The sky turned dark, then yellow, then blue balls began dropping out of the sky. Not the start of a science fiction film but Steve Hornsby's account of a strange happening in his back yard in Dorset.

Hornsby is trying to find out what the transparent, marble-sized objects that peppered his home in Bournemouth could be.

The 61-year-old said he was walking to his garage at around 4.10pm on Thursday when what he thought was an ordinary storm hit. He took shelter but once the downpour had finished he noticed the lawn was dotted with blue balls.

Hornsby, an aircraft engineer, said: "I was just about to pop into the garage to get some logs for the fire when the sky went very dark and then a strange yellow colour. There was then a short, sharp hail storm that lasted for about 20 seconds.

"I rushed to stand by the wall out of the way and it was all over very quickly. I had seen the hail come down and it looked like rock salt. But then I spotted something on the lawn and it looked like broken glass.

"But then I put my foot on it and it disappeared and I thought it was strange. Then I looked around and there were lots of others. They were definitely not there before the storm.

"They were almost impossible to pick up, they were very jelly-like. I had to get a spoon and flick them into a jam jar. They had an exterior shell with a soft inside. They only landed in our garden in an area of a couple of hundred square metres.

"It is the most peculiar thing I have ever seen – there must be about 20 complete spheres. They don't smell and they don't float. I've been an aircraft engineer for many years and I've never seen anything like it.

"I thought it could have been some kind of atmospheric pollution like a chemical that has been released into the atmosphere, got sucked into a storm cloud and solidified and then released in droplets with the hail stones. Ideally I'd like to get them chemically analysed to find out what they consist of."

Josie Pegg, a science research assistant at Bournemouth University, speculated that the objects might be "marine invertebrate eggs".