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Liquid Mirror Telescopes on the Moon

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October 9, 2008: A team of internationally renowned astronomers and opticians may have found a way to make "unbelievably large" telescopes on the Moon.

"It's so simple," says Ermanno F. Borra, physics professor at the Optics Laboratory of Laval University in Quebec, Canada. "Isaac Newton knew that any liquid, if put into a shallow container and set spinning, naturally assumes a parabolic shape—the same shape needed by a telescope mirror to bring starlight to a focus. This could be the key to making a giant lunar observatory."

Borra, who has been studying liquid-mirror telescopes since 1992, and Simon P. "Pete" Worden, now director of NASA Ames Research Center, are members of a team taking the idea for a spin.

Right: An artist's concept of a spinning liquid mirror telescope on the Moon. Credit: Univ. of British Columbia.

On Earth, a liquid mirror can be made quite smooth and perfect if it its container is kept exactly horizontal and rests on a low-vibration low-friction air bearing that is spun by a synchronous motor having one stable speed. "It doesn't need to spin very fast," says Borra. "The rim of a 4-meter–diameter mirror—the largest I've made in my lab—travels only 3 miles per hour, about the speed of a brisk walk. In the low gravity of the Moon, it would spin even slower."

Most liquid-mirror telescopes on Earth have used mercury. Mercury remains molten at room temperature, and it reflects about 75 percent of incoming light, almost as good as silver. The biggest liquid-mirror telescope on Earth, the Large Zenith Telescope operated by the University of British Columbia in Canada, is 6 meters across—a diameter 20 percent larger than the famous 200-inch mirror of the Hale telescope at Palomar Observatory in California. Yet when completed in 2005, the Canadian Palomar-class liquid-mirror telescope cost less than $1 million to build—only a few percent the cost of a solid-mirror telescope of the same diameter--and, for that matter, only a sixth of Palomar's original cost in 1948.

Sign up for EXPRESS SCIENCE NEWS delivery Those economics are making astronomers sit up and begin noodling out plans for a lunar observatory.

"Our study [with Borra] started when I was still an astronomy professor at the University of Arizona before I came to NASA in 2006," Worden recalls. "The real appeal of this approach is that we could get an unbelievably large telescope on the Moon."

Mercury is unworkable on the Moon: it's very dense and thus heavy to launch, it's very expensive, and it would evaporate quickly when exposed to the lunar vacuum. In recent years, however, Borra and his colleagues have been experimenting with a class of organic compounds known as ionic liquids. "Ionic liquids are basically molten salts," Borra explains. "Their evaporation rate is almost zero, so they would not vaporize in the lunar vacuum. They can also remain liquid at very low temperatures." He and his colleagues are now seeking to synthesize ionic liquids that remain molten even at liquid-nitrogen temperatures.

Below: The University of British Columbia's 6-meter Large Zenith Telescope uses a liquid mirror to scan the heavens. [more]

Much less dense than mercury, ionic liquids are only slightly denser than water. Although not highly reflective themselves, a spinning mirror of an ionic liquid can be coated with an ultrathin layer of silver just as if it were a solid mirror. Weirdest of all, the silver layer is so thin—only 50 to 100 nanometers—that it actually solidifies. In the vacuum of space, a liquid mirror coated with a thin solid layer of silver would neither evaporate nor tarnish.

A liquid mirror can't be tilted away from the horizontal because the fluid would pour out, destroying the mirror. But that does not mean a liquid mirror telescope cannot be pointed. Optical designers are now experimenting with ways of electromechanically warping secondary mirrors suspended above a liquid mirror—or even slightly warping the liquid mirror itself—to aim at angles away from the vertical. Similar techniques are used to point the great Arecibo radio telescope in Puerto Rico.

Furthermore, says Borra, "if the telescope is located anywhere other than exactly at the poles, with each rotation of Earth or Moon it would scan a circular strip of sky. And the rotational axis of the Moon wobbles with a period of 18.6 years; so over a period of 18.6 years, the telescope would actually look at a good-sized region of the sky."

Right: The 1000-ft Arecibo radio telescope in Puerto Rico cannot be moved, but it can still scan a wide swath of sky using movable secondary mirrors. A lunar liquid mirror telescope might employ similar techniques. [more]

Locating a major liquid-mirror telescope near the lunar poles is appealing. The telescope itself could reside near the bottom of a permanently shadowed crater where it would stay at cryogenic temperatures, desirable for the best infrared astronomy. Yet solar panels could be erected on nearby permanently illuminated mountain peaks to generate power to keep the mirror spinning.

The fact that a liquid-mirror telescope always looks straight up vastly simplifies its construction and reduces mass by eliminating heavy mounts, gearing, and pointing-control systems needed for a steerable telescope. "All you'd need is the liquid-mirror container, which might be an umbrella-like device that self-deploys, plus a nearly frictionless superconducting bearing and its drive motor," Borra says. Worden estimates that all the materials for an entire lunar telescope 20 meters across would be "only a few tons, which could be boosted to the Moon in a single Ares 5 mission in the 2020s." Future telescopes might have mirrors as large as 100 meters in diameter—larger than a football field.

"A mirror that large could peer back in time to when the universe was very young, only half a billion years old, when the first generation of stars and galaxies were forming," Borra exclaimed. "Potentially more exciting is pure serendipity: new things we might discover that we just don't expect."

Says Worden: "Putting a giant telescope on the Moon has always been an idea of science fiction, but it soon could become fact."

