Click on the logo, you will see that a search term is "unexplained phenomenon".
I'm guessing that the text is missing because that phenomenon cannot be explained...
Ahhh thanks ShendoXT, that just helped me solve the mystery.
Now this is basec on my research, but essentially the term "unexplained phenomenon" is the top term searched using the Google search engine. That explains why Google have that doodle.
"The new doodle has flummoxed web users because it does not appear to represent a specific event or launch, both of which are the usual reasons behind special Google doodle. Instead, clicking on the image of the UFO takes the user to a search for the term "unexplained phenomenon" which just happens to be one of the top trending search terms on Google today. Also in the top 10 search terms is the phrase "top 10 unexplained phenomena".
But is this chicken or is this egg? Did Google change the logo in response to the growing number of searches for "unexplained phenomenon" or is it specifically seeking to drive traffic to that term. Web users are asking if this is a precursor to some viral event or if is tied to yesterday's release of District 9."
It wouldn't have been halloween because event doodles show on the day of the day and not prior to the day.