For the last eight months, the sunspots that usually freckle the Sun have virtually disappeared, and nobody knows when they鈥檒l return, or how plentiful they鈥檒l be. The speed at which the next breakout of spots occurs should reveal how active 鈥� and potentially damaging to Earth鈥檚 satellites and power grids 鈥� the new solar cycle will be.

Sunspots are cooler, darker regions caused by the Sun鈥檚 magnetic field ripping through the star鈥檚 surface. They vary in number 鈥� going from a minimum to a maximum and back to a minimum again 鈥� about every 11 years, the same timescale on which the Sun鈥檚 magnetic poles reverse direction.

Several dozen sunspots can appear every day during periods of maximum solar activity. But only a small handful of sunspots have occurred during all of 2008 to date, suggesting the Sun鈥檚 activity is now at a minimum.

For a while, it even seemed like August would mark the first time since 1913 that no sunspots were seen for an entire month, according to record-keepers at the National Oceanic and Atmospheric Administration.

But when the final tally was made by the international authority on sunspots, the in Brussels, Belgium, one dark blip on 21 and 22 August was large enough to make the count.

Until the spots reappear, researchers say they will not know whether this 11-year solar cycle will bring heavier- or lighter-than-normal activity, or be able to resolve a raging debate about the mechanisms driving solar weather.

Anaemic cycle?

The current absence of sunspots does not necessarily foretell an anaemic cycle of solar activity to come, Leif Svalgaard of Stanford University says. Instead, sunspot watchers are waiting to see how fast the sunspot count starts to climb once they do reappear.

The quicker they return, the more active the solar weather will be for the following decade. 鈥淭he big [cycles], they start out with a bang. One month, there may be none, the next month they may be all over the place,鈥� Svalgaard told New 女生小视频.

Some space meteorologists predict that the new cycle will be relatively quiet.

The prediction is based on theories suggesting magnetic fields that sink into the Sun near its poles are transported relatively quickly back to the Sun鈥檚 surface, where they produce sunspots. Since observations show low magnetic field activity at the poles, the idea is that the coming solar cycle will be unspectacular.

鈥榃orst nightmare鈥�

Others theorise that magnetic fields travel for decades deep within the Sun鈥檚 interior before returning to punch holes in its surface, creating sunspots. These forecasters predict that a strong wave of sunspots is right around the corner.

鈥淎s scientists, we鈥檙e anxiously awaiting [the return of sunspots] because this is really going to help us weed out our different theories,鈥� says David Hathaway of NASA鈥檚 Marshall Space Flight Center in Huntsville, Alabama.

鈥淭he worst nightmare is that it鈥檚 right smack in the middle,鈥� Svalgaard says of the sunspots鈥� rate of return. 鈥淭hen all we know is [the models] are all bad.鈥�

Either way, the ramifications could be immense. Periods of strong solar magnetic activity and plentiful sunspots can interrupt communications and overload electricity grids on Earth.

Lengthy periods of low sunspot activity, on the other hand, such as the one between 1645 and 1715 called the Maunder Minimum, have been associated with cooler climate. What鈥檚 to come in this case? We鈥檒l have to wait and see.

The shifting, shimmering Northern Lights might be more ordered than anyone realised. New observations suggest that, contrary to expectations, some of the colourful light shows appear to be polarised, with their electromagnetic waves lined up in a common orientation.

If confirmed, the discovery will provide a powerful new tool to understand the Earth鈥檚 magnetic field and the atmospheres of other planets.

Auroras shine because charged particles from the Sun, such as electrons, get captured by the Earth鈥檚 magnetic field. The field channels the particles into the atmosphere above the Earth鈥檚 poles, where they collide with gas particles, causing them to glow.

But scientists have long doubted the process could lead to polarised auroras. That鈥檚 because there were thought to be too many atmospheric collisions for the resulting electromagnetic waves to be neatly aligned.

