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The Leonids 98 Friday, 4 December, 1998, 11:34 GMT
Return to mission Leonid
NASA's airborne expedition out of Okinawa
BBC Science reporter Chris Riley flew with the recent Nasa mission to study the Leonid meteor shower.

The display of shooting stars may not have lived up to its billing, but astronomers still think they recorded enough quality data during the event to keep them busy for many months to come.

Chris has written this account of the mission which sent two aircraft chasing the storm over Asia on the night of 17/18 November:

The nights before the storm

We were heading for Okinawa. Once up at 29,000 feet, everyone set to again, unpacking instruments and clamping them to windows for another night of data collection.

It felt warm on board whilst you were moving around, but as soon as you stopped for a rest or to eat a US Air Force food parcel, the chill started to march into your joints.

In the dim light at the end of the cabin, Ray Russell from the Aerospace Corporation was enveloped in clouds of vaporising liquid nitrogen. Ray told me he was attempting to scrutinise the meteors in wavelengths beyond the vision of the human eye - in the infra-red. "Some animals like rattle snakes can detect those kinds of wavelengths but for the rest of us who don't have those kinds of eyes we use instruments like this," he said.

Chris Riley
Chris Riley: Chasing meteors
He gestured at a squat silver, barrel-shaped object next to him. "It's called a Dewer - like the Scotch," he beamed. "It's basically a thermos bottle and we can keep the inside very cold, to cool the detectors so close to absolute zero that when a small amount of heat hits it they can see it. No one has got a spectrum of a meteor in the's a new thing."

Ray had already tested his experiment on the 60-inch telescope in Arizona. "We believe we could see the amount of heat given off by a match on the surface of the moon if the moon had enough atmosphere to let the match burn, so it's a very small amount of heat we're talking about.

Much of Ray's career has been devoted to analysing comets - trying to understand their composition by looking at the dust they leave behind. "Some of those dust particles are very small and they give off a particular pattern of colours just like when you burn a particular kind of gas," he continued.

"The gas on your stove is blue, the different things in your fire place turn yellow, or green or orange. Well, the different materials in a comet give off different patterns of colours as well and that pattern of colours tells you what type of material you are looking at.

"We find there are typically silicate materials such as the sand on a beach, or the material in a glass window, all broken up into tiny particles - typically an angstrom across. You'd have to have a microscope to see them. But if there are enough of them, they give off enough heat in the infra-red and we can measure that and tell what it is."

Saturday was gobbled up in a few hours as we crossed the date line en route to Okinawa. The orange-blue glow of Sunday's dawn slid along the horizon - first in a long thin strip and then widening until the thick blanket of black-grey cloud below us started to catch some colour. By the time we touched down at Kadena airforce base the sun was up and an early morning sea-side calm had settled across the sky and ocean.

Kadena was the biggest military base outside of the US. It felt like the size of Southern England as we trundled in a coach towards customs.

The two planes were full of equipment
Two polite Japanese gentlemen in peaked caps passed our luggage along a counter, gently gesturing at a painted panel of forbidden items and glancing up at us for approval that we didn't have any of the items.

The Crown Hotel was a short hop from customs and we were left in peace to sleep the day away. The next couple of days passed in the same night-shift state - working through the darkness, turning in at 4-5am and then waking at midday and working through till the early hours of the next morning.

Ten thousand miles away over UK skies, things were hotting-up - bright, multi-coloured fireballs were being reported from the Isle of White to Aberdeen. As the clouds parted briefly at dawn on Tuesday morning there were even reports of fireballs in the twilight sky over Okinawa. There was an excited buzz in the air as we ate our pre-flight supper that night. The Japanese scientists gave everyone presents of small ceramic lions - the symbol of Okinawa and an appropriate mascot for the Leonids!

Mission Night

There was a thick, low bank of cloud across much of Eastern Asia and it showed no signs of shifting. Everyone on the mission was very thankful that we were about to get above it. Those we left behind on the ground would be seeing little of the meteor storm that beckoned a few hours away.

The Leonids could be more impressive next year
The two planes roared along the runway just before 10pm local time. "Twenty-one, fifty seven ... right on time," cried out Ian Murray, a physicist from Mt Allison University in Canada - he planned to film detail of how the meteors burned up.

With a bit of bouncing through the turbulence, we broke through the clouds and burst into a clear black sky.

A handful of meteors streaked across our view, sending ripples of excitement across the intercom chatter. Five burned their trails into the phosphor on Ian's screen. His eyes sparkled with delight. Hitting his intercom button he reported into his microphone " looks like the show is here ...I've just seen five in about four seconds."

We swung around in graceful loops the size of England, turning every 30 minutes or so and sending the fixed star fields panning across the monitors. The next couple of hours passed with only one or two meteors a minute.

"You told me they'd find me," piped up Sandy, an Airforce Research Lab Scientist. "Christ ...there's supposed to be 40,000 an hour and we can't find them," retorted her colleague Tommy. "I can't find one."

With the small, blinkered field of view of their instruments, they were missing the hundreds an hour that the pilots were reporting.

"Wait till something breaks. Then they'll show up," added Tommy.

"Maybe we're up here on the wrong night," quipped Ian. He was more right than he knew. As we circled over Japan, counts from round the world were suggesting that the storm had actually broken at least 13 hours earlier than predicted.

But out of e-mail touch and oblivious to this news at 41,000 feet we were still hoping for a storm overhead. Ten thousand feet below us the other aircraft in the mission was encountering cloud, obscuring its precious view. They radioed in an urgent request to move our orbits south back into clear skies. A check was made with Japanese Air Traffic Control and we drifted further south in search of clear skies.

"It's important that we keep together with Electra," explained SETI scientist Captain Steve Butow. Stereoscopic views of the meteors were crucial for working out their trajectories and orbits later on.

"OK - crew update on the count of meteors from the cockpit," called in Kris Thompson, the plane's captain. "We've just about doubled the count last hour 73 in the last 15 minutes." By 3.45am, we were just 15 minutes away from the comet's plane and Steve was still holding out for a big storm.

"This is the very point in space where the comet has passed through just months ago," he exclaimed.

Ray Russell interrupted him: "I just got a beauty at zero altitude."

"More and more people are reporting them," added Tommy. "That's a good sign." It was 5am as we swung round for another time and headed north. The night had nearly passed and as dawn arrived again and the night sky turned a pale purple, the Leonids faded away for another year. "We've certainly seen a great shower," admitted Steve, "but I guess we'll have to wait until 1999 to see if the storm breaks over European skies".

A more complete version of this diary can be found on the BBC Tomorrow's World Website.

BBC Science reporter Chris Riley on Tomorrow's World
Links to more The Leonids 98 stories are at the foot of the page.

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