The 33-year odyssey of NASA'sVoyager 1 spacecraft has reached a distant point at the edge of our solar system where there is no outward motion of solar wind.
Now hurtling toward interstellar space some 17.4 billion kilometers (10.8 billion miles) from the sun,Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars. The event is a major milestone in Voyager 1's passage through the heliosheath, the turbulent outer shell of the sun's sphere of influence, and the spacecraft's upcoming departure from our solar system.
"The solar wind has turned the corner," said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. "Voyager 1 is getting close to interstellar space."
Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the solar wind dramatically slows down and heats up in the heliosheath.
Launched on Sept. 5, 1977, Voyager 1 crossed the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1's Low-Energy Charged Particle Instrument to deduce the solar wind's velocity. When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft's speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 17 billion kilometers (10.6 billion miles) from the sun.
Because the velocities can fluctuate, scientists watched four more monthly readings before they were convinced the solar wind's outward speed actually had slowed to zero. Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 20 kilometers per second each year (45,000 mph each year) since August 2007, when the solar wind was speeding outward at about 60 kilometers per second (130,000 mph). The outward speed has remained at zero since June.
The results were presented today at the American Geophysical Union meeting in San Francisco.
"When I realized that we were getting solid zeroes, I was amazed," said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again."
Scientists believe Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles. Scientists are putting the data into their models of the heliosphere's structure and should be able to better estimate when Voyager 1 will reach interstellar space. Researchers currently estimate Voyager 1 will cross that frontier in about four years.
"In science, there is nothing like a reality check to shake things up, and Voyager 1 provided that with hard facts," said Tom Krimigis, principal investigator on the Low-Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece. "Once again, we face the predicament of redoing our models."
A sister spacecraft, Voyager 2, was launched in Aug. 20, 1977 and has reached a position 14.2 billion kilometers (8.8 billion miles) from the sun. Both spacecraft have been traveling along different trajectories and at different speeds. Voyager 1 is traveling faster, at a speed of about 17 kilometers per second (38,000 mph), compared to Voyager 2's velocity of 15 kilometers per second (35,000 mph). In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.
SpaceX Corp. tested its Falcon 9 and a fully functioning Dragon capsule combination during a brief mission launched from Cape Canaveral Air Force Station on Dec. 8, 2010. The uncrewed capsule parachuted back to Earth about three hours after liftoff following maneuvers in orbit, a first for the privately owned company. Flames erupted from the base of the Falcon 9 at 10:43 a.m. as it sat at Launch Complex-40. A few seconds later, the rocket and its Dragon capsule pushed above the surrounding lightning towers and headed into orbit.
The first stage separated on time and the second stage took over as planned. A camera on board the rocket showed the Dragon capsule separate from the second stage and trunk to orbit on its own.
After working through its maneuvers, the Dragon fired its braking rockets to begin re-entry. Like the Apollo spacecraft of the 1960s and 70s, the Dragon pierced Earth's atmosphere protected by an ablative heat shield. Parachutes deployed and the spacecraft splashed down in the Pacific Ocean off the coast of California.
"This has really been better than I expected," said Elon Musk, the founder and CEO of SpaceX. "It's actually almost too good."
The test flight was the first under a NASA contract called COTS, short for Commercial Orbital Transportation Services. The contract was set up to encourage private companies to ship cargo to the International Space Station. "This is really an amazing accomplishment for SpaceX," said Alan Lindenmoyer, NASA's Commercial Crew and Cargo program manager. "From all indications, it looks like it was 100 percent successful."
It was the second test flight for the Falcon 9, a 180-foot-tall, medium-lift booster SpaceX developed in part to service the station. The first Falcon 9 successfully launched a Dragon capsule simulator into orbit on June 4.
"We're beyond the 'Is it possible?' We did it and now we move on," said Gwynne Shotwell, president of SpaceX.
The successful mission could clear the way for a Dragon spacecraft to rendezvous with the station sometime next year, potentially delivering cargo on that flight.
