News | How Do We Know When Voyager Reaches Interstellar Space? News | September 12, 2013 How Do We Know When Voyager Reaches Interstellar Space? Whether and when NASA's Voyager 1 spacecraft, humankind's most distant object, broke through to interstellar space, the space between stars, has been a thorny issue. For the last year, claims have surfaced every few months that Voyager 1 has "left our solar system." Why has the Voyager team held off from saying the craft reached interstellar space until now? "We have been cautious because we're dealing with one of the most important milestones in the history of exploration," said Voyager Project Scientist Ed Stone of the California Institute of Technology in Pasadena. "Only now do we have the data -- and the analysis -- we needed." Basically, the team needed more data on plasma, which is ionized gas, the densest and slowest moving of charged particles in space.

(The glow of neon in a storefront sign is an example of plasma.) Plasma is the most important marker that distinguishes whether Voyager 1 is inside the solar bubble, known as the heliosphere, which is inflated by plasma that streams outward from our sun, or in interstellar space and surrounded by material ejected by the explosion of nearby giant stars millions of years ago. Adding to the challenge: they didn't know how they'd be able to detect it. "We looked for the signs predicted by the models that use the best available data, but until now we had no measurements of the plasma from Voyager 1," said Stone. Scientific debates can take years, even decades to settle, especially when more data are needed. It took decades, for instance, for scientists to understand the idea of plate tectonics, the theory that explains the shape of Earth's continents and the structure of its sea floors. First introduced in the 1910s, continental drift and related ideas were controversial for years. A mature theory of plate tectonics didn't emerge until the 1950s and 1960s.

Only after scientists gathered data showing that sea floors slowly spread out from mid-ocean ridges did they finally start accepting the theory. Most active geophysicists accepted plate tectonics by the late 1960s, though some never did. Voyager 1 is exploring an even more unfamiliar place than our Earth's sea floors -- a place more than 11 billion miles (17 billion kilometers) away from our sun. It has been sending back so much unexpected data that the science team has been grappling with the question of how to explain all the information. None of the handful of models the Voyager team uses as blueprints have accounted for the observations about the transition between our heliosphere and the interstellar medium in detail. The team has known it might take months, or longer, to understand the data fully and draw their conclusions. "No one has been to interstellar space before, and it's like traveling with guidebooks that are incomplete," said Stone. "Still, uncertainty is part of exploration.

We wouldn't go exploring if we knew exactly what we'd find." The two Voyager spacecraft were launched in 1977 and, between them, had visited Jupiter, Saturn, Uranus and Neptune by 1989. Voyager 1's plasma instrument, which measures the density, temperature and speed of plasma, stopped working in 1980, right after its last planetary flyby. When Voyager 1 detected the pressure of interstellar space on our heliosphere in 2004, the science team didn't have the instrument that would provide the most direct measurements of plasma. Instead, they focused on the direction of the magnetic field as a proxy for source of the plasma. Since solar plasma carries the magnetic field lines emanating from the sun and interstellar plasma carries interstellar magnetic field lines, the directions of the solar and interstellar magnetic fields were expected to differ. Most models told the Voyager science team to expect an abrupt change in the magnetic field direction as Voyager switched from the solar magnetic field lines inside our solar bubble to those in interstellar space.

The models also said to expect the levels of charged particles originating from inside the heliosphere to drop and the levels of galactic cosmic rays, which originate outside the heliosphere, to jump. In May 2012, the number of galactic cosmic rays made its first significant jump, while some of the inside particles made their first significant dip. The pace of change quickened dramatically on July 28, 2012. After five days, the intensities returned to what they had been. This was the first taste of a new region, and at the time Voyager scientists thought the spacecraft might have briefly touched the edge of interstellar space. By Aug. 25, when, as we now know, Voyager 1 entered this new region for good, all the lower-energy particles from inside zipped away. Some inside particles dropped by more than a factor of 1,000 compared to 2004. The levels of galactic cosmic rays jumped to the highest of the entire mission. These would be the expected changes if Voyager 1 had crossed the heliopause, which is the boundary between the heliosphere and interstellar space.

However, subsequent analysis of the magnetic field data revealed that even though the magnetic field strength jumped by 60 percent at the boundary, the direction changed less than 2 degrees. This suggested that Voyager 1 had not left the solar magnetic field and had only entered a new region, still inside our solar bubble, that had been depleted of inside particles. Then, in April 2013, scientists got another piece of the puzzle by chance. For the first eight years of exploring the heliosheath, which is the outer layer of the heliosphere, Voyager's plasma wave instrument had heard nothing. But the plasma wave science team, led by Don Gurnett and Bill Kurth at the University of Iowa, Iowa City, had observed bursts of radio waves in 1983 to 1984 and again in 1992 to 1993. They deduced these bursts were produced by the interstellar plasma when a large outburst of solar material would plow into it and cause it to oscillate.

It took about 400 days for such solar outbursts to reach interstellar space, leading to an estimated distance of 117 to 177 AU (117 to 177 times the distance from the sun to the Earth) to the heliopause. They knew, though, that they would be able to observe plasma oscillations directly once Voyager 1 was surrounded by interstellar plasma. Then on April 9, 2013, it happened: Voyager 1's plasma wave instrument picked up local plasma oscillations. Scientists think they probably stemmed from a burst of solar activity from a year before, a burst that has become known as the St. Patrick's Day Solar Storms. The oscillations increased in pitch through May 22 and indicated that Voyager was moving into an increasingly dense region of plasma. This plasma had the signatures of interstellar plasma, with a density more than 40 times that observed by Voyager 2 in the heliosheath. Gurnett and Kurth began going through the recent data and found a fainter, lower-frequency set of oscillations from Oct. 23 to Nov. 27, 2012.

When they extrapolated back, they deduced that Voyager had first encountered this dense interstellar plasma in August 2012, consistent with the sharp boundaries in the charged particle and magnetic field data on August 25. Stone called three meetings of the Voyager team. They had to decide how to define the boundary between our solar bubble and interstellar space and how to interpret all the data Voyager 1 had been sending back. There was general agreement Voyager 1 was seeing interstellar plasma, based on the results from Gurnett and Kurth, but the sun still had influence. One persisting sign of solar influence, for example, was the detection of outside particles hitting Voyager from some directions more than others. In interstellar space, these particles would be expected to hit Voyager uniformly from all directions. "Now that we had actual measurements of the plasma environment - by way of an unexpected outburst from the sun - we had to reconsider why there was still solar influence on the magnetic field and plasma in interstellar space," Stone said. "The path to interstellar space has been a lot more complicated than we imagined." Stone discussed with the Voyager science group whether they thought Voyager 1 had crossed the heliopause.

