A chunk of ice dropped out of the sky and left a huge hole in the ground this weekend at Oakland's Bushrod Park in California, and not even astronomy experts know where it came from.
Jacek Purat, a witness to the falling ice, grabbed a piece and is storing it in his freezer. He says it came out of the southwestern sky, slammed into the ground and exploded into pieces.
It burrowed about two-and-a-half feet into the ground, where Oakland firefighters retrieved it.
"They just pulled it out and threw it on the sidewalk and it broke into pieces," Purat said.
Ron Wilson, an aviation consultant for ABC7/KGO-TV in San Francisco, said it probably didn't come from an aircraft. He believes the only possible way it could have come from an airplane is if the plane's valve for freshwater had leaked at a high elevation.
The other possibility is that it is a chunk of ice from space.
"It's very unlikely for a piece of a comet to make it down to our surface, mainly because of the shock waves it encounters as it's entering our atmosphere," said Ryan Diduck at the Chabot Space and Science Center.
If the ice contains chlorine, it more than likely came from an airplane's freshwater tank. If not, scientists would like to see if it contains impurities from space that make up the solar system, like dust and dirt.
"It produced some little bit of inflammation, sensation of the tips of your fingers as if it had a little bit acid maybe or something like that," Purat said.
So far, no one has asked to analyze Mr. Purat 's chunk of mysterious ice.
Falling ice perplexes scientists
Theories abound after 2 chunks land in state in a week.
The skies are raining big chunks of ice, and experts ranging from scientists to federal investigators are scrambling to learn what's going on.
For the second time in a week, California was the victim of an aerial, icy assault, the latest being early Thursday when a chunk of ice the size of a microwave oven plunged out of a cloudless sky into the San Bernardino County town of Loma Linda. The ice punched through the metal roof of a recreation center, leaving a hole up to 2 1/2 feet wide, then fragmented into opaque, brilliant white chunks, one as big as a bowling ball. No one was hurt.
The simplest, least controversial hypothesis is that the ice was dropped from airplanes, but there's little direct support for that view. A few experts who study such phenomena have suggested that similar occurrences around the world owe more to exotic causes, perhaps even global warming.
In both cases, the ice was clear or whitish -- not bluish, as one would expect of ice that had leaked from an airplane's restroom, for instance.
Legends about plunging ice go back for centuries. They didn't begin to receive serious scientific attention until a few years ago, however, when Spain and other countries were pelted by the mystery intruders.
Possible explanations range from the mundane to the bizarre.
One theory is that ice is somehow forming on the outside of aircraft, perhaps in areas that aren't protected by deicing equipment, said David Travis, a climatologist at the University of Wisconsin at Whitewater. Last year, he and 11 others co-wrote an article on the ice-fall mystery in the Journal of Atmospheric Chemistry.
Lead author Jesus Martinez-Frias of the Planetary Geology Laboratory in Madrid and his colleagues have collected reports of 40 cases around the world since 1999 of puzzling falling ice, or "megacryometeors," as they call the strange objects.
Martinez-Frias hypothesizes that the ice forms in the upper atmosphere by a process similar to the formation of hail inside thunderstorms but without a thunderstorm. But how can ice fall from a cloudless sky? Martinez-Frias speculates that global warming is causing the lower part of the atmosphere -- the troposphere, where we live -- to expand and rise. This means that the tropopause, which is the so-called roof of the troposphere, is forced to a greater height, where it cools more than normal.
Thus, he suggests, the new, steeper temperature difference between warm and cold air in the upper atmosphere generates turbulent up-and-down winds that repeat the hail-formation process, without a thunderstorm.