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Author: Trudy E. Bell | Editor: Dr. Tony Phillips | Credit: Science@NASA

The Day the World Didn't End

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October 10, 2008: Here's what didn't happen on Sept. 10th:

The world did not end. Switching on the world's largest and most powerful particle accelerator near Geneva, Switzerland, did not trigger the creation of a microscopic black hole. And that black hole did not start rapidly sucking in surrounding matter faster and faster until it devoured the Earth, as sensationalist news reports had suggested it might.

Of course, because you're alive and reading this article today, you already knew that. Currently the accelerator, an underground ring 5 miles across called the Large Hadron Collider (LHC), has been shut down for repairs. But once the immensely powerful machine starts back up, is there a chance that the doomsday scenario could still occur?

Relax. As Mark Twain might have said, reports of Earth's death have been greatly exaggerated.

Above: An aerial view of CERN (European Organization for Nuclear Research). The large 5-mile diameter ring traces the underground Large Hadron Collider. Image credit: CERN

"There never really was a danger from the accelerator, but that sure didn't stop people from speculating that there might be!" says Robert Johnson, a physicist at the Santa Cruz Institute for Particle Physics and a member of the science team for NASA's Fermi Gamma-ray Space Telescope, which launched in June to study gamma rays from many phenomena, including possible evaporating black holes.

There are several reasons why the world did not come to an end on Sept. 10th, and why the Large Hadron Collider isn't capable of triggering such a calamity.

First of all, yes, it is true that the LHC might create microscopic black holes. But, for the record, it could not have created one on its first day. That's because the physicists at CERN didn't steer beams of protons into each other to create high-energy collisions. Sept. 10th was just a warmup run. To date, the collider still has not produced any collisions, and it is the extreme energy of those collisions — up to 14 tera-electron volts — that could potentially create a microscopic black hole.

Right: Any micro black hole created by the LHC would quickly evaporate, losing mass and energy via Hawking radiation. [more]

Actually, once the LHC is running again and begins producing collisions, physicists will be ecstatic if it creates a tiny black hole. It would be the first experimental evidence to support an elegant but unproven and controversial "theory of everything" called string theory.

In string theory, electrons, photons, quarks, and all the other fundamental particles are different vibrations of infinitesimal strings in 10 dimensions: 9 space dimensions and one time dimension. (The other 6 space dimensions are hidden by one explanation or another, for example by being "curled up" on an extremely small scale.) Some physicists tout string theory's mathematical elegance and its ability to integrate gravity with the other forces of nature. The widely accepted Standard Model of particle physics does not include gravity, which is one reason why it does not predict that the LHC would create a gravitationally collapsed point — a black hole — while string theory does.

Many physicists have started to doubt whether string theory is true. But assuming for a moment that it is, what would happen when a black hole is born inside the LHC? The surprising answer is "not much." Even if the black hole survives for more than a fraction of a second (which it probably wouldn't), most likely it would be flung out into space. "It would only have the mass of a hundred or so protons, and it would be moving at near the speed of light, so it would easily have escape velocity," Johnson explains. Because the tiny black hole would be less than a thousandth the size of a proton and would have an exceedingly weak gravitational pull, it could easily zip through solid rock without ever touching — or sucking in — any matter. From the perspective of something this tiny, the atoms that make up "solid" rock appear to be almost entirely empty space: the vast space between the atoms' nuclei and their orbiting electrons. So a micro black hole could shoot down through the center of the Earth and out the other side without causing any damage just as easily as it could shoot up through 300 feet of the Swiss countryside. Either way, it would end up out in the near-vacuum of space, where the odds of it touching and sucking in any matter so that it could grow into a menace would be smaller still.

Right: Inside the Large Hadron Collider. Protons race down this tunnel at 99.999999% the speed of light. [more]

So the first thing a micro-black hole would do is leave the planet safely behind. But there are other, even stronger reasons why scientists believe the LHC poses no threat to Earth. For one, a black hole created in the LHC would almost certainly evaporate before it got very far, most scientists believe. Stephen Hawking, the physicist who wrote A Brief History of Time, predicted that black holes radiate energy, a phenomenon known as Hawking radiation. Because of this steady loss of energy, black holes eventually evaporate. The smaller the black hole, the more intense the Hawking radiation, and the quicker the black hole will vanish. So a black hole a thousand times smaller than a proton should disappear almost instantly in a quick burst of radiation.

"Hawking's prediction is not based on speculative string theory but rather on well understood principles of quantum mechanics and particle physics," Johnson notes.

Despite its strong theoretical foundations, Hawking radiation has never been observed directly. Still, scientists are confident that any black hole created by the LHC would pose no threat. How can they be so sure? Because of cosmic rays. Thousands of times per day, high-energy cosmic rays strike the Earth's atmosphere, colliding with molecules in the air with at least 20 times more energy than the most powerful collisions that the LHC can produce. So if this new accelerator could make Earth-devouring black holes, cosmic rays would have already done so billions of times during Earth's long history.

And yet, here we are. Let the collisions begin!

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Editor: Dr. Tony Phillips | Credit: Science@NASA

WARM WEATHER CONTINUES TO START THE WEEK...WITH ALITTLE COOL DOWN MID TO LATE WEEK...HUGE SWING IN THE JET STREAM OVER THE NATION--ALITTLE WEIRD FOR OCTOBER...RESULTING IN A HUGE CONTRAST OF WEATHER...COOL TO COLD OVER THE WEST...BIG SNOWS IN THE MOUNTAINS...THE FIRE SEASON KICKS BACK IN FULL FORCE IN THE WEST...IN CONTRAST--VERY WARM--MID-WEST AND EAST...INBETWEEN--A SLOW MOVING FRONT WITH A BATCH OF SLOW MOVING RAIN...INCLUDING THE LEFT OVER MOISTURE FROM PACIFIC HURRICANE NORBERT.

