Swarms of nanocraft could be sent into deep space by laser to take pictures of Alpha Centauri.
The planned mission to our nearest star system, dubbed 'Breakthrough Starshot', is being funded by Russian billionaire Yuri Milner -- he's made an initial pledge of US$100 million.
"This is a StarChip," said Mr Milner, holding a prototype nano aircraft between thumb and forefinger at a press conference in New York today.
"A gram-scale wafer containing cameras, photon thrusters, power supply, navigation and communications equipment. It's about the size of a large postage stamp, only a little bit thicker.
"This is the Silicon Valley approach to spaceflight: a fully functional space probe that can be held with two fingers and mass produced at the cost of an iPhone."
It would take the nanocraft 20 years to get to the star system, which is about 40 trillion kilometres away.
If successful, scientists could figure out whether Alpha Centauri contains an Earth-like planet capable of sustaining life.
The tiny aircraft, with ultra-thin light sails, would be accelerated to 20 percent the speed of light by ground-based lasers, boosting them to a cruise velocity of some 59,867km per second within a few minutes.
Each "spacecraft on a chip" would snap pictures and beam the data back to Earth using tiny on-board lasers, the faint signals arriving four years later.
Today's announcement, made with physicist Professor Stephen Hawking, follows on from 'Breakthrough Listen', a decade-long project backed by Mr Milner that monitors radio signals for signs of intelligent life across the universe.
"The limit that confronts us now is the great void between us and the stars," said Prof Hawking.
"But now we can transcend it. With light beams, light sails and the lightest spacecraft ever built, we can launch a mission to Alpha Centauri within a generation.
"Today, we commit to this next great leap into the cosmos because we are human, and our nature is to fly."
'Breakthrough Starshot' has attracted both interest and scepticism from experts, particularly over the need for a phased-array laser system, or "light beamer".
The project will take years to develop, cost billions of dollars in total, and there is no guarantee it will work.