Myst
ery of a `cosmic impact`Paris, June 30: A hundred years ago this week, a gigantic explosion ripped open the dawn sky above the swampy taiga forest of western Siberia, leaving a scientific riddle that endures to this day.
A dazzling light pierced the heavens, preceding a shock wave with the power of a thousand atomic bombs which flattened 80 million trees in a swathe of more than 2,000 square kilometres.
Evenki nomads recounted how the blast tossed homes and animals into the air. In Irkutsk, 1,500km away, seismic sensors registered what was initially deemed to be an earthquake. The fireball was so great that a day later, Londoners could read their newspapers under the night sky.
What caused the so-called Tunguska Event, named after the Podkamennaya Tunguska river near where it happened, has spawned at least a half a dozen theories.
The biggest finger of blame points at a rogue rock whose destiny, after travelling in space for millions of years, was to intersect with Earth at exactly 7.17am on June 30, 1908.
Even the most ardent defenders of the sudden impact theory acknowledge there are many gaps. They strive to find answers, believing this will strengthen defences against future Tunguska-type threats, which experts say occur with an average frequency from one in 200 years to one in 1,000 years.
"Imagine an unspotted asteroid laying waste to a significant chunk of land... and imagine if that area, unlike Tunguska and a surprising amount of the globe today, were populated," the British science journal Nature commented last week.
Comets move at far greater speeds than asteroids, which means they release more kinetic energy upon impact. A small comet would deliver the same punch as a larger asteroid. But no fragments of the Tunguska villain have ever
been found, despite many searches.
Finding a piece is important, for it will boost our knowledge about the degrees of risk from dangerous Near Earth Objects, say Italian researchers Luca Gasperini, Enrico Bonatti and Giuseppe Longo.
"(I)f the Tunguska event was in fact caused by a comet, it would be a unique occurrence rather than an important case study of a known class of phenomena," Gasperini's team write in this month's issue of Scientific American .
"On the other hand, if an asteroid did explode in the Siberian skies that June morning, why has no-one yet found fragments?"
The Italian trio believe the answers lie in a curiously-shaped oval lake, called Lake Cheko, located about 10km from ground zero. Computer models, they say, suggest it is the impact crater from a metre-sized fragment that survived the explosion. A rival theory is given an airing in this week's New Scientist .
Lake Cheko does not have the typical round shape of an impact crater, and no extraterrestrial material has been found, which means "there's got to be a terrestrial explanation," Wolfgang Kundt, a physicist at Germany's Bonn University told the British weekly.
He believes the Tunguska Event was caused by a massive escape of 10 million tonnes of methane-rich gas deep within Earth's crust. Evidence of a similar release can be found on the Blake Ridge off Norway, Kundt said.
Canada`s first dual-use space telescope
New York, June 29: Canada is building the world's first dual-use USD 12-million space telescope designed to detect and track asteroids as well as satellites.
Called NEOSSat -- near earth object surveillance satellite, this spacecraft will provide a significant improvement in surveillance of asteroids that pose a collision hazard with earth and innovative technologies for tracking satellites in orbit high above the planet.
Weighing in at a mere 65-kilogram, the mission builds upon Canada's expertise in compact "microsatellite" design.
NEOSSat will be the size of a large suitcase, and is cost-effective because of its small size and ability to "piggyback" on the launch of other spacecraft.
The mission is funded by Defence Research Development Canada (DRDC) and the Canadian Space Agency (CSA). Together CSA and DRDC formed a joint project office to manage the NEOSSat design, construction and launch phases.
NEOSSat is expected to be launched into space in 2010. The two projects that will use NEOSSat are HEOSS (High Earth Orbit Space Surveillance) and the NESS (Near Earth Space Surveillance) asteroid search programme.
"Canada continues to innovate and demonstrate its technological expertise by developing small satellites that can peer into near and far space for natural and man-made debris," said Guy Bujold, president, Canadian Space Agency.
"We are on the cutting edge, building the world's first space-based telescope designed to search for near-earth asteroids."
NEOSSat is the first follow up mission to the groundbreaking most (microvariability and oscillation of stars) spacecraft, a 60-kilogram satellite designed to measure the age of stars in our galaxy.
NEOSSat also marks the first project using Canada's multi-mission microsatellite bus. CSA's space technology branch launched the multi-mission bus project to capitalise on technology developed for the most project by making it adaptable to future satellite missions.
Captain Tony Morris of DRDC Ottawa and deputy programme manager of the NEOSSat joint project office, says, "NEOSSat is a technological pathfinder for us to demonstrate the potential of microsatellite technologies to satisfy operational requirements of the Canadian forces.
"...This would contribute to the safety of critical Canadian assets, military and civilian, in an increasingly congested space environment."
Brad Wallace leads the science team at DRDC for HEOSS, which will use NEOSSat for traffic control of earth's high orbit satellites.
Wallace says, "we have already done satellite tracking tests using most, so we know that a microsatellite can track satellites. The challenge now is to demonstrate that it can be done efficiently, reliably, and to the standards required to maximize the safety of the spacecraft that everyone uses daily, like weather and communication satellites."
The HEOSS project will demonstrate how a microsatellite could contribute to the Space Surveillance Network (SSN), a network of ground-based telescopes and radars located around the world.
"NEOSSat requires remarkable agility and pointing stability that has never before been achieved by a microsatellite," says David Cooper, general manager of Mississauga-based Dynacon Inc the prime contractor for the NEOSSat spacecraft and the manufacturer and operator of the most satellite.
"It must rapidly spin to point at new locations hundreds of times per day, each time screeching to a halt to hold rock steady on a distant target, or precisely track a satellite along its orbit, and image-on-the-run." Cooper says. "Dynacon is the world leader in this microsatellite attitude-control-system technology."
Alan Hildebrand, holder of a Canada research chair in planetary science in the University of Calgary's Department of Geoscience, leads an international science team for the Ness asteroid search project and is excited by its prospects.
Although NEOSSat's 15-centimetre telescope is smaller than most amateur astronomers', its location approximately 700 kilometres above earth's atmosphere will give it a huge advantage in searching the blackness of space for faint signs of moving asteroids.
Twisting and turning hundreds of times each day, orbiting from pole to pole every 50 minutes, and generating power from the sun, NEOSSat will send dozens of images to the ground each time it passes over Canada.
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