Scientists puzzle over ice from sky

By STUART DYE

When a mysterious ball of ice crashed through Jan Robertson's house, the 80-year-old had no idea she would plunge New Zealand into the centre of a scientific frenzy.

Geochemists, astrophysicists, meteorologists and geologists in Brazil, China, Spain and Russia believe the intrusion may have been New Zealand's first "megacryometeor".

To the layman that is hailstones - jumbo hailstones.

Early investigations by the Civil Aviation Authority suggest that the ice contained chlorine, an indication that it had been treated by man.

"We understand there were two flights over the area at the time and it's possible a leak in an aircraft water pipe caused the block," said CAA spokesman Bill Sommer.

However, inspections of both aircraft have revealed no signs of where the ice could have come from.

Mrs Robertson got used to phone calls from scientists around the world but yesterday, 10 days after the incident, she said things had quietened down.

She was cleaning her Meadowbank home and her husband, Bruce, was in the garden when the ice missile the size of a rugby ball, travelling at about 400km/h, hurtled through the kitchen roof.

The International Working Group Fall of Blocks of Ice (IWGFBI) is a fledgling team of renowned scientists dedicated to investigating megacryometeors.

There have been 50 documented cases around the world. Ice balls have punched holes in roofs, smashed car windshields and whizzed past people's heads.

The group's founder, Jesus Martinez-Frias, a planetary geologist, began investigating the ice falls after a spate in Spain three years ago.

It started with a soccer-ball-sized chunk plummeting from the sky on a sunny Madrid day and smashing through a parked car.

In something resembling a biblical plague, pieces of ice weighing up to 3kg rained on Spain out of cloudless skies for 10 days, then the phenomenon ended as suddenly as it began.

At first, scientists thought the giant hail was unique to Spain. But they have accumulated evidence that megacryometeors are a global event and have documented ice balls falling from cloudless skies everywhere from China to the United States.

They believe the 50 confirmed falls are a fraction of the actual number - most may hit unoccupied areas or melt before discovery.

The average weight is 12 to 15kg, but one whopper in Brazil tipped the scales at 200kg - the size of a V8 car engine.

Alarming as this may be for people's homes, cars and health, the scientists have a different concern.

"I'm not worried that a block of ice may fall on your head," said Professor Martinez-Frias, speaking from Madrid. "I'm worried that great blocks of ice are forming where they shouldn't exist."

His team quickly ruled out obvious explanations.

The ice balls, for instance, were not frozen water from toilets flushed on jetliners - they lacked urine or disinfectant traces.

They could not be debris from a comet as lab tests showed that megacryometeors had the distinctive chemical signature of ice in ordinary terrestrial hailstones.

That leaves monster hailstones forming in a cloudless sky - a notion that defies more than a century of research on hail formation.

Scientists are concentrating on two possibilities. One, that megacryometeors are a weird byproduct of global warming; two, that ice crystals in aircraft contrails left floating in the air for days are swept through cold, humid air pockets, forming large balls.

Neither theory is particularly popular.

"I don't like to claim that anything is impossible, but this comes awfully close," says Charles Knight, a hail expert at the University Corporation for Atmospheric Research in Colorado.

The worry is that, if megacryometeors are a result of global warming, they are likely to increase.

Professor Martinez and his colleagues are pooling their knowledge, but an answer is likely to take years.

How hail forms

* Hail forms in the updrafts and downdrafts of thunderstorms.

* Freezing particles join as they are tossed round in the wind and the hailstone grows, layer by layer.

* Megacryometeors show the telltale onion skin layering seen in hailstones.

* They also contain dust particles and air pockets found in hail.

* But they are formed in cloudless skies, a notion that defies research on hail formation.