An image of Pluto that was taken by New Horizons shortly before its flyby Tuesday shows a heart-shaped pattern on the planet's surface. NASA says Pluto "sent a love note back to Earth." NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute hide caption

itoggle caption NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute

NASA's New Horizons mission will be the first ever to visit Pluto and its moons. This artist's conception shows the probe as it passes the dwarf planet. JHUAPL/SwRI hide caption

itoggle caption JHUAPL/SwRI

On Friday, a Russian Soyuz rocket will send an unmanned cargo ship with more than 3 tons of food, water and fuel for astronauts aboard the International Space Station. Russian Federal Space Agency hide caption

itoggle caption Russian Federal Space Agency

Astronomer Chris Impey examines the possibilities of the universe in his new book Beyond. "I like the idea that the universe — the boundless possibility of 20 billion habitable worlds — has led to things that we can barely imagine," he says. In the 1970s, NASA Ames conducted several space colony studies, commissioning renderings of the giant spacecraft which could house entire cities. Rick Guidice/NASA Ames Research Center hide caption

itoggle caption Rick Guidice/NASA Ames Research Center

This image of a "red spot" on Mercury, which is thought to be the result of a volcanic explosion, was sent to Earth by the Messenger probe in 2011. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington hide caption

itoggle caption NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

A giant cluster of about 3,000 stars called Westerlund 2. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. NASA, ESA, STScI/AURA hide caption

itoggle caption NASA, ESA, STScI/AURA

A view of a phytoplankton bloom near Alaska's Pribilof Islands. The milky green and light blue shading of the water indicates the presence of vast populations of microscopic phytoplankton. NASA hide caption

itoggle caption NASA

This artist rendering shows Kepler-11, a sun-like star around which six planets orbit. A planet-hunting telescope is finding whole new worlds of possibilities in the search for alien life, including more than 50 potential planets that initially appear to be in habitable zones. The agency's chief scientist said Tuesday there will be "strong indications" of alien life within a decade. NASA/AP hide caption

itoggle caption NASA/AP

NASA astronaut Scott Kelly is seen inside a Soyuz simulator at the Gagarin Cosmonaut Training Center on March 4 in Star City, Russia. Kelly, along with Russian cosmonaut Mikhail Kornienko of the Russian Federal Space Agency, are scheduled for launch Friday aboard a Soyuz TMA-16M spacecraft from the Baikonur Cosmodrome in Kazakhstan. NASA/Bill Ingalls hide caption

itoggle caption NASA/Bill Ingalls