It’s not really big by cosmic standards. But its potential for damage is BIG. That is why astronomers are keenly waiting to watch asteroid Apophis during its next close pass to the sun in 2013.

“It will come within the geo-stationary orbit of the earth, to as close as 30,000 kms on April 13, 2029,” said William Ailor, Aerospace Corporation. (The company has developed expertise in space technology and works with Nasa and other organisations.)

Ailor was one of the delegates at the recently concluded international astronautical congress at Hyderabad. “If we are able to deflect it in 2029, there is a one in 45,000 chance that it will impact earth in 2036,” he said.

The impact could be disastrous. The 300-metre wide asteroid could cause thousands of death depending on where it falls. Even in the oceans it could set off a tsunami!

The Tunguska impact of 1908 is believed to have been caused by an object 50 metre wide, smaller than Apophis!

It set off an explosion equivalent to 10-15 tonnes of TNT. It wiped out 60 million trees over a 830-square-mile area but caused only two deaths fortunately because the area was remote. “A similar impact in New York could mean thousands of deaths,” Ailor said.

An asteroid is also believed to have been the cause of the extinction of dinosaurs. Some 12,000 years ago an extra terrestrial object exploded in the atmosphere above Canada causing temperatures to drop by 10 deg C in the northern hemisphere, following the dust storm. “It is believed to be the time when tigers went extinct in North America.”

20 impacts every day!

Hard as it may be to believe, there are at least 10-20 meteor impacts on earth every day! “Hardly 2-5 of these will be discovered and even fewer will cause injury, because luckily for us the planet is mostly water!” said Ailor.
Earth, as he says, is a “sensor being hit by all kinds of objects all the time.”

Coming to what size could cause problems, it is believed that the more frequent ones are the Tunguska kinds which are less than 20 metre wide. By virtue of being more frequent, the harm potential is more. The larger ones are less likely but “not improbable”.

To put it in perspective, Ailor sums it up as: There is 1 in 1000 chance that this century will see a civilisation ending impact. And there is 1 in million dinosaur killer impact and a 1 in 10 of the Tunguska kind of impact.
Showing a video of the population of near earth orbit objects (NEOs) which has been multiplying since 1900 to 2006, he says that there are 4500 NEOs.

Comets pose one percent of the problem but is dangerous as it is hard to predict collision given the cometary jets.

The warning time decreases as the size of the object decreases.

Deflection methods

Companies and organisations are working on strategies to deflect objects aiming for the earth. But it is crucial to have enough time for that, as Ailor notes. “We also need to know the size, mass, orbit, etc.”

Of the many techniques being suggested are: slow-push impulses where a spacecraft parks itself near the object close enough for its gravity to deflect the object from its path of destruction.

In a more invasive method, called the mass driver, the craft lands, digs and ejects material from the object at high speed. This again would alter its path. But it is difficult as the asteroid also rotates.

Using focussed solar energy to boil off material from the object, painting the object black or white to change its energy absorbing content, using pulsed laser to boil away matter, or send a high-speed projectile like Deep Impact did to comet Tempel, or nudge the object using nuclear explosive, are some imaginative ways being thrown up!

“In all these, the present focus is on building the right craft. In an earth-threatening event, we just can’t afford to lose the launch vehicle!” understates Ailor.

Estimated costs are around $10 billion. naturally the question is who funds? Is it one nation’s responsibility or the world’s? What if it turns to be a false alarm “which it could well be”? Will it end up in a blame game?

Global co-operation

It would make sense if there was an international protocol developed, and a cooperative effort for detection and hazard mitigation.

Ailor believes there is need for public awareness to eliminate the “giggle factor” which is the highly amused way in which asteroid impacts are generally perceived.

The field offers an area of research where all nations could be involved. People like Ailor also think that NEO impacts should be included in the “disaster management portfolio” of nations.

As for now, there is need to track objects less than a kilometre wide, improve deflection techniques, design mission mode, and above all “watch Apophis”.

A piece of heaven It was on July 26, 1994 when Ganesh was watching television that he heard the thud on the roof. He quickly ruled out any mischief mongers as it was late for people to be walking around the place in B R Hills. An astronomer himself, (the word amateur does not quite fit someone who is as well read and observant as he is!) he went looking for what he believed could be a meteorite. And sure enough, he found the “odd stone the size of a matchbox” searching with his torch. The Perseids meteor shower that was on around that time made him conclude the rock could be a piece of the Swift Tuttle comet. A geologist friend identified the meteorite as a chondrite, says Ganesh, the proud owner of a piece of the heavens.

What are asteroids? Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. Known as "minor planets" tens of thousands of asteroids can be found in the main asteroid belt located between the orbits of Mars and Jupiter. Asteroids are thought to be primordial material prevented by Jupiter's strong gravity from accreting into a planet-sized body when the solar system was born 4.6 billion years ago. Known asteroids range in size from the largest - Ceres, the first discovered asteroid in 1801 - at about 600 miles (1,000 kilometers) in diameter down to the size of pebbles.

Recent impact The latest one that was in the news was last month in Peru when an object exploded in the sky and rained rocks in a remote Andean village, causing a 39 metre wide, 6 metre deep crater. Geologists have confirmed it to be a rocky meteorite after analysing the fragments.