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The primary mission ended on November 20, 1980, after encounters with the [[Jupiter|Jovian]] system in 1979 and the [[Saturn]]ian system in 1980. It was the first probe to provide detailed images of the two planets and their [[Natural satellite|moons]]. As part of the [[Voyager program]], like its sister craft ''[[Voyager 2]]'', the spacecraft is in an extended mission to locate and study the regions and boundaries of the outer [[heliosphere]], and finally to begin exploring the [[interstellar medium]].
The primary mission ended on November 20, 1980, after encounters with the [[Jupiter|Jovian]] system in 1979 and the [[Saturn]]ian system in 1980. It was the first probe to provide detailed images of the two planets and their [[Natural satellite|moons]]. As part of the [[Voyager program]], like its sister craft ''[[Voyager 2]]'', the spacecraft is in an extended mission to locate and study the regions and boundaries of the outer [[heliosphere]], and finally to begin exploring the [[interstellar medium]].


On September&nbsp;12, 2013, NASA announced that ''Voyager 1'' had crossed the [[Heliopause (astronomy)|heliopause]] and entered [[interstellar space]] on August 25, 2012, making it the first spacecraft to do so.<!--<ref>{{cite web |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |title=NASA Spacecraft Embarks on Historic Journey Into Interstellar Space |work=NASA |date=12 September 2013 |accessdate=2014-05-29 |quote=NASA's Voyager 1 spacecraft officially is the first human-made object to venture into interstellar space. }}</ref>--><ref name="Landau CNN">{{cite news |last=Landau |first=Elizabeth |title=Voyager 1 becomes first human-made object to leave solar system |work=CNN |publisher=CNN |date=2 October 2013 |deadurl=no |archiveurl=http://www.cnn.com/2013/09/12/tech/innovation/voyager-solar-system/ |accessdate=2014-05-29 }}</ref><ref name="Cook2013">{{cite web |last=Cook | first=J.-R. C. |last2=Agle |first2=D.C. |last3=Brown |first3=D. |title=NASA Spacecraft Embarks on Historic Journey Into Interstellar Space |work=[http://www.nasa.gov/mission_pages/voyager NASA Voyager mission page] |publisher=NASA |date=September 12, 2013 |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |accessdate=September 14, 2013 }}</ref><ref name="NYT-20130912">{{cite news |last=Barnes |first=Brooks |title=In a Breathtaking First, NASA Craft Exits the Solar System |url=http://www.nytimes.com/2013/09/13/science/in-a-breathtaking-first-nasa-craft-exits-the-solar-system.html |date=September 12, 2013 |work=[[New York Times]] |accessdate=September 12, 2013 }}</ref><ref name="Morin2013">{{cite news |last=Morin |first=Monte |title=NASA confirms Voyager 1 has left the Solar System |url=http://www.latimes.com/science/sciencenow/la-sci-sn-nasa-confirms-voyager-1-has-exited-the-solar-system-20130912,0,3406650.story |newspaper=Los Angeles Times |date=September 12, 2013 }}</ref><ref name="agu">{{cite web |title=Voyager 1 has entered a new region of space, sudden changes in cosmic rays indicate |url=http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml |publisher=American Geophysical Union |date=March 20, 2013 |deadurl=yes |archivedate=2013-03-22 |archiveurl=https://web.archive.org/web/20130322025117/http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml }}</ref><!--<ref name="time.20130320">{{cite news |title=Report: Humanity Leaves the Solar System — Or Maybe Not |url=http://science.time.com/2013/03/20/humanity-leaves-the-solar-system-35-years-later-voyager-offically-exits-the-heliosphere/ |work=Time Magazine |date=March 20, 2013 }}</ref>--><!--<ref name="nasa.2013107">{{cite web |title=Report: NASA Voyager Status Update on Voyager 1 Location |url=http://www.jpl.nasa.gov/news/news.php?release=2013-107&cid=release_2013-107&msource=2013107 |publisher=NASA |accessdate=March 20, 2013 }}</ref>--> {{as of|2013}}, the probe was moving with a relative velocity to the Sun of about 17&nbsp;km/s.<ref name="nasa.20130906">{{cite web |url=http://voyager.jpl.nasa.gov/mission/weekly-reports/ |title=Voyager Mission Operations Status Report # 2013-09-06, Week Ending September 6, 2013 |publisher=JPL |accessdate=September 15, 2013 }}</ref><!-- Before updating, check carefully using multiple sources and delta distance calculations. --> With the velocity the probe is currently maintaining, Voyager 1 is traveling at about 325 million miles per year (520 million kilometers).<ref>{{cite news |last=Wall |first=Mike |url=http://www.space.com/22729-voyager-1-spacecraft-interstellar-space.html |title=It's Official! Voyager 1 Spacecraft Has Left Solar System |work=Space.com |date=12 September 2013 |accessdate=2014-05-30 }}</ref> The probe is expected to continue its mission until 2025, when it will be no longer supplied with enough power from its generators to operate any of its instruments.