What should they call the region were Voyager 1 is? "In the end, there was general agreement that Voyager 1 was indeed outside in interstellar space," Stone said. "But that location comes with some disclaimers - we're in a mixed, transitional region of interstellar space. We don't know when we'll reach interstellar space free from the influence of our solar bubble." So, would the team say Voyager 1 has left the solar system? Not exactly - and that's part of the confusion. Since the 1960s, most scientists have defined our solar system as going out to the Oort Cloud, where the comets that swing by our sun on long timescales originate. That area is where the gravity of other stars begins to dominate that of the sun. It will take about 300 years for Voyager 1 to reach the inner edge of the Oort Cloud and possibly about 30,000 years to fly beyond it. Informally, of course, "solar system" typically means the planetary neighborhood around our sun. Because of this ambiguity, the Voyager team has lately favored talking about interstellar space, which is specifically the space between each star's realm of plasma influence.

"What we can say is Voyager 1 is bathed in matter from other stars," Stone said. "What we can't say is what exact discoveries await Voyager's continued journey. No one was able to predict all of the details that Voyager 1 has seen. So we expect more surprises." Voyager 1, which is working with a finite power supply, has enough electrical power to keep operating the fields and particles science instruments through at least 2020, which will mark 43 years of continual operation. At that point, mission managers will have to start turning off these instruments one by one to conserve power, with the last one turning off around 2025. Voyager 1 will continue sending engineering data for a few more years after the last science instrument is turned off, but after that it will be sailing on as a silent ambassador. In about 40,000 years, it will be closer to the star AC +79 3888 than our own sun.

(AC +79 3888 is traveling toward us faster than we are traveling towards it, so while Alpha Centauri is the next closest star now, it won't be in 40,000 years.) And for the rest of time, Voyager 1 will continue orbiting around the heart of the Milky Way galaxy, with our sun but a tiny point of light among many. The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, in Pasadena, Calif. Caltech manages JPL for NASA. The Voyager missions are a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington. For more information about Voyager, visit: and . News Media Contact Jet Propulsion Laboratory, Pasadena, Calif. jccook@jpl.nasa.gov BBC Solar System – Voyager 1 is on an epic journey to the stars Voyager 1 encounters Jupiter The first detailed views of Jupiter surprise Voyager scientists. Voyager 1, launched in 1977, sent back its first images of Jupiter in the late 1970s while it was still 50 million miles away from the planet.

The gas giant's bizarre clouds and storms puzzled experts. About Voyager 1 Voyager 1 is a space probe launched by NASA on September 5, 1977. Part of the Voyager program to study the outer Solar System, Voyager 1 launched 16 days after its twin, Voyager 2. Having operated for 39 years, 3 months and 16 days, the spacecraft still communicates with the Deep Space Network to receive routine commands and return data. At a distance of 137 AU (2.05×1010 km) from the Sun as of December 2016, it is the farthest spacecraft from Earth as well as the farthest man-made object. The probe's primary mission objectives included flybys of Jupiter, Saturn, and Saturn's large moon, Titan. While the spacecraft's course could have been altered to include a Pluto encounter by forgoing the Titan flyby, exploration of the moon, which was known to have a substantial atmosphere, took priority. It studied the weather, magnetic fields, and rings of the two planets and was the first probe to provide detailed images of their moons.

After completing its primary mission with the flyby of Saturn on November 20, 1980, Voyager 1 began an extended mission to explore the regions and boundaries of the outer heliosphere. On August 25, 2012, Voyager 1 crossed the heliopause to become the first spacecraft to enter interstellar space and study the interstellar medium.Voyager 1's extended mission is expected to continue until around 2025, when its radioisotope thermoelectric generators will no longer supply enough electric power to operate any of its scientific instruments. NASA confirms Voyager 1 probe has left the solar system - CNN.com Study: Voyager 1 left heliosphere around August 25, 2012 Voyager 1 and 2 were launched in 1977, 16 days apart Voyager 1 is now the first mission to explore interstellar space At the edge of the heliosphere, you wouldn't know by looking whether you left the cradle of humanity behind and floated out into interstellar space. You would just see unfathomably empty space, no matter which side of the invisible line you were on.

But scientists now have strong evidence that NASA's Voyager 1 probe has crossed this important border, making history as the first human-made object to leave the heliosphere, the magnetic boundary separating the solar system's sun, planets and solar wind from the rest of the galaxy. "In leaving the heliosphere and setting sail on the cosmic seas between the stars, Voyager has joined other historic journeys of exploration: The first circumnavigation of the Earth, the first steps on the Moon," said Ed Stone, chief scientist on the Voyager mission. "That's the kind of event this is, as we leave behind our solar bubble." A new study in the journal Science suggests that the probe entered the interstellar medium around August 25, 2012. You may have heard other reports that Voyager 1 has made the historic crossing before, but Thursday was the first time NASA announced it. The twin spacecraft Voyager 1 and 2 were launched in 1977, 16 days apart. As of Thursday, according to NASA's real-time odometer , Voyager 1 is 18.8 billion kilometers (11.7 billion miles) from Earth.

Its sibling, Voyager 2, is 15.3 billion (9.5 billion) kilometers from our planet. JUST WATCHED 17 of 18 Photos: Images from Voyager 2 Images from Voyager 2 – Ariel, another of Uranus' satellite's, shows a densely pitted surface that is also crisscrossed with numerous valleys and fault scarps. Hide Caption 18 of 18 Voyager 1 is being hailed as the first probe to leave the solar system. But under a stricter definition of "solar system," which includes the distant comets that orbit the sun, we'd have to wait another 30,000 years for it to get that far, Stone said. Another milestone for long after we're gone: The probe will fly near a star in about 40,000 years, Stone said. How do we know? Voyager, currently traveling at more than 38,000 miles per hour, never sent a postcard saying "Greetings from interstellar space!" So whether it has made the historic crossing or not is a matter of controversy. "The spacecraft itself really doesn't know," Stone said.

"It's only instruments that can tell us whether we're inside or outside." Further complicating matters, the device aboard Voyager 1 that measures plasma -- a state of matter with charged particles -- broke in 1980. To get around that, scientists detected waves in the plasma around the spacecraft and used that information to calculate density. Vibrations in the plasma came from a large coronal mass ejection from the sun in 2012, resulting in what Stone called a "solar wind tsunami." These vibrations reached the area around Voyager this spring. Measurements taken between April 9 and May 22 of this year show that Voyager 1 was, at that time, located in an area with an electron density of about 0.08 per cubic centimeter. In the interstellar medium, the density of electrons is thought to be between 0.05 and 0.22 per cubic centimeter. The particles of interstellar plasma were created by the explosions of giant stars, and carry the magnetic field of the galaxy, scientists said. This illustration shows NASA's Voyager 1 spacecraft entering the space between stars.

Last year, between October 23 and November 27, researchers calculate that Voyager 1 was in an area with an electron density of 0.06 per cubic centimeter. That's still within the interstellar space range, and it means that over time the spacecraft passed through plasma with increasing electron density. The study, led by University of Iowa physicist Donald Gurnett, suggests that the plasma density is about 30 times higher in the interstellar medium than in the heliosphere, which is close to what scientists thought based on other kinds of measurements. The boundary is called the heliopause. Voyager mission timeline: When did it happen? Scientists have been using several kinds of measurements to figure out if and when Voyager 1 had reached the interstellar medium. Evidence from particle data had already pointed toward the conclusion that the probe succeeded. In late July and early August of 2012, scientists saw dips in the concentration of particles made in the solar system, and peaks in particles made outside. "If you just looked at that data, you'd think it's pretty clear that we've actually crossed a boundary.

