Engineers at the European Space Agency fear that they won't be able to communicate with the Philae lander after Friday. Here, lander manager Stefan Ulamec (left, in foreground) watches as data confirming the comet landing arrived Wednesday. European Space Agency hide caption

itoggle caption European Space Agency

Matthew McConaughey plays an astronaut explorer in Christopher Nolan's Interstellar. Paramount Pictures/Melinda Sue Gordon hide caption

itoggle caption Paramount Pictures/Melinda Sue Gordon

The Philae lander beamed back images showing one of its three feet on the surface of Comet 67P/Churyumov-Gerasimenko . This photo is compiled from two images; a wider version will be released later Thursday. ESA/Rosetta/Philae/CIVA hide caption

itoggle caption ESA/Rosetta/Philae/CIVA

The Philae lander took this photo of its descent onto comet 67P Wednesday, when it was about 3 kilometers from the surface. The landing site is seen with a resolution of about 3 meters per pixel. ESA/Rosetta/Philae/ROLIS hide caption

itoggle caption ESA/Rosetta/Philae/ROLIS

The unique folding tail section of the Virgin Galactic's SpaceShipTwo may have been a factor in the crash. Virgin Galactic hide caption

itoggle caption Virgin Galactic

Strontium atoms floating in the center of this photo are the heart of the world's most precise clock. The clock is so exact that it can detect tiny shifts in the flow of time itself. Courtesy of the Ye group and Brad Baxley/JILA hide caption

itoggle caption Courtesy of the Ye group and Brad Baxley/JILA

In a photo released by Scaled Composites, Michael Alsbury, who was killed while co-piloting the test flight of Virgin Galactic SpaceShipTwo on Friday, Oct. 31, 2014, is shown. Scaled Composites/AP hide caption

itoggle caption Scaled Composites/AP