The end of the world

by Tomasz CHLEBOWSKI (Delta 4/1979)

 

In February 1982 we will have the opportunity to witness a very rare phenomenon: all the bright planets, while turning around on their orbits, will lie almost on one and the same straight line, i.e., their angular distances will become quite small. For thousands of years such phenomena, like the appearance of a comet, the eclipses, bolides (very bright meteors) etc., have brought fear into peoples' hearts. Even today, when we know that a complete Sun eclipse hides no danger for the human race, many of us watch it with slight discomfort, asking oneself: is it sure it will have an end soon?

A similar thing happens with planet configurations. More often than ever you can find in newspapers, not to speak of astrological journals, various news about the end of the world to be expected in 1982, about an earthquake to destroy the richest lands of the USA, disturbances of weather and of the Earth magnetic field etc. From a scientific point of view, however, the causal relation between a planet configuration and phenomena on Earth is - as it always has been - negligible.

On such occasions we often pose the following question: we have lived on this Earth for so long, and our home planet rushes through the abyss of our universe hundred times faster than a rifle bullet, while we, with no real feeling of the fact, feel absolutely safe. However, do we have any grounds to look into our future with confidence? Will it not surprise us with a collision against another planet or star, or with an explosion of our Sun, or with any other phenomena of similar kind?

Let's start on the largest scale possible: the entire universe. Should we expect an "end of the world" and when could that be? We know that the universe simultaneously extends and becomes colder. There is an alternative: either at some moment the extension of the universe will stop, it will begin shrinking and getting hotter, or the extension will go on until infinity. More and more evidence speaks for this last possibility. If, however, the cosmological end of the world were to come, we still have about 50 billion () years to live.

Turning to smaller objects, you may ask what is the probability of crashing against another galaxy? There seems to be no danger here either: the mean time separating galaxy collisions is many times greater than the age of our universe. Besides, most galaxies fly away from each other and moreover they are so sparse, that collision between two of them would just sweep away interstellar matter into the intergalactic space, while the galaxies themselves would simply pervade each other.

Thus galaxy clashes may bring no danger, as long as there are no star clashes. However, the probability of such an event is extremely small: the mean time separating star collisions in our galaxy is about 10^13 years - a thousand times more than the age of our universe.

What about Sun explosion? The mass of the Sun is too small for that. Nevertheless, in several billions of years its evolution will lead such huge dimensions that first it will burn out the entire Earth, and then will absorb it forever. This is quite probable: if not the end of the world, then at least the end of the Earth.

Let's take a look at still smaller objects, like a planetary system. All the planets run along almost circular orbits and a collision with any one of them is practically impossible. Nevertheless, a clash is probable with smaller bodies turning around the Sun on orbits that cut orbit of the Earth.

There is a group of planetoids (little planets) that can approach the Earth. At present we know 24 such bodies, although their total is estimated at over 500. One such planetoid, the Hermes, passed near the Earth in 1937, at the distance of about 600,000 km, i.e., not much farther than the orbit of the Moon. According to E.J. "Opik, if a body of this dimension hit the Earth, it would destroy a territory of area equivalent to more than 10 percent of the area of Poland. The greatest of the "dangerous" planetoids, called Amor, would be able to destroy half of the Asian continent. A collision with a body as big as Hermes may occur only once in several million years in average, whereas a collision with Amor - once in 2-3 billion years. A clash with a comet, although much more spectacular (comets have tails), would be less dangerous than the impact of a planetoid. Most probably the meteor that hit the Earth on June 30, 1908 destroying part of the taiga in central Siberia, was the kernel of a small comet. The fall of a meteor, most common of all th clashes described above, makes the least damage. Till now we only know of one case when a meteor made a hole in a roof. The next candidate, the Moon, is fortunately moving away from Earth along a spiral and it would continue to do so for the next 40 billion years, were it not to be absorbed by the Sun together with the Earth.

However, more and more objects begin to appear on orbits around the Earth, and after some time they fall on our planet creating some real danger for its inhabitants. These objects are artificial satellites. And this leads to the following important conclusion:

As long as we don't clutter up the space with satellite wrecks and as long as we don't destroy our own atmosphere that protects us from cosmic radiation, meteors and loss of heat, the probability of a cosmic catastrophe is so small, that we can sleep in peace.