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.
Asteroid watch
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.
Beyond
imagination
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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