This artist's concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. NASA's Spitzer Space Telescope found evidence that a high-speed collision of this sort occurred a few thousand years ago around a young star, called HD 172555, still in the early stages of planet formation. The star is about 100 light-years from Earth. NASA/JPL-Caltech
Some of the coldest and darkest dust in space shines brightly in this infrared image from the Herschel Observatory, a European Space Agency mission with important participation from NASA. The image reveals a cold and turbulent region where material is just beginning to condense into new stars. It is located in the plane of our Milky Way Galaxy. Blue shows warmer material, red the coolest, while green represents intermediate temperatures. The red filaments are made up of the coldest material pictured here - material that is slightly warmer than the coldest temperature theoretically attainable in the universe. ESA/NASA/JPL-Caltech
On May 5, 1961, NASA astronaut Alan Shepard piloted his Freedom 7 Mercury capsule in a 15-minute suborbital flight, becoming America's first astronaut. In this image, he is shown being hoisted aboard a US Marine helicopter after splashdown. The flight carried him to an altitude of 116 statute miles. NASA
An exhaust cloud billowed around Launch Pad 39A at NASA's Kennedy Space Center in Florida as space shuttle Discovery lifted off to begin the STS-131 mission on April 4. The seven-member crew delivered the multi-purpose logistics module Leonardo, filled with supplies, a new crew sleeping quarters and science racks that will be transferred to the International Space Station's laboratories. NASA/Tony Gray and Tom Farrar
This view from the navigation camera on NASA's Mars Exploration Rover Opportunity shows tracks left by backing out of a wind-formed ripple after the rover's wheels had started to dig too deeply into the dust and sand of the ripple. The frames combined into this view were taken on the 1,867th Martian day, or sol, of Opportunity's mission on Mars (April 25, 2009). NASA/JPL-Caltech
A small spiral galaxy is caught between two elliptical galaxies, in this cluster called the Hickson Compact Group 90. NASA
This artist's conception shows a hypothetical young planet around a cool star. A soupy mix of potentially life-forming chemicals can be seen pooling around the base of the jagged rocks. Observations from NASA's Spitzer Space Telescope hint that planets around cool stars -the so-called M-dwarfs and brown dwarfs that are widespread throughout our galaxy - might possess a different mix of life-forming, or prebiotic, chemicals than our young Earth. Life on our planet is thought to have arisen out of a pond-scum-like mix of chemicals. Some of these chemicals are thought to have come from a planet-forming disk of gas and dust that swirled around our young sun. NASA/JPL-Caltech
On flight-day four of the STS-129 mission, a member of the crew photographed the aft section of space shuttle Atlantis through a window from aboard the International Space Station. Reflections on the window are visible in this November 2009 image. NASA
This composite image shows a small region of the Chandra Deep Field North. NASA
The Soyuz TMA-18 rocket launches from the Baikonur Cosmodrome in Kazakhstan on April 2, carrying Expedition 23 Soyuz Commander Alexander Skvortsov of Russia, Flight Engineer Mikhail Kornienko of Russia and NASA Flight Engineer Tracy Caldwell Dyson of the US to the International Space Station. NASA/Bill Ingalls
Zakariya Ismail Ahmed Hersi, a leader with the Islamic extremist group al-Shabab, surrendered to Somali police. Hersi was one of eight top al-Shabab officials the Obama administration offered a total $33 million in rewards for information leading to their capture in 2012.
ByAbdi Guled, Associated Press
A leader with the Islamic extremist group al-Shabab, who had a $3 million bounty on his head, surrendered in Somalia, a Somali intelligence official said Saturday.