A nuclear flash point

BOMBING THE MOON

 Recent reports suggest that during the heydays of the Cold War, the United States planned to bomb the moon so that the nuclear flash would intimidate rival powers. In reality, the gravitational binding energy of the moon is about ten to the power of 29 Joules, the minimal energy needed for it to blow up. This is equal to the nuke power released by trillions of Hiroshima-type bombs, writes C Sivaram.

Recent reports refer to a Cold War secret project wherein the United States planned to undertake lunar flights to drop an atomic bomb on the moon so that the nuclear flash seen from the earth would intimidate rival powers like Russia. The idea proposed more than 50 years ago was to boost the morale of the US in the aftermath of the Sputnik success in 1957.

Some leading physicists were also involved. (There was apparently also a Project COW, from the pop star nursery rhyme of the cow jumping over the moon!) The astronomer, Carl Sagan, then a student, also did some calculations on the visibility of such a blast as seen on earth.

The recent news report also talks of the United States’ plan to blow up the moon with a nuclear bomb as a cold war show of strength! This could give a wrong or highly misleading impression that it is actually possible to shatter (i.e. blow up) the moon into smithereens with nuclear bombs!.

In reality, the moon is held together by its gravitational binding energy. This gravitational binding energy of the moon works out to be about ten to the power of twenty nine Joules (or one lakh trillion trillion Joules). So this is the minimal energy required to shatter the moon. This corresponds to the nuclear energy released by a thousand trillion Hiroshima type bombs.

As the total nuclear stockpile of all the nuclear weapons possessed by all the nuclear powers is hardly equivalent to a million Hiroshima bombs, (still enough to wipe out the human race several times over, so called nuclear overkill), it is a far cry to blow up the moon indeed. We would fall short by a factor of several billion.

Even a single hydrogen bomb would have been too heavy to carry to the moon at the time the project was envisaged. At the most, a Hiroshima type bomb could have been exploded on the moon.

Could the flash from such a device be seen on earth?

A simple estimate shows that the flash would be ten per cent as bright as the full moon and last for a fraction of a second. Not quite intimidating! Especially at day time, it would be even less conspicuous. A meteorite some hundred meters across, hitting the moon’s surface would produce a similar release of energy.

What could be more serious is the blast waves from the explosion which would have reached the earth in a few days, carrying some high energy radiation. This would affect the whole earth.

Shoemaker Levy

In another context much more recently, it has been suggested that if a kilometer-size asteroid is likely to hit the earth, it could be blown up well before it strikes by exploding a nuclear bomb on it. This proposal is now debated as it may end up shattering the asteroid into pieces, some of which may hit the earth with fatal results.

  Indeed it may recalled that in July 1994, comet Shoemaker Levy, which was broken up into fragments by Jupiter’s gravity, impacted the giant planet. In particular, fragment G, three km across, impacted Jupiter with an estimated energy release corresponding to the exploding of a Hiroshima bomb every second continuously for ten years! .

If the object had collided with the earth rather than Jupiter, most life on earth would have been wiped out! Indeed it is believed that the dinosaurs along with most the species prevalent then were destroyed when a ten-km asteroid impacted the earth during the Cretaceous era, sixty million years ago. There is a cartoon showing one dinosaur telling another that they should have developed nuclear weapons and perhaps avoided such a fate.

Talking of bright flashes, the laser is much effective. Lasers were developed only in the Sixties and so could not have been suggested when the lunar nuclear flash project was considered! A ten-kilowatt continuously operating laser, if focused from the earth through a five metre telescope, would be visible on Mars, as a bright point of light many times brighter than Venus appears to us on the earth.

As first pointed out by laser pioneer Charles Towns, such a laser beam could be seen ten light years away by a large telescope. A collimated laser beam can illuminate a small area on the moon with high intensity. There is thus a high potential for laser communication over interstellar distances. Such illumination is far more effective and of course non-destructive in comparison to nuclear flashes!