Impact: Collisions and Catastrophes is advertised by a poster that looks like a still from a disaster movie: a fireball flaming over the Royal Observatory buildings in Greenwich. It is a vivid and imaginative depiction of what an incoming asteroid might look like. The fiery colour is echoed in the layout of the exhibition - and the space enclosing it unconsciously echoes the circular shape of an impact crater.
Although there are no meteorites on show in the exhibition itself, an impressive piece of an iron meteorite found in Namibia is the first thing that confronts visitors as they enter the Astronomy Galleries, along with the message that the fragment is older than the Earth.
The exhibition is a linked series of six themes that encompass the violent birth of the solar system, the frequency of impacts on Earth and the nature and origin of planets in general, leading to a discussion of the potential for other stars to host planetary systems capable of supporting life. Impact has no specific beginning or end, and its well-illustrated panels can be viewed in any order.
Perhaps the most thought-provoking section of the gallery is the interactive screen, where a map of the Earth shows the location of more than 100 major impact craters. The particular interest here is that as well as allowing visitors to call up images of the craters, the map gives them an idea of the extent of the damage caused to the planet's underlying crust. Practically the whole of the Earth's surface is affected by this small fraction of the terrestrial-cratering record.
The carefully selected images are accompanied by terrifying facts presented in a straightforward and non-sensational manner. Indeed, the matter-of-fact way in which the information is presented contributes to the daunting message of the exhibition: humanity can do its best, but is still hostage to nature's fortune.
The display at Greenwich is complemented by an online version of the exhibition, and there is a programme of talks, planetarium shows and family activities running in parallel.
As I left the observatory, I walked through Greenwich Park. I had visited Impact on one of those beautiful spring days when the sunshine and warmth bring out the picnic baskets. The park was full of families, with children flying kites, kicking around footballs and generally having a good time. Tourists were clustered at the end of Blackheath Avenue, where a spectacular view of the old Royal Naval College and the River Thames shows maritime Greenwich at its most impressive.
Then I thought of the exhibition I had just seen. Orbiting somewhere above us all, currently unknown, is an asteroid that will hit the Earth. It is inevitable. The collision might not be completely catastrophic - it might affect only part of the globe. But a greater understanding of collision dynamics has shown that it is not necessarily the impact's primary crater that leads to the most unfortunate consequences, but rather the associated secondary effects, particularly the tsunamis that will build up in the wake of the collision.
The Indian Ocean earthquake of 2004 and the Japanese earthquake last month showed the destructive force of tsunamis. In both cases, more lives were lost and property destroyed by the wave than by the earthquake that generated it.
Images of the Japanese tsunami are awesome, showing the ease with which bridges and buildings can be swept away in a matter of seconds. I tried to imagine a tsunami rushing up the Thames, engulfing the O2, toppling the chrome and glass skyscrapers of Canary Wharf and sweeping upriver to St Paul's Cathedral and the Houses of Parliament. To admit that even a short contemplation of the potential devastation was unpleasant is to understate the horror of the images called to mind.
The scientific community is doing the best it can to study asteroids, to locate and map the orbits of those that have the potential to strike the Earth, and to model mitigation strategies that would prevent disaster. Possible plans are discussed in Impact and sound fanciful: for example, focusing sunlight on one side of an incoming asteroid to cause it to change its orbit. We have never yet had to attempt such a feat with the fate of the world hanging in the balance.
So far, such scenarios have been limited to disaster movies such as Deep Impact and Armageddon (both released in 1998) - we can only hope that we do not have to try them out in a real-life situation for many years.
Disaster for the dinosaurs through global environmental changes brought about by a massive impact 65 million years ago has been well documented in terms of modelling and evidence from geochemical studies. The generation of tsunamis following impact was hypothesised; examination of the fossil and rock records associated with the event at the end of the Cretaceous period showed a sudden and violent short episode where species from different habitats were mixed in vast assemblages of death. The devastation following the recent tsunami that broke against the eastern Japanese shore was minor in comparison with that which followed the Cretaceous impact.
What lessons might we learn here? Catastrophic asteroid impacts are few and far between, and although we have no reason to believe that they are likely to get more frequent with time, we do know that should one occur, the ramifications for humanity would be profound.
I haven't looked into whether earthquake magnitude has suddenly changed with time, or whether there are more volcanoes erupting. But it does seem that there have been more natural disasters over the past decade than in at least the preceding two. We are becoming ever more concerned that global changes in climate, resulting from the careless use of Earth's resources, are leading us into an era of increasingly frequent natural disasters.
The planetary system is an incompletely understood, delicate and complex interaction between the atmosphere, the hydrosphere, the Earth's rocky surface and its deeper, hotter mantle. The biosphere is precariously balanced within this complex. If we can draw one lesson from the dire fate of the dinosaurs, it is that they were blameless in the destiny that overtook them, whereas we are in danger of bringing about our own end through negligence. And that would be a catastrophe.