Andrew Yee
October 21st 04, 05:51 PM
Armagh Observatory
Armagh, Northern Ireland
FOR FURTHER INFORMATION CONTACT:
Bill Napier via the Armagh Observatory
College Hill, Armagh, BT61 9DG
Tel.: 028-3752-2928; FAX: 028-3752-7174
e-mail: wmnarm.ac.uk
Website: star.arm.ac.uk/staff/billn.html
Chandra Wickramasinghe at the Centre for Astrobiology
Cardiff University
Tel.: 029-2087-4201; FAX: 029-2087-6425
e-mail: Wickramasinghecardiff.ac.uk
Website: www.astrobiology.cf.ac.uk
2004 October 15th
Chance of a Cometary Impact Re-assessed
The chances of the Earth suffering a collision with a cometary body may be
higher than previously thought, according to new research by astronomers Bill
Napier and Chandra Wickramasinghe. If so, international programmes designed to
detect a large class of potentially threatening objects, namely near-Earth
asteroids, as well as strategies to mitigate the worst effects of collisions,
may be in need of urgent review.
This is the disturbing conclusion reached by the astronomers in a paper which is
to be published shortly in the Monthly Notices of the Royal Astronomical
Society. Their argument is based on the known rate at which comets enter the
inner solar system from the Oort cloud, a nearly spherical swarm of some 100
billion comets that surrounds the solar system out to a distance almost halfway
to the Sun's nearest neighbouring star.
With about 1 percent of incoming comets ending up on relatively short-period
Earth-crossing orbits, it is expected that several thousand dormant comets could
be currently posing a potential threat to our planet. Recent surveys of the
Earth's immediate vicinity should have turned up some 400 such objects, whereas
only a handful have so far been found. The researchers dismiss the current
belief that all the "missing" comets have disintegrated into meteor streams. If
this had happened, they argue, then we should be seeing a far greater number of
meteor showers and a much brighter zodiacal cloud than is observed.
They propose instead that the majority of these comets have become exceedingly
black, with such low surface reflectivities that they could not be observed
against the blackness of space by optical means. Surfaces reflecting less than
0.1 percent of the incident sunlight could be formed when a comet made up of a
mixture of organic grains and ices approaches the sun and sublimates, leaving an
outer layer of loosely connected organic material.
Download full paper (PDF format):
http://star.arm.ac.uk/preprints/425.pdf
See also: NEO Impact Hazard,
http://star.arm.ac.uk/impact-hazard/
Armagh, Northern Ireland
FOR FURTHER INFORMATION CONTACT:
Bill Napier via the Armagh Observatory
College Hill, Armagh, BT61 9DG
Tel.: 028-3752-2928; FAX: 028-3752-7174
e-mail: wmnarm.ac.uk
Website: star.arm.ac.uk/staff/billn.html
Chandra Wickramasinghe at the Centre for Astrobiology
Cardiff University
Tel.: 029-2087-4201; FAX: 029-2087-6425
e-mail: Wickramasinghecardiff.ac.uk
Website: www.astrobiology.cf.ac.uk
2004 October 15th
Chance of a Cometary Impact Re-assessed
The chances of the Earth suffering a collision with a cometary body may be
higher than previously thought, according to new research by astronomers Bill
Napier and Chandra Wickramasinghe. If so, international programmes designed to
detect a large class of potentially threatening objects, namely near-Earth
asteroids, as well as strategies to mitigate the worst effects of collisions,
may be in need of urgent review.
This is the disturbing conclusion reached by the astronomers in a paper which is
to be published shortly in the Monthly Notices of the Royal Astronomical
Society. Their argument is based on the known rate at which comets enter the
inner solar system from the Oort cloud, a nearly spherical swarm of some 100
billion comets that surrounds the solar system out to a distance almost halfway
to the Sun's nearest neighbouring star.
With about 1 percent of incoming comets ending up on relatively short-period
Earth-crossing orbits, it is expected that several thousand dormant comets could
be currently posing a potential threat to our planet. Recent surveys of the
Earth's immediate vicinity should have turned up some 400 such objects, whereas
only a handful have so far been found. The researchers dismiss the current
belief that all the "missing" comets have disintegrated into meteor streams. If
this had happened, they argue, then we should be seeing a far greater number of
meteor showers and a much brighter zodiacal cloud than is observed.
They propose instead that the majority of these comets have become exceedingly
black, with such low surface reflectivities that they could not be observed
against the blackness of space by optical means. Surfaces reflecting less than
0.1 percent of the incident sunlight could be formed when a comet made up of a
mixture of organic grains and ices approaches the sun and sublimates, leaving an
outer layer of loosely connected organic material.
Download full paper (PDF format):
http://star.arm.ac.uk/preprints/425.pdf
See also: NEO Impact Hazard,
http://star.arm.ac.uk/impact-hazard/