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Life And Death In Space

April 05, 2003

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 will be explaining 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 Grady (Natural History Museum, London).

The first two speakers consider 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 describes 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 includes 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) relates the rate of incoming cometary material to periods of geological trauma on Earth, including mass extinctions. Dr. Phil Bland (Imperial College London) considers 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.

SESSION PAPERS.

C. Wickramasinghe (wickramasinghe@cf.ac.uk):
Panspermia and prospects of testing from recoveries of stratospheric cometary dust
Some form of panspermia is coming to be regarded as a plausible mechanism for the beginnings of life on the Earth. I shall discuss experiments to test this possibility which have been done using cryosamplers collecting large volumes of air at 41km in the stratosphere.

I. Wright (i.p.wright@open.ac.uk):
Insights into the potential delivery of organic materials to Earth through the study of comets
Comets contain organic materials. Comets impact the Earth. Therefore, comets may deliver organic materials to the Earth. At an appropriate time in the history of the Earth such materials may have become implicated in the processes which ultimately spawned life on the planet. To assess the possibilities of such a mechanism it is desirable to know first hand what comets are actually made of. The European Space Agency's Rosetta mission aims to address this issue. The talk will introduce Rosetta, include a description of a UK experiment (Ptolemy) on board the small craft that will land on a comet, and give an update on the status of the mission (which is currently delayed because of problems with the Ariane 5 launcher programme).

J. Greaves (jsg@roe.ac.uk):
Impacts on Extrasolar Earths
The search for planetary systems like our own is likely to concentrate on Solar-type single stars within a few parsecs. I present new data showing that some of these closest stars have belts of dusty debris much brighter than our own Kuiper Belt. This may trace a much larger population of comets that would affect the development of life on Earth analogues.

W. Napier (wmn@star.arm.ac.uk):
Multiple Bombardments and Geological Trauma
Long-period comets occupy the borderland between solar system and Galaxy, and their influx to the inner planetary system is sensitive to interstellar perturbers such as passing stars, nebulae, spiral arms and the periodic Galactic tide. Dust and debris from the largest comets injected into the planetary system may significantly reduce insolation on Earth and have prolonged biotic, climatic and other effects. Correlations are thus expected between multiple impacts, geological disturbances and mass extinctions. The statistical status of these correlations is examined.

P. Bland (p.a.bland@imperial.ac.uk):
The impact rate of small asteroids on Earth
Asteroids smaller than 1 km across constitute the most immediate impact hazard to human populations, and yet the rate at which they arrive at Earth's surface is poorly known. Small craters on Earth are rapidly eroded, and many incoming objects are disrupted in the atmosphere. New studies of more than 1000 simulated impacts by small iron and stony bodies, together with the known impact rate at the top of the atmosphere, indicate that even large stony impactors may experience severe atmospheric disruption, resulting in a calculated impact rate for these objects 40 times lower than some earlier estimates.

Royal Astronomical Society (RAS)