On September&nbsp;12, 2013, NASA announced that ''Voyager 1'' had crossed the [[Heliopause (astronomy)|heliopause]] and entered [[interstellar space]] on August 25, 2012, making it the first spacecraft to do so.<!--<ref>{{cite web |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |title=NASA Spacecraft Embarks on Historic Journey Into Interstellar Space |work=NASA |date=12 September 2013 |accessdate=2014-05-29 |quote=NASA's Voyager 1 spacecraft officially is the first human-made object to venture into interstellar space. }}</ref>--><ref name="Landau CNN">{{cite news |last=Landau |first=Elizabeth |title=Voyager 1 becomes first human-made object to leave solar system |work=CNN |publisher=CNN |date=2 October 2013 |deadurl=no |archiveurl=http://www.cnn.com/2013/09/12/tech/innovation/voyager-solar-system/ |accessdate=2014-05-29 }}</ref><ref name="Cook2013">{{cite web |last=Cook | first=J.-R. C. |last2=Agle |first2=D.C. |last3=Brown |first3=D. |title=NASA Spacecraft Embarks on Historic Journey Into Interstellar Space |work=[http://www.nasa.gov/mission_pages/voyager NASA Voyager mission page] |publisher=NASA |date=September 12, 2013 |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |accessdate=September 14, 2013 }}</ref><ref name="NYT-20130912">{{cite news |last=Barnes |first=Brooks |title=In a Breathtaking First, NASA Craft Exits the Solar System |url=http://www.nytimes.com/2013/09/13/science/in-a-breathtaking-first-nasa-craft-exits-the-solar-system.html |date=September 12, 2013 |work=[[New York Times]] |accessdate=September 12, 2013 }}</ref><ref name="Morin2013">{{cite news |last=Morin |first=Monte |title=NASA confirms Voyager 1 has left the Solar System |url=http://www.latimes.com/science/sciencenow/la-sci-sn-nasa-confirms-voyager-1-has-exited-the-solar-system-20130912,0,3406650.story |newspaper=Los Angeles Times |date=September 12, 2013 }}</ref><ref name="agu">{{cite web |title=Voyager 1 has entered a new region of space, sudden changes in cosmic rays indicate |url=http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml |publisher=American Geophysical Union |date=March 20, 2013 |deadurl=yes |archivedate=2013-03-22 |archiveurl=https://web.archive.org/web/20130322025117/http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml }}</ref><!--<ref name="time.20130320">{{cite news |title=Report: Humanity Leaves the Solar System — Or Maybe Not |url=http://science.time.com/2013/03/20/humanity-leaves-the-solar-system-35-years-later-voyager-offically-exits-the-heliosphere/ |work=Time Magazine |date=March 20, 2013 }}</ref>--><!--<ref name="nasa.2013107">{{cite web |title=Report: NASA Voyager Status Update on Voyager 1 Location |url=http://www.jpl.nasa.gov/news/news.php?release=2013-107&cid=release_2013-107&msource=2013107 |publisher=NASA |accessdate=March 20, 2013 }}</ref>--> {{as of|2013}}, the probe was moving with a relative velocity to the Sun of about 17&nbsp;km/s.<ref name="nasa.20130906">{{cite web |url=http://voyager.jpl.nasa.gov/mission/weekly-reports/ |title=Voyager Mission Operations Status Report # 2013-09-06, Week Ending September 6, 2013 |publisher=JPL |accessdate=September 15, 2013 }}</ref><!-- Before updating, check carefully using multiple sources and delta distance calculations. --> With the velocity the probe is currently maintaining, Voyager 1 is traveling at about 325 million miles per year (520 million kilometers).<ref>{{cite news |last=Wall |first=Mike |url=http://www.space.com/22729-voyager-1-spacecraft-interstellar-space.html |title=It's Official! Voyager 1 Spacecraft Has Left Solar System |work=Space.com |date=12 September 2013 |accessdate=2014-05-30 }}</ref> The probe is expected to continue its mission until 2025, when its generators will no longer supply enough power to operate any of its instruments.


