Science News

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Moon patterns explained
Electric fields enveloping magnetic bubbles create lunar swirls

By Meghan Rosen
Web edition : Wednesday, July 11th, 2012

Scientists have charged up an old moon mystery. New research suggests that swirling designs on the dusty lunar surface might be the product of electric fields generated by pockets of magnetic bubbles.

“People have been looking at these strange, mysterious structures since the invention of the telescope,” says physicist Ruth Bamford of the Rutherford Appleton Laboratory in Didcot, England. “Now we know exactly how they are made.”

The milky patterns stand out like pale flesh against darkly tanned skin. It’s as if you used sunblock to paint whorls on your arm and then spent the day outside, says planetary geologist Georgiana Kramer of the Lunar and Planetary Institute in Houston. The sun would color everything but the protected skin, leaving the whorls white.

Scientists have long suspected that weak magnetic fields near the moon’s surface might shape the looping patterns. The moon doesn’t have a dynamo-driven magnetic field like Earth’s, but researchers have found patchy magnetic bubbles scattered across the lunar crust.

A stream of charged particles (glowing purple) flows around a magnet in a solar wind tunnel experiment. Credit: Courtesy of R. Bamford

Data from the Apollo missions fed a 1970s theory that the moon’s magnetic bubbles act like a solar wind sunblock. The solar wind — a steady stream of charged particles from the sun — constantly buffets the moon, turning pale lunar dust dark. But magnetic bubbles might protect the moon’s crust, keeping silvery soil fresh and young-looking.

The mystery, Bamford says, was how such puny fields can deflect the raging solar wind. The answer is the bubbles’ electric field, she and her colleagues suggest in an upcoming Physical Review Letters.

Usually, the solar wind’s charged particles travel together. But when the wind smacks into the moon’s magnetic bubbles, flimsy negatively charged particles skirt around the bubble and hefty positive ones try to penetrate it. Splitting apart these oppositely charged particles whips up a heavy-duty electric field.

Bamford’s team created a scaled-down laboratory version to find out if man-made magnetic bubbles could also deflect rushing rivers of particles.

The researchers used a device called a solar wind tunnel to shoot a jet of blazing particles down a tube. The searing stream toasted any object in its path, except, the team discovered, a magnet. The scientists showed that a thin electric field formed around the magnet, shielding it — and anything behind it — from the scorching flow. “It works incredibly well,” Bamford says. Even a marshmallow placed in the magnet’s wake would escape melting, she says.

And if a tiny magnet — only slightly larger than an eraser tip — could make a protective electric skin, the moon’s much larger magnetic bubbles might also be able to.

“The work ties a bunch of ideas together,” says planetary scientist Ian Garrick-Bethell of the University of California, Santa Cruz. “And the lab model is really cool.”

Bright white designs called lunar swirls stretch across about 60 kilometers of the moon’s surface. Credit: NASA

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Top airports for spreading germs IDed
Major hubs with far-flung flights are most efficient

By Rachel Ehrenberg
Web edition : Friday, July 27th, 2012

An infectious disease that really wants to go global would do well boarding planes at JFK or LAX, according to a new computer simulation that ranks U.S. airports by their potential to kick-start an epidemic.

The simulation could help public health officials decide how and where to allocate resources such as vaccinations in the early days of an outbreak, says Ruben Juanes of MIT, who describes the analysis online July 19 in PLOS ONE.

Many simulations of how epidemics spread focus on the final outcome, such as how many people would ultimately be infected. This new work is mostly concerned with how the location of an initial outbreak affects the subsequent pandemic, says complex systems scientist Dirk Brockmann of Northwestern University in Evanston, Ill.

Surprisingly, the total number of passengers moving through an airport isn’t the deciding factor. By that measure, Atlanta’s airport — the busiest in the country — would be ideal for spreading germs. What’s key is how connected the airport is to other well-connected airports.

“You are a good spreader if your neighbors are good spreaders,” Juanes says. “That’s what’s really essential.”

Once an epidemic is well under way, other factors such as how the germ moves from one person to another seem to be most important, he says.

Juanes and his colleagues used air travel data on all flights originating or landing in the U.S. from January 2007 to July 2010 to construct an air transportation network made up of 1,833 airports and roughly 50,000 connections. The researchers also extracted airport waiting times from passenger itineraries. Then they developed a computer program that incorporated information on people’s travel patterns and how infectious diseases move from person to person.

