Only when a comet arriving from the Oort cloud has its orbit tweaked by a close encounter with a planet does it settle into a more regular existence.

ECONOMIST: Comet Ikeya-Zhang is enlivening the skies

Cheng says the comet is likely making its first visit to the inner solar system from the Oort cloud, a reservoir of hundreds of millions of comets encircling our solar system at a distance of about a light year.

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