Scientists are looking for help to find fragments of a meteorite.
The space rock is thought to have landed somewhere in the county.
The members of the UK Fireball Alliance spent the bank holiday searching for pieces, but no one has recovered them.
Prof Joy said the rock would be about the size of an Easter egg.
The alliance, a collaboration between academics and citizen scientists interested in meteorite recovery, has appealed to the community for help tracing it.
The University of Glasgow's Dr. Luke Daly said that a meteorite is believed to have landed in four fragments south of the county town.
Given the amount of wheat and oilseed rape in the area, we have been looking for a needle in a haystack.
Prof Joy from the Department of Earth and Environmental Sciences at Manchester University said that the meteorite won't be hot and is as safe to handle as any other rock, but please don't pick it up with your bare hands.
It may be a glossy black or brown colour, with the dark crust broken off in places.
The largest pieces won't be bigger than an Easter egg, and the smallest could be a mini egg.
It may be in a place where rocks are not usually found.
She urged people not to take risks while searching, but said scientists would be happy to look at any discoveries.
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