The program ranks 40 major U.S. airports for how influential they are at spreading a disease originating in their home city. That New York City’s John F. Kennedy International Airport came in first and Los Angeles International was second isn’t so surprising. But third on the list is Honolulu International, which is only the 25th busiest airport in the country. Yet Honolulu is supremely positioned for sending sick people to myriad far-flung destinations. The airport is well-connected to massive hubs, it sends and receives travelers from both East and West, and its flight schedule is dominated by long-range routes.

Atlanta’s airport, on the other hand, ranked eighth. While it’s very busy in terms of number of passengers, most of the travel to and from Atlanta is regional. The flights in and out are on the shorter side and are to places that aren’t well connected, notes Juanes.

For passengers in the Washington, D.C., area, traveling via Dulles really helps germs out; it ranked seventh most influential. Baltimore’s airport ranked 23rd and Reagan National 30th.

U.S. airports that are hubs and are connected to lots of other hubs, such as Honolulu International and JFK, excel at spreading infectious diseases that originate in the airport’s home city. Credit: Christos Nicolaides/MIT

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Curiosity readies for dramatic entrance
Mars rover to touch down August 5

By Nadia Drake
Web edition : Tuesday, July 31st, 2012

Editor’s note: This is the first of two articles previewing the Mars Curiosity rover’s upcoming Mars landing. This installment describes the vehicle’s landing on the Red Planet, scheduled for Sunday evening, August 5, Pacific Daylight Time; the next will cover the rover’s science mission. Science News astronomy writer Nadia Drake will be covering the landing live from NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

An enormous robot is about to hit the red dirt of Mars — not too hard, NASA hopes — in search of life-friendly environments, or remnants of them. The Curiosity rover’s off-road adventures will begin only if it survives a daring seven-minute, 125-kilometer plunge through the planet’s carbon dioxide atmosphere.

Scientists on Earth expect to observe the touchdown at 10:30 p.m. Pacific Daylight Time on August 5.

Curiosity, which is the size of a small car, is the newest and largest addition to NASA’s family of robotic planet explorers. Its target on Mars is Gale Crater, 154 kilometers wide and home to a massive peak that scientists call Mount Sharp.

After a nearly nine-month journey, the spacecraft carrying Curiosity will enter Mars’ thin atmosphere going approximately 21,250 kilometers per hour. Seven minutes later, just before the rover sets wheels on the fourth rock from the sun, it had better be going approximately zero.

“The Curiosity landing is the hardest NASA robotic mission ever attempted,” says John Grunsfeld, associate administrator for NASA’s Science Mission Directorate. “This is risky business.”

Rather than being cushioned by interplanetary airbags — as the Spirit and Opportunity rovers were in 2004 — Curiosity’s touchdown involves a “sky crane” maneuver that seems ripped from a James Bond film.

That concept includes a parachute deployment 11 kilometers above the planet, once the atmosphere has slowed the spacecraft to a relatively pokey 1,400 kilometers per hour. At 1.6 kilometers above the surface, while falling at nearly 300 kilometers per hour, the parachute is designed to separate from the rover, leaving the craft folded up like a giant bionic insect underneath what’s called the descent vehicle.

Then the descent vehicle should fire its retro-rockets, slowing the plunge even more and setting the stage for the sky crane maneuver to begin. At 20 meters above the planet’s surface — and now dropping at just 2.7 kilometers per hour — the rover will descend from the mother ship on nylon cables and the still-tethered pair will move slowly toward the surface.

“Is it crazy? Well, not so much,” says NASA’s Doug McCuistion. “Once you understand it, it’s not a crazy concept. It works.”

After the rover has stretched its legs and is safely on the ground, it will sever the umbilical cords, allowing the descent vehicle to fly off and ditch itself in the dust about half a kilometer from the landing site.

During the spacecraft’s entry, descent and landing, NASA’s Mars Odyssey orbiter will act as an interplanetary Internet router, relaying information from the rover to scientists on Earth in near real time. (It takes almost 14 minutes for radio signals to travel between the two planets.)

And there will be video: The one-ton, six-wheeled, nuclear-powered rover will film the descent with a camera on its belly. Scientists hope to release the video soon after landing. “That’s just going to be an awesome video, landing on the surface of Mars,” says project scientist John Grotzinger of Caltech. “We’re going to go swinging out like an amusement park ride, and maybe see the flank of Mount Sharp, and then come back down again and see the ground, and the other side — maybe the crater rim.”

After spending a bit of time making sure that all systems are go, the rover will make tracks, driven by scientists wielding computer commands from nearly 250 million kilometers away. “I’m really envious of the rover drivers,” Grotzinger says. “I always wanted to be a rover driver.”