We're no longer in the place where the solar system particles are being made, and we're actually out in the interstellar medium," said Marc Swisdak, associate research scientist in the Institute for Research in Electronics and Applied Physics at the University of Maryland. Swisdak was not involved in the new study, but has worked with Voyager data. Magnetic field measurements suggested otherwise. Researchers had expected to see stark changes in magnetic field direction when the probe crossed out of the heliosphere, but that wasn't supported by measurements from the probe. Swisdak and colleagues published a modeling study suggesting that the particle data is more relevant, and that the magnetic field might not change as much as people thought. They proposed a crossing-over date of July 27 -- about a month sooner than the new study. The specific date will likely be debated for some time, Swisdak said. One possible explanation is that if the heliosphere is analogous to an air-conditioned room, Voyager stepped through the doorway into a hot room on July 27. For a month it was in a metaphorical room with a mixture of hot and cold air, and finally entered the truly hot part on August 25.

Puzzles still surround the magnetic field at the edge of the heliosphere, Stone said, and "We're going to be prepared to have more surprises." NASA sends unmanned rocket to the moon What else is out there? Voyager 1 has only 68 KB of memory on board -- far less than a smartphone, said Suzanne Dodd, Voyager project manager. Scientists communicate with the spacecraft every day. "It's the little spacecraft that could," she said in a NASA press conference. The probe now has a totally new mission, Stone said. "We're now on the first mission to explore interstellar space," he said. "We will now look and learn in detail how the wind which is outside, that came from these other stars, is deflected around the heliosphere." Wind -- made of particles -- from these other stars has to go around the heliosphere the way a water in a stream flows around a rock, Stone said. Scientists are interested in learning more about the interaction between our solar wind and wind from other stars. Natural radioactive decay provides heat that generates enough electricity to help Voyager 1 communicate with Earth.

The first science instrument will be turned off in 2020, and the last one will be shut down in 2025, Stone said. Both Voyager probes carry time capsules known as "the golden record," a 12-inch, gold-plated copper disc with images and sounds so that extraterrestrials could learn about us. Let's hope they can build appropriate record players. Voyager 2 will likely leave the heliosphere in about three to four years, Stone said. Its plasma instrument is still working, Stone said, so scientists can directly measure the stellar wind's density, speed and temperature. That also means that when it crosses out of the heliosphere, Voyager 2 will send a clearer signal. At that time, it will join its twin in the vast nothingness between stars that used to be beyond our reach. 1000+ images about Voyager One on Pinterest | Solar system, Pale blue dot and Multimedia Forward Symphonies of the Planets · On its journey to the edge of the solar system, the Voyager 1 Spacecraft recorded vibrations created by interactions between the charged particles of the solar wind and the magnetospheres of various planets & moons.

These haunting soundscapes were sent home to Earth and converted into sound. The results are both stunningly familiar and utterly alien. The beautiful & haunting solar weather of planets and moons billions of kilometres from home. See More Nasa confirms that the Voyager 1 probe has entered interstellar space (again) | The Independent Tech Nasa confirms that the Voyager 1 probe has entered interstellar space (again) The spacecraft has travelled further from Earth than any other man-made object in existence, despite confusion over what constitutes ''interstellar space' Friday 11 July 2014 10:16 BST Click to follow The Independent Tech This artist's concept shows the Voyager 1 spacecraft entering the space between stars. The Space Between: This artist's concept shows the Voyager 1 spacecraft entering the space between stars. Interstellar space is dominated by plasma, ionized gas (illustrated here as brownish haze), that was thrown off by giant stars millions of years ago. NASA/JPL-Caltech After travelling for longer than 36 years and covering a distance of nearly 12 billion miles, the space probe Voyager 1 has finally entered interstellar space, according to a new report from Nasa.

The craft was launched in 1977 as part of a long-term mission to study the solar system, and after conducting flybys of both Jupiter and Saturn was set on a course straight out the solar system carrying images of Earth and a Golden LP with a track list of humanity's greatest hits . Read more What images and music is Voyager 1 taking to the stars? The problem, however, is that Voyager 1 has already entered interstellar space – at least according to some reports, with the probe making headlines last year when scientists declared that it had left the heliosphere back in August 2012. The heliosphere is the mammoth ‘bubble’ that marks the boundaries of the Sun’s magnetic influence and for many astronomers it’s as good a marker as any for what constitutes the beginning of interstellar space. Objects within the heliosphere are affected by solar wind (the streams of plasma shot out by the sun) while anything in interstellar space is influenced primarily by the ‘interstellar medium’ – a hotchpotch of matter and energy that includes various forms of gasses, dust and cosmic rays. The uncertain borders between these regions are known as the heliosheath.

An illustration showing the path of the two Voyager spacecraft. Image credit: Nasa/JPL/Caltech As you’d imagine, determining which side of the heliosheath Voyager 1 is on is pretty tricky, something akin to wandering along the Scottish-English border with your eyes closed and trying to work out which country you’re in by tasting the rain. So what makes scientist so sure this time round? It’s all thanks to a recent tsunami of plasma released by the Sun. These cosmic events - which are expected, if not predictable - create shock waves that ripple through solar system and into the interstellar matter, and leave the Voyager 1 probe bobbing like a buoy after a ship has passed by. "Normally, interstellar space is like a quiet lake," said Ed Stone of the California Institute of Technology, Voyager 1’s lead scientist since 1972. “But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later.

The wave causes the plasma surrounding the spacecraft to sing.” Instruments on Voyager not only register these waves, but also measure quite precisely the oscillations of the surrounding plasma – allowing scientists to work out whether it’s currently in metaphorical deep water or still paddling in the shallows. The latest measurement - the third in a series of recent plasma waves - confirm that Voyager is a long way out. Stone said: "The tsunami wave rings the plasma like a bell. While the plasma wave instrument lets us measure the frequency of this ringing, the cosmic ray instrument reveals what struck the bell - the shock wave from the sun." Voyager 1's current location. The scale on this map is logarithimic - meaning that the distances marked are multipled as they get further out. Credit: Wikimedia commons. However, despite these measurements Nasa are still hedging their bets somewhat, clarifying that although Voyager 1 has entered interstellar space it’s not yet exited the Solar System – a boundary usually defined by a hypothetical region of outer space known as the Oort cloud . This is thought to be a spherical cloud of mostly icy debris, small objects that are pleasingly known as ' planetesimals '.