In fact, when Australian researcher Robert Duncan announced in 1958 that he had detected one instance of polarisation in the nocturnal display after many nights of searching, his findings were disputed and the observation was dismissed within a year.

Now, scientists working on the Norwegian island of Spitsbergen far north in the Arctic have found new evidence of the phenomenon.

Polar rain

Jean Lilensten of the National Center for Scientific Research in Grenoble, France, and colleagues used a custom-built photopolarimeter to watch the sky at various times over the last two winters. They found that at an altitude of 220 kilometres, electrons from space excite oxygen atoms to emit polarised red light.

The degree of polarisation is small 鈥� amounting to just 5% of the aurora鈥檚 light. But Lilensten says it is still significant and can shed light on the physics of the process, pointing out that the polarisation of sunlight is just 1% or so. 鈥淭he 5% degree polarisation 鈥� this is a lot in geophysical conditions,鈥� Lilensten told New 女生小视频.

Lilensten鈥檚 team believes the polarisation is brought about by a stream of electrons from the Sun known as 鈥�polar rain鈥�.

Magnetic corridor

While conventional auroras form in a doughnut-shaped zone around each pole, these relatively low-energy polar rain electrons arrive directly over the poles, travelling down a magnetic corridor that can open up when the Sun鈥檚 magnetic field connects directly to the Earth鈥檚.

鈥淭he energy of the polar rain is quite constant,鈥� says Lilensten, explaining that this leads to a larger fraction of polarised light.

The observations could provide an invaluable tool for monitoring the Earth鈥檚 magnetic field lines, which are not visible to any instruments. They will also shed light on atmospheric conditions on Earth and elsewhere 鈥� Mars and Venus, for example, are both known to have oxygen in their atmospheres.

Yongliang Zhang of Johns Hopkins University in Laurel, Maryland, US, says the new work is very interesting.

But he says some questions remain. He says the polarisation might be caused by something other than the incoming electrons from space, such as the activity of oxygen ions in the atmosphere.

Reflective ice

The observations were also puzzling, he says, because the polarisation was only seen with very low-energy auroral activity 鈥� too faint, in fact, to appear to the naked eye. 鈥淲hen the auroral activity goes up, normally you would think polarisation activity would be increased,鈥� Zhang told New 女生小视频.

Lilensten says the team ruled out other potential sources for the polarisation 鈥� such as ground reflections or light pollution 鈥� by using computer models and studying the spectrum of the light.

But he acknowledges that one possible source of error does remain. Tiny, reflective ice particles in the atmosphere might produce the polarisation signal. The researchers hope to confirm the ice particles are not a factor by taking observations about 15 km above them with a stratospheric balloon.

Journal reference: (vol 35, L08804)

The Mars rover Opportunity is having trouble yet again with a faulty motor in the shoulder of its robotic arm, and the consequences could be dismal for the four-year-old mission.

NASA engineers have halted the ageing explorer en route to Cape Verde in Victoria Crater while they try to understand the cause and impacts of this latest problem.

The motor, which controls the robotic arm鈥檚 sideways motion, had begun stalling occasionally two and a half years ago. Engineers discovered they could ease the problem by boosting power to the arm, but just in case it seized up more seriously, they decided to unfold the arm each night so it would not get stuck within the rover.

The problem became more serious on April 14, when the arm stalled shortly after being unfolded, much earlier than in the case of previous stalls.

鈥淚t could be fairly serious 鈥� if we can鈥檛 move that shoulder joint it could restrict the possible motion鈥� of the arm, also called the Instrument Deployment Device, says project scientist Bruce Banerdt of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, CA, US.

The arm carries Opportunity鈥檚 cache of tools for determining the chemical and mineralogical content of Martian rocks. 鈥淚f we did lose the ability to use the instruments on the IDD, that would be a pretty big blow to the mission,鈥� he told New 女生小视频.

But JPL鈥檚 John Callas, project manager for the twin rovers Opportunity and Spirit, says all hope is not lost. 鈥淓ven under the worst-case scenario for this motor, Opportunity still has the capability to do some contact science with the arm.鈥�

Bumpy Ride

When Opportunity鈥檚 problem arose, the rover was making a challenging drive around the inside of Victoria Crater to the base of a promontory known as Cape Verde.

