Ananova:

Police have cordoned off a field after a rock which is thought could be a meteor appeared in North Yorkshire.

A woman walking her dog says she heard an explosion followed by a rush of air as she walked near a field at Hopgrove, near York.

She saw a smoking crater in the ground, said a North Yorkshire police spokeswoman.

"A curator has been down from the Yorkshire Museum and has identified that we do have a meteor and a suitable crater for it to sit in."

The area has been cordoned off by police following the incident.

But a scientist has cast doubt on whether it is a meteorite. Dr Matthew Genge, Meteoriticist at the Natural History Museum in London, says the as-yet unidentified object has a "25% chance" of being a meteorite.

He said: "It is difficult to say if this is a meteorite because usually they are unspectacular events. It is simply a rock falling from the sky, hitting the ground and making a hole. There are certain factors that identify a meteorite and from what I've heard, some things today just aren't consistent with that.

"For example, they don't smoke when they hit the ground, but then they do make a noise because, as they are travelling faster than the speed of sound, they are often accompanied by a sonic boom."

A meteorite is a piece of rock, usually from asteroids, that fall to Earth, usually over a period of millions of years.

Asteroids can collide in the main asteroid belt between Mars and Jupiter, sending fragments hurtling towards earth, or they can come from planets, Dr Genge said.

When they hit the Earth's atmosphere, they are travelling at speeds in excess of 11.2 kilometres a second and a millimetre-thick outer crust forms when the rock heats up. About 30-80 meteorites hit Britain each year, Dr Genge said.

The last one recovered in England, Scotland and Wales was at Glatton near Peterborough in 1990 and landed in an elderly man's garden.