A megacryometeor is a very large chunk of

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaqu ...

which, despite sharing many textural, hydro-chemical, and isotopic features found in large hailstones, is formed under unusual atmospheric conditions which clearly differ from those of the

cumulonimbus cloud Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...

scenario (i.e. clear-sky conditions). They are sometimes called huge hailstones, but do not need to form under

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...

conditions unlike hailstorms. Jesús Martínez-Frías, a planetary

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

and

astrobiologist Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that inves ...

at Institute of Geosciences ( es, Instituto de Geociencias, IGEO) in the

Spanish National Research Council The Spanish National Research Council ( es, Consejo Superior de Investigaciones Científicas, CSIC) is the largest public institution dedicated to research in Spain and the third largest in Europe. Its main objective is to develop and promote res ...

( es, Consejo Superior de Investigaciones Científicas, CSIC) in

Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 6.7 million. It is the Largest cities of the Europ ...

, pioneered research into megacryometeors in January 2000 after ice chunks weighing up to rained on

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

out of cloudless skies for ten consecutive days.

Mass and size

More than 50 megacryometeors have been recorded since the year 2000. They vary in mass between to several tens of kilograms. One in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

weighed in at more than . Chunks about in size also fell in Scotland on 13 August 1849.

Formation

The process that creates megacryometeors is not completely understood yet, mainly with respect to the atmospheric dynamics necessary to produce them. They may have a similar mechanism of formation that leads to the production of hailstones.The Peculiar Phenomenon of Megacryometeors
by Alan Bellows. Scientific studies show that their composition matches normal tropospheric

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...

water for the areas in which they fall. In addition, megacryometeors also display textural variations of the ice surface and hydro-chemical and isotopic heterogeneity in its composition, which gives potential evidence to a complex formation process in the lower atmosphere. It is known that they do not form from airplane toilet leakage because the large chunks of ice that occasionally do fall from airliners are distinctly blue due to the disinfectant used by them (hence their common name of " blue ice"). Some have speculated that these ice chunks must have fallen from aircraft fuselages after plain water ice accumulating on those aircraft through normal atmospheric conditions has simply broken loose. However, similar events also occurred prior to the invention of aircraft. Studies indicate that metrological fluctuations in

tropopause The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere; which are two of the five layers of the atmosphere of Earth. The tropopause is a thermodynamic gradient-stratification layer, that marks the end of ...

, associated with hydration of the lower stratosphere and stratospheric cooling, can be related to their formation. A detailed micro-Raman spectroscopic study made it possible to place the formation of the megacryometeors within a particular range of temperatures: . They are sometimes confused with

meteor A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...

s because they can leave small

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

s, though they form in the atmosphere and not from

outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...

References

External links

{{wiktionary
Megacryometeors: Resource SiteNews Report: Ice Chunk Hits Oakland, CA, USAThe Peculiar Phenomenon of MegacryometeorsGetting to the truth of falling ice chunks, Chemical Science, Katherine Davies, 2008The problem of Ice Meteorites, Martin BeechTop 100 Stories of 2008 #73: Giant Ice Meteors Fall From Clear Skies, Karen WrightHALS (blog with cases)
Precipitation