鈥淚t鈥檚 a little bit difficult 鈥� sitting on a 20掳 angle sideways and trying to make progress as you go along in an irregular surface that has pockets of dirt that have been collected,鈥� Banerdt says.

But after making good headway, Opportunity was thwarted by one particularly difficult patch. The rover was in the process of backing out and trying another route when the arm failed.

Now, Banerdt says, Opportunity will remain in the sand until engineers complete more diagnostic tests and decide whether to risk leaving the arm outstretched as the rover drives or try to stow it again, as usual.

鈥淭he arm was not designed to take that kind of stress, if it鈥檚 kind of hanging out in the breeze or the rover is going over a bump,鈥� he says.

女生小视频s were expecting to rely heavily on the robotic arm鈥檚 tools over the next few months as Opportunity visited Cape Verde and moved on to study the cobbles dotting the plain outside Victoria Crater.

Bathtub ring

The rover had just come from studying rock layers exposed within the crater walls, including one particularly eye-catching band that formed a bright 鈥�bathtub ring鈥� around the crater鈥檚 inside.

But despite driving more than 40 metres down into the crater 鈥� representing a vertical depth of about 8 metres 鈥� Opportunity spotted nothing but the same type of sulphate sandstone that it had seen everywhere else on its journey, Banerdt says.

Even layers of different colours appeared only to have either a courser or smoother texture that reflected light differently. Still, scientists are now studying the spectrometry data to learn if the layers also contain minute chemical differences that would reveal clues about the region鈥檚 ancient history.

鈥淭here鈥檚 all kind of pieces to this puzzle, and there鈥檚 a lot of them that haven鈥檛 clicked into place yet,鈥� Banerdt says.

女生小视频s have learned from looking at the crater walls that hundreds of millions or even billions of years ago the area was an active dune field, with winds moving either north to south, or south to north 鈥� much as they do now.

A dangerous winter

On the other side of the planet, the rover Spirit is sitting on the edge of an outcrop known as Home Plate, where it will stay for at least six more months until the Sun moves higher in the sky.

Though Spirit is still using its scientific instruments, engineers will soon turn them off so the rover can put all its energy toward keeping itself warm through the depths of winter, which will come in late June.

鈥淩ight now the solar panels are about 35 percent of their normal efficiency because of dust coverage, which is pretty bad,鈥� Banerdt says. 鈥淚t will be well lower than what Spirit has ever seen but analogous to what Opportunity was dealing with during the dust storm. We鈥檙e keeping our fingers crossed.鈥�

Mars Rovers 鈥� Mars is full of surprises; learn more in our continually updated .

Even though Japan鈥檚 problem-plagued Hayabusa spacecraft is now on its return trip to Earth, it might never complete the journey. A catastrophic failure of its last remaining reaction wheel, which helps point the craft, might prevent it from reaching the Earth to drop a capsule into the atmosphere, mission members say.

Hayabusa was meant to collect samples from the asteroid Itokawa by firing pellets into the surface of the 535-metre-long rock and scooping up the resulting debris. But data from two landings in November 2005 suggest the pellets never fired because the craft鈥檚 onboard computer sent conflicting signals to its collection instruments.

Still, mission officials hoped to bring the spacecraft back to Earth in case some asteroid dust had slipped into its collection chamber by chance. If it completes the trip, it is expected to drop a capsule in the Australian outback in June 2010.

But Hayabusa鈥檚 project manager, Jun鈥檌chiro Kawaguchi, told New 女生小视频 that if any other systems break down, it could be fatal to the mission. He is particularly concerned about the spacecraft鈥檚 last remaining reaction wheel. 鈥淲e are eager to make it return with our best efforts, but the situation is not optimistic,鈥� he says.

