Apparently, Galileo's John Hancock is extremely rare and is one of the most sought after autographs ever.

 

And the letter happens to be in immaculate condition too, which convinced the "Roadshow" appraiser to recommend it be insured for at least $100,000.

Fans on Twitter couldn't believe how much the letter ended up being worth, calling it impressive and amazing.

This video includes images from Portrait of Galileo Galilei by Justus Sustermans.