Angling Saturn

The Cassini spacecraft takes an angled view toward Saturn, showing the southern reaches of the planet with the rings on a dramatic diagonal.

North on Saturn is up and rotated 16 degrees to the left. This view looks toward the southern, unilluminated side of the rings from about 14 degrees below the ringplane. The rings cast wide shadows on the planet's southern hemisphere.

The moon Enceladus (313 miles, or 504 kilometers across) appears as a small, bright speck in the lower left of the image.

The image was taken with the Cassini spacecraft wide-angle camera on June 15, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.8 million miles (2.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 72 degrees. Image scale is 11 miles (17 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

Image credit: NASA/JPL-Caltech/Space Science Institute

NASA'S Chandra Shows Milky Way is Surrounded by Halo of Hot Gas

J.D. Harrington

Headquarters, Washington

202-358-5241

j.d.harrington@nasa.gov

 

Peter Edmonds

Chandra X-ray Center, Cambridge, Mass.

617-571-7279

pedmonds@cfa.harvard.edu

WASHINGTON -- Astronomers have used NASA's Chandra X-ray Observatory to find evidence our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The estimated mass of the halo is comparable to the mass of all the stars in the galaxy.

If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the "missing baryon" problem for the galaxy.

Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos. Measurements of extremely distant gas halos and galaxies indicate the baryonic matter present when the universe was only a few billion years old represented about one-sixth the mass and density of the existing unobservable, or dark, matter. In the current epoch, about 10 billion years later, a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for.

In a recent study, a team of five astronomers used data from Chandra, the European Space Agency's XMM-Newton space observatory and Japan's Suzaku satellite to set limits on the temperature, extent and mass of the hot gas halo. Chandra observed eight bright X-ray sources located far beyond the galaxy at distances of hundreds of millions of light-years. The data revealed X-rays from these distant sources are absorbed selectively by oxygen ions in the vicinity of the galaxy. The scientists determined the temperature of the absorbing halo is between 1 million and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun.

Other studies have shown that the Milky Way and other galaxies are embedded in warm gas with temperatures between 100,000 and 1 million kelvins. Studies have indicated the presence of a hotter gas with a temperature greater than 1 million kelvins. This new research provides evidence the hot gas halo enveloping the Milky Way is much more massive than the warm gas halo.

"We know the gas is around the galaxy, and we know how hot it is," said Anjali Gupta, lead author of The Astrophysical Journal paper describing the research. "The big question is, how large is the halo, and how massive is it?"

To begin to answer this question, the authors supplemented Chandra data on the amount of absorption produced by the oxygen ions with XMM-Newton and Suzaku data on the X-rays emitted by the gas halo. They concluded that the mass of the gas is equivalent to the mass in more than 10 billion suns, perhaps as large as 60 billion suns.

"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus. "It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large."

The estimated mass depends on factors such as the amount of oxygen relative to hydrogen, which is the dominant element in the gas. Nevertheless, the estimation represents an important step in solving the case of the missing baryons, a mystery that has puzzled astronomers for more than a decade.

Although there are uncertainties, the work by Gupta and colleagues provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy. The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection.

The paper describing these results was published in the Sept. 1 issue of The Astrophysical Journal. Other co-authors were Yair Krongold of Universidad Nacional Autonoma de Mexico in Mexico City; Fabrizio Nicastro of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; and Massimiliano Galeazzi of University of Miami in Coral Gables, Fla.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.

For Chandra images, multimedia and related materials, visit http://www.nasa.gov/chandra.

For an additional interactive image, podcast and video on the finding, visit http://chandra.si.edu.

- end -

Coverage Set for Space Station Departure of European Cargo Ship

Joshua Buck

Headquarters, Washington          

202-358-1100

jbuck@nasa.gov

 

Kelly Humphries

Johnson Space Center, Houston

281-483-5111

kelly.o.humphries@nasa.gov

WASHINGTON -- The departure of the third European Space Agency Automated Transfer Vehicle (ATV-3) cargo spacecraft from the International Space Station will be broadcast live on NASA Television beginning at 6:15 p.m. EDT, Tuesday, Sept. 25.

The 13-ton "Edoardo Amaldi," named for the 20th-century Italian physicist regarded as one of the fathers of European spaceflight, launched from Kourou, French Guiana, on March 23. It arrived at the space station March 28 with several tons of supplies and experiments for the station's crew.

Now loaded with items no longer needed on the station, ATV-3 will undock from the aft docking port of the station's Russian Zvezda service module at 6:35 p.m., Sept. 25. The craft will back away from the orbiting laboratory to a safe distance for an engine firing that will enable it to make a planned destructive return through Earth's atmosphere.

ATV-3 will carry the Re-entry Breakup Recorder (REBR) as it descends into Earth's atmosphere. REBR is a system that records data during the re-entry and breakup of the vehicle and returns the data for analysis. Understanding how vehicles behave during re-entry can enhance design efficiencies and safety; potentially remove the need for deorbit propulsion, which could decrease cost and complexity and increase mission life of spacecraft; and could minimize hazards to people and property if spacecraft became uncontrollable and re-entered randomly.

For NASA TV streaming video, downlink and scheduling information, visit http://www.nasa.gov/ntv.

For International Space Station information, visit http://www.nasa.gov/station.

- end -

STS-122 Heads to the Pad: A Tribute to Alan Poindexter

In this image from December 2008, the STS-122 mission crew members stride out of the Operations and Checkout Building, eager to ride to the launch pad and take their seats in space shuttle Atlantis. On the left, front to back, are Alan Poindexter, followed by Leland Melvin, Stanley Love and Leopold Eyharts. On the right, front to back, are Commander Steve Frick, followed by Rex Walheim and Hans Schlegel. Schlegel and Eyharts represent the European Space Agency.

Poindexter died on Sunday, July 1, 2012, while vacationing with his family.

A Navy Captain, he was accepted to the Astronaut Corps in 1998. During his career with NASA, Poindexter commanded the STS-131 space shuttle Discovery mission to the International Space Station in 2010, delivering more than 13,000 pounds of hardware and equipment. He also served as the pilot of the STS-122 mission, which delivered and installed the European Space Agency's Columbus laboratory on the station in 2008. He also served as a spacecraft communicator, or CAPCOM, for multiple missions.

Poindexter retired from NASA in 2010 and returned to serve in the United States Navy as Dean of Students at the Naval Postgraduate School.

Image Credit: NASA/Kim Shiflett

Picture Perfect Landing

The Soyuz TMA-03M spacecraft is seen as it lands with Expedition 31 Commander Oleg Kononenko of Russia and Flight Engineers Don Pettit of NASA and Andre Kuipers of the European Space Agency in a remote area near the town of Zhezkazgan, Kazakhstan, on Sunday, July 1, 2012.

Pettit, Kononenko and Kuipers returned from more than six months onboard the International Space Station where they served as members of the Expedition 30 and 31 crews.

Image Credit: NASA/Bill Ingalls