Weak thrusters

Mission managers are now pointing Hayabusa using jets of xenon gas from the craft鈥檚 ion propulsion system. The relatively weak thrusters, which use electric fields to accelerate a beam of xenon ions, were originally designed only to propel the craft forwards on its 2-billion-kilometre round trip to Itokawa.

Without the ability to aim the spacecraft, mission engineers could not maintain communication with Hayabusa or keep it on the right trajectory to return to Earth. The team lost contact once before, in late 2005, and regained it only three months later. A glitch this time would probably be permanent.

Despite these worries, mission planners could still pull off a safe landing, according to Hayabusa team member Don Yeomans of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California, US. 鈥淚 wouldn鈥檛 bet against them 鈥� they鈥檙e doing pretty well,鈥� he says.

Indeed, the team from the Japanese Aerospace Exploration Agency has managed to keep Hayabusa flying despite a long list of near-catastrophic failures, including the leaks of critical fuel and a temporary loss of contact with the spacecraft that caused its return to Earth to be delayed by three years.

Plucky spacecraft

鈥淵eah, the spacecraft is hurting,鈥� Yeomans says. 鈥淚t鈥檚 a credit to the Japanese that they鈥檝e had some work-arounds. It鈥檚 the little spacecraft that could.鈥�

During the mission, engineers also suffered the disappearance of the miniature robot Minerva, which was supposed to hop across the surface of asteroid surface but instead was accidentally released to drift off into space.

Despite these setbacks, Hayabusa was successful in returning 鈥渟tunning images鈥� of Itokawa, Yeomans says. The pictures and other data collected by the craft revealed an unexpectedly crater-free surface and loosely compacted body.

鈥淚t seems to be what we call a rubble pile, an object that was blasted apart and is held together by not much more than its own gravity,鈥� he says.

鈥淢ostly we鈥檙e just marking time until the sample capsule gets back,鈥� Yeomans adds. 鈥淗opefully the sample will get back.鈥�

Asteroids 鈥� Learn more in our .

How does one weigh a supermassive black hole that is anywhere between a million and a billion times the mass of the Sun? The answer could be as easy as taking a snapshot of its surrounding galaxy.

A team of astronomers has concluded that the larger the black hole at the centre of a spiral galaxy, the tighter the galaxy鈥檚 arms wrap around itself. If correct, the simple relationship would give researchers an easy way to learn about black holes up to 8 billion light years away 鈥� thousands of times farther than most black hole masses can be resolved today.

Marc Seigar of the University of Arkansas in Little Rock, US, and colleagues studied 37 spiral galaxies, including the Milky Way and our neighbour, Andromeda.

Those with the smallest black holes had their arms outstretched at angles of as much as 43掳 (scroll down for image), while those with the biggest black holes hugged themselves much more tightly, with as few as 7掳 separating the galaxies鈥� arms from their cores.

It鈥檚 not the first time that astronomers have noticed a link between supermassive black holes, which they can鈥檛 see, and their surrounding galaxies, which they can.

Speedy stars

Previously, researchers have observed that the bulge of stars forming the galaxy鈥檚 centre is larger for more massive black holes. But 鈥渢o estimate the bulge mass at very high distances, there would be a lot of uncertainty,鈥� Seigar told New 女生小视频.

Astronomers also weigh black holes by studying the motions of stars that orbit around them 鈥� the bigger the black hole, the faster the stars move. But the stars can only be resolved in galaxies a few tens of millions of light years away.

鈥淎s you get farther away, basically that method gets harder to use 鈥� even with the Hubble Space Telescope 鈥� because you don鈥檛 have the resolution to do it,鈥� Seigar told New 女生小视频. 鈥淭he spiral arms are just easier to detect at very high distances.鈥�

Indeed, the most distant black holes hold the most allure for astronomers because they are being seen as they were in the early universe, Seigar says.

Dark matter

As a result, they can shed light on how galaxies evolve, as well as on a cosmological component that is even harder to pin down 鈥� dark matter. Galaxies are thought to take shape in giant cradles of the mysterious matter, which is detected by its gravitational pull on visible matter.

