A massive lump of ice falling from the sky and landing at your feet is not what you would expect on a lovely sunny day, but unusual events like these have been known to happen. It has been speculated whether they could be giant hailstones or maybe ice from aircraft, but a team of Spanish scientists has found that the answer actually lies within complex natural processes in the atmosphere.

Jesus Martinez-Frias at the Centre for Astrobiology, Madrid, and a multidisciplinary team of scientists have looked at the formation of large ice conglomerations, known as megacryometeors, in our atmosphere.  There have been more than 100 recorded events of ice chunks falling from the sky, explained Martinez-Frias, but up to now their formation has not been fully understood.  

The team focussed on a ten kilogram ice chunk which fell from a clear sky in a town close to Madrid in 2007 - the Mejorada del Campo megacryometeor. Using a multianalytical approach the team found that the chunks have the texture, hydrochemical features and isotopic values that prove they come from atmospheric processes. The water in the megacryometeor is clearly tropospheric, explained Martinez-Frias.

Martinez-Frias used the analogy of an atmospheric 'symptom' to say that the real cause of these ice chunks will only be 'diagnosed' with an interdisciplinary approach. 'Megacryometeors do fall. This is an indisputable fact and we encourage other scientists to study these events all around the world to ascertain whether they obtain similar results and reach similar conclusions about their formation.'

Bernd Michael Rode, professor of theoretical and inorganic chemistry at the University of Innsbruck, Austria, said, 'the team's work shows that our atmosphere still provides surprising and unresolved problems.' He echoed the words of Martinez-Frias, saying that this field of research 'requires interdisciplinary co-operation on a very wide scale.'