The comet cometh!


Threats from space are easily neglected. In general, people have a propensity to disregard infrequent hazards. Extraterrestrial as well as subterranean threats should strengthen our feeling of a common destiny on this planet of ours. When the asteroid arrives we must be prepared to take our destiny into our own hands – otherwise we have only ourselves to blame.

The comet cometh!

In the beginning, about 4.5 billion years ago, earth was bombarded by asteroids; the biggest was Mars-sized and gave rise to our moon. The bombardment has continued at lengthening intervals and devastating meteoric impacts have repeatedly extinguished major parts of the biosphere. The latest cataclysm took place 65 million years ago when the dinosaurs were wiped out. The threat is not over by any means. The Tunguska comet struck Siberia in 1908 with an assessed power of half a dozen hydrogen bombs according to the latest estimates. Such impacts can be expected several times in a millennium.

NASA (National Aeronautics and Space Administration) is funding a surveillance system (NEAT, Near-Earth Asteroid Tracking) which can identify close-to-earth asteroids bigger than about one kilometer. An improved but less than watertight system should be in place by 2009. It will detect objects bigger than 140 meters which still leaves a fatal gap in the in the relatively frequent range between 50 and 150 meters. Outside the United States, there has been scant interest in asteroid tracking.

The public has occasionally been scared by the prospects of immediate disaster. Therefore the textual part of the Torino impact hazard scale, which gauges the risk for a collision by numbers between 0 and 10, was recently made more intelligible. The asteroid 2004 MN4, later dubbed Anophis, attained level 4, the highest reading so far. “Level four indicates a close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of a collision, capable of regional devastation. Most likely, new telescopic observations will lead to re-assignment to Level 0. Attention by the public and by public officials is merited if the encounter is less than a decade away.” Later observations reduced the collision risk to zero but Anophis is calculated to pass earth in April 2029 at a distance of only 30,000 km. And Anophis will be back in 2036.

Space defense

Countermeasure capability is at least as important as an adequate early warning; we cannot be content with a passive policy of civil defense. In the United States voluntary organizations act as pressure groups. The most visible is the B612 foundation chaired by the astronaut Russell Schweickart. He recommends the expansion of NASA’s Prometheus project to include the active defense against the asteroid threat.

If the threat is detected well in advance of the potential impact, very gentle deflection methods can be effective. The course of an asteroid could, for instance, be changed by a gigantic sun sail which would exploit the sun wind to produce the necessary momentum. The same effect could be achieved with a gravitational ‘tractor’, a spaceship placed in front of or behind the asteroid. The job could also be left to nuclear-armed missiles but the explosion could create a multitude of dangerous fragments which have to be dealt with separately. When a comet is threatening, nuclear warheads may be the only expedient because the loose comet material does not provide any anchorage.

Threats from space are easily neglected. In general, people have a propensity to disregard infrequent hazards. The survivors of devastating earthquakes and floods soon return to business as usual, often without any intention to invest in protective measures. In the developed countries, the cities at risk such as Tokyo and Los Angeles are reasonably prepared. Nevertheless, great human suffering and huge material loss can be foreseen when the big quake strikes. Most poor countries have so far preferred to accept the inevitable, despite very distressing experiences.

Earthquakes cannot be avoided but the the threats from space can be averted. For once everyone is equally exposed on this planet. A joint effort to prepare for all eventualities should be mandatory for the major powers (G8 or G20 or whatever). But the political pressure is not there.