NASA Space Telescope Finds Fewer Asteroids Near Earth

Pasadena, CA – New observations by NASA’s Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.

Astronomers now estimate there are roughly 19,500 — not 35,000 — mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought.
NEOWISE observations indicate that there are at least 40 percent fewer near-Earth asteroids in total that are larger than 330 feet, or 100 meters. Our solar system's four inner planets are shown in green, and our sun is in the center. Each red dot represents one asteroid. Object sizes are not to scale. (Image credit: NASA/JPL-Caltech)

However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth’s orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.

“NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population,” said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA’s Jet Propulsion Laboratory in Pasadena, CA. “It’s like a population census, where you poll a small group of people to draw conclusions about the entire country.”

WISE scanned the entire celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. NEOWISE observed more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth.

WISE captured a more accurate sample of the asteroid population than previous visible-light surveys because its infrared detectors could see both dark and light objects. It is difficult for visible-light telescopes to see the dim amounts of visible-light reflected by dark asteroids. Infrared-sensing telescopes detect an object’s heat, which is dependent on size and not reflective properties.

Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found. This fulfills the initial “Spaceguard” goal agreed to with Congress. These large asteroids are about the size of a small mountain and would have global consequences if they were to strike Earth. The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found. None of them represents a threat to Earth in the next few centuries. It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

“The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced,” said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, MA.

Long way to the chemist’s: a rough guide to distances in the universe

Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”

Douglas Adams, The Hitchhikers Guide to the Galaxy

We all know the universe is large, very large, but is it possible to really comprehend just how large it really is? Sit down, take a deep breath, and we can give it a go.

In my previous scale article, we considered the sizes of stars, and finished by imagining the sun being the size of an orange. On this scale, the nearest star to the sun, also the size of an orange, would be 2,300 kilometres away.

Even through stars can be immense on human scales, they are dwarfed by the distances between them.

On a clear night, away from the lights of civilisation, we may be able to pick out a few thousand individual stars as mere points of light.

The smooth swathe of light that accompanies them, however, is the combined light of many more distant stars. How many? It turns out the Milky Way is home to more than 200 billion stars, lots of stars like the sun, a few spectacular giants, and many, many faint dwarfs.

To get a handle on the size of the Milky Way, let’s pretend the distance across it is 3,000km, roughly the distance between Sydney and Perth.

On this scale, the separation between the sun and its nearest neighbour would be about 100 metres, whereas the diameter of the sun itself would be about a tenth the thickness of a human hair. Other than a bit of tenuous gas, there’s a lot of empty space in the Milky Way.

For much of human history, we have prided ourselves on being at the centre of the universe, but as Douglas Adams pointed out, we live in the “unfashionable end of the Western Spiral arm of the Galaxy”.

If the small town of Ceduna in South Australia, sitting roughly midway between Sydney and Perth, was the centre of the Milky Way, our sun would be orbiting 850km away, somewhere beyond Mildura in north-western Victoria (and, no, I’m not suggesting Mildura is unfashionable!)

So the Milky Way is huge, and light, traveling at 300,000 kilometres a second, takes 100,000 years to cross from side to side.

But we know that we share the universe with many other galaxies, one of the nearest being a sister galaxy to our own, the large spiral galaxy in Andromeda.

'Accelerating universe' could be just an illusion

In 1929, cosmologists discovered that the universe is expanding — that space-time, the fabric of the cosmos, is stretching. Then in 1998, light coming from exploding stars called supernovas suggested that the universe is not only expanding, but that it has recently begun expanding faster and faster; its expansion has entered an "accelerating phase." This was bad news for the fate of the cosmos: An accelerating universe is ultimately racing toward a "Big Rip," the moment at which its size will become infinite and, in a flash, everything in it will be torn apart.

The discovery was bad news for the state of cosmology, too. Because gravity pulls stuff inward rather than pushing it out, cosmologists believed that the expansion of the universe ought to be slowing down, as everything in it felt the gravitational tug of everything else. They didn't understand the mechanism that seemed to be opposing the force of gravity, so to explain their observations, they invoked the existence of "dark energy," a mysterious, invisible substance that permeates space and drives its outward expansion.

