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It was a fitting tribute to Carl Sagan’s imagination, optimism, and starry-eyed wonder. On Monday, which would have been Sagan’s 75th birthday, the Planetary Society announced that it is pushing ahead with a plan for experimental spacecraft that will ride on sunbeams, powered by solar sails. The first small craft will be sent into orbit in 2010, if all goes well, and will be followed by two others, which may venture farther. Sagan was a founder of the Planetary Society and a big booster of solar sail plans.

Solar sail technology, which has not yet been tested in space, relies on the tiny impacts created by the light particles streaming from the sun as they hit a reflective surface. The force on a solar sail is gentle, if not feeble, but unlike a rocket, which fires for a few minutes at most, it is constant. Over days and years a big enough sail, say a mile on a side, could reach speeds of hundreds of thousands of miles an hour, fast enough to traverse the solar system in 5 years. Riding the beam from a powerful laser, a sail could even make the journey to another star system in 100 years, that is to say, a human lifespan [The New York Times].

The spacecraft that is scheduled for orbit in 2010, the LightSail-1, has been made possible by an anonymous donation to the Planetary Society. The recent donation reinvigorates the Society’s solar sail hopes, which were dashed in 2005 when the Russian Volna rocket carrying its first solar sail prototype, Cosmos 1, failed to reach orbit…. In addition to the Cosmos 1 disappointment, NASA’s NanoSail-D attempt was lost in the third failed flight of SpaceX’s Falcon 1 rocket in 2008 [SPACE.com].

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Image: The Planetary Society

Today in the innermost region of our solar system, NASA’s Messenger space probe will swoop past Mercury for the third and final time. The maneuver will give scientists a close look at the dense, iron-rich, oddball planet, and will also alter the probe’s trajectory and prepare it to begin orbiting Mercury in March 2011.

As Messenger travels within 142 miles of Mercury at 12,000 miles per hour, the spacecraft’s camera will swivel to stare at a succession of craters and other geological features…. One target will be an old 90-mile-wide crater. Another will be young 13-mile crater and a splash of light-colored soil surrounding it. A third crater of interest has materials of unusual color perhaps produced by violent volcanic eruptions [The New York Times]. When this third flyby is complete, 95 percent of the planet will have been mapped in high resolution.

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The solar probe Ulysses has circled the sun for more than 18 years–almost as long as the Greek hero Odysseus, also called Ulysses, was absent from home due to the Trojan War and his prolonged journey home–but the space probe doesn’t have a homecoming in its future. Ulysses will receive its final transmission tomorrow, as researchers say the scientific findings sent home by the failing spacecraft no longer justify the mission’s costs. After shut-off, Ulysses will continue to orbit the Sun, becoming in effect a man-made ‘comet’. “Whenever any of us look up in the years to come, Ulysses will be there, silently orbiting our star, which it studied so successfully during its long and active life” [SPACE.com], says mission manager Richard Marsden.

The craft has already exceeded expectations. In February 2008, mission engineers announced with great solemnity and with heaps of praise for the orbiter that the craft would fall silent within a few months. Its power supply had grown too weak to keep the craft’s fuel lines from freezing. Not so fast: Engineers figured out that they could keep the lines warm by firing the craft’s thrusters in short bursts every couple of hours [The Christian Science Monitor]. Using that clever fix, Ulysses soldiered on for another year.

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When the Messenger spacecraft swooped low past the planet Mercury on October 6 2008, it gathered up a wealth of data that will have planetary scientists puzzling for years. As researchers sort through findings regarding Mercury’s volcanic past, meteor impacts, and the effect of the solar wind on the innermost planet’s magnetosphere, one broad conclusion stands out: Mercury isn’t just a boring chunk of rock. Marilyn Lindstrom, a NASA program scientist, said the Messenger findings show that Mercury is “just an amazingly dynamic planet, both in the past and in the present” [Baltimore Sun].

Superficially, Mercury looks a lot like the moon: small, grayish-brown and pockmarked with craters. Some scientists assumed that Mercury’s surface formed the same way the moon’s did, with lighter rocks rising to the surface of a magma ocean and congealing into a brittle crust early on. But the new observations reveal that 40 percent of the surface was formed by volcanoes. “Up until before Messenger’s arrival, we weren’t even sure that volcanism existed on Mercury” [Wired],  says researcher Brett Denevi. The presence of titanium oxide also suggests that the planet was hot enough in its first 100 million years to be covered in magma oceans.

