Archive for Outer Space

Color of Jupiter’s great red spot comes from epic sunburn

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The Great Red Spot’s clouds are much higher than those elsewhere on Jupiter. (NASA/JPL-Caltech/ Space Science Institute)

The Great Red Spot on Jupiter’s face is secretly dull in color. But the swirling storm looks crimson thanks to something like a cosmic “sunburn,” scientists say.

New experiments show that the gases in the upper atmosphere of Jupiter turn a reddish hue when they’re hit with sunlight. Underneath, the Great Red Spot probably looks gray or white.

“Spot” might be a bit of a misnomer for the most powerful storm in the solar system. The vortex is wider than two Earths, at about 7,500 miles across, and it packs winds up to 425 mph. The storm is also extremely long-lived; it has been present on Jupiter ever since astronomers started observing the planet through telescopes, making it centuries old at least. [Jupiter’s Great Red Spot in Photos]

Scientists were treated to incredibly detailed views of Jupiter and its big spot when NASA’s Cassini spacecraft flew past the giant planet in December 2000. Cassini has since moved on and is currently in orbit around its main destination, Saturn. But data from the probe’s Jupiter flyby inspired Cassini scientists at NASA’s Jet Propulsion Laboratory, Pasadena, California, to figure out what makes the Great Red Spot red.

In the lab, the researchers created clouds of ammonia and acetylene gases to mimic the clouds in the upper reaches of Jupiter’s atmosphere. They blasted these chemicals with ultraviolet light to simulate the sun’s effects. This produced a reddish material, which had the same light-scattering properties as the Great Red Spot, the researchers said.

“Our models suggest most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material,” Kevin Baines, a Cassini team scientist, said in a statement from NASA. “Under the reddish ‘sunburn’ the clouds are probably whitish or grayish.”

At first, Baines and colleagues thought the red color might be produced by the breakdown of ammonium hydrosulfide, the chemical that makes up one of Jupiter’s main cloud layers. But in the lab, this substance turned bright green when hit with UV light. After that mismatch, they tested which combinations of ammonia with hydrocarbons would produce the best fit for the Great Red Spot. It turned out to be ammonia and acetylene, the researchers said.

Baines presented the findings this week at the American Astronomical Society’s Division for Planetary Science Meeting in Tucson, Arizona.

Comet lander still ‘talking,’ but scientists face race against time

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A panoramic image of the comet’s surface taken by the Philae lander. (ESA/Rosetta/Philae/CIVA)

The European Space Agency’s Rosetta spacecraft has regained contact with its history-making Philae comet lander, although scientists now face a race against time to extract as much data as possible from the probe before its battery runs out on Saturday.

Scientists had endured an agonizing wait Friday before the Rosetta orbiter re-established contact with the probe. After finally touching down in the wrong location on Wednesday, there were fears that the lander would run out of battery power before the connection could be made.

“Philae still talking!” declared the agency, in a blog post late on Friday, confirming that Rosetta’s “communication pass” began at 5:29 p.m. ET.

The Philae lander made history on Wednesday when it became the first probe to land on a comet. 67P/Churyumov-Gerasimenko, which  is about 2.5 miles wide and travels at speeds up to 84,000 miles per hour, is 317 million miles from earth.

The challenge for scientists now is to grab as much information as possible from the probe  before its power is exhausted. The probe’s exact location on the comet also remains unknown, according to the ESA.

“While the search for the final landing site is still on-going, the lander is racing against the clock to meet as many of the core science goals as possible before the primary battery is exhausted,” explained the ESA, in its blog post. “Under the low illumination conditions at Philae’s location, it is unlikely that the secondary batteries will charge up enough to enable extended surface operations.”

With Philae’s solar panels unlikely to generate enough long-term power for the secondary batteries, the probe’s mission is expected to end sometime on Saturday, according to the ESA.  “Future contacts are possible if the illumination conditions change as the comet orbits closer to the Sun, enabling solar power to flow again,” it added.

