Origin Of Key Cosmic Explosions Still A Mystery

by Staff Writers
Cambridge MA (SPX) Jul 13, 2010
When a star explodes as a supernova, it shines so brightly that it can be seen from millions of light-years away. One particular supernova variety - Type Ia - brightens and dims so predictably that astronomers use them to measure the universe's expansion.

The resulting discovery of dark energy and the accelerating universe rewrote our understanding of the cosmos. Yet the origin of these supernovae, which have proved so useful, remains unknown.

"The question of what causes a Type Ia supernova is one of the great unsolved mysteries in astronomy," says Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics (CfA).

Astronomers have very strong evidence that Type Ia supernovae come from exploding stellar remnants called white dwarfs. To detonate, the white dwarf must gain mass until it reaches a tipping point and can no longer support itself.

There are two leading scenarios for the intermediate step from stable white dwarf to supernova, both of which require a companion star. In the first possibility, a white dwarf swallows gas blowing from a neighboring giant star. In the second possibility, two white dwarfs collide and merge. To establish which option is correct (or at least more common), astronomers look for evidence of these binary systems.

Given the average rate of supernovae, scientists can estimate how many pre-supernova white dwarfs should exist in a galaxy. But the search for these progenitors has turned up mostly empty-handed.

To hunt for accreting white dwarfs, astronomers looked for X-rays of a particular energy, produced when gas hitting the star's surface undergoes nuclear fusion. A typical galaxy should contain hundreds of such "super-soft" X-ray sources. Instead we see only a handful. As a result, a recent paper suggested that the alternative, merger scenario was the source of Type Ia supernovae, at least in many galaxies.

That conclusion relies on the assumption that accreting white dwarfs will appear as super-soft X-ray sources when the incoming matter experiences nuclear fusion. Di Stefano and her colleagues have argued that the data do not support this hypothesis.

In a new paper, Di Stefano takes the work a step further. She points out that a merger-induced supernova would also be preceded by an epoch during which a white dwarf accretes matter that should undergo nuclear fusion.

White dwarfs are produced when stars age, and different stars age at different rates. Any close double white-dwarf system will pass through a phase in which the first-formed white dwarf gains and burns matter from its slower-aging companion. If these white dwarfs produce X-rays, then we should find roughly a hundred times as many super-soft X-ray sources as we do.

Since both scenarios - an accretion-driven explosion and a merger-driven explosion - involve accretion and fusion at some point, the lack of super-soft X-ray sources would seem to rule out both types of progenitor.

The alternative proposed by Di Stefano is that the white dwarfs are not luminous at X-ray wavelengths for long stretches of time. Perhaps material surrounding a white dwarf can absorb X-rays, or accreting white dwarfs might emit most of their energy at other wavelengths.

If this is the correct explanation, says Di Stefano, "we must devise new methods to search for the elusive progenitors of Type Ia supernovae."

Di Stefano's paper has been accepted for publication in The Astrophysical Journal and is available online.Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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ILS Successfully Launches The Echostar XV

by Staff Writers
Baikonur, Kazakhstan (SPX) Jul 12, 2010
International Launch Services (ILS) has successfully carried the EchoStar XV satellite into orbit on an ILS Proton for DISH Network. EchoStar Satellite Services manages DISH Network's space programs and will begin in-orbit testing of the satellite later this month.

The ILS Proton launched from Pad 39 at the Cosmodrome at 00:40 local time (10 July, 14:40 EDT; 18:40 GMT). After a 9 hour 13 minute mission, the Breeze M successfully released the EchoStar XV satellite into geosynchronous transfer orbit. This is a high energy orbit that will enable the satellite to have approximately 20 years of service life.

The EchoStar XV launch was the 24th successful consecutive Proton launch in 24 months, and the second ILS Proton launch of a DISH Network satellite this year.

The satellite was built by Space Systems/Loral (SS/L) on the flight-proven 1300 platform, weighing 5,521 kg at separation. EchoStar XV, located at 61.5 degrees West, is poised to provide expanded services, including HD programming, for DISH Network's more than 14 million direct-to-home television subscribers. EchoStar XV was the 15th SS/L satellite launched on an ILS Proton.

This was the 358th launch for Proton since its inaugural flight in 1965, and the 61st ILS Proton launch overall. The Proton Breeze M launch vehicle was developed and built by Khrunichev Research and Production Space Center of Moscow, one of the pillars of the Russian space industry and the majority shareholder in ILS.

