Jan 11 2012

From The Space Library

RELEASE: 12-012 HUBBLE SOLVES MYSTERY ON SOURCE OF SUPERNOVA IN NEARBY GALAXY

WASHINGTON -- Using NASA's Hubble Space Telescope, astronomers have solved a longstanding mystery on the type of star, or so-called progenitor, which caused a supernova seen in a nearby galaxy. The finding yields new observational data for pinpointing one of several scenarios that trigger such outbursts. Based on previous observations from ground-based telescopes, astronomers knew the supernova class, called a Type Ia, created a remnant named SNR 0509-67.5, which lies 170,000 light-years away in the Large Magellanic Cloud galaxy. Theoretically, this kind of supernova explosion is caused by a star spilling material onto a white dwarf companion, the compact remnant of a normal star, until it sets off one of the most powerful explosions in the universe. Astronomers failed to find any remnant of the companion star, however, and concluded that the common scenario did not apply in this case, although it is still a viable theory for other Type Ia supernovae. "We know Hubble has the sensitivity necessary to detect the faintest white dwarf remnants that could have caused such explosions," said lead investigator Bradley Schaefer of Louisiana State University (LSU) in Baton Rouge. "The logic here is the same as the famous quote from Sherlock Holmes: 'when you have eliminated the impossible, whatever remains, however improbable, must be the truth.'" The cause of SNR 0509-67.5 can be explained best by two tightly orbiting white dwarf stars spiraling closer and closer until they collided and exploded. For four decades, the search for Type Ia supernovae progenitors has been a key question in astrophysics. The problem has taken on special importance during the last decade with Type Ia supernovae being the premier tools for measuring the accelerating universe. Type Ia supernovae release tremendous energy, in which the light produced is often brighter than an entire galaxy of stars. The problem has been to identify the type of star system that pushes the white dwarf's mass over the edge and triggers this type of explosion. Many possibilities have been suggested, but most require that a companion star near the exploding white dwarf be left behind after the explosion. Therefore, a possible way to distinguish between the various progenitor models has been to look deep in the center of an old supernova remnant to search for the ex-companion star. In 2010, Schaefer and Ashley Pagnotta of LSU were preparing a proposal to look for any faint ex-companion stars in the center of four supernova remnants in the Large Magellanic Cloud when they discovered the Hubble Space Telescope already had taken the desired image of one of their target remnants, SNR 0509-67.5, for the Hubble Heritage program, which collects images of especially photogenic astronomical targets. In analyzing the central region, they found it to be completely empty of stars down to the limit of the faintest objects Hubble can detect in the photos. Schaefer suggests the best explanation left is the so-called "double degenerate model" in which two white dwarfs collide. The results are being reported today at the meeting of the American Astronomical Society in Austin, Texas. A paper on the results will be published in the Jan. 12 issue of the journal Nature. There are no recorded observations of the star exploding. However, researchers at the Space Telescope Science Institute in Baltimore, Md. have identified light from the supernova that was reflected off of interstellar dust, delaying its arrival at Earth by 400 years. This delay, called a light echo of the supernova explosion also allowed the astronomers to measure the spectral signature of the light from the explosion. By virtue of the color signature, astronomers were able to deduce it was a Type Ia supernova. Because the remnant appears as a nice symmetric shell or bubble, the geometric center can be determined accurately. These properties make SNR 0509-67.5 an ideal target to search for ex-companions. The young age also means that any surviving stars have not moved far from the site of the explosion. The team plans to look at other supernova remnants in the Large Magellenic Cloud to further test their observations. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