Before the launch, NASA voiced a high level of support for the mission. "Getting this far this fast has been a remarkable achievement," said Phil McAlister, NASA's acting director of Commercial Space Flight Development. "No matter how this spaceflight goes, we are committed to this program."
NASA wants rockets like the Falcon 9 and Orbital Sciences' Taurus II to carry important supplies, experiments and equipment to the space station after the space shuttle fleet is retired in 2011.
The rockets and capsules could one day carry astronauts to the station as well. But for this flight, the pressure was on SpaceX to demonstrate its nine-engine booster and accompanying capsule would work as advertised.
Long before a space shuttle crew spots its intended landing target, mission controllers closely monitor the spacecraft, the astronauts and the weather at a roster of runways around the globe. Meanwhile, support crews are ready and eager to usher the astronauts in on the last leg of their journey.
The preferred finish line is the shuttle's home base at NASA's Kennedy Space Center in Florida -- a 15,000-foot-long runway that is about as wide as the length of a football field. "The 'go' for deorbit burn is usually done about the time we're in our last briefing," said Richard Merritt, a landing support manager with United Space Alliance. "You know they're not going to California, they're definitely coming here. So everybody kind of hoots and hollers and then we head out to the vehicles."
Construction of Kennedy's Shuttle Landing Facility wrapped up in 1976, but the site didn't host any shuttles until 1984. From the first shuttle mission in 1981, the primary landing site was Edwards Air Force Base, adjacent to NASA's Dryden Flight Research Center in California.
Merritt said Florida's marshy terrain was the main reason it took nearly a decade to move from one coast to another.
"If you didn't make the runway here, you'd be talking to the alligators," Merritt said. "Out in the desert, we landed on the dry lakebed. It's just lots of room to land if you had some kind of problem and you didn't quite make the runway."
Columbia was the first shuttle to complete a spaceflight when it touched down on the desert's dry, expansive target April 14, 1981, ending the STS-1 mission.
As NASA's back-up site today, mainly because of Florida's often-finicky weather, Edwards has welcomed home more than 50 shuttle crews.
NASA Convoy Commander and Ground Operations Manager Dean Schaaf said the main difference in landing at Kennedy and Edwards is all in the processing. At Kennedy, ground crews get a shuttle ready to be moved off the runway to its hangar, then three or four hours later, it's towed to an orbiter processing facility. "Out there, we tow it up to the mate-demate device, the MDD, and we have side access platforms that lower down and around the orbiter and we do all the processing," Schaaf said. "It takes us seven days from landing to being ready to ferry after we attach the tailcone and back out and everything."
As expected, Schaaf said, processing outdoors has its share of hurdles.
"It's all done out in the elements and we have had rain, and hail and lightning . . . all of those elements to work around out there at Dryden."
Kennedy and Edwards aren't the only options for the shuttle. There's also White Sands Space Harbor in New Mexico, which is where astronauts practice landing their Shuttle Training Aircraft because of its close proximity to NASA's Johnson Space Center in Houston. It's only been called upon one time to host a real shuttle landing, though: Columbia on the STS-3 mission on March 30, 1982.
It wasn't easy processing the shuttle in the gypsum-filled desert, though. And Merritt said there's a reason it's called "white sands."
"Parts of it look like a moon with dunes. It's just pure, pure white, part of the desert is. So it's a real fine powder . . . not quite like flour, but it's real fine and gets into everything," Merritt said. After that first-and-only landing, NASA chose to relocate the processing turnaround area to minimize the wind. However, Schaaf said it would still take about 46 days to prepare a shuttle for its return to Kennedy.
"We’ve built a tow way from the lakebed over to the west side of the range and we're out of the blowing gypsum. We have a pad, a 100 by 100-foot turnaround pad there, that the shuttle would be parked on. And all the processing would be done off of that concrete slab," Schaaf said.