The gravitational attraction of dark matter may also dictate the reach of a galaxy鈥檚 arms, the heft of its central bulge and the mass of its black hole, Seigar says, although the theory has yet to be proven.

Seigar鈥檚 team will next study more distant active black holes, which are in the process of devouring their surroundings. These are easier to measure than their tranquil cousins but rarer, and currently can only be weighed if they are within about 5 billion light years from Earth.

The researchers want to make sure that the simple relationship they found between spirals and black hole mass does not change as the galaxies evolve over time. Says Seigar: 鈥淲e have to make sure the correlation itself doesn鈥檛 evolve.鈥�

Journal reference: (forthcoming)

Video: Expert technicians make giant telescope鈥檚 mirror

Imagine having to melt 24 tonnes of glass to make an 8.4-metre-wide telescope mirror. Now imagine if that were the easy part of the project.

The mirror-making for the ambitious Large Synoptic Survey Telescope (LSST) project is now underway, but the greatest challenges still lie ahead.

By 2015, the new $400 million observatory should begin recording the entire night sky every three days from its perch in the Chilean Andes. It will provide a vast treasure trove of data invaluable for tracking near-Earth asteroids, watching supernovae explosions and mulling the mysteries of dark matter and dark energy.

Before then, though, LSST project managers must perfect how to gather the faint starlight, capture it for posterity and share the images with the world.

Spin Cycle

At the telescope鈥檚 heart is its primary mirror. Its unusual design will incorporate a tertiary mirror ground into the middle, as if someone had taken a giant-sized ice cream scoop from the glass surface. To accommodate this extra depth, the mirror was built especially thick 鈥� almost a third of a metre at its centre, and about a metre at its edge.

Late in March, workers at the University of Arizona鈥檚 Steward Observatory Mirror Laboratory fired up the furnaces around the mirror mould, heating the glass until it melted to the consistency of heavy molasses.

Then, they set the mould spinning, giving the mirror surface a gentle curve and eliminating the need for nearly 14 tonnes of extra glass that would otherwise have been ground away.

With the melting and rough shaping now complete, the mirror will rest in a computer-controlled cool-down for the next three months to avoid generating any stresses within the glass.

Trickier than Hubble

So far, the mirror appears to be in good shape, says LSST Project Manager Don Sweeney. 鈥淲e鈥檒l only know for sure after it鈥檚 down to room temperature,鈥� he told New 女生小视频. 鈥淏ut everything looks very, very good; it鈥檚 very unlikely that there will be a problem.鈥�

For mirror lab director Roger Angel, though, the hard work is just beginning. Once the mirror cools, it will have to be ground and polished to gather light perfectly.

鈥淭here鈥檚 quite a lot of testing there to make sure we get the curves right,鈥� he told New 女生小视频. 鈥淭he mirrors that we make now are way more difficult in testing than the Hubble mirror.鈥�

Wide-eyed

With its vast primary mirror, 3.4-metre secondary mirror and sizable tertiary mirror, the LSST will be able to see a patch of sky about 40 times the size of the Full Moon (other large telescopes can only see a fraction of the Moon at one time).

Capturing and storing such large images is not easy, though. Developing sensors for the camera, which has a 60-centimetre-wide focal plane covered in 10-micron pixels, is one of the biggest challenges left to be solved before the telescope is up and running.

Another is developing a way to process and publish the 30 terabytes of data captured each night. 鈥淪cientifically, it is the world鈥檚 biggest database,鈥� Sweeney says. 鈥淵ou have to process all of that data as fast as it comes up, because if you get behind, you鈥檒l never catch up.鈥�

On the heels of a grim congressional report about problems with the development of the space shuttle鈥檚 successor, NASA says it has everything under control with at least one potentially fatal issue 鈥� a violent shaking of the craft during lift-off.

The space shuttles are due to be retired in 2010. NASA is currently designing their replacement, a rocket called Ares I and a crew capsule called Orion, which should begin flights in 2015.

