Does the video above show a UFO "mothership" and a fleet of spacecraft hovering in the sky over London, England?

It certainly seems to be sparking interest. Since being posted on YouTube Friday, it's been viewed more than 835,000 times.

The video, taken by a pedestrian on a London street, shows three shining circular dots moving around the sky. Then a larger shape appears and hovers for a while, before abruptly moving behind a cloud.

"There's a UFO up there," says a man in the crowd.

Two similar videos have also appeared on YouTube recently. That's led some to question whether the whole thing might just be a clever promotional campaign—a less alien concept in a world city today.

Whatever the truth about the video, some experts think we're likely to come into contact with alien life forms sooner or later--perhaps sooner. "Life exists on other planets, and we will find it within 20 years," a top Russian astronomer said Monday.

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