WHEN WORLDS COLLIDE will be presented by Dr. Kevin Zahnle of NASA-Ames Research Center.

Planet Earth is regularly being struck by interplanetary debris: fine dust, rocks, boulders (big enough to outshine the Sun as they streak through the atmosphere), asteroids, comets, and even small stray planets. Some of these collision events offer glorious night-time views; others can cause planetary annihilation. Infall of secondary debris ("shrapnel" from the original impact) can raise atmospheric temperatures by  hundreds  of degrees, globally.

About our speaker:

Dr Zahnle received his PhD. from University of Michigan in 1985, was a NRC (postdoc) at NASA Ames 1985-1987, at Stanford University 1987-1988 (postdoc) and has worked at  NASA Ames Research Center 1988 to the present working in Photochemical modeling; geochemical modeling of atmophiles; impact processes (both ab initio modeling and data-driven modeling); impact frequencies; atmospheric escape processes; planetary accretion. Dr. Zahnle is responsible for the studies involving whether impacts created the Martian valley river networks and the runaway greenhouse studies for Mars and Venus-like planets.