The end of a mission is not the only time NASA focuses on a landing site. If a shuttle were to encounter a problem during launch, it could go to a transoceanic abort landing site, also called a TAL site. There are two in Spain -- Moron and Zargoza --and one in southern France -- Istres. Other countries that once hosted TAL sites include the Republic of the Gambia, Senegal and Morocco.
"The Shuttle Landing Facility reminds me of the site we used to have in Ben Guerir, Morocco. It was a landing strip out in the middle of the desert with a tower and very little else. And we built a building there and we used that for missions all the way up until the early 2000s when we closed that site and opened up Istres, France," Schaaf said.
Glen Lockwood, also a NASA ground operations manager, flies out to a TAL site before every launch and said even if it's a perfect day in Florida, bad weather elsewhere could be a showstopper.
"Our No. 1 concern here is safety," Lockwood said. "One site needs to be ready to support an orbiter landing for every launch. That's why we augment three TAL sites, because weather sometimes eliminates one site, perhaps two, sometimes all three TAL sites. If all three TAL sites are down because of weather, then we cannot launch."
In the Space Shuttle Program's nearly 30-year-history, a TAL site has never been needed, but that doesn't change the intensity of preparations for the team.
"I remember back in '99, it was Eileen Collins' mission. I think she was commander at that time, and we had some technical problem with the vehicle upon launch. And so we were concerned that we might be needed, but we weren't, thankfully," Lockwood said. "We've never been used. And of course everybody when we go over there, we are basically programmed to be ready, but we are all hoping that we will not be needed." Along with TAL sites, there are a myriad of commercial airports and military-operated air stations and bases that could be used to land the shuttle in an emergency situation. Personnel at those sites receive training from NASA on what to do if a shuttle heads their way.
As the Space Shuttle Program comes to an end, landing support team members are looking forward to getting their hands on each space shuttle for the last time.
"It's just awesome to see this big heavy, bulky thing coming out of the sky. And almost coming straight down like a brick," Merritt said. "I always say it's like a brick, and it just glides down and lands.
"It's excitement and anxiousness, and some sadness in there because you know it's wrapping up. And each one, as we get closer to the end means a lot to everybody."
After nine years of scanning the sky, the Wilkinson Microwave Anisotropy Probe (WMAP) space mission has concluded its observations of the cosmic microwave background, the oldest light in the universe. The spacecraft has not only given scientists their best look at this remnant glow, but also established the scientific model that describes the history and structure of the universe.
"WMAP has opened a window into the earliest universe that we could scarcely imagine a generation ago," said Gary Hinshaw, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., who manages the mission. "The team is still busy analyzing the complete nine-year set of data, which the scientific community eagerly awaits." WMAP was designed to provide a more detailed look at subtle temperature differences in the cosmic microwave background that were first detected in 1992 by NASA's Cosmic Background Explorer (COBE). The WMAP team has answered many longstanding questions about the universe's age and composition. WMAP acquired its final science data on Aug. 20. On Sept. 8, the satellite fired its thrusters, left its working orbit, and entered into a permanent parking orbit around the sun.
"We launched this mission in 2001, accomplished far more than our initial science objectives, and now the time has come for a responsible conclusion to the satellite's operations," said Charles Bennett, WMAP's principal investigator at Johns Hopkins University in Baltimore.
WMAP detects a signal that is the remnant afterglow of the hot young universe, a pattern frozen in place when the cosmos was only 380,000 years old. As the universe expanded over the next 13 billion years, this light lost energy and stretched into increasingly longer wavelengths. Today, it is detectable as microwaves.
WMAP is in the Guinness Book of World Records for "most accurate measure of the age of the universe." The mission established that the cosmos is 13.75 billion years old, with a degree of error of one percent.
WMAP also showed that normal atoms make up only 4.6 percent of today's cosmos, and it verified that most of the universe consists of two entities scientists don't yet understand.
