Letter: Comets are now more exotic

Sir: In relation to a brief new addition to the night sky, comet Hyukatake, Charles Arthur asserted that comets are "frozen bodies of gas, liquid and rocks" (19 March).

Though this view was once held by the majority of scientists, it is now known to be erroneous. For new explorations of comet Halley show us that the material of comets is far more exotic than Mr Arthur makes out. Some 30 per cent of the comet was found to be made up of extremely complex organic chemicals - the stuff of life itself.

K Wickramasinghe

Cardiff