Now, a new theory suggests that the accelerating expansion of the universe is merely an illusion, akin to a mirage in the desert. The false impression results from the way our particular region of the cosmos is drifting through the rest of space, said Christos Tsagas, a cosmologist at Aristotle University of Thessaloniki in Greece. Our relative motion makes it look like the universe as a whole is expanding faster and faster, while in actuality, its expansion is slowing down — just as would be expected from what we know about gravity.

If Tsagas' theory is correct, it would rid cosmology of its biggest headache, dark energy, and it might also save the universe from its harrowing fate: the Big Rip. Instead of ripping it to bits, the universe as Tsagas space-time envisions it would just roll to a standstill, then slowly start shrinking.

Cruising through space-time
Tsagas' alternative version of events, detailed in a recent issue of the peer-reviewed journal Physical Review D, builds on a recent discovery by Alexander Kashlinsky, a cosmologist at NASA's Observational Cosmology Laboratory. In a series of papers over the past three years, Kashlinsky and his colleagues have shown that the huge region of space-time in which we live — a region at least 2.5 billion light-years across — is moving relative to the rest of the universe, and fast.

Some cosmologists remain skeptical about the newfound "dark flow," as it's called, and say that more evidence is needed to persuade them that the strange phenomenon is real. But the evidence that does exist is compelling. Based on light collected from galaxy clusters, our enormous bubble of space-time appears to be drifting at a rapid clip of up to 2 million miles per hour. No one knows why, exactly — there may be something beyond the part of the universe we can see, tugging on us — but Tsagas argues that the dark flow is skewing our perspective on the behavior of the universe as a whole.

"My article discusses how observers living inside such a large-scale 'dark flow' could arrive at the (false) conclusion that the universe is accelerating, while it is actually decelerating," Tsagas told Life's Little Mysteries. In his paper, he illustrates that dark flow would cause the space-time within our moving bubble to expand faster than the space-time outside of it (which is not accelerating). Without considering the dark flow, but just knowing that light we observe from nearby galaxies left its source more recently than light from galaxies farther away, we get the false impression that the whole of space-time recently entered an accelerating phase.

Saturn's Moon Enceladus Spreads its Influence

Chalk up one more feat for Saturn's intriguing moon Enceladus. The small, dynamic moon spews out dramatic plumes of water vapor and ice -- first seen by NASA's Cassini spacecraft in 2005. It possesses simple organic particles and may house liquid water beneath its surface. Its geyser-like jets create a gigantic halo of ice, dust and gas around Enceladus that helps feed Saturn's E ring. Now, thanks again to those icy jets, Enceladus is the only moon in our solar system known to influence substantially the chemical composition of its parent planet.

In June, the European Space Agency announced that its Herschel Space Observatory, which has important NASA contributions, had found a huge donut-shaped cloud, or torus, of water vapor created by Enceladus encircling Saturn. The torus is more than 373,000 miles (600,000 kilometers) across and about 37,000 miles (60,000 kilometers) thick. It appears to be the source of water in Saturn's upper atmosphere.

Though it is enormous, the cloud had not been seen before because water vapor is transparent at most visible wavelengths of light. But Herschel could see the cloud with its infrared detectors. "Herschel is providing dramatic new information about everything from planets in our own solar system to galaxies billions of light-years away," said Paul Goldsmith, the NASA Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The discovery of the torus around Saturn did not come as a complete surprise. NASA's Voyager and Hubble missions had given scientists hints of the existence of water-bearing clouds around Saturn. Then in 1997, the European Space Agency's Infrared Space Observatory confirmed the presence of water in Saturn's upper atmosphere. NASA's Submillimeter Wave Astronomy Satellite also observed water emission from Saturn at far-infrared wavelengths in 1999.

While a small amount of gaseous water is locked in the warm, lower layers of Saturn's atmosphere, it can't rise to the colder, higher levels. To get to the upper atmosphere, water molecules must be entering Saturn's atmosphere from somewhere in space. But from where and how? Those were mysteries until now.

Build the model and the data will come.