During a press conference early on Friday, ESA scientists said that the probe may receive enough solar power to communicate when its orbit nears the sun in August 2015.

Known as a “short period comet,” 67P/Churyumov-Gerasimenko takes 6.6 years to orbit the sun.

The culmination of an audacious 10-year mission, the Philae lander separated from its Rosetta mothership and successfully descended to the comet Wednesday. The touchdown, however, was fraught with problems, and the lander bounced twice before landing in the shadow of a cliff – a serious problem for the solar panels designed to provide long-term power to Philae after its primary battery is exhausted.

In Friday’s press conference, ESA scientists discussed altering Philae’s position by activating its landing gear in an attempt to illuminate its solar panels.

On Friday evening ESA Operations tweeted that Philae’s landing gear “lifted 4cm” (1.6 inches), adding that probe’s “main body rotation” was complete.

Designed to collect a host of data, one of Philae’s key tools is a drill, which will help scientists analyze the comet’s structure.

On Friday the ESA confirmed that the drill has extended around 10 inches from the lander’s base plate, but were unable to tell whether it has penetrated the comet’s substrate.

Early on Thursday, the ESA released the first picture taken by the probe after determining that the craft had stabilized following its tension-filled landing. The agency subsequently released the first panoramic picture taken from the lander. The three feet of Philae’s landing gear can be seen in some of the frames.

Philae and the Rosetta spacecraft planned to use 21 instruments to analyze the comet. Scientists hope the $1.62 billion mission will help them better understand comets and other celestial objects, as well as possibly answer questions about the origins of life on Earth

Jupiter’s Great Red Spot isn’t what we thought it was: researchers

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Jupiter's Great Red Spot isn't what we thought it was: researchers

This undated composite handout image provided by NASA, taken by the Hubble Space Telescope, shows the Great Red Spot in 2014, left; in 1995, top right; 2009, center right; and 2014, bottom right. (AP Photo/NASA)

Scientists have made their own version of Jupiter’s Great Red Spot in a lab, and it suggests that the spot’s cause is very different from what’s been postulated.

An existing theory holds that the spot is the result of chemicals underneath the planet’s clouds. But following the new research, experts say that the sun is responsible for the color: Sunlight may break up chemicals in Jupiter’s atmosphere, Phys.org reports.

Scientists in Pasadena, Calif., came to the conclusion after re-creating the effects at NASA’s Jet Propulsion Laboratory. They were able to get a Spot-like red effect by directing ultraviolet light at ammonia and acetylene, gases that are both found on the planet.

Their new theory: “Most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material,” says a researcher.

“Under the reddish ‘sunburn’ the clouds are probably whitish or grayish.” So why is it confined to just one spot? “The Great Red Spot … reaches much higher altitudes than clouds elsewhere on Jupiter,” the expert notes.

The Spot is actually a storm with winds of up to hundreds of miles per hour, theDaily Mail reports. Wind in the area brings ammonia particles closer to the sun, and a vortex keeps them there, the researchers say.

The Spot, by the way, is a lot smaller than it used to be.

Philae probe reaches comet, makes space history

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    This image of 67P/CG was shot by Philae’s ROLIS instrument during descent. The lander was approximately 2 miles from the comet’s surface when the image was taken. (ESA/Rosetta/Philae/ROLIS/DLR)

The European Space Agency’s Philae lander has made space history by successfully reaching the surface of comet 67P/Churyumov-Gerasimenko.

The landing, which took place at 11:03 a.m. ET, was accompanied by rapturous scenes at the ESA’s control room in Darmstadt, Germany.

Philae is the first probe to land on a comet.

“This is a big step for human civilization,” said ESA Director General Jean-Jacques Dordain, during a press conference in the Darmstadt control room.

Just before 1 p.m. ET ESA released an image of the comet taken by Philae during its descent, when the lander was about 2 miles above the surface of 67P/Churyumov-Gerasimenko.

Earlier on Wednesday, the ESA released the first image of its Philae lander separating from the Rosetta mothership on its ambitious mission toward the surface of comet 67P/Churyumov-Gerasimenko.

