
When the American team launched its first satellite, Explorer 1, into space, Van Allen had the prescience to attach a self-designed radiation detector to it. While the team didn't manage to beat the Russians into space, his instrument sent back data giving the first evidence of the donut-shaped rings circling the Earth.
Working to the end
Frank McDonald, Senior Research Scientist at the University of Maryland, was a post-doctoral student at the University of Iowa during Van Allen's early days there. He worked with him on so-called "rockoons," rockets attached to balloons, which measured space radiation even before Explorer 1 went up.
McDonald says the recent paper on asteroids, which he describes as more educational than revolutionary, is evidence of Van Allen's commitment to teaching.
"He was an outstanding mentor, and one of his missions in life was training students," McDonald said. In addition to teaching science, Van Allen also taught students to be savvy fundraisers for it. "You learned that when you wanted to get something from a group, to go in with a statement already written about what you wanted--whenever I was in D.C., he always urged me to visit the Office of Naval Research."
That Van Allen would still be publishing into his nineties comes as no surprise to McDonald. "You're talking to somebody who just turned 81 and comes in every day, so it doesn't surprise me at all. I couldn't imagine him not doing it and not having him there ten years ahead of me," he said. "And this is a heck of a lot more fun than retiring to Florida. We're still seeing things we never expected to see."
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