Dr. David J. Asher

The NewScientist article “Dark” comets may pose threat to Earth said

SWATHES of dark comets may be prowling the solar system, posing a deadly threat to Earth.
 
Hazardous comets and asteroids are monitored by various space agencies under an umbrella effort known as Spaceguard. The vast majority of objects found so far are rocky asteroids. Yet UK-based astronomers Bill Napier at Cardiff University and David Asher at Armagh Observatory in Northern Ireland claim that many comets could be going undetected. “There is a case to be made that dark, dormant comets are a significant but largely unseen hazard,” says Napier.
 
Periodic comet showers appear to correlate with the dates of ancient impact craters found on Earth, which would suggest that most impactors in the past were comets, not asteroids.
 
Now Napier and Asher warn that some of these comets may still be zipping around the solar system. Other observations support their case. The rate that bright comets enter the solar system implies there should be around 3000 of them buzzing around, and yet only 25 are known.

David J. Asher, D.Phil. is Research Fellow at Armagh Observatory. His main area of specialization is computational studies in solar system dynamics. His work embraces comets, asteroids and meteor streams, and he has published numerous papers on meteor shower predictions and the impact hazard.
 
David was part of Duncan Steel’s Anglo-Australian Near-Earth Asteroid Survey (AANEAS) in the mid-1990s, and later worked at the Bisei Spaceguard Center at the invitation of Syuzo Isobe of the Japan Spaceguard Association.
 
He authored Meteor outburst profiles and cometary ejection models, and coauthored The Tunguska impact event and beyond, Quasi-Hilda Comet 147P/Kushida-Muramatsu: Another long temporary satellite capture by Jupiter, Apollo asteroids 1566 Icarus and 2007 MK6: Icarus family members?, The fundamental role of the Oort cloud in determining the flux of comets through the planetary system, The Human Orrery: a new educational tool for astronomy, and Earth in the cosmic shooting gallery.
 
David earned his D.Phil. at Oxford University’s Department of Astrophysics in 1992 with the thesis The Taurid meteoroid complex. He earned his M.Sc. at The University of Edinburgh’s Department of Artificial Intelligence in 1993.
 
Read Why Asteroid 2008 TC3 Represents a Landmark – Dr David Asher, from Armagh Observatory, Explains.