If something's still a part of the Oort cloud then it's still in the gravitational grip of the Sun - meaning it's still, technically, a part of the Solar System. And how long will it be since Voyager 1 gets through this part of space? Current predictions are 300 years to reach the edge of the Oort Cloud and then another 30,000 to exit it. Voyager 1 may have travelled further from Earth than any other man-made object in existence, but to quote sci-fi author Douglas Adams, “that’s just peanuts compared to space.” Meet the Spacecraft Exploring the Solar System Meet the Spacecraft Exploring the Solar System By Mike Wall, Space.com Senior Writer | January 3, 2013 06:00am ET MORE Our solar system is a vast place, with lots of mostly empty space between planets. But out there are comets, asteroids and more rocky, frozen objects (including dwarf planets) yet to be discovered in the Kuiper Belt and Oort Cloud. Credit: NASA NASA's Spirit rover landed on Mars nine years ago today (Jan.

3), kicking off a surface mission that's still operational thanks to the amazing endurance of Spirit's twin Opportunity. Mars is currently host to five active space missions, commanding more attention than any planet apart from Earth. But unmanned probes are also exploring many other solar system bodies, from the sun out to Pluto and beyond. Here's a brief rundown of some of the intrepid spacecraft that are currently sending data home from beyond Earth orbit. (For the sake of brevity, this list does not include the extensitve fleet of satellites currently orbiting Earth, though some notable ones are NASA's Solar Dynamics Observatory and iconic Hubble Space Telescope .) Sun-studying spacecraft Wind: This NASA probe launched in November 1994 to study the solar wind, the stream of charged particles flowing from the sun. The Wind spacecraft operates from a halo orbit around the sun-Earth Lagrange point 1 (L1), a spot about 900,000 miles (1.5 million kilometers) from Earth (in the direction of the sun). At sun-Earth L1, the gravitational pulls of the two bodies interact in such a way that a probe can essentially park there.

[ Gallery: Solar System's Deep-Space Probes ] Solar and Heliospheric Observatory: SOHO, a joint effort between the European Space Agency (ESA) and NASA, launched in December 1995 and also orbits around sun-Earth L1. In addition to its sun-studying duties, SOHO has discovered more than 2,300 comets . The total mission cost is about 1 billion euros ($1.32 billion at current exchange rates). Advanced Composition Explorer (ACE): This $107 million NASA spacecraft launched in August 1997 to help researchers better understand and predict space space weather . ACE also orbits sun-Earth L1. Solar Terrestrial Relations Observatory: NASA's $550 million sun-studying STEREO mission, which blasted off in October 2006, consists of two spacecraft, known as A and B. Both probes are in a heliocentric orbit, with A zipping around the sun faster than Earth and B lagging somewhat behind.

Mercury Messenger: NASA's $446 million Messenger mission (short for Mercury Surface, Space Environment, Geochemistry and Ranging) launched in August 2004 and arrived in orbit around the solar system's innermost planet in March 2011. Messenger has found solid evidence of water ice and carbon-containing organic compounds in the permanentaly shadowed craters near Mercury's poles. Venus Venus Express: This $290 million ESA spacecraft blasted off in November 2005 and began orbiting Earth's hellishly hot "sister planet" in April 2006. Its main goal is to help scientists better understand the evolution of Venus ' thick atmosphere. Akatsuki: The $300 million Akatsuki mission, which launched in May 2010, was Japan's second attempt to send a probe to another planet, after 2003's ill-fated Nozomi mission to Mars. Akatsuki has had troubles as well, failing to insert into Venus orbit as planned in December 2010. The probe is now circling the sun, and mission managers plan to take another shot at Venus in November 2015.

Credit: NASA/GSFC/Arizona State University Earth's moon Lunar Reconnaissance Orbiter: LRO launched on June 18, 2009, and arrived in lunar orbit five days later. The $504 million, car-size NASA spacecraft is studying the lunar surface for scientific and exploration purposes; its observations should help researchers decide where to put a future human colony on the moon, NASA officials say. Artemis: The two ARTEMIS spacecraft — short for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun — completed their unusual journey from Earth orbit to lunar orbit in July 2011. They had originally been part of a five-satellite, $200 million NASA mission called THEMIS (Time History of Events and Macroscale Interactions during Substorms), which launched in February 2007. [ 10 Coolest Moon Discoveries ] Deep space beyond the moon Credit: CSLEP Chang'e 2: This well-traveled Chinese spacecraft launched in October 2010 to scout out locations for a future lunar lander, which China is readying for launch in 2013.

After completing its mission at the moon in June 2011, Chang'e 2 headed out to sun-Earth Lagrange point 2 to help test China's deep-space tracking and control network. Then, in mid-April of this year, it departed to do a flyby of the near-Earth asteroid Toutatis , accomplishing the feat on Dec. 13. Several other spacecraft are also parked at sun-Earth L2, including the European Space Agency's Herschel and Planck space observatories. NASA's prolific Spitzer Space Telescope, meanwhile, is in an Earth-trailing orbit around the sun, and the agency's Deep Impact probe is headed toward a possible 2020 rendezvous with a near-Earth asteroid called 2002 GT. Deep Impact launched in January 2005 and slammed an impactor into Comet Tempel 1 on July 4 of that year. In November 2010, it accomplished a flyby of Comet Hartley 2. Deep Impact has traveled more than 4.2 billion miles (6.75 billion km) in space thus far.

Mars Mars Odyssey: This venerable NASA orbiter launched in April 2001 and arrived at the Red Planet six months later to look for signs of past and present water activity. The $297 million spacecraft also serves as a communications relay between NASA's Mars rovers and their controllers on Earth. Mars Express: This 150 million-euro ($198 million) ESA probe's main objective is to look for subsurface water from orbit. It launched in June 2003 and arrived at Mars in December of that year. Mars Express also aimed to put a lander, called Beagle 2, on the Martian surface, but this aspect of the mission failed. Mars Reconnaissance Orbiter: NASA's $720 million MRO spacecraft launched in August 2005 and achieved Mars orbit in March 2006. Since then, it has been mapping the Red Planet's surface with unprecedented precision. In addition to their scientific value, MRO's observations have helped NASA decide where to land surface missions on the Red Planet. MRO is also the chief communications link between Mars surface craft and Earth.

During its 84 and 85 day (sol) on Mars, Curiosity snapped this newest mosaic self-portrait. Credit: NASA / JPL-Caltech Opportunity Rover: This golf-cart-size robot launched in July 2003 and landed in January 2004, three weeks after its twin, Spirit. Spirit and Opportunity were tasked with three-month missions to search for signs of past water activity on Mars; both found plenty of such evidence and kept on roving. Spirit stopped communicating with Earth in March 2010, but Opportunity is still going strong. NASA has spent about $900 million on the rovers' mission to date. Curiosity Rover: The $2.5 billion Curiosity rover dwarfs Spirit and Opportunity; it's the size of a small car and weighs a ton. Curiosity launched in November 2011 and pulled off a dramatic sky-crane landing on Aug. 5, 2012. Its main mission is to determine if its Gale Crater landing site has ever been capable of supporting microbial life.

