A man was left baffled after stumbling on a bizarre white goo on moorland while walking his dog.
The strange milky substance was found near junction 22 of the M62 near Huddersfield.
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Andrew Holden, who lives in Shaw, Oldham, has spent hours trying to find out what the bizarre material is - but has hit a dead end.
He said: "It looks like frogspawn but it definitely isn't. It doesn't look normal and I didn't notice a smell."
"There are no plants that could secrete something like that. As I moved further on I found some more but this wasn't as jelly like - this was more crystallised, like salt.
"I tried to keep my dogs, Marley and Willow, away from it but they didn't seem bothered by it."
Speaking to the Huddersfield Examiner, he added: "I took pictures and video and put them on Instagram, but nobody knew anything about it.
"I spent all afternoon looking on the internet to find out what it was because it was driving me mad, but nobody seems to know what it is."
The goo has been spotted all over the world and its origin has never been definitely explained.
Reports of the substance date back as far as the 14th century when physician John of Gaddesden detailed 'stella terrae' in his medical writings - describing it as "a certain mucilaginous substance lying upon the earth," and suggesting it could be used to treat abscesses.
A 14th century Latin medical glossary describes 'uligo', "a certain fatty substance emitted from the earth, that is commonly called 'a star which has fallen'".
And in 1440 an English-Latin dictionary has an entry for 'sterre slyme', a falling or shooting star.
The gunk is also known as star jelly, astromyxin, astral jelly, star rot, star shot or moon poo.
In Mexico it is called caca de luna (moon excrement), while a National Geographic video dubbed it 'mystery goo rain'.
A 6ft domed disc of quivering jelly was discovered in Pennsylvania in 1950 - reports of which inspired the 1958 film The Blob.
In 1996 a meteor shower was reported in Kempton, Australia - and the following day, a white translucent slime was reportedly discovered on the lawns and pavements of the town.
Reports such as this lead some people to believe it is deposited on the earth during meteor showers, but others say it is the remains of frogs, toads, or worms.
Andrew said: "I have seen two different kinds - one is more crystallised.
"Next time I see it I'm going to collect some in a plastic tub and freeze it so I can get it tested. People were saying it comes from space but I don't know - I can't make my mind up.
"I believe in aliens but whether this comes from outer space... I don't know."