Dark matter, which makes up 23 percent of the universe, is a material that has yet to be detected in the laboratory. Dark energy is a gravitationally repulsive entity which may be a feature of the vacuum itself. WMAP confirmed its existence and determined that it fills 72 percent of the cosmos.
Another important WMAP breakthrough involves a hypothesized cosmic "growth spurt" called inflation. For decades, cosmologists have suggested that the universe went through an extremely rapid growth phase within the first trillionth of a second it existed. WMAP's observations support the notion that inflation did occur, and its detailed measurements now rule out several well-studied inflation scenarios while providing new support for others.
"It never ceases to amaze me that we can make a measurement that can distinguish between what may or may not have happened in the first trillionth of a second of the universe," says Bennett.
WMAP was the first spacecraft to use the gravitational balance point known as Earth-Sun L2 as its observing station. The location is about 930,000 miles or (1.5 million km) away.
"WMAP gave definitive measurements of the fundamental parameters of the universe," said Jaya Bapayee, WMAP program executive at NASA Headquarters in Washington. "Scientists will use this information for years to come in their quest to better understand the universe."
Launched as MAP on June 30, 2001, the spacecraft was later renamed WMAP to honor David T. Wilkinson, a Princeton University cosmologist and a founding team member who died in September 2002.
PASADENA, Calif. - Earlier today, navigators and mission controllers for NASA's EPOXI mission watched their computer screens as 23.6 million kilometers (14.7 million miles) away, their spacecraft successfully performed its 20th trajectory correction maneuver. The maneuver refined the spacecraft's orbit, setting the stage for its flyby of comet Hartley 2 on Nov. 4. Time of closest approach to the comet was expected to be about 10: 02 a.m. EDT (7:02 a.m. PDT).
Today's trajectory correction maneuver began at 2 p.m. EDT (11 a.m. PDT) today, when the spacecraft fired its engines for 60 seconds, changing the spacecraft's velocity by 1.53 meters per second (3.4 mph).
"We are about 23 million miles and 36 days away from our comet," said EPOXI project manager Tim Larson of NASA'sJetPropulsion Laboratory in Pasadena, Calif. "I can't wait to see what Hartley 2 looks like."
On Nov. 4, the spacecraft will fly past the comet at a distance of about 700 kilometers (435 miles). It will be only the fifth time in history that a spacecraft has been close enough to image a comet's nucleus, and the first time in history that two comets have been imaged with the same instruments and same spatial resolution. "We are imaging the comet every day, and Hartley 2 is proving to be a worthy target for exploration," said Mike A'Hearn, EPOXI principal investigator from the University of Maryland, College Park.
EPOXI is an extended mission that utilizes the already "in flight" Deep Impact spacecraft to explore distinct celestial targets of opportunity. The name EPOXI itself is a combination of the names for the two extended mission components: the extrasolar planet observations, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft will continue to be referred to as "Deep Impact."
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the EPOXI mission for NASA's Science Mission Directorate, Washington. The University of Maryland, College Park, is home to the mission's principal investigator, Michael A'Hearn. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead for the mission's extrasolar planet observations. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.
The small car-sized spacecraft will plunge directly into the sun's atmosphere approximately four million miles from our star's surface. It will explore a region no other spacecraft ever has encountered. NASA has selected five science investigations that will unlock the sun's biggest mysteries.
As the spacecraft approaches the sun, its revolutionary carbon-composite heat shield must withstand temperatures exceeding 2550 degrees Fahrenheit and blasts of intense radiation. The spacecraft will have an up close and personal view of the sun enabling scientists to better understand, characterize and forecast the radiation environment for future space explorers.
NASA invited researchers in 2009 to submit science proposals. Thirteen were reviewed by a panel of NASA and outside scientists. The total dollar amount for the five selected investigations is approximately $180 million for preliminary analysis, design, development and tests.
The selected proposals are: -- Solar Wind Electrons Alphas and Protons Investigation: principal investigator, Justin C. Kasper, Smithsonian Astrophysical Observatory in Cambridge, Mass. This investigation will specifically count the most abundant particles in the solar wind -- electrons, protons and helium ions -- and measure their properties. The investigation also is designed to catch some of the particles in a special cup for direct analysis.