On December&nbsp;4, 2013, [[NASA]] presented the [[Voyager program|Voyager Project]] Scientist [[Edward C. Stone|Ed Stone]] with a [[NASA Distinguished Public Service Medal]] <ref name="nasa.stone">{{cite web |url=http://voyager.jpl.nasa.gov/news/ed_stone_colbert.html |title=Honouring ED Stone |publisher=NASA-JPL |date= |accessdate=December 8, 2013 }}</ref> and 2014 [[Howard Hughes Memorial Award]] by Aero Club of Southern California.<ref name="nasa.hughes">{{cite web |url=http://voyager.jpl.nasa.gov/news/howard_hughes_award.html |title=Howard Hughes Memorial Award |publisher=JPL |accessdate=March 23, 2014 }}</ref>
On December&nbsp;4, 2013, [[NASA]] presented the [[Voyager program|Voyager Project]] Scientist [[Edward C. Stone|Ed Stone]] with a [[NASA Distinguished Public Service Medal]] <ref name="nasa.stone">{{cite web |url=http://voyager.jpl.nasa.gov/news/ed_stone_colbert.html |title=Honouring ED Stone |publisher=NASA-JPL |date= |accessdate=December 8, 2013 }}</ref> and 2014 [[Howard Hughes Memorial Award]] by Aero Club of Southern California.<ref name="nasa.hughes">{{cite web |url=http://voyager.jpl.nasa.gov/news/howard_hughes_award.html |title=Howard Hughes Memorial Award |publisher=JPL |accessdate=March 23, 2014 }}</ref>

Revision as of 20:36, 4 July 2014

For other uses, see Voyager 1 (disambiguation).

Voyager 1
Voyager 1, its extended booms deploying instruments (right) and RTGs (left). The golden record, included to communicate with extraterrestrials, is below the high-gain antenna.
Mission typeOuter planetary, heliosphere, and interstellar medium exploration
OperatorNASA / JPL
COSPAR ID1977-084A[1]
SATCAT no.10321[2]
Websitevoyager.jpl.nasa.gov
Mission duration46 years, 9 months and 26 days elapsed
Planetary mission: 3 years, 3 months, 9 days
Interstellar mission: 43 years, 6 months and 17 days elapsed (continuing)
Spacecraft properties
ManufacturerJet Propulsion Laboratory
Launch mass721.9 kilograms (1,592 lb)
Power420 watts
Start of mission
Launch dateSeptember 5, 1977, 12:56:00 (1977-09-05UTC12:56Z) UTC
RocketTitan IIIE
Launch siteCape Canaveral LC-41
Flyby of Jupiter
Closest approachMarch 5, 1979
Distance349,000 kilometers (217,000 mi)
Flyby of Saturn
Closest approachNovember 12, 1980
Distance124,000 kilometers (77,000 mi)
 

Voyager 1 is a 722-kilogram (1,592 lb) space probe launched by NASA on September 5, 1977 to study the outer Solar System. Operating for 46 years, 9 months and 26 days as of 1 July 2024, the spacecraft communicates with the Deep Space Network to receive routine commands and return data. At a distance of about 127.44 AU (1.906×1010 km) from the Earth as of June 27, 2014,[3][4] it is the farthest spacecraft from Earth.[5][6]

The primary mission ended on November 20, 1980, after encounters with the Jovian system in 1979 and the Saturnian system in 1980. It was the first probe to provide detailed images of the two planets and their moons. As part of the Voyager program, like its sister craft Voyager 2, the spacecraft is in an extended mission to locate and study the regions and boundaries of the outer heliosphere, and finally to begin exploring the interstellar medium.