[ Latest Photos from the Curiosity Rover ] Asteroid belt and environs Dawn: NASA's $466 million Dawn spacecraft launched in September 2007 and arrived at the protoplanet Vesta — the second-largest denizen of the main asteroid belt between Mars and Jupiter — in July 2011. Dawn departed Vesta in September 2012 to head to the belt's biggest body, Ceres. It should reach the dwarf planet in February 2015. Rosetta: This ambitious ESA mission, which costs about 1 billion euros ($1.32 billion), aims to orbit and drop a lander on the comet 67P Churyumov-Gerasimenko. Rosetta launched in March 2004, executed flybys of two different asteroids in 2008 and 2010 and is set to meet up with the comet in mid-2014 near the orbit of Jupiter, about 420 million miles (675 million km) from Earth.

Jupiter Juno: This $1.1 billion NASA spacecraft launched in August 2011 and is slated to arrive at Jupiter in August 2016. Over the course of one Earth year, Juno will study the gas giant's atmosphere, internal structure and magnetic field from orbit. Juno is the first solar-powered spacecraft ever to venture as far as Jupiter. Credit: NASA/JPL-Caltech/Space Science Institute Saturn Cassini: The $3.2 billion Cassini-Huygens mission, a joint effort involving NASA, ESA, and the Italian Space Agency, launched in October 1997 and achieved Saturn orbit in July 2004. The Cassini spacecraft has been studying Saturn, its rings and the planet's many moons ever since. In January 2005, the probe also delivered the Huygens lander to the surface of Titan, Saturn's largest moon. Pluto New Horizons: This super-speedy NASA spacecraft launched in January 2006 and is set to fly by the Pluto system in July 2015, giving researchers their first-ever up-close look at the dwarf planet.

After that, the $700 million probe may also fly by one or more objects in the Kuiper Belt, the ring of icy bodies beyond Neptune's orbit. Solar system's edge Voyager 1 and 2: NASA's twin Voyager probes launched in 1977 to study Saturn, Jupiter and their moons. The pair made many discoveries about these far-flung bodies, then checked out Uranus and Neptune and kept on flying. Both spacecraft are now studying the unique conditions at the edge of the solar system, knocking on the door of interstellar space. Voyager 1 — the most distant manmade object ever launched — is currently about 11 billion miles (18 billion km) from Earth, while Voyager 2 is 9 billion miles (15 billion km) from home. NASA has spent about $1 billion on the mission to date. Follow SPACE.com senior writer Mike Wall on Twitter @michaeldwall or SPACE.com @Spacedotcom . We're also on Facebook and Google+ . Editor's Recommendations NASA - What Does the Edge of the Solar System Look Like? Ask Voyager. What Does the Edge of the Solar System Look Like? Ask Voyager.

11.05.03 Voyager is reaching the edge of the solar system. This is no Christopher Columbus false call, mind you. Eight billion miles from the Sun, Voyager's 26-year journey has made it the farthest-reaching spacecraft in the solar system and it is about to set a new record. All of the planets and objects within our solar system are surrounded by a sort-of bubble created by supersonic wind from the Sun. The spacecraft that first laid its robotic eyes on Jupiter and Saturn, is about to burst through that bubble, or may have already, according to some scientists. This still shows the locations of Voyager 1 & 2 Voyager 1 is traveling faster, reaching the termination shock sooner. The dramatic orange border to the left represents the bow shock, a theoretical area created as interstellar gas runs into the solar atmosphere. The location of the termination shock, or the boundary into the area where interstellar gas and solar wind start to mix, has been a mystery to scientists because it moves with regard to the power of the solar wind. Click on the image for movie. Also avail: color print-resolution & other movie formats or black & white high res .

Credit: NASA "There has to be a sense of wonder in that this is the first manmade object that is touching interstellar space and this has never happened," said Dr. Tom Krimigis of the Applied Physics Laboratory (APL), Johns Hopkins University. "We're getting out of the protective cocoon of the Sun and this clearly marks a milestone in humanity's knowledge of our environment." It makes sense that the Voyager mission, consisting of two identical spacecraft launched in the heady robotic exploration era of the 1970s should be the farthest traveled manmade objects ever, nearly four billion miles from Pluto's orbit. Voyager 1 provided the first views of volcanoes outside of Earth on one of Jupiter's moon, Io, as well as close-ups of Saturn's rings and evidence of a ring around Jupiter in 1979. Voyager 2 provided the very first look at Uranus and Neptune in 1986 and 1989, respectively.

Also significant, both are appointed planetary ambassadors - they each carry a 12-inch gold-plated copper disk containing sounds and images selected to portray the culture and diversity of Earth and meant to be played by an alien form of life that may encounter Voyager. Where's the Edge? Christopher Columbus had to sail the high seas to prove the world was round; how are scientists so certain a bubble blown by the solar wind surrounds us? Scientists call the murky region to the left of the Voyager trajectory in the image the heliosheath, because everything within it is influenced by the Sun ('helio' in Greek). What's out there at the boundaries of our solar system? Starting out at a view of our Milky Way galaxy, the orange gas in the animation represents the interstellar medium. The bow shock is created because the heliosphere is moving through like a boat through the water, crashing through the interstellar gases. The bow shock in front of the moving heliosphere is similar to the one observed by the Hubble Space Telescope. Click for animation. Credit: NASA The heliopause is the last boundary of that region where interstellar space, or matter from other stars, takes over as the ruler of the roost.

Voyager isn't expected to reach the area for another 20 years. Entering the fluid region known as the heliosheath, past the theoretical boundary of the 'termination shock,' however, marks the first step toward that ultimate goal. The heliosheath represents a mixing bowl-region in which smaller amounts of solar wind mix with gas from outside our solar system. NASA Scientist Dr. Eric Christian imagines the theoretical boundary looks a lot like the water that bounces off a plate in the sink. It's not a defined straight (or round) line, but more fluid so the boundary moves a little bit. This movement has been a problem for researchers. It's very hard to know when Voyager has crossed the line - in fact, two science teams are lining up right now with different interpretations of unusual readings in their data stream from the spacecraft. Left: video of water running on a plate: the first border formed is like the termination shock and the water between the shock and the rim is the heliosheath. Water runs out toward the rim and then rushes back, similar to solar wind and indeed the reason scientists know the boundaries exist.

Like the heliopause, once the water runs off the rim, it's out in the sink, or in this case, interstellar space. Credit: NASA/ESA. Right: solar wind raging into space as seen by the spacecraft SOHO after the solar storms of October 28. Credit: NASA/ESA. The European Space Agency has more on solar wind . And then there are the implications of this discovery. Voyager scientists are about to re-write a lot of textbooks and update a lot of theories. As Dr. Krimigis said, "the models that predict what the Sun and Voyager do are very crude." Uncharted Territory Both Dr. Frank McDonald of the University of Maryland and Dr. Krimigis have spent the better part of their careers tracking the fascinating adventure that has been the Voyager mission. And they represent the two opposing sides to this new controversy. In August 2002, Voyager scientists saw data that they had never seen before. Namely a large amount of low-energy particles flowing away from the Sun. The APL group interpreted this as the energy from the Sun reaching a dead end in this particular area.

