A CONTROVERSIAL, decades-old theory that the Earth is being bombarded daily
by house-sized snowballs from space resurfaced last week. And despite new
photographs that are supposed to show nine of these mini-comets, most
astronomers don’t believe they exist.
Space physicists Louis Frank and John Sigwarth from the University of Iowa
believe that around 30,000 ice balls weighing tens of tonnes collide with Earth
each day, vaporising as they enter the atmosphere and adding 580,000 tonnes of
water to the planet daily
(91av, 12 July 1997, p 24). Frank
first put forward the theory after identifying numerous dots on satellite
photographs as balls of ice.
Sceptics dismiss these dots as instrument noise. But now Frank has presented
new evidence. He commissioned photographs from a ground-based telescope, using a
technique which he says eliminates the possibility that the dots are just noise
(Journal of Geophysical Research, vol 106, p 3665).
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The telescope at the Iowa Robotic Observatory in Arizona used different
exposure times to pick out genuine objects from noise. The telescope’s camera
took a 20-second exposure, waited 10 seconds and then took a further
exposure of 10 seconds. Any object moving across the sky would produce one
longer trail followed by a second trail half as long.
Frank claims to have found nine comet trails in the photographs. He says the
objects he detected were 50,000 kilometres from the Earth and travelling at 10
kilometres per second, which agrees with his theoretical predictions. “This
simple shutter operation for the telescope’s camera provides full assurance that
real extraterrestrial objects are being detected,” says Frank.
But Robert Mutel of the University of Iowa, who took the photos, thinks these
trails are too dim to be reliable. Last November he published a paper in the
same journal as Frank, concluding that any object so faint was too dark or small
to fit the theory. “Even if one accepts the reality of the detections, they
aren’t the small comets Frank predicts,” he says. Frank argues that a thin
dusting of carbon would make the comets hard to spot, consistent with his
findings.
“He’s dipping into the noise until something shows,” says Alan Harris of
NASA’s Jet Propulsion Laboratory in Pasadena. Harris says radar instruments
would surely have spotted any small comets. “Numerous scientists pursued the
various aspects of the hypothesis and came up empty handed,” he says.
Frank and Sigwarth are now applying for time on a larger telescope in order
to obtain spectrographic information and determine what the objects are made of.