Sky & Telescope - December 2024 - 14

Meteor Science
comet 55P/Tempel-Tuttle also came around.
The fundamental understanding necessary for predicting
meteor storms had already taken shape as early as the 1890s,
and the essential theoretical framework was largely complete
by the time Fred Whipple published his " dirty snowball "
model for comets in 1950. The story unfolds like this:
Comets are composed of collections of ice, rock, and dust.
They warm up when approaching the Sun and launch dust
particles into space. The dust particles orbit the Sun along
with their parent comet. However, the combination of sunlight's
pressure and gravitational tugs from the major planets
gradually amplify small differences in the particles' trajectories,
slowly turning the dust cloud into a stream along
the comet's orbit. This stream eventually dissipates into the
interplanetary dust, which is itself primarily made of comet
and asteroid debris, becoming part of the zodiacal light that
we see under dark, pristine skies.
Predicting meteor showers' behavior thus requires accurately
projecting the evolution of these dust clouds forward in
time, then finding the times when Earth intercepts them.
This work is a tricky endeavor: Planets and comets are
single, solid bodies, but meteoroid streams are long, continuous
structures made of countless particles. So instead of
calculating the location of one representative dot, one needs
to calculate the locations of many small bits, each representing
a segment of the meteoroid stream. As you can imagine,
these calculations were exceedingly difficult for astronomers
relying on pencil and paper, however fantastic their computational
skills were.
The development of modern computers provided critical
help in solving this challenging problem. In 1962, John
Davies and Władysław Turski of the University of Manchester
in England pioneered the use of modern computers in
meteoroid-stream simulations. They used the Ferranti Mercury
computer - an early commercial computer that operated
How Meteor Storms Form
at a speed 100 million times slower than an iPhone 14 - to
study past cometary ejecta. They found out that the Draconid
meteor storms in 1933 and 1946 were caused by earlier cometary
activity around the turn of the century.
In the following four decades, three groups of researchers
across the globe independently developed a method to
accurately predict future meteor storms. At the time, the
researchers were unaware of one another's work, in part due
to difficulties with access to scientific publications in that era.
First came Edward K. L. Upton (University of California,
Los Angeles), who in 1977 propagated cometary ejecta into
the future and correctly predicted the 1999 Leonid storm that
came two years before the storm I saw as a teenager. Upton's
work, however, was written as a popular-science article (it
won first prize in the Griffith Observer writing contest that
year) rather than as a research paper, and so it was not fully
appreciated by the research community until years later.
Then, in 1985, Ekaterina Kondrat'eva and Evgenij Reznikov
at Kazan State University in Russia independently devised a
similar method based on a series of studies by themselves and
other Russian scientists in the 1970s. They also correctly predicted
the 1999 Leonid storm. However, their original paper
was written in Russian and wasn't widely known in other
parts of the world for many years.
Finally, in 1999, David Asher of Northern Ireland's
Armagh Observatory and Robert McNaught of Australian
National University also independently arrived at the same
method and made the same prediction. They published their
results in well-circulated journals. The earlier works by Upton
and Kondrat'eva and others were subsequently noticed and
finally received full attention. Meteor-storm prediction finally
became a reality.
All of these works also explained why my family and I
didn't see a storm in 1998: That year, Earth simply missed the
bulk of the meteoric material when it flew by.
A comet or asteroid coughs out a dust cloud when sunlight warms it.
14 DECEMBER 2024 * SKY & TELESCOPE
The dust cloud envelops the comet and travels with it around the Sun.
BEATRIZ INGLESSIS / S&T
Sky & Telescope - December 2024

Table of Contents for the Digital Edition of Sky & Telescope - December 2024