"All models and theories have been telling us that's where the edge of the solar system begins to feel the pressure from the interstellar space," said Dr. Krimigis. "When you're sitting on the beach, depending on the wind, the waves can become very strong and blow over you, and at other times you're perfectly dry. Solar wind blows hot and cold - when hot, it [washes over Voyager] and when it's cold it retreats." The Voyager 1 and 2 spacecraft are identical with different flight paths. Voyager 2 was actually launched first, on August 20, 1977; Voyager 1 was launched September 5. Both are about 8 billion miles from the Sun, but Voyager 1 is traveling at a speed of 3.6 AU per year while Voyager 2 is speeding along at about 3.3 AU per year. One 'AU' equals the distance between the Sun and Earth, or 93 million miles. Credit: NASA This strange data appeared from August through February, convincing the APL team that for six months Voyager had entered into the heliosheath.

In February, it was as if the heliosheath retreated like water moving back toward the ocean at the beach, and Voyager was back within the solar wind. Meanwhile Dr. McDonald's team analyzed data from their instruments and concluded that they had merely rubbed against the boundary of the termination shock, but had not entered it. While both groups are uncertain what happened for those six months, they are both convinced that Voyager is currently back within the bubble of the solar wind, and will be crossing that termination shock either again in the next year, or for the first time. "We say we're just in the suburbs approaching the termination shock. They would say we're downtown, we're there," said Dr. McDonald. A Great Educated Guess Scientists are basing their theories on examples of this termination shock phenomenon they have seen before. The Hubble Space Telescope snapped a picture of a bow shock created as the wind from a star more powerful than that of our Sun's collided with a young star in the nearby Orion Nebula. As the fast stellar wind ran into slow moving gas, a shock front was formed, like the wave created when a boat moves through water. The Hubble Space Telescope imaged this view in February 1995.

The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow. For more information on this image, see HubbleSite. Click on the image for a very large version. Credit: NASA, The Hubble Heritage Team (STScI/AURA) Unfortunately, the instrument on Voyager 1 that measures solar wind has stopped working. A few of the remaining instruments have tried to pick up the slack, but that makes for a bit more guesswork and legwork on the part of scientists to prove their case. The excitement resulting from the controversy is inspiring the science community and the many people who continue to be fascinated by Voyager's journey. It also provides a great example of the uncertainty scientists deal with on a daily basis as they create theories, and then modify them again and again. In the meantime, as Dr. McDonald put it, "We keep making new discoveries, going places no one has ever been before." And isn't that the point of exploration?

More Voyager Resources Voyager 1 enters interstellar space (again) - Unexplained Mysteries Voyager 1 enters interstellar space (again) Posted on Friday, 11 July, 2014 | In interstellar space at last ? Image Credit: NASA/JPL-Caltech NASA's legendary space probe is now believed to have finally exited the solar system after 36 years. Launched in 1977 as part of an ambitious mission to explore the outer planets, Voyager 1 has traveled more than 12 billion miles and has long been suspected of becoming the first man-made object to leave our solar system behind. It has however been rather difficult to determine exactly at what point this milestone has been reached as the specific point at which the solar system ends and interstellar space begins is far from clear. Over the years there have been several announcements suggesting that the probe had finally achieved this goal, but each time further research had indicated that the celebrations had been premature. This time though NASA believes that it has it right thanks to a recent tsunami of plasma from the sun. "Normally, interstellar space is like a quiet lake," said lead Voyager 1 scientist Ed Stone.

"But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later. The wave causes the plasma surrounding the spacecraft to sing." By analyzing the oscillations of the surrounding plasma using the probe's instruments it has been possible to confirm that Voyager 1 has finally found itself in interstellar space. Whether this will really be the final word on the matter however remains to be seen. Recent comments on this story #9 Posted by shrooma on 11 July, 2014, 16:35 Considering how much we know about 'the edge of the Solar system' it could just bounce off 'something' and return back : . i reckon, Sir, that if it was gonna hit something that, at that speed, would make it rebound, it wouldn't do it any favours at all! besides, we all know we'll be seeing it again in 2273, when it comes back in Blofeld mode for some unfathomable reason. . or summat.... .

#10 Posted by toast on 11 July, 2014, 17:02 So if i understand correctly, when there's no more sun's plasma hitting the Voyager probe, they will assume it went out the sun's reach, therefore out of the solar system? I am just wondering how do they know this probe is travelling straight ahead and not simply moving in circles within our solar system boundaries. It`still sending signals so its position and track can be determinated well. #11 Posted by shrooma on 11 July, 2014, 18:48 It`still sending signals so its position and track can be determinated well. . pretty obvious, really. . #12 Posted by coolguy on 12 July, 2014, 4:28 This is awesome this thing is still working. #13 Posted by Scuzzy on 12 July, 2014, 5:34 This certainly emphasizes the futility of traveling to another star system given our current level of technology, 36 years and we are only now leaving our own solar system.

And this, I believe, is the fastest object humanity has launched into space, due largely to the "sling-shot" effect of using the gravity of the outer planets. No one who launches a probe to another star will live long enough to know if it arrived. Not if NASA's warp drive works... #14 Posted by MyOtherAccount on 12 July, 2014, 6:01 Talk about bang for your buck! Just think in 40 years the kids of that generation will be saying Vouger I is a hoax. And Nostradamus predicted it. #15 Posted by Hawkin on 12 July, 2014, 15:23 What do scientist consider the boundary between our solar system and interstellar space? The last planet or The Oort Cloud? #16 Posted by toast on 12 July, 2014, 17:16 What do scientist consider the boundary between our solar system and interstellar space? The last planet or The Oort Cloud? None of both.

The region that marks the border of the solar system is called Heliopause, the outer layer of the Heliosphere #17 Posted by Waspie_Dwarf on 12 July, 2014, 23:07 What do scientist consider the boundary between our solar system and interstellar space? The last planet or The Oort Cloud? Certainly not the last planet. The last known planet is Neptune which would Pluto and other Kuiper belt objects outside the solar system... which is clearly nonsensical. The region that marks the border of the solar system is called Heliopause, the outer layer of the Heliosphere This is the border of the solar system in terms of the Sun's influence by way of energetic particles. The solar wind no longer rules and the interstellar wind takes precedence. It is a measurable ... [More] #18 Posted by Sir Smoke aLot on 21 August, 2014, 9:45 Was just thinking about gravity, thanks for info Waspie_Dwarf.