The separation, which took place around 4 a.m. ET, marked the start of a 7-hour journey to the comet’s surface. The Rosetta spacecraft and its Philae lander have been on a decade-long mission through the solar system to rendezvous with the comet.

The comet, which is about 2.5 miles wide, travels at speeds up to 84,000 miles per hour.

The washing machine-sized lander was designed to drift down to the comet and latch on using harpoons and screws. During the descent, scientists were powerless to do anything but watch, because the vast distance to Earth — 311 million miles — made it impossible to send instructions in real time.

“The harpoon is going down, we’re sitting on the surface,” said an ESA official in the agency’s  control room, shortly after 11 a.m. ET.

Later, however, Philae’s telemetry data suggested that the probe experienced something of a bumpy landing.

Indications were that the spacecraft touched down almost perfectly, save for an unplanned bounce, said Stephan Ulamec, head of the lander operation.

Thrusters that were meant to push the lander onto the comet’s surface, and harpoons that would have anchored it to the comet failed to deploy properly. Initial data from the spacecraft indicated that it lifted off again, turned and then came to rest.

“Today we didn’t just land once; we maybe even landed twice,” said Ulamac.

Scientists were still trying to fully understand what happened but so far most of the instruments are working fine and sending back data as hoped, he added.

The plan is that Rosetta and Philae will accompany the comet as it hurtles toward the sun and becomes increasingly active as it heats up. Using 21 different instruments, they will collect data that scientists hope will help explain the origins of comets and other celestial bodies.

The $1.6 billion mission launched in 2004.

Massive radio telescope probes sky for black holes, Milky Way

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The midterm election

The Arizona Radio Observatory’s newly acquired 40-foot dish is probing far into the sky, and bringing new light to galaxies far, far away.

The massively powerful radio telescope can detect galaxy matter other telescopes miss. Dr. Lucy Ziurys is the director of the Arizona Radio Observatory.

She explains the telescope is different in that it doesn’t detect light. Instead, scientists use it to detect very short radio waves, known as millimeter waves.

“By using this radio telescope, we can actually determine the chemical composition of our galaxy, stars, of material forming around stars. And we also use these telescopes to study black holes in our galactic center, and in the center of other galaxies,” said Dr. Ziurys.

The radio telescope is stationed at Kitt Peak National Observatory, just outside of Tucson. The scientists working with the dish come from various backgrounds, including astronomy, chemistry and biology.

“Our research relates to the interesting chemistry that occurs out in interstellar space… it relates to the origin of life, and the pre-biotic compounds that might be present out in space,” said Dr. Ziurys.

The telescope contains performance-enhancing features, like a reflector surface made of panels and a $14 million antenna that can move as fast as six degrees per second.

“It’s faster than all the other telescopes that have been built in the past. It’s about twenty times more accurate in terms of where it can point in the sky. So we’ll be able to look deeper into the molecular universe than we’ve ever been able to before,” said Dr. Ziurys.

The University of Arizona commissioned the telescope through an agreement with the European Southern Observatory. It is now the only university in the U.S. to own a modern radio telescope.

Virgin Galactic’s SpaceShipTwo crashes, one pilot killed

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Witness describes SpaceShipTwo explosion over desert

Virgin Galactic’s SpaceShipTwo space tourism rocket crashed during a test flight over the Mojave Desert Friday, killing one of the two pilots aboard and seriously injuring the other.

No cause of the crash has yet been determined.

Speaking at a press conference, Stuart Witt, CEO of the Mojave Air and Space Port, where the test took place, confirmed that an “inflight anomaly” occurred about two minutes after SpaceShipTwo was released from WhiteKnightTwo, the ‘mothership’ plane that carries it to a high altitude.

“I had confirmation of a mishap a few moments later, about 25 miles north of the airport,” he said.

Witt also confirmed one fatality in the crash, adding that the surviving pilot was treated at the scene and taken to a local hospital.

