NASA satellite plunges into Pacific off California

Source: Yahoo 7 news

WASHINGTON (AFP) - A bus-sized US satellite that hurtled unpredictably toward Earth crossed over Africa and the northern Atlantic before likely plunging into the Pacific Ocean off California, NASA said on Saturday.

 

The six-tonne Upper Atmosphere Research Satellite (UARS) fell from the sky between 11:23 pm Friday and 1:09 am Saturday (0323-0509 GMT Saturday), the space agency said, but there were no sightings or reliable accounts of damage.

"We have got no reports of anyone seeing anything that we believe are credible," NASA chief orbital scientist Nick Johnson said, noting that the "vast majority" of its flight track had been over water.

The best and latest estimate, made by the Joint Space Operations Center at Vandenberg Air Force Base in California at two hours before entry, put the re-entry time at 0416 GMT.
"If the re-entry point was at 0416 GMT, then all that debris wound up in the Pacific Ocean," said Johnson.

NASA had maintained that the risk of the satellite causing harm to people on land was remote.
Since the satellite was circling Earth just about every hour and a half before it fell, it covered a vast amount of territory in its final loop, according to a map NASA posted on its website at nasa.gov/uars.
It started off on the eastern coast of Africa before going over the Indian Ocean, up the Pacific over Canada, over the northern Atlantic and then down western Africa before ending in the Indian Ocean again, Johnson said.

The final resting place of the 20-year-old satellite's remains could stay shrouded in mystery.
"We may never know," Johnson said, noting that NASA relies on the public as well as aviation and naval personnel to report evidence of satellite debris.

The satellite was expected to break into 26 pieces as it plummeted toward Earth, with surviving parts including titanium fuel tanks, beryllium housing and stainless steel batteries and wheel rims.
"Twenty-six satellite components, weighing a total of about 1,200 pounds (550 kilograms), could have survived the fiery re-entry and reach the surface of Earth. However, NASA is not aware of any reports of injury or property damage," the space agency said.

UARS was launched in 1991 to measure the ozone layer and other atmospheric conditions and was decommissioned in 2005. The last of its fuel was used up to change its orbit so it would return to Earth sooner.

Influence from solar activity and the tumbling motion of the satellite made it difficult to narrow down where it would penetrate Earth's atmosphere, and it was expected to leave a 500-mile (800-kilometer) debris footprint.

UARS was the biggest NASA spacecraft to fall since the 85-ton Skylab crashed into western Australia in 1979.

A 40-tonne Russian space station Salyut 7 scattered over Argentina in 1991 after an uncontrolled return to Earth.

Despite the media frenzy that surrounded the UARS landing, orbital debris experts said space junk actually falls from the sky regularly, even weekly, according to Johnson.

"This is not an unusual event. We do not always know where these re-entries occur," he said.

'Small chance' satellite may hit Australia

Source: yahoo 7 NewsBy Matthew Sadler, AAP
September 23, 2011, 5:17 pm

Australians may want to keep an eye on the sky this weekend with space junk set to crash back to Earth in the next 24 hours.

Scientists say there is a small chance debris from a satellite due to crash to Earth this weekend could land in Australia.

NASA's Upper Atmosphere Research Satellite (UARS), which weighs more than five tonnes, is expected to re-enter the Earth's atmosphere at 1058 AEST on Saturday.

The US-based Centre for Orbital and Re-entry Debris Studies estimates that re-entry could occur up to seven hours before or after this time.
The satellite's flight path includes several passes over Australia.

The Australian Space News website said the satellite poses a negligible threat to life and property on Earth.

"Most of the satellite will burn up on re-entry, with perhaps as many as 26 stronger or harder small pieces surviving to reach the surface," editor Jonathan Nally said in a statement.

"But with the majority of the Earth comprising oceans or uninhabited (or very sparsely populated) remote regions, the chances are overwhelming that any pieces of UARS that survive re-entry will fall harmlessly and never be seen again."

The UARS was launched in September 1991 and was decommissioned in December 2005.
After the satellite's productive days were over, NASA deliberately placed it into an orbit about 200 kilometres lower than its operational orbit.

"This was done to accelerate its eventual demise and means it is re-entering the atmosphere 20 years earlier than it would otherwise have done," explains Mr Nally.