The answer came by combining Herschel's observations of the giant cloud of water vapor created by Enceladus' plumes with computer models that researchers had already been developing to describe the behavior of water molecules in clouds around Saturn.

One of these researchers is Tim Cassidy, a recent post-doctoral researcher at JPL who is now at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder. "What's amazing is that the model," said Cassidy, "which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren't expecting such detailed 'images' of the torus, and the match between model and data was a wonderful surprise."

The results show that, though most of the water in the torus is lost to space, some of the water molecules fall and freeze on Saturn's rings, while a small amount -- about 3 to 5 percent -- gets through the rings to Saturn's atmosphere. This is just enough to account for the water that has been observed there.

Herschel's measurements combined with the cloud models also provided new information about the rate at which water vapor is erupting out of the dark fractures, known as "tiger stripes," on Enceladus' southern polar region. Previous measurements by the Ultraviolet Imaging Spectrograph (UVIS) instrument aboard the Cassini spacecraft showed that every second the moon is ejecting about 440 pounds (200 kilograms) of water vapor.

"With the Herschel measurements of the torus from 2009 and 2010 and our cloud model, we were able to calculate a source rate for water vapor coming from Enceladus," said Cassidy. "It agrees very closely with the UVIS finding, which used a completely different method."

"We can see the water leaving Enceladus and we can detect the end product -- atomic oxygen -- in the Saturn system," said Cassini UVIS science team member Candy Hansen, of the Planetary Science Institute, Tucson, Ariz. "It's very nice with Herschel to track where it goes in the meantime."

Complete Coverage of NASA's Falling Satellite UARS

A dead NASA satellite, called the Upper Atmosphere Research Satellite (UARS), is falling uncontrolled toward Earth and is expected to crash to the ground today (Sept. 23) or Saturday. Agency officials are unable to pinpoint the exact time and location of the fall, but have said there is little risk of debris landing in populated areas. SPACE.com is providing full coverage of the UARS re-entry, including a look at the issues surrounding orbital debris and space situational awareness.

Editor's note: If you snap a photo or observe the re-entry of NASA's UARS satellite and want to share it with SPACE.com for a story or gallery, contact managing editor Tariq Malik at: tmalik@space.com.

"NASA’s decommissioned Upper Atmosphere Research Satellite fell back to Earth between 11:23 p.m. EDT Friday, Sept. 23 and 1:09 a.m. EDT Sept. 24. The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean. The precise re-entry time and location are not yet known with certainty."

Space Junk: NASA Can't Predict Re-Entry With Certainty

Re-entry of the NASA's abandoned UARS satellite into earth's atmosphere is expected in the early evening today. While NASA maintains that it will not be over North America at that time, they also insist it's too early to predict the time and location of re-entry with any certainty.

Some 26 chunks of the old NASA satellite -- roughly the size of a bus -- will be dropping straight down at hundreds of miles per hour over an area of some 500 square miles at some point Friday night.

"We believe that the risk is sufficiently low that no one needs to, to change their behaviors," NASA's Mark Matney said Thursday.

As UARS – short for Upper Atmosphere Research Satellite - enters the atmosphere, everything changes. Bit by bit, pieces will cross the threshold about 60 miles up, enter the atmosphere and then drop straight down like stones -- travelling at several hundred miles an hour depending on their shape.

The chunks will fall at different points along the satellite's path, meaning debris will cover 500 miles.

This is the largest NASA satellite to fall back to Earth uncontrolled since Skylab in 1979.

Bill Ailor, principal engineer of the Aerospace Corporation, studies incoming space junk for the Air Force. He says that some frighteningly huge pieces of other satellites have come crashing down into villages, farms-and random datelines around the planet.

"I actually think a lot of this kind stuff comes down and nobody knows what it is and just thinks it's junk and ignores it," Ailor told ABC News.

The Aerospace Corporation, a private firm that is tracking UARS, offered a more specific prediction, saying the satellite would likely come down off the coast of Chile at 6:06 p.m. EST.

We're safe! Incredible footage shows doomed NASA satellite starting its descent to Earth but experts say it will NOT hit U.S.

