When two Swedish treasure hunters searched for champagne in shipwrecks, they came across something unusual, something they had never seen before. Our correspondent in Stockholm has more.
When two Swedish treasure hunters went out in June this year searching for ancient bottles of champagne in shipwrecks in the Baltic Sea, they found more than they'd bargained for.
Dennis Åsberg and Peter Lindberg didn't find any champagne, they found something else.
A huge disc-shaped object showed up in their sonar pictures 197 feet in diameter, as big as a jumbo jet.
[Peter Lindberg, Ocean Explorer]:
"I magnified it, looked at it and realized that this is very unusual, in my years as a treasure hunter I have many hours in front of the sonar, I've never seen anything like it."
On the sonar it looked like a point of impact, as though something had hit the ocean floor, continuing 4000 feet, creating a track before it came to a halt. It had dug into the sea bed making a sand bar on its right side.
The object is about 275 feet deep, the Baltic sea floor is dead with no underwater currents to create such sandbars.
Recently another object was found about 500 feet from the mysterious disc.
According to Peter this object comes from the same direction as the disc and could be a part of it.
Sonar shows the objects are made of hard material. It could be something like hard concrete, granite or of some kind of metals.
The two explorers have been in contact with many experts around the world and no one can say what it is.
But many speculate on things like a Russian ship from the World Wars, a meteorite or a UFO.
[Dennis Åsberg, The ocean explorer team]:
"We live in a universe that is gigantically big. It's not impossible that it is so. Well then we have found it, that's cool, but as I said, I believe more that it would be something that is dumped perhaps a submarine base that the Russians had or something like that"
Dennis says that finding a financier for this project is not as easy as when they search for antique wine bottles or historic artifacts.
For those who can afford it there will soon be a chance to follow the ocean explorer team in a submarine on their first trip down to the hidden mystery in May 2012.