Kern County Sheriff Donny Youngblood said that the survivor had suffered major injuries.

“Our primary thoughts at this time are with the crew and families,” added George Whitesides, CEO of Virgin Galactic. “We’re doing everything that we can for them now.”

Kevin Mickey, president of Virgin Galactic’s partner Scaled Composites, which was conducting the powered test flight, said that investigators from the National Transportation Safety Board are expected to arrive on the scene Saturday morning. “We expect that the investigation will take several days,” he said.

Virgin Galactic founder Richard Branson is also on his way to the test site, and is expected to arrive Saturday morning. It was not immediately clear what effect the crash would have on the future of Virgin’s ambitious space tourism project.

Mickey confirmed that the two crash victims were Scaled Composites test pilots, but did not reveal their names.

Earlier on Friday, Virgin Galactic tweeted that SpaceShipTwo was flying under rocket power and then tweeted that it had “experienced an in-flight anomaly.”

Mickey was asked about SpaceShipTwo’s rocket motor during the press conference.

“We were flying a rocket motor today that had been thoroughly tested on the ground – we expected no anomalies with this motor today,” he said. “This motor configuration had flown a few times in the past.”

The Scaled Composites president added that a “new fuel formulation” was used during Friday’s test flight, but said that it had “been tested on the ground, many times.”

Friday’s flight marked the 55th for the spaceship, which was intended to be the first of a line of craft that would open space to paying civilians. At 60 feet long, SpaceShipTwo features two large windows for each of up to six passengers, one on the side and one overhead.

Virgin Galactic – owned by Branson’s Virgin Group and Aabar Investments PJS of Abu Dhabi – sells seats on each prospective journey for $250,000, with full payment due at the time of booking. The company says that “future astronauts,” as it calls customers, have visited Branson’s Caribbean home, Necker Island, and gone through G-force training.

Stephen Hawking, Justin Bieber, Ashton Kutcher and Russell Brand are among the celebrities to sign up for flights. Virgin Galactic reports taking deposits totaling more than $80 million from about 700 people.

A related venture, The Spaceship Co., is responsible for building Virgin Galactic’s space vehicles.

During testing for the development of a rocket motor for SpaceShipTwo in July 2007, an explosion at the Mojave spaceport killed three workers and critically injured three others. A California Division of Occupational Safety and Health report said the blast occurred three seconds after the start of a cold-flow test of nitrous oxide – commonly known as laughing gas – which is used in the propulsion system of SpaceShipTwo. The engine was not firing during that test.

Ken Brown, a photographer who witnessed Friday’s crash, saw the space tourism craft explode after it was released from WhiteKnightTwo.

“I could see that it was tumbling, and it wasn’t one piece,” Brown told Fox News’s Shepard Smith.

Branson says ‘we will persevere’ after Virgin Galactic’s SpaceShipTwo crash

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Richard Branson comments on SpaceShipTwo crash

Richard Branson, the founder of Virgin Galactic, whose SpaceShipTwo blew apart Friday after being released from a carrier aircraft, said Saturday that if they learn what went wrong– and can overcome it– the program will continue.

Branson, who was in Mojave, Calif., was asked at a press conference about the future of the program. He paused and said, “we would love to finish what we started some years ago.”

Federal accident investigators arrived to begin a probe into the cause of an accident that destroyed a prototype space tourism rocket ship during a test flight, killing one pilot and injuring another.

More than a dozen investigators in a range of specialties were forming teams to examine the crash site, collect data and interview witnesses, National Transportation Safety Board Acting Chairman Christopher A. Hart told a press conference at Mojave Air and Space Port, where the winged spacecraft was under development.

Hart said the investigation will have similarities to a typical NTSB probe as well as some differences.

“This will be the first time we have been in the lead of a space launch (accident) that involved persons onboard,” said Hart, noting that the NTSB did participate in investigations of the Challenger and Columbia space shuttle disasters.

Hart said he did not immediately know the answers to such questions as whether the spaceship had flight recorders or the altitude of the accident, but noted that test flights are usually well documented.