IDEAS FOR THE WEEK:

*** BIG TROUGH IN THE UPPER ATMOSPHERE SLOWLY MOVES WEST TO EAST THIS WEEK.

*** STILL WARM TO START...COOLER MID TO LATE WEEK

*** RAIN SHOWERS WITH A FEW FEW STORMS(LIMITED) TUESDAY AND WEDNESDAY.

*** BIGGER COLD SNAP ARRIVES NEXT WEEK

*** HURRICANE SEASON STILL COOKING IN OCTOBER

FREEZE DATES FOR STL:

*** THE AVERAGE FREEZE DATE FOR STL IS OCTOBER 20TH--THE AVERAGE FIRST FROST IS OCTOBER 12TH.

*** THE EARLIEST FIRST FREEZE...SEPTEMBER 28, 1944 AND THE LATEST FIRST FREEZE IS NOVEMBER 27, 1942.

*** THE FALL FORECAST IS ONLINE....WINTER FORECAST OUT IN NOVEMBER.

CLICK HERE TO READ THE FALL 2008 FORECAST

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Mercury as Never Seen Before

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Oct. 7, 2008: Yesterday, NASA's MESSENGER spacecraft flew past Mercury and photographed a broad swath of never-before-seen terrain. The first of more than 1,200 high-resolution images are arriving back at Earth now.

"The MESSENGER team is extremely pleased by the superb performance of the spacecraft and the payload," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "We are now on the correct trajectory for eventual insertion into orbit around Mercury, and all of our instruments returned data as planned."

This spectacular image – one of the first to be returned – was snapped by the spacecraft's Wide Angle Camera (WAC) about 90 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 27,000 kilometers (about 17,000 miles):

Above: New photographs of Mercury's unseen side reveal a dramatic system of globe-straddling rays. [full caption]

The most striking characteristic of this newly imaged area is the large pattern of rays streaking downward from the planet's northern regions. The ray system appears to emanate from a relatively young crater previously seen in Earth-based radar images but photographed by a spacecraft for the very first time just yesterday. This view of the planet is distinctly unique from what MESSENGER saw during its first flyby in Jan. 2008.

In the mid-1970s when Mariner 10 flew past Mercury three times, the probe imaged less than half the planet. MESSENGER's first flyby in January of this year covered another 20 percent of the planet's surface. Yesterday, Oct. 6th, MESSENGER successfully completed its second flyby of Mercury, unveiling another 30 percent of Mercury's surface that had never before been seen by spacecraft.

"When these data have been digested and compared, we will have a global perspective of Mercury for the first time," notes Solomon.

Data from the flyby continue to stream down to Earth, including higher resolution close-up images of this previously unseen terrain.

Visit the MESSENGER photo gallery for updates.

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Editor: Dr. Tony Phillips | Credit: Science@NASA

How Round is the Sun?

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Oct. 2, 2008: Scientists using NASA's RHESSI spacecraft have measured the roundness of the sun with unprecedented precision, and they find that it is not a perfect sphere. During years of high solar activity the sun develops a thin "cantaloupe skin" that significantly increases its apparent oblateness. Their results appear the Oct. 2nd edition of Science Express.

"The sun is the biggest and smoothest natural object in the solar system, perfect at the 0.001% level because of its extremely strong gravity," says study co-author Hugh Hudson of UC Berkeley. "Measuring its exact shape is no easy task."

The team did it by analyzing data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager, RHESSI for short, an x-ray/gamma-ray space telescope launched in 2002 on a mission to study solar flares. Although RHESSI was never intended to measure the roundness of the sun, it has turned out ideal for the purpose. RHESSI observes the solar disk through a narrow slit and spins at 15 rpm. The spacecraft's rapid rotation and high data sampling rate (necessary to catch fast solar flares) make it possible for investigators to trace the shape of the sun with systematic errors much less than any previous study. Their technique is particularly sensitive to small differences in polar vs. equatorial diameter or "oblateness."

Above: "Cantaloupe ridges" on the sun. The glowing white magnetic network is what gives the sun its extra oblateness during times of high solar activity. Los Angeles astronomer Gary Palmer took the picture in July 29, 2005, using a violet calcium-K solar filter. [larger image]

"We have found that the surface of the sun has rough structure: bright ridges arranged in a network pattern, as on the surface of a cantaloupe but much more subtle," describes Hudson. During active phases of the solar cycle, these ridges emerge around the sun's equator, brightening and fattening the "stellar waist." At the time of RHESSI's measurements in 2004, ridges increased the sun's apparent equatorial radius by an angle of 10.77 +- 0.44 milli-arcseconds, or about the same as the width of a human hair viewed one mile away.

Sign up for EXPRESS SCIENCE NEWS delivery "That may sound like a very small angle, but it is in fact significant," says Alexei Pevtsov, RHESSI Program Scientist at NASA Headquarters. Tiny departures from perfect roundness can, for example, affect the sun's gravitational pull on Mercury and skew tests of Einstein's theory of relativity that depend on careful measurements of the inner planet's orbit. Small bulges are also telltale signs of hidden motions inside the sun. For instance, if the sun had a rapidly rotating core left over from early stages of star formation, and if that core were tilted with respect to its outer layers, the result would be surface bulging. "RHESSI's precision measurements place severe constraints on any such models."