RELEASE: 12-013 NASA'S KEPLER MISSION FINDS THREE SMALLEST EXOPLANETS

WASHINGTON -- Astronomers using data from NASA's Kepler mission have discovered the three smallest planets yet detected orbiting a star beyond our sun. The planets orbit a single star, called KOI-961, and are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars. All three planets are thought to be rocky like Earth, but orbit close to their star. That makes them too hot to be in the habitable zone, which is the region where liquid water could exist. Of the more than 700 planets confirmed to orbit other stars -- called exoplanets -- only a handful are known to be rocky. "Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us." Kepler searches for planets by continuously monitoring more than 150,000 stars, looking for telltale dips in their brightness caused by crossing, or transiting, planets. At least three transits are required to verify a signal as a planet. Follow-up observations from ground-based telescopes also are needed to confirm the discoveries. The latest discovery comes from a team led by astronomers at the California Institute of Technology in Pasadena. The team used data publicly released by the Kepler mission, along with follow-up observations from the Palomar Observatory, near San Diego, and the W.M. Keck Observatory atop Mauna Kea in Hawaii. Their measurements dramatically revised the sizes of the planets from what originally was estimated. The three planets are very close to their star, taking less than two days to orbit around it. The KOI-961 star is a red dwarf with a diameter one-sixth that of our sun, making it just 70 percent bigger than Jupiter. "This is the tiniest solar system found so far," said John Johnson, the principal investigator of the research from NASA's Exoplanet Science Institute at the California Institute of Technology in Pasadena. "It's actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy." Red dwarfs are the most common kind of star in our Milky Way galaxy. The discovery of three rocky planets around one red dwarf suggests that the galaxy could be teeming with similar rocky planets. "These types of systems could be ubiquitous in the universe," said Phil Muirhead, lead author of the new study from Caltech. "This is a really exciting time for planet hunters." The discovery follows a string of recent milestones for the Kepler mission. In December 2011, scientists announced the mission's first confirmed planet in the habitable zone of a sun-like star: a planet 2.4 times the size of Earth called Kepler-22b. Later in the month, the team announced the discovery of the first Earth-size planets orbiting a sun-like star outside our solar system, called Kepler-20e and Kepler-20f. For the latest discovery, the team obtained the sizes of the three planets called KOI-961.01, KOI-961.02 and KOI-961.03 with the help of a well-studied twin star to KOI-961, or Barnard's Star. By better understanding the KOI-961 star, they then could determine how big the planets must be to have caused the observed dips in starlight. In addition to the Kepler observations and ground-based telescope measurements, the team used modeling techniques to confirm the planet discoveries. Prior to these confirmed planets, only six other planets had been confirmed using the Kepler public data. NASA's Ames Research Center in Moffett Field, Calif., manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission's development.

RELEASE: 12-015 NASA ASSOCIATE ADMINISTRATOR FOR HUMAN SPACEFLIGHT RECEIVES AIAA VON KARMAN AWARD

WASHINGTON -- The American Institute for Aeronautics and Astronautics (AIAA) has honored Bill Gerstenmaier, associate administrator for the Human Exploration and Operations Mission Directorate with the Von Karman Lectureship in Astronautics. The award is given annually to someone who has performed notably and distinguished themselves technically in the field of astronautics. Gerstenmaier was recognized for his 30 years of accomplishment in human spaceflight, culminating in the leadership of the Space Shuttle and International Space Station Programs. As part of the award, Gerstenmaier delivered the speech "Global Outpost in Space: A Platform for Discovery -- The International Space Station" Wednesday during the AIAA's 50th Aerospace Sciences Meeting in Nashville, Tenn. The award honors Theodore von Karman, an early astronautics pioneer responsible for breakthroughs in understanding supersonic and hypersonic airflow characterization and the value of the swept wing design. "It is truly an honor to receive this special recognition from the AIAA and to have the opportunity to speak at this year's conference about the International Space Station and its importance to the future of human exploration," Gerstenmaier said. "Serving as a test bed for research and new technologies, the space station is the centerpiece for space operations and a stepping stone toward future exploration destinations." Gerstenmaier began his NASA career in 1977 at the Glenn Research Center in Cleveland performing aeronautical research, after receiving a B.S. aeronautical engineering from Purdue University. In 1988, he became head of the Orbital Maneuvering Vehicle (OMV) Operations Office, Systems Division at the Johnson Space Center. Gerstenmaier also served as Shuttle/Mir Program Operations Manager from 1995 to 1997. In 1998, he became manager of Space Shuttle Program Integration. In December 2000, he was named deputy manager of the International Space Station Program, becoming the associate administrator for space operations in 2005. Currently, he heads the agency's Human Exploration and Operations Mission Directorate.