"The fact that this is the second ILS Proton launch for DISH Network this year shows the strength of our relationship with our customer, EchoStar. The ILS and Khrunichev team continues to be committed to expanding DISH Network's business, and are proud to have launched EchoStar XV on schedule, less than four months after we launched EchoStar XIV," said ILS President, Frank McKenna.

"The launch of EchoStar XV was executed well ahead of our original schedule. This schedule assurance is what we rely upon and what sets ILS apart. The performance of the Proton Breeze M launch vehicle provides increased performance-and this results in a longer spacecraft mission lifetime. As EchoStar and our customer, DISH Network, continue to grow, we look forward to future launches on ILS Proton," said Rohan Zaveri, vice president of Space Programs for EchoStar.

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NASA And Partners Assign Crews For Upcoming ISS Missions

File image.

by Staff Writers
Washington DC (SPX) Jul 09, 2010
NASA and its international partners, the Russia Federal Space Agency and the Japan Aerospace Exploration Agency (JAXA), have assigned four new International Space Station crews.

The crews include NASA astronauts Joe Acaba, Sunita Williams and Kevin Ford. Acaba was born in Inglewood, Calif., and raised in Anaheim, Calif. Williams was born in Euclid, Ohio, but considers Needham, Mass., her hometown. Ford was born in Portland, Ind., and considers Montpelier, Ind., his hometown.

Russian cosmonaut Oleg Konenenko, European Space Agency astronaut Andre Kuipers and NASA astronaut Don Pettit were previously announced as Expedition 31 crew members. Expedition 31 begins when Soyuz 28 undocks from the station in March 2012.

Soyuz 30 is set to launch in April 2012 with the following crew members who have been added to Expedition 31:

+ NASA astronaut Joe Acaba, flight engineer

+ Russian cosmonaut Gennady Padalka, flight engineer

+ Russian cosmonaut Konstantin Valkov, flight engineer (Soyuz 30)

Expedition 32 will begin with the undocking of Soyuz 29 in May 2012. Soyuz 31 is set to launch in June 2012 with the crew members listed below who will join the three station residents already aboard.

+ Russian cosmonaut Gennady Padalka, station commander (Soyuz 30)

+ NASA astronaut Joe Acaba, flight engineer (Soyuz 30)

+ Russian cosmonaut Konstantin Valkov, flight engineer (Soyuz 30)

+ NASA astronaut Sunita Williams, flight engineer (Soyuz 31)

+ Russian cosmonaut Yuri Malenchenko, flight engineer (Soyuz 31)

+ JAXA astronaut Akihiko Hoshide, flight engineer (Soyuz 31)

Expedition 33 will begin with the undocking of Soyuz 30 in September 2012. Soyuz 32 is set to launch in October 2012 with the crew members listed below who will join the three station residents already aboard.

+ NASA astronaut Sunita Williams, station commander

+ Russian cosmonaut Yuri Malenchenko, flight engineer

+ JAXA astronaut Akihiko Hoshide, flight engineer

+ NASA astronaut Kevin Ford, flight engineer (Soyuz 32)

+ Russian cosmonaut Oleg Novitskiy, flight engineer (Soyuz 32)

+ Russian cosmonaut Evgeny Tarelkin, flight engineer (Soyuz 32)

Expedition 34 will begin with the undocking of Soyuz 31 in November 2012.

+ NASA astronaut Kevin Ford, station commander (Soyuz 32)

+ Russian cosmonaut Oleg Novitskiy, flight engineer (Soyuz 32)

+ Russian cosmonaut Evgeny Tarelkin, flight engineer (Soyuz 32)

Three additional crew members for Expedition 34 have yet to be assigned. They will travel to and from the station aboard Soyuz 33.

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Planck Takes It All In

This image of the microwave sky was synthesized using data spanning the range of light frequencies detected by Planck. Image credit: ESA, HFI and LFI consortia (2010).

by Staff Writers
Paris, France (ESA) Jul 08, 2010
A new image from the Planck mission shows what it's been up to for the past year - surveying the entire sky for clues to our universal origins. Planck, a European Space Agency mission with significant participation from NASA, has been busily scanning the whole sky at nine frequencies of light, with the ultimate goal of isolating fluctuations in the cosmic microwave background - or light from the beginning of time.

These fluctuations represent the seeds from which structure in our universe evolved.

"This image shows both our Milky Way galaxy and the universe 380,000 years after the Big Bang in one expansive view," said Charles Lawrence, the NASA project scientist for the mission at the Jet Propulsion Laboratory in Pasadena, Calif.

"The radiation from the Milky Way traveled hundreds or thousands of years to reach us, while the radiation from the early universe traveled 13.7 billion years to reach us. What we see in this picture happened at very different times."