Considering that the Sun is moving very fast around center of galaxy ( i find speed is 220km/s, from wikipedia ) is it possible that Voyager 1 can leave the Suns gravity influence at all? And if it do leave at some point we would loose contact with it forever anyway. Please Login or Register to post a comment. On the forums Voyager probe 'leaves Solar System' - BBC News BBC News Voyager probe 'leaves Solar System' By Jonathan Amos Science correspondent, BBC News 12 September 2013 Image caption Voyager will live out its days circling the centre of our Milky Way Galaxy The Voyager-1 spacecraft has become the first manmade object to leave the Solar System. Scientists say the probe's instruments indicate it has moved beyond the bubble of hot gas from our Sun and is now moving in the space between the stars. Launched in 1977, Voyager was sent initially to study the outer planets, but then just kept on going. Today, the veteran Nasa mission is almost 19 billion km (12 billion miles) from home. This distance is so vast that it takes 17 hours now for a radio signal sent from Voyager to reach receivers here on Earth.

Voyager's epic journey Find out how long it would take you "This is really a key milestone that we'd been hoping we would reach when we started this project over 40 years ago - that we would get a spacecraft into interstellar space," said Prof Ed Stone, the chief scientist on the venture. "Scientifically it's a major milestone, but also historically - this is one of those journeys of exploration like circumnavigating the globe for the first time or having a footprint on the Moon for the first time. This is the first time we've begun to explore the space between the stars," he told BBC News. Sensors on Voyager had been indicating for some time that its local environment had changed. The data that finally convinced the mission team to call the jump to interstellar space came from the probe's Plasma Wave Science (PWS) instrument. This can measure the density of charged particles in Voyager's vicinity. Readings taken in April/May this year and October/November last year revealed a near-100-fold jump in the number of protons occupying every cubic metre of space.

Media captionProject scientist Prof Ed Stone: "We got there!" Scientists have long theorised such a spike would eventually be observed if Voyager could get beyond the influence of the magnetic fields and particle wind that billow from the surface of the Sun. When the Voyager team put the new data together with information from the other instruments onboard, they calculated the moment of escape to have occurred on or about 25 August, 2012. This conclusion is contained in a report published by the journal Science . "This is big; it's really impressive - the first human-made object to make it out into interstellar space," said Prof Don Gurnett from the University of Iowa and the principal investigator on the PWS. On 25 August, 2012, Voyager-1 was some 121 Astronomical Units away. That is, 121 times the separation between the Earth and the Sun.

Breaching the boundary, known technically as the heliopause, was, said the English Astronomer Royal, Prof Sir Martin Rees, a remarkable achievement: "It's utterly astonishing that this fragile artefact, based on 1970s technology, can signal its presence from this immense distance." Although now embedded in the gas, dust and magnetic fields from other stars, Voyager still feels a gravitational tug from the Sun, just as some comets do that lie even further out in space. But to all intents and purposes, it has left what most people would define as the Solar System. It is now in a completely new domain. Nasa's Voyager probes Voyager 2 launched on 20 August 1977; Voyager 1 lifted off on 5 September the same year Their official missions were to study Jupiter and Saturn, but the probes were able to continue on The Voyager 1 probe is now the furthest human-built object from Earth Both probes carry discs with recordings designed to portray the diversity of culture on Earth To boldly go beyond the Solar System Voyager-1 departed Earth on 5 September 1977, a few days after its sister spacecraft, Voyager-2.

The pair's primary objective was to survey the planets Jupiter, Saturn, Uranus and Neptune - a task they completed in 1989. They were then steered towards deep space. It is expected that their plutonium power sources will stop supplying electricity in about 10 years, at which point their instruments and their 20W transmitters will die. Voyager-1 will not approach another star for nearly 40,000 years, even though it is moving at 45km/s (100,000mph). "Voyager-1 will be in orbit around the centre of our galaxy with all its stars for billions of years," said Prof Stone. Image caption In 1990, Voyager-1 looked back and took a picture of Earth - a "pale blue dot" The probe's work is not quite done, however. For as long as they have working instruments, scientists will want to sample the new environment. The new region through which Voyager is now flying was generated and sculpted by big stars that exploded millions of years ago. There is indirect evidence and models to describe the conditions in this medium, but Voyager can now measure them for real and report back.

The renowned British planetary scientist Prof Fred Taylor commented: "As a young post-doc, I went to [Nasa's Jet Propulsion Laboratory] and worked for a while with the team that was doing the science definition study for the Outer Planets Grand Tour, which later became Voyager. "It seemed so incredible and exciting to think we would see and explore Jupiter and Saturn close up, let alone Uranus and Neptune. "The idea that the spacecraft would then exit the Solar System altogether was so way out, figuratively as well as literally, that we didn't even discuss it then, although I suppose we knew it would happen someday.

Forty-three years later, that day has arrived, and Voyager is still finding new frontiers." Image caption The Sun sits in an extensive bubble of hot gas called the heliosphere Solar wind: The stream of charged particles blown off the Sun and travelling at "supersonic" speeds (white arrows) Termination shock: Area where particles from the Sun begin to slow and clash with matter from deep space Heliosheath: A vast, turbulent expanse where the solar wind piles up as it presses outward against interstellar matter Heliopause: The boundary between the solar wind and the interstellar wind, where the pressure of both are in balance Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos More evidence emerges to show Voyager 1 has exited our solar system to become the first man-made object to reach deep space | Daily Mail Online More evidence emerges to show Voyager 1 has exited our solar system to become the first man-made object to reach deep space Deep space probe has detected an increase in intergalactic cosmic rays There has also been a dramatic fall in charged particles hitting the craft comments Deep space probe Voyager 1 is showing new signs that it may have exited our solar system, which would make it the first man-made

 object to reach deep space.

Nasa is yet to make any announcement about what would be one of the most significant achievements in space exploration, but observers say new data from the spacecraft is evidence it may have crossed over. If the signs are correct, it would mark a historic moment in the history of space exploration and could herald a new era of interstellar exploration. Scroll down for video Crossing to the other side... Voyager 1 has observed a sustained increase in galactic cosmic rays in previous months and there has been a dramatic drop in charged particles from the sun striking the craft The Voyager probe has been travelling towards the outer reaches of the solar system since 1977 - it has enough batteries to last until 2020, scientists estimate Nasa scientists have said that they would need to observe three things to be certain that Voyager has actually travelled across the edge of our solar system: An increase in high-energy cosmic rays originating from outside our solar system; A drop in the level of lower-energy charged particles coming from our sun; And a change in the direction of the magnetic field detected by the spacecraft.

RELATED ARTICLES Share this article Share Scientists have previously revealed that Voyager 1 observed a sustained increase in galactic cosmic rays in previous months and that there's been a dramatic drop in charged particles from the sun striking the craft. The only remaining piece question is whether the magnetic field affecting Voyager has changed, and for that the data is not yet definitive, Chron's SciGuy blog reports. Bombarded: This graph shows an increase in the number of galactic cosmic rays striking voyager Precipitous: The rate at which the probe is being bombarded by charged particles from our Sun has fallen dramatically However, Texas A&M University astronomer Nick Suntzeff told the blog that based on the precipitous fall in the detection of charged particles, something is definitely going on that Nasa should comment on. 'Even without the magnetometer data, the Voyager 1 data shows that it has gone through a huge barrier at the edge of the solar system,' Professor Suntzeff told SciGuy. Even without data to show the decoupling of the magnetic fields, the astronomer added, 'the fact remains that the satellite has gone through a discontinuity in cosmic ray fluxes that is incredible. 'It is interacting with the boundary of the Solar System.