Branson has been the front-runner in the fledgling race to give large numbers of paying civilians a suborbital ride that would let them experience weightlessness at the edge of space.

The NTSB investigators were expected to head to an area about 20 miles from the Mojave airfield where debris from the spaceship fell over a wide area of uninhabited desert.

The spacecraft broke up after being released from a carrier aircraft at high altitude, according to Ken Brown, a photographer who witnessed the plane breaking apart.

One pilot was found dead inside the spacecraft and another parachuted out and was flown by helicopter to a hospital, Kern County Sheriff Donny Youngblood said.

The accident occurred just as it seemed commercial space flights were near, after a period of development that lasted far longer than hundreds of prospective passengers had expected.

Branson once envisioned operating flights by 2007. Last month, he talked about the first flight being next spring with his son.

“It’s a real setback to the idea that lots of people are going to be taking joyrides into the fringes of outer space any time soon,” said John Logsdon, retired space policy director at George Washington University.

Friday’s flight marked the 55th for SpaceShipTwo, which was intended to be the first of a fleet of craft. This was only the fourth flight to include a brief rocket firing. The rockets fire after the spacecraft is released from the underside of a larger carrying plane. During other flights, the craft either was not released from its mothership or functioned as a glider after release.

At 60 feet long, SpaceShipTwo featured two large windows for each of up to six passengers, one on the side and one overhead.

The accident’s cause was not immediately known, nor was the altitude at which the blast occurred. The first rocket-powered test flight peaked at about 10 miles above Earth. Commercial flights would go 62 miles or higher.

The problem happened about 50 minutes after takeoff and within minutes of the spaceship’s release from its mothership, said Stuart Witt, CEO of the Mojave Air and Space Port.

Virgin Galactic — owned by Branson’s Virgin Group and Aabar Investments PJS of Abu Dhabi — sells seats on each prospective journey for $250,000. The company says that “future astronauts,” as it calls customers, include Stephen Hawking, Justin Bieber, Ashton Kutcher and Russell Brand. The company reports receiving $90 million from about 700 prospective passengers.

Ken Baxter was one of those who had signed up to be among the first to make the flight.

Despite the disaster, Las Vegas resident Baxter said he was confident that the flight will happen one day.”It’s very sad for the test pilots, but I’m ready to go into space with Richard Branson,” he said.

Friday’s accident was the second this week involving private space flight. On Tuesday, an unmanned commercial supply rocket bound for the International Space Station exploded moments after liftoff in Virginia.

SpaceShipTwo is based on aerospace design maverick Burt Rutan’s award-winning SpaceShipOne prototype, which became the first privately financed manned rocket to reach space in 2004.

“It’s an enormously sad day for a company,” Rutan told The Associated Press in a phone interview from his home in Idaho, where he has lived since retiring.

Friday’s death was not the first associated with the program. Three people died during a blast at the Mojave Air and Space Port in 2007 during testing work on a rocket motor of SpaceShipTwo.

Unmanned Antares rocket explodes after liftoff

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NASA officials warned people to keep away from potentially hazardous debris after an unmanned cargo rocket bound for the International Space Station exploded Tuesday over a launchpad in Virginia.

No injuries were reported following the first catastrophic launch in NASA’s commercial spaceflight effort.

The accident at Orbital Sciences Corp.’s launch complex at Wallops Island was sure to draw criticism over the space agency’s growing reliance on private U.S. companies in this post-shuttle era. NASA is paying billions of dollars to Orbital Sciences and the SpaceX company to make station deliveries, and it’s counting on SpaceX and Boeing to start flying U.S. astronauts to the orbiting lab as early as 2017. This was the fourth flight by Orbital Sciences to the orbiting lab.

Orbital Sciences’ executive vice president Frank Culbertson said things began to go wrong 10 to 12 seconds into the flight and it was all over in 20 seconds when what was left of the rocket came crashing down. He said he believes the range-safety staff sent a destruct signal before it hit the ground. The company said everyone at the site had been accounted for, and the damage appeared to be limited to the facilities.