The picture has been color-coded to show how the sky looks over the range of frequencies observed by Planck. Planck detects light that we can't see with our eyes - light with low frequencies ranging from 30 to 857 gigahertz. The disk of the Milky Way galaxy, seen edge-on from Earth's perspective, is the bright band running horizontally down the middle.

Diffuse, huge clouds of gas and dust relatively close to us in our galaxy can be seen above and below this band. The cosmic microwave background is apparent as the grainy structure towards the top and bottom of the image.

Scientists want to study this grainy signature across the entire sky, which means seeing through the "fog" of our Milky Way. The Planck teams are busy now removing this foreground fog, a meticulous process akin to identifying and removing all the hay in a haystack to reveal the needle within.

The process will take about two more years, with the first processed data being released to the scientific community toward the end of 2012.

The U.S. Planck team is helping with this task, with a primary tool being the Franklin supercomputer at the National Energy Research Scientific Computing Center in Berkeley, Calif. One of the world's fastest computers, Franklin will handle the most computationally intensive analysis jobs for the Planck team worldwide.

Meanwhile, this fog is not something to discard. It contains a treasure trove of information about our galaxy and its structure, in addition to many other galaxies. The U.S. Planck team is responsible for releasing the first batch of this astronomy data, called the Early Release Compact Source Catalogue, an event schedule for January 2011.

Planck will continue surveying the sky until at least the end of January 2012, completing almost five all-sky scans.

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NASA releases videogame, Moonbase Alpha

by Staff Writers
Washington (AFP) July 6, 2010
NASA has abandoned plans to return to the Moon but videogamers can explore the lunar landscape with a free new online game released by the US space agency.

"Moonbase Alpha" allows players to join an exploration team in a futuristic 3D settlement on the south pole of the Moon.

"In Moonbase Alpha, you assume the exciting role of an astronaut working to further human expansion and research," NASA said in an explanation of the game.

"Returning from a research expedition, you witness a meteorite impact that cripples the life support capability of the settlement.

"With precious minutes ticking away, you and your team must repair and replace equipment in order to restore the oxygen production to the settlement," NASA said

To accomplish their mission, players of the "first-person explorer" game use an interactive command center, lunar rover and mobile robotic repair units.

"Proper use and optimal allocation of their available resources are key to the team's overall success," NASA said.

NASA said the game is designed to "engage and educate students about agency technologies, job opportunities and the future of space exploration."

Moonbase Alpha can be played by one or up to six players. NASA said it is a precursor to a planned NASA-based "multiplayer online game project."

The game is available at MoonbaseAlphaGame.com.

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Cassini Takes A Dive Through A Titantic Atmosphere

by Staff Writers
Pasadena CA (JPL) Jul 07, 2010
As American schoolchildren head out to pools for a summer splash, NASA's Cassini spacecraft will be taking its own deep plunge through the Titan atmosphere this week.

The altitude for the upcoming Titan flyby, whose closest approach occurs in the evening of July 6, Pacific and Eastern time (or shortly after midnight on July 7, Coordinated Universal Time) will be about 125 kilometers (78 miles) higher than the super-low flyby of June 21. The altitude of this flyby - 1,005 kilometers (624 miles) - is still considered a low dip into Titan's atmosphere. Cassini will not go lower again until May 2012.

During closest approach, Cassini's ion and neutral mass spectrometer will be sniffing out the chemical composition of Titan's atmosphere to refine estimates of the densities of nitrogen and methane there.

The radar instrument will be mapping an area south of the dark region known as Senkyo and the Belet sand seas. It is an area that had not been well studied by radar until this flyby.

Because the geometry of this flyby is similar to the previous one, the magnetometer and other instruments measuring the magnetic bubble around Saturn will be conducting similar experiments.

Though the magnetometer will be too high to detect any whisper of an internal magnetic field from Titan - which was the focus of the search on the last flyby - scientists will be looking into the interaction of Titan's atmosphere with the magnetic bubble around Saturn.

This latest flyby is dubbed "T71," though planning changes early in the orbital tour have made this the 72nd targeted flyby of Titan.

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Philae And Rosetta Gear Up For Asteroid Lutetia

Artist's conception of Philae lander on Comet 67P/Churyumov-Gerasimenko.

by Staff Writers
Paris, France (ESA) Jul 06, 2010
The Rosetta orbiter, which carries the DLR lander Philae, has completed more than two thirds of its journey to the comet Churyumov-Gerasimenko. The most comprehensive cometary investigation ever, the mission will deliver DLR's Philae lander to the comet's surface for in situ studies. The spacecraft and lander are due to close in on 21 Lutetia, a large Main Belt Asteroid on 10 July.

