The 75-year-old had been in his bedroom when he heard a smash and found the football-sized lump of extra terrestrial debris in the loft of his home in Hull.
The great-grandfather said: 'It was a hell of a shock. If it had landed in the street and hit anybody it would have killed them.'
As it was too hot to handle he brought it downstairs using oven gloves.
The 4lb dark grey object was removed by Humberside Police before being taken away by the Ministry of Defence for investigation.
Mr Welton and wife Mair, 62, then received a phone call from the RAF, who said the metal mass was most likely to be space junk. This could mean anything from part of a spacecraft to a piece of abandoned satellite.
RAF spokesman Squadron Leader Jeff Brock confirmed the finding, which was the first the RAF's Defence Flying Complaints Investigation Team had encountered.
He said: 'Following consultations with the European Space Agency and Nasa, we are confident the object is more than likely space debris which was orbiting in excess of a decade.
'This is the first bit of space debris that we have got our hands on - we have never until this occasion had anything relating to it at all.'
The DFCIT, based in Henlow, in Bedfordshire, investigates complaints related to military flying. Experts initially thought the object may have come from an aircraft.
However, its size and appearance was found to be 'entirely consistent' with space junk, and its heavy mass meant it was more likely to have been in a state of decaying orbit for a decade or more.
Russia (then the Soviet Union) put the first object into space just 51 years ago - Sputnik One. Since then we have created a swarm of perhaps tens of millions of items of space junk. The debris ranges in size from paint flecks to defunct satellites.
The oldest piece of space junk still circling is the Vanguard 1 communications satellite that was launched by the U.S in 1958, but stopped working in 1964.
Most hug close to the surface, 200-300 miles up in low-earth-orbit, where they are a hazard to telescopes and the astronauts on the International Space Station.
Most debris will eventually burn up in the atmosphere, but larger objects can reach the ground intact. Most have come down over the Pacific Ocean or sparsely populated areas.
There has only been one recorded incident of a person being hit by human-made space debris. In 1997, Lottie Williams from Oklahoma was hit in the shoulder by a 5.1" piece of blackened metal. It was later confirmed to be part of the a rocket fuel tank launched the year before. Luckily she was not injured.
Despite narrowly escaping being hit, Mrs Mair said she was excited to hear the experts' findings.
'I think it's wonderful,' she said.
Mail's online video report on the event
... makes me laugh. Satellites crashed into each other. No one is talking. The pieces are coming down. A decade old me arse.
Wasn't someone hollerin' at my positing this 'afore, sumpin'bout pieces so small breakin' up'n'th'atmosphere?