Bill Wrobel, director of NASA’s Wallops Flight Facility, said crews were letting the fires burn out late Tuesday and set up a perimeter to contain them in the darkness

There was no hint of any trouble until the rocket exploded. This was the second launch attempt for the mission. Monday evening’s try was thwarted by a stray sailboat in the rocket’s danger zone. The restrictions are in case of just such an accident that occurred Tuesday.

Culbertson said the top priority will be repairing the launch pad “as quickly and safely as possible.”

He said he could not guess how long it will take to determine the cause of the accident and to make repairs. Culbertson said the company carried insurance on the mission, which he valued at more than $200 million, not counting repair costs.

He stressed that it was too soon to know whether the Russian-built engines, modified for the Antares and extensively tested, were to blame.

“We will understand what happened — hopefully soon — and we’ll get things back on track,”Culbertson told his team an hour after the failure. “We’ve all seen this happen in our business before, and we’ve all seen the teams recover from this, and we will do the same.”

The Wallops facility is small compared to NASA’s major centers like those in Florida, Texas and California, but vaulted into the public spotlight in September 2013 with a NASA moonshot and the first Cygnus launch to the space station.

Michelle Murphy, an innkeeper at the Garden and Sea Inn, New Church, Virginia, where launches are visible across a bay about 16 miles away, witnessed the explosion.

“It was scary. Everything rattled,” she said. “There were two explosions. The first one we were ready for. The second one we weren’t. It shook the inn, like an earthquake.”

The roomful of engineers and technicians were ordered to maintain all computer data for the ensuing investigation. Culbertson advised his staff not to talk to news reporters and to refrain from speculating among themselves.

“Definitely do not talk outside of our family,” said Culbertson, a former astronaut who once served on the space station.

This newest Cygnus cargo ship — named for the swan constellation — had held 5,000 pounds of space station experiments and equipment for NASA, as well as prepackaged meals and eagerly awaited crab cakes, freeze-dried for safe eating. It had been due to arrive at the orbiting lab Sunday.

By coincidence, the Russian Space Agency was proceeding with its own supply run on Wednesday, planned well before the U.S. mishap. And SpaceX is scheduled to launch another Dragon supply ship from Cape Canaveral in December; some items may be changed out to replace what was lost on the Cygnus.

NASA space station program manager Mike Suffredini told reporters that the station and its crew have plenty of supplies on board — about five months’ worth — even without the upcoming launches.

Among the science instruments that were lost: a meteor tracker and 32 mini research satellites, along with numerous experiments compiled by schoolchildren. Suffredini promised the experimenters would get a chance to refly their work.

The two Americans, three Russians and one German on the orbiting lab were informed promptly of the accident.

Until Tuesday, all of the supply missions by the Virginia-based Orbital Sciences and California-based SpaceX had been near-flawless.

President Obama has long championed this commercial effort, urging that NASA focus its human spaceflight effort less on nearby orbit and more on destinations like asteroids and Mars. He was in Wisconsin for a campaign rally Tuesday evening and was kept abreast of the accident and its developments.

SpaceX’s billionaire founder and chief officer Elon Musk — whose company is the face, in many ways, of the commercial effort — said he was sorry to learn about the failure. “Hope they recover soon,” he said in a tweet.

Support poured in from elsewhere in the space community late Tuesday night.

“We are with you @OrbitalSciences and @NASA,” former NASA astronaut Leland Melvin said via Twitter.

“Very sorry to see the Antares rocket launch failure,” said Chris Hadfield, a former Canadian astronaut who served as space station commander last year. “Spaceflight is hard. Very glad that no one was hurt. Now time to sort out why & effects.”

John Logdson, former space policy director at George Washington University, said it was unlikely to be a major setback to NASA’s commercial space plans. But he noted it could derail Orbital Sciences for a while given the company has just one launch pad and the accident occurred right above it.