Nasa has said a six-ton satellite doomed to fall to Earth this week will not hit the U.S. as incredible video was captured showing the start of the spacecraft's descent.

Scientists today said that the Upper Atmospheric Research Satellite (UARS) will make its final fiery plunge on Friday afternoon when it is not due to be passing over North America.

Americans had been warned that the 20-year-old bus sized satellite could cause injuries and damage to property as it falls through the atmosphere and drops about two dozen pieces of debris on to Earth weighting up to 300lbs.

NASA set to fund space taxi systems

CAPE CANAVERAL — NASA next year will fund the development of at least two space taxi systems that could return astronauts to orbit aboard U.S. vehicles by late 2016.

The agency this week released draft terms of a contract that aims to complete designs of those systems by 2014, after which one or more would be chosen for a follow-up phase that builds and tests vehicles.

The draft request for proposals proves the agency's commitment "to outsource our space station transportation so NASA can focus its energy and resources on deep space exploration," NASA Administrator Charles Bolden said in a statement.

Potential providers of the outsourced crew flights, which would launch from the Space Coast, have a month to review and comment on the draft before a final version is released late this year.

A SpaceX spokesman said the company was still reviewing the draft language.

SpaceX is one of the four companies that shared nearly $270 million in NASA funding this year to advance designs of spacecraft able to fly people to and from the International Space Station.

Blue Origin, The Boeing Co. and Sierra Nevada Corp. Space Systems were the others.

The next contract phase intends to develop integrated transportation
systems, combining spacecraft with launch vehicles, escape systems and all the ground systems necessary to launch at least four astronauts to the station.

Expected to be awarded next summer, the next contract phase could be worth $1.6 billion between 2012 and 2014, NASA says.

But actual funding could be significantly lower than the total proposed in the Obama administration's 2012 budget.

Some companies and commercial space advocates fear limited funding and NASA's new contracting strategy could slow or derail the development program.

"From a technical standpoint (the companies) are proceeding well, but there's a concern about both the future funding and how the contracting is going to be structured in this next phase," said Jeff Foust, an industry analyst with Futron Corp.

NASA last week announced it would abandon the use of more simple Space Act Agreements in favor of federal contracts that some companies consider more costly and bureaucratic.

Neptune is *really* far away

Mike Brown is an astronomer, specifically one who studies Kuiper Belt Objects, those giant frozen iceballs that haunt the solar system out past Neptune.

In fact, Neptune’s biggest moon Triton has a lot of characteristics similar KBOs — it may be one captured by Neptune — so observing it gives an interesting opportunity for a compare-and-contrast study. So this past weekend Mike was using the Keck telescope in Hawaii to observe Triton along with its (adoptive?) parent planet, and took this fantastic image of the pair:

This false-color image shows the two worlds in the infrared, specifically at a wavelength of about 1.5 microns, twice what the human eye can see. Methane strongly absorbs this color of light, so where Neptune (in the upper left) looks dark you’re seeing lots of methane clouds, and where it’s bright there are clouds higher up, above the methane. Triton is in the lower right, and is bright because it’s covered in ice which is highly reflective.

Now this is all very pretty and interesting and sciencey, but if you know me at all you know there’s more to this story.

Mike tweeted about the image, and I oohed and ahhhed at it, of course. But then he tweeted again, saying he was also observing Jupiter’s moon Europa, but it was too bright to get good images using the monster 10-meter Keck telescope. It "saturated the detector" which is astronomer-speak for "overexposed".

Small distant galaxies host supermassive black holes

Using the Hubble Space Telescope to probe the distant universe, astronomers have found supermassive black holes growing in surprisingly small galaxies. The findings suggest that central black holes formed at an early stage in galaxy evolution.

"It's kind of a chicken or egg problem: Which came first, the supermassive black hole or the massive galaxy? This study shows that even low-mass galaxies have supermassive black holes," said Jonathan Trump, a postdoctoral researcher at the University of California, Santa Cruz. Trump is first author of the study, which has been accepted for publication in the Astrophysical Journal and is currently available online.

