[meteorite-list] James Van Allen's Last Science Paper: Likelihood of Asteroids Impacting Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 29 12:20:20 2006
Message-ID: <200608291617.JAA22429_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/060829_science_tuesday.html

James Van Allen's Last Science Paper
By Abigail W. Leonard
space.com
29 August 2006

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."
Received on Tue 29 Aug 2006 12:17:32 PM PDT