"This was a very responsible thing to do. The longer a spacecraft stays in orbit, the more chance it has of being hit by other orbital debris, leading to a destructive breakup and therefore more bits of debris."

Debris from SkyLab, another satellite which plunged to Earth, was scattered over parts of Western Australia in 1979. Skylab weighed about 77 tonnes, many times more than the UARS.

Dr Alice Gorman of the Department of Archaeology at Flinders University in Adelaide said the re-entry of the UARS brings back memories of Skylab 32 years ago.

"There is the same exaggeration of the hazard through the media, public anxiety as the advance warning allows for speculation, and a lack of understanding of what the risks actually are," Dr Gorman said in a statement.

"Should it land in Australia, we might expect the same rush for souvenirs as we saw with Skylab, as anything that has been in space has a special meaning on Earth."

Thousands of ticking time bomb stars set to explode

Look and read this important article about the universe

Source: space.com and yahoo 7 news

Thousands of ticking time bomb stars set to explode at any moment are hidden throughout our galaxy, according to a new study.

When massive stars reach the end of their lives, they can explode in fiery fits called supernovas. Astronomers calculate that about three stars explode in a specific category of supernova called Type 1a every thousand years in the Milky Way.

That means that within a few thousand light-years of Earth there should be dozens of stars on the verge of exploding.

Yet while scientists know these stars are out there, they've had trouble so far identifying which stars are nearing the explosion point. But the new research offers hope of finding the ticking time bombs more easily by looking for features that had previously been ignored.

"We haven’t found one of these 'time bomb' stars yet in the Milky Way, but this research suggests that we've been looking for the wrong signs," astrophysicist Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement. "Our work points to a new way of searching for supernova precursors."

Unsolved mysteries

Di Stefano and her colleagues offer a new model for how these stars explode that could explain some niggling unsolved mysteries.

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The reigning theory behind Type 1a supernovas is that they are caused when old, dense stars called white dwarfs slowly steal mass from nearby companion stars until they reach a tipping point, becoming too massive to fight against the inward pull of gravity, and collapse.

This weight limit, about 1.4 times the mass of the sun, is called the Chandrasekhar mass.
But if that is the case, scientists would expect to find these companion stars left over after supernovas fade from sight.

They also predict small amounts of hydrogen and helium gas would have been left nearby, representing material that wasn't sucked into the white dwarf, or that was dislodged from the companion in the explosion.

Amazing space photos. Photo: Getty Images

Yet none of these smoking gun clues appear to be present around known supernovas.
'''Slowing down'''
Perhaps, Di Stefano and her colleagues propose, white dwarfs are able to reach the Chandrasekhar mass but postpone the inevitable by spinning quickly.

As a star gobbles up more mass, it also increases its angular momentum, which causes it to spin up. This increased spin can act as a stabilizing force, allowing the white dwarf to tip the scales over the Chandrasekhar mass without exploding.

After the star stops eating its neighbor's mass, however, it will gradually slow down, and eventually succumb to gravity in a supernova.

Yet the spinning effect could give the star a buffer, perhaps of up to a billion years, between when the white dwarf stops accreting mass, and when it explodes. During this lag, the leftover gas from the companion star may dissipate, and the companion could evolve into a white dwarf itself.

Bomb squad

The new model suggests a new tack for hunting impending supernovas. According to the research, astronomers could start to look for white dwarf stars that have already reached the Chandrasekhar limit, and are in the process of spinning down. [Video: Supernovas: Destroyers and Creators]
"We don’t know of any super-Chandrasekhar-mass white dwarfs in the Milky Way yet, but we're looking forward to hunting them out," said co-author Rasmus Voss of Radboud University Nijmegen in the Netherlands.

The researchers reported their findings in the Sept. 1 issue of The Astrophysical Journal Letters.

An out-of-this-world view. Photo: Getty Images

'Invisible' alien planet discovered

Impacting news from NASA's Kepler telescope was detected new planets in the universe UJWQ2TFPABYK

Source: Yahoo 7 News
space.com
September 9, 2011, 2:22 pm

For the first time, scientists have definitively discovered an "invisible" alien planet by noticing how its gravity affects the orbit of a neighboring world, a new study reports.
NASA's Kepler space telescope detected both alien planets, which are known as Kepler-19b and Kepler-19c. Kepler spotted 19b as it passed in front of, or transited, its host star. Researchers then inferred the existence of 19c after observing that 19b's transits periodically came a little later or earlier than expected. The gravity of 19c tugs on 19b, changing its orbit.