The "cantaloupe ridges" are magnetic in nature. They outline giant, bubbling convection cells on the surface of the sun called "supergranules." Supergranules are like bubbles in a pot of boiling water amplified to the scale of a star; on the sun they measure some 30,000 km across (twice as wide as Earth) and are made of seething hot magnetized plasma. Magnetic fields at the center of these bubbles are swept out to the edge where they form ridges of magnetism. The ridges are most prominent during years around Solar Max when the sun's inner dynamo "revs up" to produce the strongest magnetic fields. Solar physicists have known about supergranules and the magnetic network they produce for many years, but only now has RHESSI revealed their unexpected connection to the sun's oblateness.

Right: In this diagram, the sun's oblateness has been magnified 10,000 times for easy visibility. The blue curve traces the sun's shape averaged over a three month period. The black asterisked curve traces a shorter 10-day average. The wiggles in the 10-day curve are real, caused by strong magnetic ridges in the vicinity of sunspots. [larger image]

"When we subtract the effect of the magnetic network, we get a 'true' measure of the sun's shape resulting from gravitational forces and motions alone," says Hudson. "The corrected oblateness of the non-magnetic sun is 8.01 +- 0.14 milli-arcseconds, near the value expected from simple rotation."

"These results have far ranging implications for solar physics and theories of gravity," comments solar physicist David Hathaway of the NASA Marshall Space Flight Center. "They indicate that the core of the sun cannot be rotating much more rapidly than the surface, and that the sun's oblateness is too small to change the orbit of Mercury outside the bounds of Einstein's General Theory of Relativity."

Further analysis of RHESSI oblateness data could also help researchers detect a long-sought type of seismic wave echoing through the interior of the sun: gravitational oscillations or "g-modes." The ability to monitor g-modes would open a new frontier in solar physics—the study of the sun's internal core.

"All of this," marvels Hathaway, "comes from clever use of data from a satellite designed for something entirely different. Congratulations to the RHESSI team!"

The paper reporting these results, "A large excess in apparent solar oblateness due to surface magnetism," was authored by Martin Fivian, Hugh Hudson, Robert Lin and Jabran Zahid, and appears in the Oct. 2nd issue of Science Express.

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Author: Dr. Tony Phillips | Credit: Science@NASA

MESSENGER Returns to Mercury

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Oct. 1, 2008: NASA's MESSENGER spacecraft is returning to Mercury. On Monday, Oct. 6, 2008, the probe will conduct the second of three planned flybys and photograph most of Mercury's remaining unseen surface.

At closest approach MESSENGER will pass just 125 miles above Mercury's cratered surface, taking more than 1200 pictures. The flyby also will provide a critical gravity assist needed for MESSENGER to become, in March 2011, the first spacecraft to actually orbit the innermost planet.

Above: A color image of Mercury's giant Caloris Basin recorded during MESSENGER's first flyby on Jan. 14, 2008. [more]

During MESSENGER's first flyby on Jan. 14, 2008, its cameras photographed approximately 20 percent of Mercury's surface never before seen by space probes. The spacecraft spotted ancient volcanoes ringing Mercury's Caloris Basin, found that Mercury's magnetic field is "alive" (generated by an active dynamo in Mercury's core) and discovered a surprisingly rich plasma nebula trapped in Mercury's magnetic field. And those were just a few of the surprises; see Science@NASA's New Discoveries at Mercury for details.

Sign up for EXPRESS SCIENCE NEWS delivery "This second flyby will show us a completely new area of Mercury's surface, opposite from the side of the planet we saw during the first," said Louise M. Prockter, instrument scientist for the spacecraft's Mercury Dual Imaging System at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

The second flyby is expected to yield even more surprises. A laser altimeter on the spacecraft will measure the planet's topography, allowing scientists, for the first time, to correlate high-resolution topography measurements with high-resolution images. At the same time, MESSENGER's sensors will analyze the chemical and mineralogical composition of Mercury's surface.

Below: Much of Mercury's surface is still unknown. This map shows areas that will be covered by the second flyby of MESSENGER on Oct. 6, 2008. Solid purple denotes places that have never been photographed by a spacecraft before. [larger image]

"We will be able to do the first test of differences in the chemical
compositions between the two hemispheres viewed in the two flybys," says Ralph McNutt, the mission's project scientist at APL.

"The results from MESSENGER's first flyby of Mercury settled debates that were more than 30 years old," notes Sean C. Solomon, the mission's principal investigator from the Carnegie Institution of Washington. "This second encounter should uncover even more information about the planet."

Stay tuned to Science@NASA for results from the flyby.

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Editor: Dr. Tony Phillips | Credit: Science@NASA

Hi Folks...this is a great read...a real important factor in the winter forecast...dave

Spotless Sun: Blankest Year of the Space Age

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Sept. 30, 2008: Astronomers who count sunspots have announced that 2008 is now the "blankest year" of the Space Age.

As of Sept. 27, 2008, the sun had been blank, i.e., had no visible sunspots, on 200 days of the year. To find a year with more blank suns, you have to go back to 1954, three years before the launch of Sputnik, when the sun was blank 241 times.

"Sunspot counts are at a 50-year low," says solar physicist David Hathaway of the NASA Marshall Space Flight Center. "We're experiencing a deep minimum of the solar cycle."