“It shows the wisdom of having more than one source” for launches, Logsdon said. Nevertheless, he added, “This is going to put the logistics chain for the station under some stress for a period of time.”

U.S. Sen. Bill Nelson, a Florida Democrat who flew on a space shuttle right before the 1986 Challenger disaster, said in a statement, “Space flight is inherently risky. As we push the frontiers of space there will be setbacks. But our commercial space ventures will ultimately be successful.”

The explosion also hit Orbital Science’s stock, which fell more than 15 percent in after-hours trading.

Saturn’s ‘Death Star’ moon Mimas is weird inside

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A photo of Saturn’s moon Mimas. (NASA/JPL)

There’s something strange going on below the surface of Saturn’s Death Star-looking moon Mimas, a new study suggests.

Mimas’ rotation and its orbit around Saturn make the moon look like it’s rocking and back forth and oscillating similar to the way a pendulum swings. The rocking motion is called libration, and it’s commonly observed in moons that are influenced by the gravity from neighboring planets. However, using images of the moon captured by the Cassini spacecraft, Radwan Tajeddine, a research associate at Cornell University, discovered that the satellite’s libration was much more exaggerated in one spot than predicted. Heexpects it must be caused by the moon’s weird interior.

“We’re very excited about this measurement because it may indicate much about the satellite’s insides,” Tajeddine said in a statement. “Nature is essentially allowing us to do the same thing that a child does when she shakes a wrapped gift in hopes of figuring out what’s hidden inside.” [See photos of Mimas, Saturn’s Death Star Moon]

Feel the libration

Astronomers have long been using the rotation and orbit of celestial bodies to guess what their interiors might be like. Most of the rocking is explained by the interacting forces from Mimas’ rotation and orbit, but one libration was much larger than expected.

Tajeddine and the team tested five different models of what Mimas might look like below the surface to see which one could explain the exaggerated rocking. They quickly ruled out the possibility that Mimas has a uniform interior, an interior with two different layers or an abnormal mass under the moon’s 88-mile-long crater that makes it look like the Death Star from the “Star Wars” franchise.

However, the last two models could both explain Mimas’ extreme libration. One idea is that the moon has an elongated, oval-shaped core. This elongation might have happened as the moon formed under the push and pull of Saturn’s rings. The teeter tottering could also come from a subsurface ocean, similar to the one on Jupiter’s moon Europa.

While it’s still a possibility, Tajeddine thinks the subsurface ocean is an unlikely explanation. Astronomers have not observed any evidence of liquid water on Mimas, unlike some of Saturn’s other moons. The heat radiating from the core escapes through the moon’s ice-covered shell and would cause any subsurface ocean that existed to quickly freeze.

3D Mimas map

Mimas is the smallest and closest of Saturn’s main eight moons. Its giant crater covers almost one-third of the moon’s icy surface.

For the past 10 years,the Cassini space probe has been collecting data on Mimas, Saturn and the ringed wonder’s other natural satellites. The Imaging Science Subsystem (ISS) onboard Cassini is a two-camera system that captures ultraviolet and infrared images of Saturn and its moons.

Tajeddine and a team of researchers sifted through dozens of images captured by ISS and created a 3D map of the moon from the photos to study how Mimas spins and orbits Saturn.

The new research was published this week in the journal Science.

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    This NASA graphic shows the visibility area of the partial total solar eclipse of Oct. 23, 2014. The eclipse will be visible from most of the United States, weather permitting. (Science@NASA)

Mark Thursday (Oct. 23) on your calendar as “Solar Eclipse Day,” for if the weather cooperates, you should have no difficulty observing a partial eclipse of the sun.

Nearly all of North America, except for a portion of eastern Canada and a slice of eastern New England, will experience the partial solar eclipse this week. People who live east of a line running from roughly Quebec City to Montauk Point, New York, will miss out on the solar show, since the sun will set before the dark disc of the moon begins to encroach upon it.