But during a design review for Ares I in October 2007, engineers calculated that the rocket might vibrate so severely in the first few minutes of launch that the shaking could actually kill the crew and destroy the spacecraft.

The problem was made public in January, after the independent website and the Associated Press questioned NASA and filed Freedom of Information Act requests with the agency.

But at a media teleconference on Thursday, NASA officials said a panel of experts had since found that the shaking was milder than first thought, and had developed a number of possible mitigation measures.

鈥淲hat we have found as we go along the way is that this is a very manageable issue,鈥� said Steve Cook, manager of Ares Projects for NASA鈥檚 Marshall Space Flight Center in Huntsville, Alabama, US. 鈥淚t is not a show stopper.鈥�

Swirling vortices

At the root of the problem is vibration common to all solid rocket motors, including those used to launch the space shuttle. As the first stage of the rocket fires, disturbances in the flow of fuel create swirling vortices of gas within the rocket chamber similar to the wake behind a speeding boat.

Unlike with the shuttle, however, the solid motor vibrations of Ares I would nearly match the natural frequency of the entire launch craft, which includes the crew-bearing Orion capsule.

The result is a wrenching, amplified rattling that would make the spacecraft expand and contract like a bouncing .

鈥淚t鈥檚 like pushing your kid on the swing,鈥� said Garry Lyles, associate director for technical management at Marshall Space Flight Center. 鈥淚f you push your child at just the right frequency, you can really get them going high.鈥�

Adding weight

A team of in-house and industry experts assembled by NASA in the months since the discovery of the design flaw has found that the vibrations are not as violent as once thought. Still, the shaking remains two to three times stronger than NASA hopes to achieve for the safety of crew and craft.

NASA has proposed several mitigation measures. The leading candidate would counteract vibrations by using 鈥渢uned mass dampers鈥� 鈥� masses on springs that cancel out the spacecraft鈥檚 oscillations by moving in the opposite direction.

Another option, Lyles said, is to alter the natural frequency of the launch vehicle until it no longer matches that of the solid motor during lift-off. The launch vehicle鈥檚 vibration frequency could be decreased by adding weight to the craft or by making it less stiff.

Shock absorbers

NASA鈥檚 goal is to lower the impact of the shaking to a force of 2 gs. Modifications to the Orion crew capsule, such as shock absorbers in the astronaut鈥檚 seats, would further decrease the effect on the crew to between 0.14 and 0.30 gs.

鈥淎t those limits, they鈥檙e able to read the console, to flip switches, to write, to do anything that they need to be doing,鈥� Lyles said.

Despite NASA officials鈥� assurances that the vibration problem can and will be solved, though, the effort to replace the ageing shuttle fleet remains dogged by many other challenges, according to the Government Accountability Office, the investigative arm of the US Congress.

In a released on Wednesday in advance of a congressional hearing on NASA鈥檚 exploration initiative, the GAO highlighted many concerns that it says leave 鈥渃onsiderable unknowns as to whether NASA鈥檚 plans for these vehicles can be executed within schedule goals鈥� and 鈥減ose risks to the successful outcome of the projects鈥�.

The GAO lists several concerns, including:

聲 A history of weight problems with the Ares I and Orion designs that could keep Orion from actually reaching orbit;

聲 Development of an essentially new engine for Ares I鈥檚 upper stage;

聲 The lack of industry capability to produce the heat shields that Orion will need to re-enter Earth鈥檚 atmosphere; and

聲 Insufficient test facilities for Ares I鈥檚 new engine, for replicating the engine鈥檚 vibration and acoustic environment, and for testing the thermal protection system for the Orion vehicle.

At this time, however, none of the problems are severe enough to foil NASA鈥檚 next-generation spacecraft, Cristina Chaplain, the GAO鈥檚 director of acquisition and sourcing management, said at the hearing.

There are no problems 鈥渢hat we have determined to be a fatal flaw鈥�, she said.