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. Image credit: NASA/JPL-Caltech (Click Image To Enlarge)
PASADENA, Calif. -- NASA's Voyager 1 spacecraft officially is the first human-made object to venture into interstellar space. The 36-year-old probe is about 12 billion miles (19 billion kilometers) from our sun.
New and unexpected data indicate Voyager 1 has been traveling for about one year through plasma, or ionized gas, present in the space between stars. Voyager is in a transitional region immediately outside the solar bubble, where some effects from our sun are still evident. A report on the analysis of this new data, an effort led by Don Gurnett and the plasma wave science team at the University of Iowa, Iowa City, is published in Thursday's edition of the journal Science.
Ed Stone, Voyager project scientist based at the California Institute of Technology, Pasadena, said.
"Now that we have new, key data, we believe this is mankind's historic leap into interstellar space. The Voyager team needed time to analyze those observations and make sense of them. But we can now answer the question we've all been asking -- 'Are we there yet?' Yes, we are."
Voyager 1 first detected the increased pressure of interstellar space on the heliosphere, the bubble of charged particles surrounding the sun that reaches far beyond the outer planets, in 2004. Scientists then ramped up their search for evidence of the spacecraft's interstellar arrival, knowing the data analysis and interpretation could take months or years.
This artist's concept shows NASA's Voyager 1 spacecraft in a new region at the edge of our solar system where the amount of high-energy particles diffusing into our solar system from outside has increased. Voyager 1 is in an area scientists are calling the stagnation region, at the outer layer of the heliosphere, or magnetic bubble that the sun blows around itself (Click Image To Enlarge)
Voyager 1 does not have a working plasma sensor, so scientists needed a different way to measure the spacecraft's plasma environment to make a definitive determination of its location. A coronal mass ejection, or a massive burst of solar wind and magnetic fields, that erupted from the sun in March 2012 provided scientists the data they needed. When this unexpected gift from the sun eventually arrived at Voyager 1's location 13 months later, in April 2013, the plasma around the spacecraft began to vibrate like a violin string. On April 9, Voyager 1's plasma wave instrument detected the movement. The pitch of the oscillations helped scientists determine the density of the plasma. The particular oscillations meant the spacecraft was bathed in plasma more than 40 times denser than what they had encountered in the outer layer of the heliosphere. Density of this sort is to be expected in interstellar space.
The plasma wave science team reviewed its data and found an earlier, fainter set of oscillations in October and November 2012. Through extrapolation of measured plasma densities from both events, the team determined Voyager 1 first entered interstellar space in August 2012.
This artist's concept shows the outer layers of our solar bubble, or heliosphere, and nearby interstellar space. NASA's Voyager 1 just passed through the Sun's heliopause or outer edge of the heliosheath and is officially in the region known as interstellar space, which is the space between stars that still feels charged particle and magnetic field influences from the heliosphere. The magnetic field lines (yellow arcs) appear to lie in the same general direction as the magnetic field lines emanating from our sun. (Click Image To Enlarge)
"We literally jumped out of our seats when we saw these oscillations in our data -- they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble. Clearly we had passed through the heliopause, which is the long-hypothesized boundary between the solar plasma and the interstellar plasma."
The new plasma data suggested a timeframe consistent with abrupt, durable changes in the density of energetic particles that were first detected on Aug. 25, 2012. The Voyager team generally accepts this date as the date of interstellar arrival. The charged particle and plasma changes were what would have been expected during a crossing of the heliopause.
Suzanne Dodd, Voyager project manager, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif., said.
"The team's hard work to build durable spacecraft and carefully manage the Voyager spacecraft's limited resources paid off in another first for NASA and humanity. We expect the fields and particles science instruments on Voyager will continue to send back data through at least 2020. We can't wait to see what the Voyager instruments show us next about deep space."
Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. Both spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and Neptune. Voyager 2, launched before Voyager 1, is the longest continuously operated spacecraft. It is about 9.5 billion miles (15 billion kilometers) away from our sun.
Beyond the Bubble: The general locations of Voyager 1 and 2 are shown in this illustration at the edge of the heliosphere, the bubble created by solar wind. Image by NASA-JPL-Caltech (Click Image To Enlarge)
Voyager mission controllers still talk to or receive data from Voyager 1 and Voyager 2 every day, though the emitted signals are currently very dim, at about 23 watts -- the power of a refrigerator light bulb. By the time the signals get to Earth, they are a fraction of a billion-billionth of a watt. Data from Voyager 1's instruments are transmitted to Earth typically at 160 bits per second, and captured by 34- and 70-meter NASA Deep Space Network stations. Traveling at the speed of light, a signal from Voyager 1 takes about 17 hours to travel to Earth. After the data are transmitted to JPL and processed by the science teams, Voyager data are made publicly available.