If the spacecraft comes down safely, team members will begin working in shifts on Mars time, synchronizing their days and nights to match the Martian day, which is roughly 40 minutes longer than an Earth day. It’s like being perpetually jet-lagged. “Every day, you come in to work 40 minutes later,” says Ryan Anderson, a planetary scientist at the U.S. Geological Survey Astrogeology Science Center in Flagstaff, Ariz. “If you started in the morning, several weeks later, you’re starting in the middle of the night.”

For at least 90 days, Curiosity will trundle along during the Martian day while scientists on Earth work the Red Planet’s night shift. “We wake up when the rover is going to sleep and work through the Mars night so that by morning, we can send the rover new commands for the next day,” Anderson says.

Of course, all that assumes Curiosity will land safely. If it doesn’t? “We don’t talk about that much,” Anderson says.

Curiosity, NASA’s newest Mars rover, will search for signs of life-friendly environments on Mars — if it survives the journey to the Martian surface on August 5. The journey’s final step is a maneuver that engineers call the sky crane (illustrated), in which a hovering spacecraft lowers the rover to the reddish soil. Credit: NASA; JPL-Caltech

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BLOG: Mission control before the party
Days before Curiosity's planned Martian landing, Nadia Drake checks out JPL's space central

By Nadia Drake
Web edition : Friday, August 3rd, 2012

Though nearly empty Thursday afternoon, mission control at NASA’s Jet Propulsion Laboratory will be packed with more than 100 people when the Mars rover Curiosity is set to touch down this Sunday, August 5.

But for now, the control room is quiet, illuminated by a dim, soothing blue light. Data and images flash across the enormous screens hanging at the front of the room, which also serves as the nerve center for the Deep Space Network, an array of telescopes tasked with tracking the spacecrafts JPL sends zooming around the solar system.

One of the displays tells the team which of these 24 spacecraft are currently phoning home and where on Earth the call is received. At this moment, the Mars Reconnaissance Orbiter is talking to a telescope near Madrid. The Dawn spacecraft, in orbit around the asteroid Vesta, is listening as an antenna in Canberra, Australia, relays instructions. And Juno, on the way to Jupiter, is phoning in to Goldstone, Calif. “There’s a minimum of five engineers here at all times,” says Jim McClure, the facility’s operations manager. “They’re monitoring the data flow from the spacecraft.”

Atop the oxymoronic clean dirt in the In-Situ Instrument Laboratory are Mars Science Laboratory test conductor James Wang, Curiosity's twin on Earth ... and the rubber chicken, perched on the pile of rocks at back, added to the scene during the testing one of the rover’s imaging instruments. Credit: N. Drake

Staffed 24 hours a day since 1964, the Space Flight Operations Facility — which houses mission control — is now a U.S. historical landmark.

In the next room over is the cruise mission support area, a space lined with rows of computers set in front of a large American flag. Here, engineers are responsible for shooting the Mars Science Laboratory spacecraft toward Gale Crater like a well-aimed, cone-shaped meteorite. “We actually picked it up just a few minutes after it launched from Florida, and have been controlling it from here ever since,” says flight director David Oh.

An hour before landing on Sunday evening, a can of peanuts will be popped open and passed around the room — scientists too, it seems, are superstitious and adhere to decades-old rituals. “It’s always been a lucky charm for us,” Oh says. “I think missions have always seemed to work out better when we had the peanuts there.”

In another building on the JPL campus, a mock Curiosity rover is trundling around atop a seeming paradox: clean dirt, a grayish substance that serves as a stand-in for Mars’ red sands. “It’s actually crystals. Small, crushed crystals,” says Eric Aguilar, systems integration and tech manager for the Mars Science Laboratory. “It doesn’t cause as much dust.”

Here, in the In-Situ Instrument Laboratory, scientists test drive landing strategies and practice rover maneuvers. Years ago, the airbags that cushioned the Mars Exploration Rovers Spirit and Opportunity once filled the room to its ceiling. And later, when Spirit found herself stuck on a rock, scientists rolled out her Earthly twin and began sorting out how to free the rover from hundreds of millions of kilometers away.

Now, the team is getting ready for Curiosity’s surface operations — under the watchful eye of a rubber chicken perched atop a pile of rocks. The chicken moved in while the team was testing the Mars Descent Imager, a camera mounted on the rover’s belly. “We needed something to take an image of,” Aguilar explains. “We like to surprise the operations team as they get the data down and take a look.”

The mission control room at JPL in Pasadena, Calif., will be buzzing on the night of August 5, when the NASA rover Curiosity is set to touch down on Mars. Before the big day, the room’s screens relay information about the status of JPL’s 24 interplanetary spacecraft. Credit: N. Drake