A megacryometeor is a very large chunk of ice which, despite sharing many textural, hydro-chemical, and isotopic features detected in large hailstones, is formed under unusual atmospheric conditions which clearly differ from those of the cumulonimbus cloud scenario (i.e. clear-sky conditions). They are sometimes called huge hailstones, but do not need to form under thunderstorm conditions. Jesús Martínez-Frías, a planetary geologist and astrobiologist at Institute of Geosciences (Spanish: Instituto de Geociencias, IGEO) in the Spanish National Research Council (Spanish: Consejo Superior de Investigaciones Científicas, CSIC)[1] in Madrid, pioneered research into megacryometeors in January 2000 after ice chunks weighing up to 6.6 pounds (3.0 kg) rained on Spain out of cloudless skies for ten days.