One more step for mankind

In nearly all cultures, the pattern of stars in the night skies is taken as eternal and unchanging, so that when a comet appears, stretching like a luminous great finger across the skies, it creates great excitement and wonder, but, maybe because of mankind's inherent pessimism, also terror as a portent of disaster, never as good news.  Even when a comet appeared in the evening skies over Windhoek in 2007, a businessman was murdered when up on a hill trying to observe it.  

Comets must have seemed spectacular in the days before people lived in cities with smoke, dust and light pollution dimming the heavens - nowadays, even when the arrival of a comet is much hyped in the media, you usually see barely a smudge in the sky.  Practically, comets have no influence over the earth and its inhabitants.

Astronomically however they are very interesting.  They are debris left over from the formation of the solar system,  like piles of unused broken bricks and tiles left at the edge of a building site.  Mostly, they originate in a vast area called the Kuiper belt beyond the furthest planets, and only a very few of them are pulled in towards the sun by the force of gravity, and become visible to us.  They really consist of a lumpy head or nucleus, composed of of ice, dust and fragments of rock,plus maybe organic compounds which excite scientists because comets colliding with earth thousands of millions of years ago may have brought the necessary materials (plus water) for life.  The comet's 'tail' consists of water vapour and dust which are boiled off the comet by the heat of the sun - it is blown away from the direction of the sun by the solar wind, so sometimes the tail can precede the head of the comet.  So examining the make-up of the head of the comet is like looking back in time to the beginning of the solar system, giving us crucial information about this and maybe even about the origin of life.

The European Space Agency sent up a probe 10 years ago to follow, catch up with and eventually land on this comet, with a difficult Ukrainian name.  In a hugely complicated path, it had to circle the earth's orbit three times, picking up enough momentum to fling itself out beyond the orbit or Mars, and eventually rendezvous with the comet - it was, like somebody said, like firing a gun in New York, the bullet bouncing off a rock in Africa and eventually hitting a bird in Beijing.  Yesterday it made it, and though the landing was not perfect, it was an astonishing feat, and an amazing feat of human planning, science and skill.  Definitely another great step for mankind.