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A pair of solar observers known as the STEREO spacecraft have taken the first 3-D pictures of the sun’s powerful storms, during which billions of tons of charged particles erupt from the sun’s surface. The two spacecraft have taken up two positions about 100 million miles apart: Not unlike human eyes, the satellites’ two points of view allow for combination images that render scenes in three dimensions [National Geographic News]. 

Solar storms can have serious repercussions here on Earth. They can disrupt GPS signals and power grids, damage satellites, and bombard astronauts with solar radiation, experts said [National Geographic News]. But with the STEREO system, researchers say they can predict when a fierce storm will hit Earth 24 hours in advance (an improvement over previous 12-hour predictions). Says researcher Chris Davies: “That’s ample time to power down a satellite until the worst of the storm has passed; and if you’re an astronaut on the space station, you would have had plenty of time to get into an area that has much better shielding” [BBC News]. While STEREO is a temporary scientific research mission, researchers say it provides an example of how a “space weather” early-warning system would work.

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Researchers have discovered the our planet’s atmosphere regularly expands and contracts in a short cycle of about nine days, and say that this “breathing” is caused by powerful gusts of solar wind. While researchers already knew that ultraviolet light from the sun can heat and swell the atmosphere, the discovery of short, cyclical fluctuations “was a surprising finding” that wasn’t correlated with any variation in solar UV flux [Science News], says atmospheric scientist Jeffrey Thayer.

The breathing cycle seems to reach its peak when solar features called coronal holes are facing Earth. These dark spots in the sun’s corona—a sort of solar atmosphere—are areas where the sun’s magnetic field has been blown open by pressurized solar wind, sending the “winds” toward Earth at high speed. As the fast winds streaming from coronal holes approach Earth, they cause gases in our upper atmosphere to heat up and expand, then cool down and contract, changing the upper atmosphere’s density [National Geographic News].

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The magnetic field that surrounds our planet and protects us from the sun’s harmful radiation sometimes springs a couple of large leaks that let in blasts of solar wind, researchers have discovered. While humanity isn’t in any imminent danger, researchers say that during intense solar storms the rents in what’s known as the magnetosphere will let in streams of charged solar particles, which can interfere with satellites and electricity grids.

Researchers knew previously that cracks in the magnetosphere sometimes occur, but they didn’t understand their potential size and had some misunderstandings about how they formed. Previously, scientists believed that the holes form when the sun’s magnetic field is aligned in the opposite direction from the Earth’s. But the new study showed that 20 times more solar particles enter the Earth’s magnetic field when it is aligned in the same direction as the sun’s magnetic field. The alignment causes the two magnetic fields to connect and tears holes in the Earth’s magnetic field over the poles. “What we observed was the breach in the levee,” said Jimmy Raeder, a physicist at the University of New Hampshire. “This has taken us completely by surprise” [Reuters].

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Researchers have tested a small, portable magnetic field that could be just the protection required for a manned expedition to Mars, when astronauts would need to be protected from radiation from solar storms. Researchers say the lab experiment is the proof of concept for a magnetic force-field that mimics the protective qualities of the Earth’s magnetosphere, which shields our planet from that same radiation.

Outside Earth’s protective atmosphere and magnetic field, supersonic particles from stellar processes run amok, screaming through space and tearing through just about anything in their path—including the bodies of astronauts, where they can wreak havoc on genetic material [Scientific American]. Astronauts on the International Space Station are within Earth’s protective magnetic field, so the Apollo astronauts who went to the moon are the only humans who have been exposed to this radiation; happily, there were no major solar storms during their quick trips to the moon and back. However, a manned mission to Mars would take about six months each way, leaving astronauts much more vulnerable.

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On Sunday, a small space probe with a big mission took off from Earth in a flawless launch, setting off on a two-year assignment to map the edge of our solar system. The Interstellar Boundary Explorer soared into space aboard an Orbital Space Sciences Pegasus rocket that fired as planned at 12:48 p.m. CDT, moments after dropping from the belly of a modified airliner that flew across the South Pacific near Kwajalein Atoll [San Antonio Express-News].

The $169 million NASA probe will settle into a long, elliptical orbit around Earth that takes it beyond the interference of our planet’s magnetosphere, and almost as far as the moon. From there the IBEX will record the impacts of particles that are formed at the edge of our solar system’s protected space, a region known as the heliosphere. The solar wind, a stream of charged particles spewing from the sun at 1 million miles per hour, carves out a protective bubble around the solar system. This bubble … shields against most dangerous cosmic radiation that would otherwise interfere with human spaceflight [AP]. At the edge of the heliosphere, the solar wind slows down as it slams into interstellar space; IBEX will observe the particles created in this “termination shock” to chart the solar system’s perimeter.