A spotless day looks like this:

The image, taken by the Solar and Heliospheric Observatory (SOHO) on Sept. 27, 2008, shows a solar disk completely unmarked by sunspots. For comparison, a SOHO image taken seven years earlier on Sept. 27, 2001, is peppered with colossal sunspots, all crackling with solar flares: image. The difference is the phase of the 11-year solar cycle. 2001 was a year of solar maximum, with lots of sunspots, solar flares and geomagnetic storms. 2008 is at the cycle's opposite extreme, solar minimum, a quiet time on the sun.

And it is a very quiet time. If solar activity continues as low as it has been, 2008 could rack up a whopping 290 spotless days by the end of December, making it a century-level year in terms of spotlessness.

Hathaway cautions that this development may sound more exciting than it actually is: "While the solar minimum of 2008 is shaping up to be the deepest of the Space Age, it is still unremarkable compared to the long and deep solar minima of the late 19th and early 20th centuries." Those earlier minima routinely racked up 200 to 300 spotless days per year.

Above: A histogram showing the blankest years of the last half-century. The vertical axis is a count of spotless days in each year. The bar for 2008, which was updated on Sept. 27th, is still growing. [Larger images: 50 years, 100 years]

Some solar physicists are welcoming the lull.

"This gives us a chance to study the sun without the complications of sunspots," says Dean Pesnell of the Goddard Space Flight Center. "Right now we have the best instrumentation in history looking at the sun. There is a whole fleet of spacecraft devoted to solar physics--SOHO, Hinode, ACE, STEREO and others. We're bound to learn new things during this long solar minimum."

Sign up for EXPRESS SCIENCE NEWS delivery As an example he offers helioseismology: "By monitoring the sun's vibrating surface, helioseismologists can probe the stellar interior in much the same way geologists use earthquakes to probe inside Earth. With sunspots out of the way, we gain a better view of the sun's subsurface winds and inner magnetic dynamo."

"There is also the matter of solar irradiance," adds Pesnell. "Researchers are now seeing the dimmest sun in their records. The change is small, just a fraction of a percent, but significant. Questions about effects on climate are natural if the sun continues to dim."

Pesnell is NASA's project scientist for the Solar Dynamics Observatory (SDO), a new spacecraft equipped to study both solar irradiance and helioseismic waves. Construction of SDO is complete, he says, and it has passed pre-launch vibration and thermal testing. "We are ready to launch! Solar minimum is a great time to go."

Coinciding with the string of blank suns is a 50-year record low in solar wind pressure, a recent discovery of the Ulysses spacecraft. (See the Science@NASA story Solar Wind Loses Pressure.) The pressure drop began years before the current minimum, so it is unclear how the two phenomena are connected, if at all. This is another mystery for SDO and the others.

Who knew the blank sun could be so interesting? More to come...

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Author: Dr. Tony Phillips | Credit: Science@NASA

Solar Wind Loses Power, Hits 50-year Low

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Sept. 23, 2008: In a briefing today at NASA headquarters, solar physicists announced that the solar wind is losing power.

"The average pressure of the solar wind has dropped more than 20% since the mid-1990s," says Dave McComas of the Southwest Research Institute in San Antonio, Texas. "This is the weakest it's been since we began monitoring solar wind almost 50 years ago."

McComas is principal investigator for the SWOOPS solar wind sensor onboard the Ulysses spacecraft, which measured the decrease. Ulysses, launched in 1990, circles the sun in a unique orbit that carries it over both the sun's poles and equator, giving Ulysses a global view of solar wind activity:

Above: Global measurements of solar wind pressure by Ulysses. Green curves trace the solar wind in 1992-1998, while blue curves denote lower pressure winds in 2004-2008. [Larger image]

Curiously, the speed of the million mph solar wind hasn't decreased much—only 3%. The change in pressure comes mainly from reductions in temperature and density. The solar wind is 13% cooler and 20% less dense.

"What we're seeing is a long term trend, a steady decrease in pressure that began sometime in the mid-1990s," explains Arik Posner, NASA's Ulysses Program Scientist in Washington DC.

How unusual is this event?

"It's hard to say. We've only been monitoring solar wind since the early years of the Space Age—from the early 60s to the present," says Posner. "Over that period of time, it's unique. How the event stands out over centuries or millennia, however, is anybody's guess. We don't have data going back that far."

Flagging solar wind has repercussions across the entire solar system—beginning with the heliosphere.

The heliosphere is a bubble of magnetism springing from the sun and inflated to colossal proportions by the solar wind. Every planet from Mercury to Pluto and beyond is inside it. The heliosphere is our solar system's first line of defense against galactic cosmic rays. High-energy particles from black holes and supernovas try to enter the solar system, but most are deflected by the heliosphere's magnetic fields.

Right: The heliosphere. Click to view a larger image showing the rest of the bubble.

"The solar wind isn't inflating the heliosphere as much as it used to," says McComas. "That means less shielding against cosmic rays."

In addition to weakened solar wind, "Ulysses also finds that the sun's underlying magnetic field has weakened by more than 30% since the mid-1990s," says Posner. "This reduces natural shielding even more."

Unpublished Ulysses cosmic ray data show that, indeed, high energy (GeV) electrons, a minor but telltale component of cosmic rays around Earth, have jumped in number by about 20%.

These extra particles pose no threat to people on Earth's surface. Our thick atmosphere and planetary magnetic field provide additional layers of protection that keep us safe.

But any extra cosmic rays can have consequences. If the trend continues, astronauts on the Moon or en route to Mars would get a higher dose of space radiation. Robotic space probes and satellites in high Earth orbit face an increased risk of instrument malfunctions and reboots due to cosmic ray strikes. Also, there are controversial studies linking cosmic ray fluxes to cloudiness and climate change on Earth. That link may be tested in the years ahead.