-- Wide-field Imager: principal investigator, Russell Howard, Naval Research Laboratory in Washington. This telescope will make 3-D images of the sun's corona, or atmosphere. The experiment actually will see the solar wind and provide 3-D images of clouds and shocks as they approach and pass the spacecraft. This investigation complements instruments on the spacecraft providing direct measurements by imaging the plasma the other instruments sample.
-- Fields Experiment: principal investigator, Stuart Bale, University of California Space Sciences Laboratory in Berkeley, Calif. This investigation will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the sun's atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna.
-- Integrated Science Investigation of the Sun: principal investigator, David McComas of the Southwest Research Institute in San Antonio. This investigation consists of two instruments that will take an inventory of elements in the sun's atmosphere using a mass spectrometer to weigh and sort ions in the vicinity of the spacecraft.
-- Heliospheric Origins with Solar Probe Plus: principal investigator, Marco Velli of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Velli is the mission's observatory scientist, responsible for serving as a senior scientist on the science working group. He will provide an independent assessment of scientific performance and act as a community advocate for the mission.
The Solar Probe Plus mission is part of NASA's Living with a Star Program. The program is designed to understand aspects of the sun and Earth's space environment that affect life and society. The program is managed by NASA'S Goddard Space Flight Center in Greenbelt, Md., with oversight from NASA's Science Mission Directorate's Heliophysics Division. The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., is the prime contractor for the spacecraft.
35th Anniversary of Mars Viking Mission: From the perennial Mars hoax to Ray Bradbury's The Martian Chronicles, no other body in our solar system has so captured the human imagination. Throughout history mankind has gazed into the night sky wondering what civilizations awaited those who landed on the Red Planet's surface. The novels of Burroughs and others tout the planet's allure and films have warned humanity of its dangers. In 1965, the Mariner 4 spacecraft sent the first images of another planet to waiting scientists on Earth. Since that image, the Red Planet has revealed a world strangely familiar, yet challenging. Each time scientists feel close to understanding Mars, new discoveries send them back to the drawing board to revise existing theories.
In the 35 years since NASA launched Viking 1 on Aug. 20, 1975, the ambitious mission only whetted the scientific world and public's enthusiasm for future space exploration. In the ensuing years, NASA has launched the Phoenix Mars Lander, Mars Reconnaissance Orbiter and Mars Exploration Rovers, among others. Perhaps the most successful of these missions is Mars Exploration Rovers. Launched in June and July 2003, respectively, Spirit and Opportunity landed on Mars each for a 90-day mission that continues after more than 6 years.
For centuries, scientists wondered if Mars might be covered with vegetation -- or even inhabited by intelligent beings. Today, we know Mars to be quite different. It is a frozen desert world with now silent volcanoes and deep canyons. Polar ice caps expand and contract with the Martian seasons.
While the story began years earlier, it culminated in August and September 1975 with the launch of two large, nearly identical spacecraft from Cape Canaveral, Fl. Vikings 1 and 2, named for the fearless Nordic explorers of Earth, finally give humans a close-up look at this alien world.
Viking 1 and 2, each consisting of an orbiter and a lander, became the first space probes to obtain high resolution images of the Martian surface; characterize the structure and composition of the atmosphere and surface; and conduct on-the-spot biological tests for life on another planet.
Among the discoveries about Mars over the years, one stands out above all others: the possible presence of liquid water, either in its ancient past or preserved in the subsurface today. Water is key because almost everywhere water is found on Earth, so is life. If Mars once had liquid water, or still does today, it's compelling to ask whether any microscopic life forms could have developed on its surface.
