When Stephen Hawking was first diagnosed with motor neuron disease at the age of 21, doctors optimistically gave him two to three years of survival. 49 years later, as the planet's most famous physicist gets ready to turn 70 on Sunday, his mental persistence and stunning scientifics achievements are being honored around the world.

"He's a very witty, humorous guy. It's amazing, under the circumstances, how he keeps his spirits up and brightens the atmosphere," Nobel laureate and long time friend Frank Wilczek told The Guardian. "It's an inspiration that he's been able to control his world and make genuine scientific contributions under very difficult situations and keep up his good work. It's a fantastic human story."

Hawking's humor was most recently on display when New Scientist asked him what he thinks about most often. His answer? "Women. They are a complete mystery."

During a recent radio interview in celebration of his birthday, Hawkings once again reiterated his belief that humans should - and must - begin to colonize beyond Earth. He firmly believe that either global warming, nuclear war, or some other manmade calamity will ruin the planet within the next 1,000 years.

"I believe that we will eventually establish self-sustaining colonies on Mars and other bodies in the Solar System although probably not within the next 100 years," he told Radio 4 listeners in the U.K. "I am optimistic that progress in science and technology will eventually enable humans to spread beyond the Solar System and out into the far reaches of the Universe."

Festivities this weekend honoring Hawking include a meeting of some of the world's top scientists at Cambridge University for a conference called "The State of the Universe". According to the Guardian, the topics discussed will include black holes, cosmology, and fundamental physics. A public symposium will be held Sunday in which Hawking will give a rare public lecture entitled "A Brief History of Mine."

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Happy 70th birthday, Stephen Hawking
World's most famous living physicist to be honored internationally Sunday.