Above: The temperature and density of electrons in the solar wind have dropped since the mid-1990s. [Larger image]

Some of most dramatic effects of the phenomenon may be felt by NASA's two Voyager spacecraft. After traveling outward for 30+ years, the two probes are now at the edge of the heliosphere. With the heliosphere shrinking, the Voyagers may soon find themselves on the outside looking in, thrust into interstellar space long before anyone expected. No spacecraft has ever been outside the heliosphere before and no one knows what the Voyagers may find there.

NASA is about to launch a new spacecraft named IBEX (short for Interstellar Boundary Explorer) that can monitor the dimensions of the heliosphere without actually traveling to the edge of the solar system. IBEX may actually be able to "see" the heliosphere shrinking and anticipate the Voyager's exit. Moreover, IBEX will reveal how our solar system's cosmic ray shield reacts to changes in solar wind.

"The potential for discovery," says McComas, "is breathtaking."

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Author: Dr. Tony Phillips | Credit: Science@NASA

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The latest U.S. Drought Monitor shows improvement in drought conditions over the Plains and the Midwest, in part due to landfalling tropical systems, and also shows lingering drought for the interior Southeast, south-central Texas, and California. And as of September 16, the contiguous U.S. has the lowest coverage of all levels of drought (21.9 percent), including severe drought (7.5 percent), since January 2006.

“U.S. drought coverage has decreased from nearly 30 percent between mid-June and early August to about 20 percent now,” said Douglas Le Comte, drought specialist at NOAA’s Climate Prediction Center. “During the past 12 weeks there has been a pronounced reduction in extreme to exceptional drought in many areas of the country.”

High resolution (Credit: NOAA)

Heavy rain associated with the Southwest and Florida rainy seasons along with tropical storms have had a significant impact. June through August precipitation across the contiguous United States averaged 9.05 inches, 0.8 inch above the 1901–2000 average, making this the 15th wettest summer since 1895.

Of all the tropical cyclones, Tropical Storm Fay had the greatest impact on U.S. drought. In August, Fay dropped more than five inches of rain on parched sections of Georgia, Alabama, Mississippi, Tennessee, and North and South Carolina. While Fay’s rains eased drought in the southern Appalachians, more rain is needed to erase drought conditions stemming from rainfall deficits exceeding 20 inches over two years. Hurricane Gustav ended drought in Louisiana, while Tropical Storm Hanna eliminated drought over central North Carolina and south-central Virginia, but its track failed to provide relief for the western Carolinas.

Multiple storms – Hurricane Dolly (July), Hurricane Edouard (August), and Hurricane Ike (September) – greatly minimized much of the drought in coastal Texas. However, the rains from these storms largely missed the drought over south-central Texas.

High resolution (Credit: NOAA)

The U.S. Seasonal Drought Outlook, also updated today, shows improvement may be more limited into early winter over the interior Southeast, with drought forecast to persist in Kentucky, Tennessee, and western North Carolina. Some improvement is expected farther south and east. Lower temperatures and less water use across the region mean that reservoirs and wells should begin to revive by late autumn 2008. In Texas, lingering drought is predicted to persist in south-central areas but improve near the coast. On the West Coast, where drought impacts have worsened over the summer, Pacific storms should begin to ease drought over northern California, while little change is expected over southern California through early winter.

f you are lucky, you live in one of those parts of the world where Nature has one last fling before settling down into winter's sleep. In those lucky places, as days shorten and temperatures become crisp, the quiet green palette of summer foliage is transformed into the vivid autumn palette of reds, oranges, golds, and browns before the leaves fall off the trees. On special years, the colors are truly breathtaking.

How does autumn color happen?

For years, scientists have worked to understand the changes that happen to trees and shrubs in the autumn. Although we don't know all the details, we do know enough to explain the basics and help you to enjoy more fully Nature's multicolored autumn farewell. Three factors influence autumn leaf color-leaf pigments, length of night, and weather, but not quite in the way we think. The timing of color change and leaf fall are primarily regulated by the calendar, that is, the increasing length of night. None of the other environmental influences-temperature, rainfall, food supply, and so on-are as unvarying as the steadily increasing length of night during autumn. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with Nature's autumn palette.

Where do autumn colors come from?

A color palette needs pigments, and there are three types that are involved in autumn color.

• Chlorophyll, which gives leaves their basic green color. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. Trees in the temperate zones store these sugars for their winter dormant period.

   

• Carotenoids, which produce yellow, orange, and brown colors in such things as corn, carrots, and daffodils, as well as rutabagas, buttercups, and bananas.

   

• Anthocyanins, which give color to such familiar things as cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums. They are water soluble and appear in the watery liquid of leaf cells.

Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.

During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors.

Certain colors are characteristic of particular species. Oaks turn red, brown, or russet; hickories, golden bronze; aspen and yellow-poplar, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson. Maples differ species by species-red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel up and fall, exhibiting little color other than drab brown.

The timing of the color change also varies by species. Sourwood in southern forests can become vividly colorful in late summer while all other species are still vigorously green. Oaks put on their colors long after other species have already shed their leaves. These differences in timing among species seem to be genetically inherited, for a particular species at the same latitude will show the same coloration in the cool temperatures of high mountain elevations at about the same time as it does in warmer lowlands.

How does weather affect autumn color?