Viking 1 arrived at Mars on June 19, 1976. On July 20, 1976, the Viking 1 lander separated from the orbiter and touched down at Chryse Planitia. Viking 2 was launched Sept. 9, 1975, and entered Mars orbit Aug. 7, 1976. The Viking 2 lander touched down at Utopia Planitia on Sept. 3, 1976
Making the stuff of science fiction into reality, NASA engineers are testing solar sails--a unique propulsion technology that one day could enable deep space missions. Much like the wind pushing a sailboat through water, solar sails rely on sunlight to propel vehicles through space. The sail captures constantly streaming solar particles, called photons, with giant sails built from a lightweight material. Over time, the buildup of these particles provides enough thrust for a small spacecraft to travel in space.
This image is of a four-quadrant solar sail system, measuring 66 feet on each side that is being tested in the world's largest vacuum chamber at NASA's Glenn Research Center at Plum Brook Station in Sandusky, Ohio.
IBEX Spacecraft Finds Discoveries Close to Home Imagine floating 35,000 miles above the sunny side of Earth. Our home planet gleams below, a majestic whorl of color and texture. All seems calm around you. With no satellites or space debris to dodge, you can just relax and enjoy the black emptiness of space.IBEX Spacecraft Finds Discoveries Close to Home But looks can be deceiving.
In reality, you've unknowingly jumped into an invisible most pit of electromagnetic mayhem — the place in space where a supersonic "wind" of charged particles from the Sun crashes head-on into the protective magnetic bubble that surrounds our planet. Traveling at a million miles per hour, the solar wind's protons and electrons sense Earth's magnetosphere too late to flow smoothly around it. Instead, they're shocked, heated, and slowed almost to a stop as they pile up along its outer boundary, the magnetopause, before getting diverted sideways.
Space physicists have had a general sense of these dynamic goings-on for decades. But it wasn't until the advent of the Interstellar Boundary Explorer or IBEX, a NASA spacecraft launched in October 2008, that they've been able to see what the human eye cannot: the first-ever images of this electromagnetic crash scene. They can now witness how some of the solar wind's charged particles are being neutralized by gas escaping from Earth's atmosphere. A New Way to See Atoms
IBEX wasn't designed to keep tabs on Earth's magnetosphere. Instead, its job is to map interactions occurring far beyond the planets, 8 to 10 billion miles away, where the Sun's own magnetic bubble, the heliosphere, meets interstellar space.
Only two spacecraft, Voyagers 1 and 2, have ventured far enough to probe this region directly. IBEX, which travels in a looping, 8-day-long orbit around Earth, stays much closer to home, but it carries a pair of detectors that can observe the interaction region from afar.
Here's how: When fast-moving protons in the solar wind reach the edge of the heliosphere, they sometimes grab electrons from the slower-moving interstellar atoms around them, like batons getting passed between relay runners. This charge exchange creates electrically neutral hydrogen atoms that are no longer controlled by magnetic fields. Suddenly, they're free to go wherever they want — and because they're still moving fast, they quickly zip away from the interstellar boundary in all directions.
Some of these "energetic neutral atoms," or ENAs, zip past Earth, where they're recorded by IBEX. Its two detectors don't take pictures with conventional optics. Instead, they record the number and energy of atoms arriving from small spots of sky about 7 degrees across (the apparent size of a tennis ball held at arm's length). Because its spin axis always points at the Sun, the spacecraft slowly turns throughout Earth's orbit and its detectors scan overlapping strips that create a complete 360 degrees map every six months.
A Collision Zone Near Earth
Because IBEX is orbiting Earth, it also has a front-row seat for observing the chaotic pileup of solar-wind particles occurring along the "nose" of Earth's magnetopause, about 35,000 miles out. ENAs are created there too, as solar-wind protons wrest electrons from hydrogen atoms in the outermost vestiges of our atmosphere, the exosphere.
Other spacecraft have attempted to measure the density of the dayside exosphere, without much success. NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft probably detected ENAs from this region a decade ago, but its detectors didn't have the sensitivity to pinpoint or measure the source.