All massive galaxies host a central supermassive black hole, which may shine brightly as an active galactic nucleus if the black hole is pulling in nearby gas clouds. In the local universe, however, active black holes are rarely seen in small "dwarf" galaxies. The galaxies studied by Trump and his coauthors are about 10 billion light-years away, giving astronomers a view of galaxies as they appeared when the universe was less than a quarter of its current age.

"When we look 10 billion years ago, we're looking at the teenage years of the universe. So these are very small, young galaxies," Trump said.

The study, part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), used a powerful new instrument on the Hubble Space Telescope.

The "slitless grism" on Hubble's WFC3 infrared camera provided detailed information about different wavelengths of light coming from the galaxies. Spectroscopy allows researchers to spread out the light from an object into its component colors or wavelengths. With Hubble's high spatial resolution, the researchers were able to get separate spectra from the center and the outer part of each galaxy. This enabled them to identify the tell-tale emissions from a central black hole.

"This is the first study that is capable of probing for the existence of small, low-luminosity black holes back in time," said coauthor Sandra Faber, University Professor of astronomy and astrophysics at UC Santa Cruz and CANDELS principal investigator. "Up to now, observations of distant galaxies have consistently reinforced the local findings--distant black holes actively accreting in big galaxies only. We now have a big puzzle: What happened to these dwarf galaxies?"

NASA's Kepler Mission Discovers a World Orbiting Two Stars

The existence of a world with a double sunset, as portrayed in the film Star Wars more than 30 years ago, is now scientific fact. NASA's Kepler mission has made the first unambiguous detection of a circumbinary planet -- a planet orbiting two stars -- 200 light-years from Earth.

Unlike Star Wars’ Tatooine, the planet is cold, gaseous and not thought to harbor life, but its discovery demonstrates the diversity of planets in our galaxy. Previous research has hinted at the existence of circumbinary planets, but clear confirmation proved elusive. Kepler detected such a planet, known as Kepler-16b, by observing transits, where the brightness of a parent star dims from the planet crossing in front of it.

"This discovery confirms a new class of planetary systems that could harbor life," Kepler principal investigator William Borucki said. "Given that most stars in our galaxy are part of a binary system, this means the opportunities for life are much broader than if planets form only around single stars. This milestone discovery confirms a theory that scientists have had for decades but could not prove until now."

A research team led by Laurance Doyle of the SETI Institute in Mountain View, Calif., used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets. Kepler is the first NASA mission capable of finding Earth-size planets in or near the "habitable zone," the region in a planetary system where liquid water can exist on the surface of the orbiting planet.

Scientists detected the new planet in the Kepler-16 system, a pair of orbiting stars that eclipse each other from our vantage point on Earth. When the smaller star partially blocks the larger star, a primary eclipse occurs, and a secondary eclipse occurs when the smaller star is occulted, or completely blocked, by the larger star.

Memorial Image Taken on Mars on September 11, 2011

PASADENA, Calif. -- A view of a memorial to victims of the Sept. 11, 2001, attacks on the World Trade Center towers was taken on Mars yesterday, on the 10th anniversary of the attacks.

The memorial, made from aluminum recovered from the site of the twin towers in weeks following the attacks, serves as a cable guard on a tool on NASA's Mars Exploration Rover Opportunity and bears an image of the American flag.

The view combining exposures from two cameras on the rover is online at: http://www.nasa.gov/mission_pages/mer/multimedia/pia14750.html .

The memorial is on the rover's rock abrasion tool, which was being made in September 2001 by workers at Honeybee Robotics in lower Manhattan, less than a mile from the World Trade Center.

Opportunity's panoramic camera and navigation camera photographed the tool on Sept. 11, 2011, during the 2,713th Martian day of the rover's work on Mars. Opportunity completed its three-month prime mission on Mars in April 2004 and has worked for more than seven years since then in bonus extended missions.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington. Additional information about Opportunity and its rover twin, Spirit, is online at http://marsrovers.jpl.nasa.gov and http://www.nasa.gov/rovers

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Shirley Williams plunges NHS reforms into fresh turmoil

The future of the government's health reforms has been plunged into fresh doubt as the Liberal Democrat peer Shirley Williams raises new concerns, and secret emails reveal plans to hand over the running of up to 20 hospitals to overseas companies. The revelations come as MPs prepare to return to Westminster on Tuesday for what promises to be a crucial stage of the flagship health and social care bill.

