Ever since its formation at the birth of the Solar System, some 4570 million years ago, planet Earth has resembled a giant bulls-eye in space, a target for asteroids and comets of all shapes and sizes.
Clearly, this violent history has influenced the planet’s surface and atmosphere, as well as the evolution of life. Some impactors bring water and organic compounds, ingredients that may have been the building blocks of life. Other, more massive, bodies may arrive in a blaze of fire and fury, the results of their impacts being death, destruction and extinction.
Meanwhile, with the discovery of planets orbiting other stars, we must also assess their potential as impact targets.
On Wednesday 9 April, five experts in the study of asteroids, comets and impacts explained to the UK/Ireland National Astronomy Meeting in Dublin their ideas about the effects on the Earth and other planets of bombardment by extraterrestrial objects. The convenor of the session is Dr. Monica M. Grady (Natural History Museum, London).
The first two speakers considered the beneficial aspect of bombardment. Professor Chandra Wickramasinghe (Cardiff University) puts forward the controversial proposition that life itself came from beyond the Earth, in the form of bacteria.
He described experiments that have been carried out to test the hypothesis and discusses his results. In contrast, Dr. Ian Wright (Open University) considers the delivery of organic molecules to the Earth in comet dust, and how they might have acted as the building blocks for life.
The second part of the session included three speakers who look at the more destructive aspects of bombardment. Dr. Jane Greaves (Royal Observatory Edinburgh) looks beyond our own Solar System to consider evidence that some extra-solar planets might be surrounded by much larger swarms of comets than the Oort Cloud around our own Sun.
Following on from this, Professor Bill Napier (Armagh Observatory) related the rate of incoming cometary material to periods of geological trauma on Earth, including mass extinctions. Dr. Phil Bland (Imperial College London) considered the impact rate of smaller asteroids, and, in an optimistic vein, concludes that perhaps fewer than had been predicted actually survive intact before striking the Earth’s surface.