The discovery of Kepler-19c marks the first time this method — known as transit timing variation, or TTV — has robustly found an exoplanet, researchers said. But it almost certainly won't be the last.
"My expectation is that this method will be applied dozens of times, if not more, for other candidates in the Kepler mission," said study lead author Sarah Ballard, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Finding two new planets

The Kepler spacecraft launched in March 2009. It typically hunts for alien worlds by measuring the telltale dips in a star's brightness caused when a planet crosses the star's face from the telescope's perspective, blocking some of its light.

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Kepler has been incredibly successful using this so-called transit method, spotting 1,235 candidate alien planets in its first four months of operation. That's the way it detected Kepler-19b, a world 650 light-years away from Earth in the constellation Lyra.

Kepler-19b has a diameter about 2.2 times that of Earth, researchers said, and orbits 8.4 million miles (13.5 million kilometers) from its parent star. The planet likely has a surface temperature around 900 degrees Fahrenheit (482 degrees Celsius).

Kepler-19b transits its host star once every nine days and seven hours. But that number isn't constant, Ballard and her team found; transits can occur up to five minutes early or five minutes late. That variation told them another planet was tugging on 19b, alternately speeding it up and slowing it down.

In our own solar system, scientists used similar methods to predict the existence of the planet Neptune. Astronomers noticed that Uranus did not orbit the sun exactly as expected, and surmised that an unseen planet was pulling on it. This prediction was borne out when telescopes confirmed Neptune in 1846.

Researchers know little about Kepler-19c at the moment. It takes the alien world 160 days or less to zip around its host star, and 19c's mass could range from a few times that of Earth to six times that of Jupiter, researchers said.

But 19c should start coming into clearer focus soon.

"It's a mystery world, but of course we don't expect it to remain a mystery," study co-author David Charbonneau, also of the Harvard-Smithsonian Center for Astrophysics, told SPACE.com in an email. "Kepler, and large ground-based telescopes, should help us figure out its true identity soon enough!"
The study will be published in The Astrophysical Journal.

A first for a new method

The new study isn't the first to report evidence of a new alien planet using the TTV method. Last year, for example, a different research team announced the possible discovery of a planet called WASP-3c using the technique.

But WASP-3c is still somewhat ambiguous, researchers said.
"The authors consider that result tentative, though, and are collecting more data to confirm that there are timing variations," study co-author Daniel Fabrycky, of the University of California, Santa Cruz, told SPACE.com in an email. "The detection is much more certain in our case, as the data come from a single instrument and nearly every transit has been detected over a few cycles of the signal."
Ballard voiced similar sentiments, saying other potential TTV exoplanet finds — such as another possible world in the WASP-10 star system — aren't quite definitive.

"We are just claiming that the Kepler-19 system is the first robust discovery," Ballard told SPACE.com. "The detection we have is a better-sampled one, and it's also higher signal to noise."
Further, she added, in all other potential TTV finds, the "perturbed" alien planet has been a gas giant orbiting extremely close to its parent star — a so-called "hot Jupiter." But the Kepler mission has shown that hot Jupiters tend to be singletons, circling their stars alone.

"It puts doubt in my mind about the likelihood of an additional perturbing planet in a hot Jupiter system," Ballard said. "I'm not saying it's impossible, but it makes it a little more unlikely."
That's in contrast to Kepler-19b, which is a so-called "super-Earth" just 2.2 times wider than our own planet.

Hunting for alien Earths

Kepler's first TTV exoplanet discovery is in the books, but many more could be coming. Charbonneau, for example, estimated that Kepler might eventually discover hundreds of planets using the technique.

Many of these finds would likely not be possible using the traditional transit method, which requires a precise alignment of star, planet and spacecraft to work, he added.

The TTV technique is also sensitive enough to find smaller planets — those that are closer to Earth-size, some of which may even be Earth-like.

"That is the promise of transit timing variations," Ballard said. "I do believe it could discover Earth-mass planets, to say the least. Whether they're Earth-like, I don't know. That would require a lot more study."