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On October 19, NASA will launch the small Interstellar Boundary Explorer (IBEX) into orbit on a mission to map the turbulent edge of our solar system, where the solar wind slams into interstellar space. While it won’t actually travel beyond all the planets to investigate the solar system’s far reaches, the coffee table-sized spacecraft must escape the area where Earth’s magnetic field reigns, which could interfere with its measurements. The $169 million observatory is due to climb 200,000 miles (322,000 kilometers) above Earth and settle into orbit there for a mission of at least two years. For comparison, the moon orbits about 240,000 miles (385,000 km) from Earth [SPACE.com].

The edge of the solar system is currently being explored directly by the Voyager 1 and Voyager 2 spacecrafts; both Voyagers launched 31 years ago and recently passed the point where the solar wind is slowed by interactions with the interstellar plasma, a point known as the termination shock. These crafts “are mak­ing fas­ci­nat­ing ob­serva­t­ions of the lo­cal con­di­tions at two points be­yond the ter­mina­t­ion shock that show to­tally un­ex­pected re­sults and chal­lenge many of our no­tions,” said [IBEX researcher David] Mc­Co­mas [World Science].

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The solar wind, a steady stream of charged subatomic particles that stream out from the sun at a speed of one million miles per hour, has dwindled to its weakest state since recording began, researchers say. While researchers already knew that solar winds fluctuate in 11-year cycles, the current doldrums trump the declines seen over the past 50 years. “We know that the sun has been this cool before, this inactive before,” said [physicist] Nancy Crooker…. “But that was prior to the Space Age, so we didn’t have actual physical measurements until now” [SPACE.com].

The data was collected by the first solar explorer, the Ulysses probe, which was launched in 1990 as a joint venture between NASA and the European Space Agency. The 17-year-old space probe, which circles the sun from a distance of about 337 million miles, has been studying the environment above and below the poles of the sun. It is just months away from shutting down because of freezing fuel [AP].

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A remarkable stellar event that mesmerized astronomers in 1843 may have been a previously unknown kind of explosion, researchers say. That explosion, which made the star Eta Carinae one of the brightest in the Southern sky, could have been the precursor to the star’s expected explosion into a supernova.

Researchers began watching Eta Carinae after the star mysteriously brightened 1843, and astronomers in recent decades have photographed and studied the resulting cloud of gas and dust, known as the Homunculus Nebula, that billows away from the star. A farther-out faint shell of debris from an earlier explosion is also visible, probably dating from around 1,000 years ago. “Looking at other galaxies, astronomers have seen stars like Eta Carinae that get brighter, but not quite as bright as a real supernova,” said [lead researcher] Nathan Smith…. “We don’t know what they are. It’s an enduring mystery as to what can brighten a star that much without destroying it completely” [SPACE.com].

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The exact mechanism that triggers the colorful auroras that dance across the night sky near the Earth’s two poles has been revealed by a quintet of NASA satellites. Scientists already knew that disturbances in the Earth’s magnetic field, called “substorms,” bring charged particles into the Earth’s upper atmosphere, where they collide with gas particles. Those gas particles then release energy as light, which flickers across the sky in waves of greens, reds, and blues.

Now, researchers with NASA’s THEMIS mission say they’ve discovered what sets off those magnetic disturbances. The substorms begin far out in space, roughly a third of the way to the Moon, where magnetic fields from the Earth are thrown together and reconnect to sling charged particles back toward the planet, they say [New Scientist].

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When the private space company SpaceX launches its Falcon 1 rocket at the end of July, it will bring an intriguing experiment into orbit: a small NASA satellite that could be maneuvered through space with an attached “solar sail.” The sail would be powered by photons from the sun hitting the reflective surface, a series of tiny impacts that can provide a boost in the frictionless void of space.

In a video, NASA scientists show off a satellite about the size and shape of a shoebox with four masts that spring out to support the sail, which measures 100 square feet when unfurled. If the sail is successfully deployed, NASA will experiment with using the sail to control the satellite’s altitude and orbital maneuvering.

To understand this technology’s potential, consider that it took the Voyager probes 30 years to get to the edge of the solar system where they are still hurtling outward further every day. Although slower to get started, a solar sail could catch up with a Voyager spacecraft in a single decade [Wired News].

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