Atlantis rolls back
Battered by an intense hail storm six days earlier, space shuttle Atlantis retreated off launch pad 39A and returned to the cavernous Vehicle Assembly Building on March 4 to undergo thorough inspections and repairs.
STS-112: ISS expansion
Atlantis made a week-long visit to the International Space Station in October 2002 that began the outward expansion of the outpost's truss backbone. Attachment of the 14.5-ton Starboard 1 segment was primary objective of the STS-112 mission. The astronauts tell the story of the flight in this post-flight movie.
Hail delays Atlantis
Launch of space shuttle Atlantis is postponed after golf ball-sized hail from a severe storm damaged the foam insulation on the external fuel tank. NASA announces the delay and plans to return the shuttle to the Vehicle Assembly Building for repairs.
STS-116: ISS re-wiring
Spacewalking astronauts on the December 2006 flight of shuttle Discovery performed a delicate re-wiring of the International Space Station's electrical system and retracted a stubborn solar array wing. The work accomplished critical steps in preparing the station to power the upcoming international science laboratory modules. Some members of the STS-116 crew narrate the highlights of the mission in this post-flight film.
STS-111: ISS arm gets new mobility
Shuttle Endeavour's visit to the space station in June 2002 brought up the Expedition 5 long-duration resident crew, a load of supplies and the Mobile Base System to serve as the platform for moving the station's robotic arm up and down the truss backbone. The shuttle crew also performed some surgery on the robot arm by replacing a failed joint. The crew narrates the highlights of STS-111 in this post-flight film.
Delta 2 launches THEMIS
The United Launch Alliance Delta 2 rocket roared away from Cape Canaveral Saturday carrying a quintet of NASA probes that seek to understand the physics behind auroral displays.
STS-117: Astronauts meet the press
The STS-117 astronauts meet the press during the traditional pre-flight news conference held at the Johnson Space Center a month prior to launch. The six-person crew will deliver and activate a solar-power module for the International Space Station.
A hot start might explain geysers on Enceladus NASA/JPL NEWS RELEASE Posted: March 12, 2007
A hot start billions of years ago might have set into motion the forces that power geysers on Saturn's moon Enceladus.
"Deep inside Enceladus, our model indicates we've got an organic brew, a heat source and liquid water, all key ingredients for life," said Dr. Dennis Matson, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "And while no one is claiming that we have found life by any means, we probably have evidence for a place that might be hospitable to life."
Credit: NASA/JPL/Space Science Institute
Since NASA's Voyager spacecraft first returned images of the moon's snowy white surface, scientists have suspected Enceladus had to have something unusual happening within that shell. Cameras on NASA's Cassini orbiter seemed to confirm that suspicion in 2005 when they spotted geysers on Enceladus ejecting water vapor and ice crystals from its south polar region. The challenge for researchers has been to figure out how this small ice ball could produce the levels of heat needed to fuel such eruptions.
A new model suggests the rapid decay of radioactive elements within Enceladus shortly after it formed may have jump-started the long-term heating of the moon's interior that continues today. The model provides support for another recent, related finding, which indicates that Enceladus' icy plumes contain molecules that require elevated temperatures to form.
"Enceladus is a very small body, and it's made almost entirely of ice and rock. The puzzle is how the moon developed a warm core," said Dr. Julie Castillo, the lead scientist developing the new model at JPL. "The only way to achieve such high temperatures at Enceladus is through the very rapid decay of some radioactive species."
The hot start model suggests Enceladus began as a mixed-up ball of ice and rock that contained rapidly decaying radioactive isotopes of aluminum and iron. The decomposition of those isotopes over a period of about 7 million years would produce enormous amounts of heat. This would result in the consolidation of rocky material at the core surrounded by a shell of ice. According to the theory, the remaining, more slowly decaying radioactivity in the core could continue to warm and melt the moon's interior for billions of years, along with tidal forces from Saturn's gravitational tug.
The ice jets of Enceladus send particles streaming into space hundreds of kilometers above the south pole of this spectacularly active moon. Credit: NASA/JPL/Space Science Institute
Scientists have also found the model helpful in explaining how Enceladus might have produced the chemicals in the plume, as measured by Cassini's ion and neutral mass spectrometer. Matson is lead author of a new study of the plume's composition, which appears in the April issue of the journal Icarus. Although the plume is predominantly made up of water vapor, the spectrometer also detected within the plume minor amounts of gaseous nitrogen, methane, carbon dioxide, propane and acetylene.
Scientists were particularly surprised by the nitrogen because they don't think it could have been part of Enceladus' original makeup. Instead, Matson's team suggests it is the product of the decomposition of ammonia deep within the moon, where the warm core and surrounding liquid water meet.
The thermal decomposition of ammonia would require temperatures as high as 577 degrees Celsius (1070 degrees Fahrenheit), depending on whether catalysts such as clay minerals are present. And while the long-term decay of radioactive species and current tidal forces alone cannot account for such high temperatures, with the help of the hot start model, they can.
The scalding conditions are also favorable for the formation of simple hydrocarbon chains, basic building blocks of life, which Cassini's spectrometer detected in small amounts within Enceladus' plume. The team concludes that so far, all the findings and the hot start model indicate that a warm, organic-rich mixture was produced below the surface of Enceladus and might still be present today, making the moon a promising kitchen for the cooking of primordial soup.
To gather more information about the chemistry within Enceladus, the team plans to directly measure the gas emanating from the plume during a flyby scheduled for March 2008.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL.