This just to note the big meteorite that exploded today over the Chelyabinsk area in Russia this morning. It is said to have had a kinetic energy corresponding to 20 Hiroshima bombs, but of course this kind of energy does not cause radioactivity. It did cause some light and heat, but most of the energy was spent in a sonic boom that destroyed windows and to some extent doors and walls in the nearest city, wounding more than a thousand people, but most of them lightly. Most of the territory is however sparsely populated, so the damage was moderate. If one of these rocks had exploded right above a major city with millions of inhabitants, things would have looked far worse.

A few hours later, an asteroid big enough to end the Age of Mammals flew harmlessly by Earth, so close that it could be seen with binoculars. Lately, with our better telescopes, we are kind of getting used to those fly-bys. There will probably be some questions of the type “What is NASA doing to detect and prevent an asteroid impact”, and a few days later most of us have forgotten it until next time.