I think that the data stand on their merit – something wonderful has happened.' Voyager 1 set off on its epic journey 35 years ago and for some months researchers have expected it to finally hit the solar system's edge. For the past year, Voyager 1 used its instruments to explore the new region. It appeared to be the cosmic doldrums where solar winds streaming out from the sun at 1 million mph have dramatically eased Perhaps no one on Earth will relish the moment more than 76-year-old Ed Stone, a space scientist at Nasa who has toiled on the project from the start. 'We're anxious to get outside and find what's out there,' he said. COULD WE BE ON THE VERGE OF DEVELOPING A 'WARP DRIVE'? As it gears up to leave our solar system for the first interstellar journey, Voyager 1 has managed to pick up a quite phenomenal speed of one billion miles every three years. However, that's not quite fast enough for it to reach even the closest star within many lifetimes on Earth. Despite our desire to explore the stars, we are limited by the speeds we can achieve.

Even if we managed to match the speed of light, the fastest theoretically possible physical velocity, we would still be listing our voyages from star to star in years, centuries or millennia. But, in what could be a huge breakthrough, theorists from Nasa say there is 'hope' that we can achieve faster-than-light travel, after physicists found a theoretical possibility for warp speed travel. While nothing can break the speed of light, scientists have long considered the fantasy of warp speed travel, where spaceships could bend space and time on itself to move through loopholes in space. Equations based on the laws of relativity have allowed warp speed in theory: but the energy required to make it happen would require the energy-mass of a Jupiter-sized planet. Mexican physicist Miguel Alcubierre's theories are the most practical, mooting a ring around a sphere-shaped spaceship, which would contract space in front of the ship, and expand space behind it. But Nasa scientist Harold 'Sonny' White recently announced a way to use the same idea, but with far less energy.

He says that instead of enclosing a spacecraft in a space-time bubble, it could instead sit within a doughnut shape allowing the warp drive to be powered by a mass the size of a small car. He told Space.com: 'The findings I presented today change it from impractical to plausible and worth further investigation. 'The additional energy reduction realized by oscillating the bubble intensity is an interesting conjecture that we will enjoy looking at in the lab.' His rhetorical question to the crowd at the 35th anniversary events held last month at the Jet Propulsion Laboratory in California was: 'The question is, how much further is it to the heliopause? 'We don't know.... whether we're dancing along the edge of a new region which is connected to the outside.' When NASA's Voyager 1 and Voyager 2 first rocketed out of Earth's grip in 1977, no one knew how long they would live. Now, they are the longest-operating spacecraft in history and the most distant, at billions of miles from Earth but in different directions. September 5 marked the 35th anniversary of Voyager 1's launch to Jupiter and Saturn.

It is now flitting around the fringes of the solar system, which is enveloped in a giant plasma bubble. This hot and turbulent area is created by a stream of charged particles from the sun. Outside the bubble is a new frontier in the Milky Way - the space between the stars. Once it ploughs through, scientists expect a calmer environment by comparison. When that would happen is anyone's guess. Voyager 1 is in uncharted celestial territory. One thing is clear: The boundary that separates the solar system and interstellar space is near, but it could take days, months or years to cross that milestone. Voyager 1 is currently more than 11billion miles from the sun. Its twin, Voyager 2, which celebrated its launch anniversary two weeks ago, trails behind at 9billion miles from the sun. They're still ticking despite being relics of the early Space Age. Each only has 68 kilobytes of computer memory. To put that in perspective, the smallest iPod - an 8-gigabyte iPod Nano - has 100,000 more storage space. Each also has an eight-track tape recorder. Today's spacecraft use digital memory.

The Voyagers' original goal was to tour Jupiter and Saturn, and they sent back postcards of Jupiter's big red spot and Saturn's glittery rings. They also beamed home a torrent of discoveries: erupting volcanoes on the Jupiter moon Io; hints of an ocean below the icy surface of Europa, another Jupiter moon; signs of methane rain on the Saturn moon Titan. Voyager 2 then journeyed to Uranus and Neptune. It remains the only spacecraft to fly by these two outer planets. Voyager 1 used Saturn as a gravitational slingshot to catapult itself toward the edge of the solar system. 'Time after time, Voyager revealed unexpected - kind of counterintuitive - results, which means we have a lot to learn,' said Professor Stone, Voyager's chief scientist and a professor of physics at the California Institute of Technology. Voyager is now detecting the first traces of 'interstellar winds' - the signs it is finally reaching the edges of solar system These days, a handful of engineers diligently listen for the Voyagers from a satellite campus not far from the NASA Jet Propulsion Laboratory, which built the spacecraft.

The control room, with its cubicles and carpeting, could be mistaken for an insurance office if not for a blue sign overhead that reads 'Mission Controller' and a warning on a computer: 'Voyager mission critical hardware. Please do not touch!' There are no full-time scientists left on the mission, but 20 part-timers analyse the data streamed back. Since the spacecraft are so far out, it takes 17 hours for a radio signal from Voyager 1 to travel to Earth. For Voyager 2, it takes about 13 hours. Cameras aboard the Voyagers were turned off long ago. The nuclear-powered spacecraft, about the size of a subcompact car, still have five instruments to study magnetic fields, cosmic rays and charged particles from the sun known as solar wind. They also carry gold-plated discs containing multilingual greetings, music and pictures - in the off-chance that intelligent species come across them. Since 2004, Voyager 1 has been exploring a region in the bubble at the solar system's edge where the solar wind dramatically slows and heats up. Over the last several months, scientists have seen changes that suggest Voyager 1 is on the verge of crossing over.

When it does, it will be the first spacecraft to explore between the stars. Space observatories such as the Hubble and Spitzer space telescopes have long peered past the solar system, but they tend to focus on far-away galaxies. Voyager 1 and its twin, Voyager 2, were launched in 1977 to tour the outer planets including Jupiter, Saturn, Uranus and Neptune As ambitious as the Voyager mission is, it was scaled down from a plan to send a quartet of spacecraft to Jupiter, Uranus, Neptune and Pluto in what was billed as the "grand tour" of the solar system. But the plan was nixed, and scientists settled for the Voyager mission. American University space policy expert Howard McCurdy said it turned out to be a boon. They 'took the funds and built spacecraft robust enough to visit all four gas giants and keep communicating' beyond the solar system, McCurdy said. The double missions so far have cost $983million (£612million) in 1977 dollars, which translates to $3.7billion (£2.3billion) now. The spacecraft have enough fuel to last until around 2020.

By that time, scientists hope Voyager will already be floating between the stars.

Question: Which space probe, launched in 1977, is set to reach the edge of the known solar system and be the first man made object to experience interstellar space?
Answer: Voyager 1