The Geo- Files:The unearthly cases in Geology: Ice from the Sky

Like in every other science also in geology there are presumed mysterious, unexplainable cases or artefacts - but most of these cases consists only of a collection of anecdotes or are simply retold without sceptic inquiry, but sometimes behind stories there are some interesting facts.

April 27. 2010 at 10.17 in the German village of Hettstadt (near the city of Würzburg): an ice block, 50 kilogram heavy, felt from the clear sky, breaking off branches of shrubs, damaging a pavement slab and excavating three craters, the largest 22 centimetre deep.
Such "megacryometeors" findings are reported from around the world, Jesús Martínez-Frías, researcher on the Centre for Astrobiology in Madrid, has documented 76 such impacts since 2002. One of the largest of these specimens is a presumed 400 kilogram block crashed in the Spanish city of Toledo in 2004.

Fig.1. (A) Megacryometeor in situ that fell in La Milana, Soria (27 January 2002). It landed near a startled farmer who was riding his tractor. More than 16 kg of ice was recovered by the environmental police of the Guardia Civil (Seprona). The size of the small impact crater generated by the megacryometeor was ca. 50 cm.
(B) One of the fragments of the megacryometeor that fell in San Feliz de Lena (Asturias) (26 January 2000) (artificial illumination to highlight its textural features), from MARTINEZ-FRIAS 2006.

The origin of the ice block remained a mystery, speculation about giant hailstones, defect airplane toilettes, ice meteorites and even terroristic attacks emerged.

The German Meteor however was analyzed by the meteorologist Frank Böttcher (Instituts für Wetter- und Klimakommunikation - IWK, a private company).
The chemical composition of the specimen of Hettstadt showed no differences to rain, the ice therefore was formed in the atmosphere, and is not of extraterrestrial origin. The lack of traces of human urine, disinfection solutions or other artificial chemical components also excludes the provenance of the water from an airplane toilette or an elaborated fraud.

The airspace of the village in the morning of the event was over flown by two airplanes in an elevation of 10.730m and 11.890m, calculating the time for the block to reach the surface, and considering the direction of the impact (deduced from the form of the impact crater and the broken branches) Böttcher showed that it is possible that the ice came from the location of one of the airplanes.
It's not unusual that ice forms by condensing vapour on wings of airplanes, also it is possible that blocks large enough reach the surface. The origin of ice from the hull of planes will probably explain the majority of reported cases of ice - "meteors", maybe also a in part misleading name for a terrestrial phenomena.

Nevertheless it´s seems that not all cases can be explained by ice coming from airplanes, Martínez-Frías in his archive collected reports of ice felt from the sky in the first half of the 19th century, when planes didn't exist; also some recent cases of ice blocks do not correlate with planes passing by the site of discovery.
At least a part of the ice chunks must have a natural origin without planes interference , possibly like hailstones strong air currents hold them floating until the weight is to great and they crash onto earth.

Bibliography:

MARTINEZ-FRIAS. J. & HUERTAS, A.D. (2006): Megacryometeors: Distribution on Earth and Current Research. AMBIO: A Journal of the Human Environment 35(6): 314-316

Online Resources:

BOJANOWSKI, A. (23.08.2010): Einschlag bei Würzburg: Forscher löst Rätsel der fliegenden Eisbombe. (Accessed 27.08.2010)
MARTINEZ-FRIAS, J. (2000-2010): Megacryometeors - Extreme atmospheric events. (Accessed 27.08.2010)