Now, thanks to IBEX, we know just how tenuous the outer exosphere really is. "Where the interaction is strongest, there are only about eight hydrogen atoms per cubic centimeter," explains Stephen A. Fuselier, the Lockheed Martin Space Systems researcher who led the mapping effort. His team's results appear in the July 8 issue of Geophysical Research Letters.
The key observations were made in March and April 2009, when IBEX was located far from Earth — about halfway to the Moon's orbit — and its detectors could scan the region directly in front of the magnetopause. During some of the March observations, the European Space Agency's Cluster 3 spacecraft was positioned just in front of the magnetopause, where it measured the number of deflected solar-wind protons directly. "Cluster played a very important role in this study," Fuselier explains. "It was in the right place at the right time."
The new IBEX maps show that the ENAs thin out at locations away from the point of peak intensity. This falloff makes sense, Fuselier says, because Earth's magnetopause isn't spherical. Instead, it has a teardrop shape that's closest to Earth at its nose but farther away everywhere else. So at locations well away from the magnetopause's centerline, even fewer of the exosphere's hydrogen atoms are hanging around to interact with the solar wind. "No exosphere, no ENAs," he explains. A Versatile Spacecraft
Since its launch, IBEX has also scanned another nearby world, with surprising results. The moon has no atmosphere or magnetosphere, so the solar wind slams unimpeded into its desolate surface. Most of those particles get absorbed by lunar dust. In fact, space visionaries wonder if the moon's rubbly surface has captured enough helium-3, an isotope present in tiny amounts in the Sun's outflow, to serve as a fuel for future explorers.
Yet cosmic chemists have long thought that some solar-wind protons must be bouncing off the lunar surface, becoming ENAs through charge exchange as they do. So does the moon glow in IBEX's scans? Indeed it does, says David J. McComas of Southwest Research Institute in San Antonio, Texas, who serves as the mission's Principal Investigator.
In a report published last year in Geophysical Research Letters, McComas and other researchers conclude that about 10 percent of the solar-wind particles striking the Moon escape to space as ENAs detectable by IBEX. That amounts to roughly 150 tons of recycled hydrogen atoms per year.
Meanwhile, the squat, eight-sided spacecraft continues its primary task of mapping the interactions between the outermost heliosphere and the interstellar medium that lies beyond. McComas and his team are especially eager to learn more about the mysterious and unexpected "ribbon" of ENAs that turned up in the spacecraft's initial all-sky map.
At NASA's Goddard Space Flight Center in Greenbelt, Md., IBEX Mission Scientist Robert MacDowall says the spacecraft should be able to continue its observations through at least 2012. "We weren't sure those heliospheric interactions would vary with time, but they do," he explains, "and it's great that IBEX will be able to record them for years to come."
Cassini Hunting Enceladus 'Tigers' with Night Vision NASA's Cassini spacecraft will be hunting for heat signatures at the "tiger stripes" in the dim south polar region of Saturn's moon Enceladus on Friday, Aug. 13. The closest approach will bring the spacecraft to within about 2,500 kilometers (1,600 miles) of the surface of Enceladus. The tiger stripes -- which are actually giant fissures that spew jets of water vapor and organic particles hundreds of kilometers, or miles, out into space - are hard to see in the visible-light spectrum because winter is beginning to darken the moon's southern hemisphere. Cassini, however, has its own version of "night vision goggles" -- the composite infrared spectrometer instrument -- which can track heat even when visible light is low. The instrument will map temperatures in the transverse fractures between the tiger stripes Cairo Sulcus and Alexandria Sulcus. It will also scan part of the tiger stripe Damascus Sulcus.
The relatively high flyby allows the composite infrared spectrometer to track the tiger stripe surface smoothly throughout the flyby. That kind of coverage is more difficult at lower altitudes because the surface whooshes by very quickly.
In addition, the visual and infrared mapping spectrometer will collect data on the composition of Enceladus, and the imaging cameras will take pictures.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter was designed, developed and assembled at JPL.