Since launch, Rosetta has travelled roughly 5 billion kilometres. The solar-powered orbiter was launched on an Ariane 5 in 2004. It has used several gravity assist manoeuvres - three from Earth and one from Mars - to gain the necessary momentum, refine its trajectory and match the orbit of the comet once it reaches the outer Solar System.

The orbiter will circle the comet and, after delivering Philae to the surface, eventually escort the comet on its way to the Sun.

At 100 kilometres in size, 21 Lutetia is one of the larger Main Belt Asteroids. The lander will investigate whether the asteroid has a magnetic field and an exosphere, and study their characteristics.

Philae will first be switched on between 12:45 and 15:05 CEST on 7 July so the team can prepare the lander for activities around closest approach. The lander will perform science observations on 10 July.

Philae to help uncover Lutetia's true nature
This observation sequence will take place during the asteroid flyby itself, with the lander switching on at 08:45 CEST on 10 July. It will be on throughout the flyby; closest approach is scheduled for 17:45 CEST. The lander and orbiter will be 3169 kilometres from Lutetia, according to recent estimates.

Three instruments on the lander will be switched on during the flyby:

+ The Rosetta Lander Magnetometer and Plasma Monitor, ROMAP, is a magnetometer and plasma monitor that will study the local magnetic field and monitor the interactions between the comet and the solar wind.

+ MODULUS PTOLEMY is one of two evolved gas analysers, which obtains accurate measurements of isotopic ratios of light elements by heating solid samples to release volatiles.

+ The Cometary Sampling and Composition experiment, COSAC, is also an evolved gas analyser. It detects and identifies complex organic molecules from their elemental and molecular composition.

ROMAP will be measuring continuously while it is on (between 7:06 am and 5:50 pm CEST) and will be looking for interactions between the asteroid's magnetic field and the solar wind. COSAC and PTOLEMY will perform a series of 'sniff' measurements (five by PTOLEMY and two by COSAC), which will be used to help determine whether or not the asteroid has an exosphere.

Scientists are not sure whether Lutetia is an M-class (metallic) asteroid or if it is a C-type (chondrite). The lander observations will help to ascertain this by studying the composition of the possible exosphere, and by studying the asteroid's thermal history and the presence of magnetic minerals. This will help identify Lutetia's age and asteroid type.

The orbiter began refining its path to Lutetia using its optical navigation cameras on 31 May. Unusually, the lander will be illuminated by the Sun around the time of the Luteita flyby. This is why the team will put the lander into a special thermal configuration to keep it within its nominal thermal range.

Operating Philae
At closest approach, Rosetta will be travelling past Lutetia at 15 kilometres per second - or 54,000 kilometres per hour. This is comparable to sending a radio-controlled car down an autobahn at roughly 100 kilometres per hour to take pictures of a stationary object it passes in the next lane (just about six metres away), with the exact timing of the commands fixed a month in advance.

If that doesn't sound hard enough, the planning would also have to be done from so far away that the autobahn would be twice as far as the Moon is from Earth.

The DLR team at the Philae Lander Control Centre in Cologne works closely with ESA's European Space Operations Centre, ESOC, where the Rosetta Mission Control Centre is located.

The Lander Control Centre is responsible for operating the lander, but the Lander Operations Team cannot command the lander directly themselves in such a way as to push a button and have a command sent.

The Mission Control Centre is informed of the commands to be sent to the lander by the team in Cologne via a formal interface, and the Rosetta Mission Operations Team in ESOC uploads them to the orbiter. The orbiter stores these commands in its mission timeline and then relays these commands to the lander at a specified time; finally, the lander executes those commands at another specified time.

Using a similar method to that employed for telecommanding, the lander passes its telemetry to the orbiter, which then transmits it back to Earth. It is worth noting that the commands and telemetry are radio transmissions, which travel at the speed of light - but even so, the enormous distance between Rosetta and Earth means it will take 25 minutes for these messages to travel to or from the spacecraft.

Thus, when a command is sent, it takes almost an hour before confirmation of receipt of that command sent by the spacecraft arrives back on Earth.

Because of this delay, all commands are stored in the spacecraft's mission timeline well in advance of an event; indeed, the commands for the flyby are already on board. The spacecraft will execute them automatically at the relevant time, although it would still be possible to send additional commands in the event of an emergency.

During the flyby on 10 July, the team will be monitoring the lander telemetry very closely from the control room and will keep an eye on the lander's health. Since all the commands for the flyby are already in the orbiter's mission timeline, the team does not expect to have to send any commands during the event.

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