Meteors are icy messengers, not fire-breathers

Last updated 10:14 22/12/2008
MARK DWYER
New Plymouth astronomer Rodney Austin discovered a comet 26 years ago and it was named after him.

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TALK of a meteorite causing a fire in an Auckland warehouse has sparked a trail of news stories. One joker even suggested it could have been the International Space Station toolbag. But the rogue bag the largest item lost in space by an astronaut is being tracked by satellites and is still out there. Back in New Zealand, Taranaki comet spotter Rodney Austin dismisses any chance the fire was caused by a flaming meteorite.

In space, meteors are freezing cold. When they enter the Earth's atmosphere, they do fire up, but throw off that heat, remaining cold inside.

"Meteorites have been found minutes after landing, covered in ice."

Austin only knows of one reported case where a meteorite has definitely caused a fire on Earth and that was at Tunguska, Siberia, on June 30, 1908. The meteorite, believed to be about 36 metres across, scorched into the Earth's atmosphere at an estimated 54,000km/h. It exploded between 5km and 10km above the surface of the Earth, causing a fireball that released energy equivalent to about 185 Hiroshima bombs. About 80 million trees in an area of about 2000 square kilometres were destroyed instantly, but there were no reports of people being killed. The Tunguska blast wave would have flattened London.

It could easily happen again.

"It's not so much a matter of if as when."

Meteorites hammer the Earth at a rate of about a dozen a day, but meteors are far more frequent, he says.

They begin as meteoroids, which are small rocks orbiting the sun. When a meteoroid enters the Earth's atmosphere, it becomes a meteor. Most people know these as shooting stars. This bright flare is the meteor burning up. Most disintegrate before the rock fragment ever hits our planet. If it does land, this object is called a meteorite.

The Tunguska rock didn't land, but scientists decided that because it did have an impact on the Earth that it should be called a meteorite. On November 26 that same year, an unrelated meteorite streaked across Taranaki and landed in Mokoia. The 100-year anniversary of that event was retold in this paper's Saturday magazine section last month.

"I wasn't alive then," says Austin, who can not only name major meteorite events with the ease of a man remembering birthdays past, but has personally seen some magnificent meteors light up the sky.

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But before recapping those brilliant moments in 1967, 1986 and 2004, let's look at some of the "ites" that fell to Earth.

Austin says that in 1930, a cow was killed by a meteorite in the United States. The only record of a person being hit by a space rock was in Oak Grove, Alabama, on November 30, 1954. Ann Elizabeth Hodges was snoozing on a couch when a grapefruit-sized meteorite crashed through the roof and hit her. She was badly bruised on one side of her body, but still able to walk. Hodges died in 1972.

Another couch incident happened closer to home. On June 12, 2004, a meteorite crashed through the roof of Brenda and Phil Archer's home in Ellerslie, Auckland.

"It bounced off a leather couch and hit the ceiling before coming to rest on the floor, where their grandson had been playing a few minutes earlier," says a report on Te Ara: The Encyclopaedia of New Zealand website.

Another famous event happened in Peekskill, New York, on October 9, 1992. A Chevy Malibu owned by Michelle Knapp was hit by a 12.5kg meteorite, caving in the trunk of the car. The car has since travelled the world as a museum exhibit.

Austin says there is a legend that a bunch of warriors on chariots in China were hit and killed by a meteorite in about 1100AD. But there are no reliable records of that event.

So the count stands at one cow dead, one woman hurt, one Chevrolet written off.

There have been many more near misses and thousands of complete misses (most we'll never know about).

"Most fall in the sea, because that covers 60% of the Earth surface," Austin says.

Then there are the lights in the sky.

"I've seen thousands of them."

Twice he's seen meteors so bright they have "drowned out" a full moon. The first was in 1967, when he was driving on Big Jim's Hill near Waitara. He can't remember the time of year or the date "It will be in my notebooks." just the dramatic bloom of a celestial body in an already bright night sky. But he is more specific about his second full-moon meteorite.

"It was on April 24th, 1986. It was my last night at the Halley watch site at Omarama."

The South Canterbury site was closing down because Halley's Comet had moved on. It was also the night before a total eclipse of the moon. In between these major heavenly happenings, the fiery rock came flying.

"It's pretty stunning when you get a meteor that bright."

Austin's meteor trilogy occurred just four years ago. The stargazer was driving up Waitara Road about 4am when the sky erupted.

"I thought Motunui had exploded it even lit up the mountain."

The meteor never landed. "It just blew itself to bits."

The man with a comet to his name has a hankering for a bit of space rock.

"Tell you what, I would love one to land in my backyard."

And if it did, Austin believes it would be as cold as ice not a fabled firestarter.

Freaky facts

1. An asteroid hit the Earth on October 7 this year. The rock, just a few metres in diameter, made a spectacular fireball entry into Earth's atmosphere above northern Sudan, says Nasa's Near-Earth Object Program website. "Although such small impact events occur several times per year around the globe, this case was unprecedented because the asteroid was actually discovered the day before it reached the Earth and the impact location and time were for the first time predicted in advance," Nasa scientists say.

2. The Nakhla meteorite, a rare lump of Mars, landed in pieces in Egypt on June 28, 1911. Legend has it that one of the fragments hit a dog, vaporising it. However, because there were no other eyewitness reports and no remnants of the dog ever found, this story remains a fable.

3. Asteroids and meteoroids tell us of our beginnings. These rocks are the primitive, leftover building blocks of the solar system formation process. Therefore, when they do fall to Earth, they offer clues to the chemical mixture from which the planets formed about 4.6 billion years ago.

4. A meteorite the size of a car landed in a Mexican desert on February 8, 1969. The Allende meteorite is the largest carbonaceous chondrite ever found on Earth and is often described as "the best-studied meteorite in history" because it landed amidst the hype of the Moon-landing space age. The meteorite exploded, scattering stones over a large area. Even today, people are still finding specimens of this rock.

5. The largest meteorite ever found weighs about 60 tonnes. It fell at Hoba West, a farm near Grootfontein, Namibia. The Hoba meteorite is thought to have landed over 80,000 years ago.

- Taranaki Daily News

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