The logo, showing a classic saucer-shaped spacecraft shining a light down on the search-engine's regular logo, has been the subject of much speculation.
The world's internet voices want to now whether the all-powerful web giant is trying to tell us something.
Google regularly changes its logo to mark important event such as the recent 40th anniversary of the moon landings.
But nobody can work out why Google has chosen this date to put a UFO logo on the world's most visited web page.
"Does anybody know what's going on?" asks one.
"Aliens landed on Earth this day last year," offers another blogger by way of explanation.
Some think Google's global dominance may extend beyond this planet.
"If Google says the aliens are coming, I'm getting out of here," says one US blogger.
One of the things bothering the online community is that early on Saturday morning the new logo could be seen in some places, but not others.
"Am I the one that is going crazy?" asks a blogger in Arizona who can't see the logo.
If you click on the alien logo you are given the results for "unexplained phenomena".
In Google's top tend most searched terms "unexplained phenomena" merits two entries.
It is unclear whether Google is responding to popular demand or dictating what the public should be interested in.
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