Winter 2005
PEOPLE
Physics
Professor Solving Curious Case of Missing Meteors
By Mary E. McCrank
A modern-day astronomical mystery has one of the top space scientists
on the case: Geneseo Distinguished Professor of Physics David D. Meisel.
Meisel, who specializes in searching for interstellar micrometeors, has
found himself in the middle of a modern "whodunit" that has
been playing out at the Arecibo Observatory of the National Astronomy
and Ionospheric Center in Puerto Rico, operated by Cornell University.
Meisel and other members of an international interdisciplinary team have
discovered that the micrometeors, previously detected at the observatory
for five years in a row, suddenly disappeared in the years 2002 and 2003,
only to reappear in 2004.
Meisel has been studying the case for eight years and has made a half-dozen
trips to the observatory to use the world’s most powerful radar.
"The disappearance is very important because up to now it was thought
that such extrasolar dust should bombard the Earth at a constant rate,
and that is certainly not the case," Meisel said. "Understanding
why this can happen is vital to modeling the flow of dust throughout the
solar system."
Meisel has presented his findings at conferences, including the American
Astronomical Society’s conference in June in Denver and a conference
on meteoroids in August at the University of Western Ontario in London,
Ontario, Canada. His talk is titled "Heliospheric Modulation of the
Extrasolar Micrometeors Detected with Arecibo UHF Radar."
Geneseo junior Emily Bauer, a physics major from West Seneca, N.Y.,
worked with Meisel on the National Science Foundation (NSF)-sponsored
project in the summer of 2004. In November, Bauer presented an updated
version of the paper to the Astronomical Society of New York at its fall
meeting at Rensselaer Polytechnic Institute in Troy, N.Y.
The NSF has sponsored this research for the past six years, mainly in
collaboration with the Communications and Space Sciences Laboratory at
Penn State.
Meteors — often called shooting stars — were traditionally observed
with the naked eye or a camera. After World War II, scientists started
using radar to observe meteors, determining their speed, direction, size
and weight. It was found that meteors span a tremendous range of sizes,
all the way from objects the size of a comet or asteroid down to the smallest
units observed — dust, particles that are millionths of an inch across.
It is these dust particles that mainly are detected at the Arecibo Observatory.
Among these hundreds of events per hour, between one and three percent
have speeds that indicate they come from beyond the solar system. Over
the years, the existence of extrasolar particles has been controversial.
In the 1930s, all meteors were considered extrasolar, but by the 1960s,
evidence for extrasolar origin disappeared and meteors were thought to
exclusively be permanent members of the solar system. But in 1993, the
Ulysses spacecraft saw true extrasolar dust coming into the solar system.
This material was much smaller than the meteor radar could see. In 1995,
an Australian team claimed it detected larger-mass extrasolar meteors.
The detections at Arecibo are a follow-up to these earlier discoveries.
Because these particles are so small, they have been known to be subject
to a variety of effects other than gravity for many years. Among the effects
is the radiation pressure of sunlight, and because the dust is electrically
charged, interactions with interplanetary magnetic fields also occur.
Many theoretical models for this behavior have been made, against which
the observations can be compared.
Since the sun is the main source of interplanetary magnetism, it ultimately
contributes to the behavior of the dust.
"The sun has figured out a way to move these particles in ways we
don’t understand," said Meisel. "It means the amount of
extrasolar material falling toward the Earth isn’t constant all the
time."
"It’s unclear where the material comes from," he said,
adding it could be from comets, asteroids or interstellar space. "It’s
a guessing game at this point."
But regardless of its origin, the dust has now been observed under direct
control of the sun.
Because the solar cycle is 11 years or so long, and the team has observed
for more than seven years, it means that the search must continue for
at least another five years.
"Now, we’ve got to find out what’s causing the problem,"
said Meisel. "You go the way the evidence points, regardless of your
preconceived notions. Every scientist is a pattern watcher, and when you
see something out of the ordinary, you know you’ve got something
unusual going on."
In 1997, Meisel thought Jupiter was going to play a role in this. In 2000,
the particles were still coming in, but by 2002 they began to decline
in number. By 2003, they had totally disappeared, only to reappear in
2004.
"It can’t be Jupiter. We don’t know where it’s happening.
Jupiter doesn’t even enter the picture anymore," he said.
With the prospect of five more years of observations, the team is being
expanded to include researchers in dust plasma interactions at West Virginia
University and solar wind modelers at the Jet Propulsion Laboratory in
Pasadena, Calif.
With such a diverse group of scientists working on this problem, it is
hoped that a good explanation will be forthcoming.