This schematic shows our solar bubble moving through nearby interstellar space, or the space between stars. Interstellar space is shown in blue because it is filled with plasma, or ionized gas, that has a lower temperature than what is inside our solar bubble, also known as the heliosphere. Blue is about 10,000 degrees Fahrenheit (6,000 Kelvin). Red indicates hotter temperatures of about 2 million degrees Fahrenheit (1 million Kelvin). The black lines indicate the flow of the solar wind inside our solar bubble, and the flow of the interstellar wind in interstellar space. (Click To Enlarge Image)
John Grunsfeld, NASA's associate administrator for science in Washington, said.
"Voyager has boldly gone where no probe has gone before, marking one of the most significant technological achievements in the annals of the history of science, and adding a new chapter in human scientific dreams and endeavors. Perhaps some future deep space explorers will catch up with Voyager, our first interstellar envoy, and reflect on how this intrepid spacecraft helped enable their journey."
Scientists do not know when Voyager 1 will reach the undisturbed part of interstellar space where there is no influence from our sun. They also are not certain when Voyager 2 is expected to cross into interstellar space, but they believe it is not very far behind.
JPL built and operates the twin Voyager spacecraft. The Voyagers Interstellar Mission is a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA's Science Mission Directorate in Washington. NASA's Deep Space Network, managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions.
The cost of the Voyager 1 and Voyager 2 missions -- including launch, mission operations and the spacecraft's nuclear batteries, which were provided by the Department of Energy -- is about $988 million through September.
For a sound file of the oscillations detected by Voyager in interstellar space, animations and other information, visit:http://www.nasa.gov/voyager and http://www.jpl.nasa.gov/interstellarvoyager/ .
For an image of the radio signal from Voyager 1 on Feb. 21 by the National Radio Astronomy Observatory's Very Long Baseline Array, which links telescopes from Hawaii to St. Croix, visit: http://www.nrao.edu .
COMMENTARY: Pioneers 10 and 11, which preceded Voyager, both carried small metal plaques identifying their time and place of origin for the benefit of any other spacefarers that might find them in the distant future. With this example before them, NASA placed a more ambitious message aboard Voyager 1 and 2-a kind of time capsule, intended to communicate a story of our world to extraterrestrials. The Voyager message is carried by a phonograph record-a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth.
The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University, et. al. Dr. Sagan and his associates assembled 115 images and a variety of natural sounds, such as those made by surf, wind and thunder, birds, whales, and other animals. To this they added musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages, and printed messages from President Carter and U.N. Secretary General Waldheim.
Each record is encased in a protective aluminum jacket, together with a cartridge and a needle. Instructions, in symbolic language, explain the origin of the spacecraft and indicate how the record is to be played. The 115 images are encoded in analog form. The remainder of the record is in audio, designed to be played at 16-2/3 revolutions per minute. It contains the spoken greetings, beginning with Akkadian, which was spoken in Sumer about six thousand years ago, and ending with Wu, a modern Chinese dialect.
Following the section on the sounds of Earth, there is an eclectic 90-minute selection of music, including both Eastern and Western classics and a variety of ethnic music. Once the Voyager spacecraft leave the solar system (by 1990, both will be beyond the orbit of Pluto), they will find themselves in empty space.
It will be forty thousand years before they make a close approach to any other planetary system. As Carl Sagan has noted,
"The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space. But the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet."
The definitive work about the Voyager record is "Murmurs of Earth" by Executive Director, Carl Sagan, Technical Director, Frank Drake, Creative Director, Ann Druyan, Producer, Timothy Ferris, Designer, Jon Lomberg, and Greetings Organizer, Linda Salzman. Basically, this book is the story behind the creation of the record, and includes a full list of everything on the record. "Murmurs of Earth", originally published in 1978, was reissued in 1992 by Warner News Media with a CD-ROM that replicates the Voyager record. Unfortunately, this book is now out of print, but it is worth the effort to try and find a used copy or browse through a library copy.
Bon Voyage to Voyager 1 as it enters interstellar space and continues on its journey to other solar systems, perhaps making contact with intelligent beings like us.
Courtesy of an article dated September 12, 2013 appearing in NASA JPL