The several hundred thousand people who inhabit parts of Siberia will get a brief view around local sunrise time — but on Friday (Oct. 24), because this part of the eclipse visibility zone is to the west of the International Date Line. So, for this part of the world, the event will begin on the day after it ends! [Partial Solar Eclipse of October 2014: Visibility Maps]

Greatest eclipse, with more than four-fifths of the sun’s diameter covered by the moon, will occur over the Canadian Arctic at M’Clintock Channel, an arm of the Arctic Ocean, which divides Victoria Island from Prince of Wales Island in the territory of Nunavut.

The rest of North America will see less of the sun covered.

For much of Alaska, western and central Canada, the Pacific Northwest and the northern Plains, more than 60 percent of the sun’s diameter will be covered by the passing new moon. For the Southwest and central and southern Plains, the eclipse magnitude diminishes to between 40 and 60 percent. Across the Ohio, Tennessee and Mississippi valleys, maximum eclipse will coincide with sunset, while farther to the east, the moon will only begin its encroachment onto the sun’s disc as it sets.

In the United States, more than half of the sun’s diameter will be covered north of a line extending from San Francisco to the Oklahoma panhandle. But this will occur in the mid- to late-afternoon hours — too late to dim the landscape abnormally. Some people might still attempt to record the gradual fading and recovery of the sunlight with sensitive photographic exposure meters. These can be set to view a light-colored wall that faces toward the Southwest.

Be careful!

Unlike a total eclipse of the sun, which concentrates viewing excitement into a few fleeting minutes, a partial solar eclipse can be watched without urgency.

Observations can be made with the naked eye, binoculars or telescopes of any size. Of course, eyes and instruments must be protected by special filters from the intense light and heat of the focused solar rays. Keep in mind that the sun is no less dangerous to look at during a partial eclipse than it is on a normal sunny day. Don’t be tempted to squint at the spectacle or steal unsafe glances just because part of the sun’s surface is blocked by the moon! [How to Safely Observe the Sun (Infographic)]

During the eclipse, drawings and photographs can be made to show the moon’s progress across the solar disc. If your camera is capable of taking multiple exposures through a wide-angle lens, the whole phenomenon might be captured on a composite scene, but a telephoto lens is necessary if you’re trying to bring out the jagged profile of the lunar limb. The moon may temporarily hide some sunspots.

At locations where sunset occurs before the end of partial eclipse, some unusual pictures might be obtained, especially if horizon conditions favor the occurrence of the atmospheric phenomenon known as the green flash on the sun’s upper rim.

But again, be careful! Only attempt such observations if you have the proper solar filters. If you don’t have them, don’t watch the eclipse directly, either with the naked eye or through binoculars or a telescope — serious and permanent eye damage will likely result.

Pinhole eclipses

People who aren’t expecting the event will probably not notice it, although some might see the peculiar shape of “pinhole” images of the sun cast by trees and bushes. Indoors, closed Venetian blinds in a southwest-facing window may produce rows of such images, where sunlight passes through small openings.

Also, a small hole pierced in a dark shade will cast a sizable eclipse image onto a wall, floor or screen.  Thus, even a person confined indoors can watch this celestial phenomenon.

Local circumstances and eclipse times for the United States can be found here:http://eclipse.gsfc.nasa.gov/OH/OHtables/OH2014-Tab05.pdf

And information for a number of cities in Canada and Mexico is listed here:

http://eclipse.gsfc.nasa.gov/OH/OHtables/OH2014-Tab04.pdf

These data are courtesy of eclipse expert Fred Espenak, who works at NASA’s Goddard Space Flight Center in Maryland.

A warm-up for 2017

While Thursday’s solar eclipse will be exciting, some skywatchers in North America are already looking ahead three years.

On Aug. 21, 2017, the first total eclipse of the sun to be visible from the contiguous 48 states in nearly four decades will sweep in an east-southeast direction from Oregon to South Carolina. So, for many, Oct. 23 will provide a rehearsal for the big event of 2017.

Although it lacks many phenomena that occur during a total eclipse, a partial one nonetheless provides an excellent opportunity to try out instruments and procedures