Baroness Williams, one of the original leaders of a Lib Dem rebellion against health secretary Andrew Lansley's plans – who appeared to have been pacified after changes were made over the summer – said she had new doubts, having re-examined the proposals. "Despite the great efforts made by Nick Clegg and Paul Burstow [the Lib Dem health minister], I still have huge concerns about the bill. The battle is far from over," she said.

Writing in Sunday's Observer, Williams raises a series of issues that she says must be addressed. Chief among them is a legal doubt as to whether the secretary of state will any longer be bound to deliver "a comprehensive health service for the people of England, free at the point of need".

Some critics of Lansley believe the Tories are bent on a mission to privatise the NHS, gradually handing it to the private sector. They fear that moves to end the legal obligation on the secretary of state to deliver comprehensive services may be a deliberate part of the process.

Concerns that ministers want more private involvement will be strengthened by details of email exchanges involving senior health officials about handing the management of 10 to 20 NHS hospitals to international private companies. The emails, which were made public following a freedom of information request and were obtained by non-profit-making investigations company Spinwatch, show that officials have been planning since late last year to bring in international companies. This is despite repeated insistences by both David Cameron and Nick Clegg that there will be no privatisation of the NHS. On 16 May, Cameron said: "Let me make clear: there will be no privatisation." Clegg said: "Yes to reform of the NHS, but no to the privatisation of the NHS."

One of the emails released by the department shows that officials at the private sector firm McKinsey, which advises ministers, were in active discussion about bringing in overseas firms to take over up to 20 hospitals in return for contracts running into hundreds of millions of pounds. An email to Ian Dalton, head of provider development at the Department of Health, who is heavily involved in the reform programme, in November last year talks about "interest in new solution for 10-20 hospitals but starting from a mindset of one at a time with various political constraints".

The emails show that McKinsey is acting as a broker between the department and "international players" that are bidding to run the NHS. The documents even lay out some of the conditions required by "international hospital provider groups" for running NHS hospitals. "International players can do an initiative if 500 million revenue [is] on the table." They also need to have "a free hand on staff management". The NHS would be allowed to "keep real estate and pensions".

The Department of Health attempted to play down the significance of the emails, saying they were referring to what might be done if any one hospital trust asked for the private sector to become involved in running a failing hospital. A spokesman said: "It is not unusual for the Department of Health to hold meetings with external organisations. Any decisions to involve organisations, such as the independent sector or foundation trusts, in running the management of NHS hospitals would be led by the NHS locally and in all cases NHS staff and assets would remain wholly owned by the NHS."

But a spokesman for the public service union Unison said: "Regardless of what Cameron and Clegg say in public, it is clear that behind the scenes the government is planning to privatise the NHS. Private companies will only run hospitals if they see a profit in it. This, together with lifting the cap off the number of private patients NHS hospitals can treat, will completely change the culture of the NHS. It will be profits before patients.

"We demand that the government come clean on their plans. If this is true, patient choice is a complete sham. The move to any qualified provider is clearly about creating a market for private companies. Any MP who votes for the health and social care bill is voting for the end of the NHS."

Williams also raises worries about the extent to which the role of the private sector is being expanded. "I am not against a private element in the NHS, which may bring innovatory ideas and good practice, provided it is within the framework of a public service …" she writes. "But why have they tried to get away from the NHS as a public service, among the most efficient, least expensive and fairest anywhere in the world? Why have they been bewitched by a flawed US system that is unable to provide a universal service and is very expensive indeed?"

She adds: "The remarkable vision of the 1945 Attlee government, of a public service free at the point of need for all the people of England, should not be allowed to die."

John Healey, Labour's shadow health secretary, said: "As David Cameron's government railroads the health bill through parliament, MPs are being denied their constitutional role to properly scrutinise his plans for the NHS. The prime minister has already done a political fix with Nick Clegg on the health bill, and now he's trying to force it through with a procedural fix."