The Greatest Nuclear-Powered Space Missions of All Time.

Most spacecraft power themselves by absorbing the sun's energy with solar panels. Beyond Earth’s comfortable, brightly lit cradle, however, outer space assaults probes with deep cold, deeper darkness and intense bursts of radiation.

To keep a spacecraft safely aloft in the void seems to require magic. Thanks to the Cold War-era space race, U.S. engineers found some: Plutonium-238, a byproduct created during the production of weapons-grade plutonium-239.

Unsuitable for use in weapons but perfect in a spacecraft, plutonium-238′s gradual decay gives off warmth that safeguards fragile electronics. More importantly, wrapping plutonium with heat-to-electricity converting materials, called thermoelectrics, turns the radioactive metal into a nuclear battery.

“Plutonium-238 is perhaps the main reason why other nations haven’t gone as deep into space as we have,” saidJim Adams, NASA’s deputy chief technologist and former deputy director of the space agency’s planetary science division. “They don’t have access to material to make reliable, lightweight [nuclear batteries].”

Powering Cassini around Saturn, for example, would require solar panels the size of two tennis courts and weigh thousands of pounds. Barring a radical and unforeseen breakthrough in power systems, or heavy multiplying of NASA’s budget (launch costs range between $5,000 and $10,000 per pound), no other energy source is as practical as a nuclear battery.

As the world’s supply of plutonium-238 comes disastrously close to running out, WIRED reviews the greatest space missions of all time — some of which still phone home decades after launch and billions of miles away from Earth.

INTO THE WORLD OF ANTS

World's Thinnest Glass Created Accidentally By Researchers In U.S., Germany

Researchers captured a microscopic photo of a sheet of glass only two atoms thick. Here it is blended with an artist's conception to show the structural rendering.

Researchers accidentally discovered the world's thinnest sheet of glass, just two atoms thick.

Their chance finding — now immortalized in the 2014 edition of the Guinness Book of World Records, out this week — gives scientists a glimpse into the puzzling properties of glass, which behaves like both a solid and a liquid.

Researchers at Cornell University and Germany's University of Ulm were creatinggraphene, one of the thinnest and strongest materials in the world. Sheets of graphene are just one carbon atom thick, with those atoms arranged in a honeycomb lattice. 

Using an electron microscope, the researchers inspected some "muck" on the graphene, finding that it was essentially a 2D sheet of common glass, made up of silicon and oxygen atoms.

The glass layer likely was created when an air leak caused copper foils, which are involved in the graphene-making process, to react with a furnace made up quartz, a mineral that is comprised of silicon and oxygen, the researchers say.

The researchers' observations were first described in January 2012 in the journal Nano Letters. They say their microscopic photos of the ultra-thin pane may help to solve some long-standing uncertainties about glass, which is not exactly a liquid or a solid.

Most solids when they cool arrange their atoms in a rigid lattice. Though glass is hard and has a solid appearance, atoms that make up glass are arranged in a disordered network, more like a liquid.

The structure of the 2D glass that the Cornell researchers saw is similar to theoretical models of the irregular structure of glass dating back to the 1930s.

"This is the work that, when I look back at my career, I will be most proud of," David Muller, professor of applied and engineering physics at Cornell, said in a statement. "It's the first time that anyone has been able to see the arrangement of atoms in a glass."

Though it was an accidental discovery, the researchers say such deliberately created 2D glass could find its way into nanotechnology and could even one day be used in transistors.