The amount and brilliance of the colors that develop in any particular autumn season are related to weather conditions that occur before and during the time the chlorophyll in the leaves is dwindling. Temperature and moisture are the main influences.

A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions-lots of sugar and lots of light-spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year.

The amount of moisture in the soil also affects autumn colors. Like the weather, soil moisture varies greatly from year to year. The countless combinations of these two highly variable factors assure that no two autumns can be exactly alike. A late spring, or a severe summer drought, can delay the onset of fall color by a few weeks. A warm period during fall will also lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.

What triggers leaf fall?

In early autumn, in response to the shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.

What does all this do for the tree?

Winter is a certainty that all vegetation in the temperate zones must face each year. Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh wintertime influences. Stems, twigs, and buds are equipped to survive extreme cold so that they can reawaken when spring heralds the start of another growing season. Tender leaf tissues, however, would freeze in winter, so plants must either toughen up and protect their leaves or dispose of them.

The evergreens-pines, spruces, cedars, firs, and so on-are able to survive winter because they have toughened up. Their needle-like or scale-like foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic. Evergreen needles survive for some years but eventually fall because of old age.

The leaves of broadleaved plants, on the other hand, are tender and vulnerable to damage. These leaves are typically broad and thin and are not protected by any thick coverings. The fluid in cells of these leaves is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. Thus leaf fall precedes each winter in the temperate zones.

Needles and leaves that fall are not wasted. They decompose and restock the soil with nutrients and make up part of the spongy humus layer of the forest floor that absorbs and holds rainfall. Fallen leaves also become food for numerous soil organisms vital to the forest ecosystem.

It is quite easy to see the benefit to the tree of its annual leaf fall, but the advantage to the entire forest is more subtle. It could well be that the forest could no more survive without its annual replenishment from leaves than the individual tree could survive without shedding these leaves. The many beautiful interrelationships in the forest community leave us with myriad fascinating puzzles still to solve.

Where can I see autumn color in the United States?

You can find autumn color in parks and woodlands, in the cities, countryside, and mountains - anywhere you find deciduous broadleaved trees, the ones that drop their leaves in the autumn. Nature's autumn palette is painted on oaks, maples, beeches, sweetgums, yellow-poplars, dogwoods, hickories, and others. Your own neighborhood may be planted with special trees that were selected for their autumn color.

New England is rightly famous for the spectacular autumn colors painted on the trees of its mountains and countryside, but the Adirondack, Appalachian, Smoky, and Rocky Mountains are also clad with colorful displays. In the East, we can see the reds, oranges, golds, and bronzes of the mixed deciduous woodlands; in the West, we see the bright yellows of aspen stands and larches contrasting with the dark greens of the evergreen conifers.

Many of the Forest Service's 100 plus scenic byways were planned with autumn color in mind. In 31 States you can drive on over 3,000 miles of scenic byways, and almost everyone of them offers a beautiful, colorful drive sometime in the autumn.

When is the best time to see autumn color?

Unfortunately, autumn color is not very predictable, especially in the long term. Half the fun is trying to outguess Nature! But it generally starts in late September in New England and moves southward, reaching the Smoky Mountains by early November. It also appears about this time in the high-elevation mountains of the West. Remember that cooler high elevations will color up before the valleys. The Forest Service's Fall Color Hotline (1-800-354-4595) can provide you with details as the autumn color display progresses.

FOR THE FALL COLORS IN MISSOURI GO TO:

http://mdc.mo.gov/nathis/seasons/fall/

FOR THE FALL COLORS ALONG THE GREAT RIVER ROAD:

http://www.greatriverroad.com/Fall/falIndex.htm

Pollen Alert!

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Sept. 19, 2008: When you stroll through your front door in the morning, does the yellow haze coating the porch send you leaping back into the house? Can the mere word "pollen" make you start to sniffle, sneeze and reach for the tissue to blow your nose?

If you answered "yes" to these questions, you're probably one of millions of people in the United States suffering from hay fever. Pollen can do more, however, than just make you sneeze. If you have asthma, cardiovascular disease, chronic obstructive pulmonary disease or pneumonia, pollen can be downright dangerous. While most of the particles we inhale end up in shallow portions of our airways -- trouble enough! -- the tiniest shards can make their way dangerously deep into the lungs.

Some studies suggest that these little fragments of misery have extreme inflammatory potential and can impair human respiratory and cardiovascular-related health. For example, a study in the Netherlands uncovered a strong association between day-to-day variations in pollen concentrations and deaths from cardiovascular disease, chronic obstructive pulmonary disease, and pneumonia.

Right: Juniper unleashing a cloud of pollen into the atmosphere. Image Credit: New Mexico Department of Health

A NASA team, with help from academia, industry and health agencies, is exploring this tantalizing link between pollen, in this case juniper pollen, and some of these dangerous health conditions.

"Our research could really help people with pollen-related health issues," says team lead Jeff Luvall, Earth scientist at NASA's Marshall Space Flight Center in Huntsville, Ala.

The Center for Disease Control and Prevention is one of NASA's partners in the study. Len Flowers, from CDC's Environmental Public Health Tracking Program at the New Mexico Department of Health in Albuquerque, New Mexico, says, "We're exploring the relationship between two unprecedented recent juniper pollen peaks in northern New Mexico and the amount of sick leave taken by state employees at those times. We’re also looking at the asthma emergency department visits and hospitalizations in our communities, and at other respiratory and cardiovascular hospitalizations."

Sign up for EXPRESS SCIENCE NEWS delivery And what if they find the link they expect?

