Abstract
The danger to Earth because of impacts from asteroids and
comets is receiving a lot of attention in present times. Coincidentally
when this abstract is being prepared, there is a close approach of
asteroid 2013 TX68 approaching Earth within a distance lower than the
geostationary satellites. The recent spectacular fireball on 2015 Mar 15
over Switzerland got widespread media attention in Europe. The
remarkable event on 2013 Feb 15 over the Russian city of Chelyabinsk
boosted public awareness of the importance of threat analysis on the
bodies from outer space. The pathways by which these dangerous bodies
arrive at our planet are the same as those of the benign shooting stars
(they originate from comets or asteroids) we see every night. The
difference is only one of scale, between a romantic flicker of light on
the sky and a dangerously explosive case such as the Chelyabinsk event.
Various telescopic surveys and observational databases are able to give
rough estimates of size frequency distribution for Earth impacts and
they help in calibrating the risk level to a certain degree. In this
talk, the aim is to give a brief background into the calculations
concerning various scenarios of Earth impacts. The idea is to present
some analytical, geometric and numerical approaches which help us to
assess the possible dynamics of impacts on Earth. Some very simple to
not-so-simple cases would be presented so that one gets to understand
how the nature of calculations can get tricky as one broadens the scope
of studies with different classes of bodies in their past, present and
future evolution in our solar system.