Interstellar dust

About one hundred tonnes of dust-sized material falls, from space, into the Earth's atmosphere each day. Most of this mass comes in particles a few tenths of a millimetre across which are travelling at such speed that friction with the atmosphere causes them to completely burn up at about 100 kilometres above the earth's surface. The heat generated is sufficient to ionize electrons and a trail forms behind the particles much like the vapour trail that forms behind a high flying aircraft. The trails formed by particles a centimetre across are sufficiently bright to be seen as faint meteors with the un-aided eye on a dark night -- so called 'shooting stars'.

Most of the dust arriving at earth has been boiled off comets as they travelled through the inner solar system sometime during the last 100,000 years; a moderate fraction has probably been blasted off asteroids during the same interval.

(F) Fuzzy exceptional problems