This is where NASA shines. Luvall's team has a solution ready -- and it comes from space. "Tiny pollen grains are transported in the wind, and we're using NASA satellite data to help predict pollen movement," says Luvall.

Accurate forecasts of pollen transport and dispersal could help reduce many of the maladies mentioned above by forewarning vulnerable people about pollen headed their way. In short, they'd know when to "take cover."

"The overarching goal is to use satellite images of greening plants to predict pollen bursts before they happen so that preventive measures can be taken," says Flowers.

How does it all work? We'll come to that in a moment. First, a pollen primer:

Basically, pollen is a container. It holds the male half of future offspring's genetic material. Its aim in life is to get to the female half by hook or by crook, by land or by sea, or, in this case, by wind or by bee. Wind-pollinated plants produce masses of pollen to ensure that at least some of it reaches its target. The real trouble begins when pollen is shattered into microscopic shards by changes in humidity while powerful thunderstorms suck up tremendous amounts of air and pollen from the surface of the Earth. Vigorous updrafts in thunderheads blast the pollen grains upward into the tops of clouds where the air is freezing, smashing the grains into fragments. Then the colder air sweeps back downward, swamping the draughts of air we breathe with shards of pollen.

Above: A false-color electron microscope scan of prairie hollyhock pollen. Image Credit: Dartmouth College/Charles Daghlian

Each research partner organization involved in this study wields a unique weapon to wage the pollen war. The first weapon is a forecaster's dream.

Slobodan Nickovic first conceived this DREAM, short for Dust Regional Atmospheric Model, to simulate how dust sweeps through the atmosphere across wide swaths of a continent. Now, with his assistance, the model has been modified at the University of Arizona to use pollen data instead of dust.

NASA has introduced MODIS, or the Moderate Resolution Imaging Spectroradiometer, into the pollen battle. MODIS is a sensor that resides on two NASA satellites -- Terra and Aqua. MODIS senses the growth stages of different plant species by looking at color changes that occur in the plant canopy. Certain color changes reveal when the plants are about to release their pollen hordes.

The New Mexico Department of Health's "weapon" takes the form of health record statistics that are crucial to the study.

In addition, the New Mexico Environmental Public Health Tracking Project and the ARES Corporation have alert systems that can be used to warn public health officials, doctors, hospitals, and schools, about incoming pollen. The health agency maintains a website that will alert the public to pollen events, and ARES Corporation's SYRIS, or Syndrome Reporting Information System, is a web-based system for alerting public health officials.

For this study, the researchers used data from MODIS to identify when and where juniper communities were pollinating. Alfredo Huete from the University of Arizona identified these time periods, via the MODIS data, for six different juniper communities throughout the U.S. southwest. These first DREAM pollen transport simulations modeled the pollen transport for 66 hours. The researchers propose next to establish a network of ground sampling stations to verify the model so it can be put to use in the future to help the pollen-endangered among us.

All of this is good news for the American public -- and for Luvall. "I do have a selfish reason for wanting this project to succeed," he confesses. "I'm allergic to tree pollen."

It's always good to be invested in your own work.

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Author: Dauna Coulter | Credit: Science@NASA

Polar Crown Prominences

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Sept. 17, 2008: Warning: Material contained in this story may make you wish to become a solar physicist.

Japan's Hinode spacecraft, launched in 2006 on a mission to study the sun, is beaming back movies that astonish even seasoned investigators. Click to play:

Click to play a 7 MB Quicktime movie

"That was a polar crown prominence recorded by Hinode on Nov. 30, 2006," says Dr. Thomas Berger of Lockheed Martin's Advanced Technology Center in Palo Alto, California. "It is a curved wall of 10,000o plasma about 90,000 km long and 30,000 km tall." A stack of planets three Earths high would barely make it to the top.

Solar astronomers have seen prominences like this before, thousands of them, but never so clearly. The new view is challenging long-held ideas: In the past, researchers thought of prominences as mainly static structures, held motionless above the surface of the sun by magnetic force fields. "Now we know those ideas are too simple. Just watch the movie!"

Berger lists the surprises:

Sign up for EXPRESS SCIENCE NEWS delivery 1. "There are dark tadpole-shaped plumes rising up from the base of the prominence. These have never been seen before and we're not sure what they are."

2. "Narrow streams of plasma at the top of the prominence are constantly falling back to the bottom, much like a waterfall." Mysteriously, the streams plummet faster than ambient magnetic forces seem to allow1.

3. "Finally, within the wall itself, there are swirls and vortices" bearing an eerie resemblance to van Gogh's surreal Starry Night.

The inescapable conclusion: "There's no such thing as a static prominence." Furthermore, he says, "we don't understand how the sun's magnetic field is doing all these things."

Berger is co-Investigator for Hinode's Solar Optical Telescope (SOT), which makes such movies on a regular basis. "SOT can see details on the sun as small as a few hundred kilometers wide. Its view is never blurred by Earth's atmosphere so it can make movies up to 12 hours long with perfect clarity." The growing archive of movies is a treasure trove for researchers.

It turns out that polar crown prominences pop up almost every day. They occupy a ring (or "crown") around the sun's poles bracketed approximately by solar latitudes 60o and 70o. Geometrically, the crowns resemble the auroral ovals of Earth. Instead of Northern Lights, however, the sun's ovals are filled with dancing sheets of plasma.

Above: The sun's southern "polar crown," outlined by a long filament/prominence photographed in June 1999: more.

Studying polar crown prominences could be a key to f