(November 4, 2010)

MONTREAL - Great balls of fire were reported swooping recently over Eastern Canada and several U.S. states and there are different theories about what caused the sightings.

Even NASA's on the case.

An agency spacecraft got a closer look at one of the possible sources when it made a scheduled flight past the Hartley 2 comet on Thursday.

It took closeup pictures of the comet, which is roughly 1.2 kilometres wide and spews deadly cyanide gas.

The comet made one of its closest passes by Earth this week, flying by at a still-reassuring distance of 18 million kilometres from our planet.

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