On September 12, 2013, NASA announced that Voyager 1 had crossed the heliopause and entered interstellar space on August 25, 2012, making it the first spacecraft to do so.[7][8][9][10][11] As of 2013, the probe was moving with a relative velocity to the Sun of about 17 km/s.[12] With the velocity the probe is currently maintaining, Voyager 1 is traveling at about 325 million miles per year (520 million kilometers).[13] The probe is expected to continue its mission until 2025, when its generators will no longer supply enough power to operate any of its instruments.

On December 4, 2013, NASA presented the Voyager Project Scientist Ed Stone with a NASA Distinguished Public Service Medal [14] and 2014 Howard Hughes Memorial Award by Aero Club of Southern California.[15]

Mission background

History

In the 1960s, a Grand Tour to study the outer planets was proposed. This prompted NASA to begin work on a mission in the early 1970s.[16]

Information gathered by the Pioneer 10 spacecraft helped Voyager's engineers design Voyager to cope more effectively with the intense radiation environment around Jupiter.[17]

Originally, Voyager 1 was planned as "Mariner 11" of the Mariner program. Due to budget cuts, the mission was scaled back to be a flyby of Jupiter and Saturn and renamed the Mariner Jupiter-Saturn probes. As the program progressed, the name was later changed to Voyager, since the probe designs began to differ greatly from previous Mariner missions.[18]

Golden record

Main article: Voyager Golden Record
Voyager Golden Record added to communicate with extraterrestrials

The Voyager space probe carries a gold-plated audio-visual disc in the event that either spacecraft is ever found by intelligent life forms from other planetary systems.[19] The discs carry photos of the Earth and its lifeforms, a range of scientific information, spoken greetings from people such as the Secretary-General of the United Nations and the President of the United States and a medley, "Sounds of Earth," that includes the sounds of whales, a baby crying, waves breaking on a shore, and a collection of music, including works by Mozart, Blind Willie Johnson, Chuck Berry's "Johnny B. Goode", and Valya Balkanska. Other Eastern and Western classics are included, as well as various performances of indigenous music from around the world. The record also contains greetings in 55 different languages.[20]

Spacecraft design

Main article: Voyager program § Spacecraft design
The 3.7 m diameter high gain dish antenna used on the Voyager craft

Voyager 1 was constructed by the Jet Propulsion Laboratory.[7][21][22] It has 16 hydrazine thrusters, three-axis stabilization gyroscopes, and referencing instruments to keep the probe's radio antenna pointed toward Earth. Collectively, these instruments are part of the Attitude and Articulation Control Subsystem (AACS), along with redundant units of most instruments and 8 backup thrusters. The spacecraft also included 11 scientific instruments to study celestial objects such as planets as it travels through space.[23]

Communication system

The radio communication system of Voyager 1 was designed to be used up to and beyond the limits of the Solar System. The communication system includes a 3.7 meters (12 ft) diameter parabolic dish high-gain antenna to send and receive radio waves via the three Deep Space Network stations on the Earth.[24] Voyager 1 normally transmits data to Earth over Deep Space Network Channel 18, using a frequency of either 2296.481481 MHz or 8420.432097 MHz, while signals from Earth to Voyager are broadcast at 2114.676697 MHz.[25]

When Voyager 1 is unable to communicate directly with the Earth, its digital tape recorder (DTR) can record up to 69.63 kilobytes of data for transmission at another time.[26] As of 2013, signals from Voyager 1 take over 17 hours to reach Earth.[9]

Power

Voyager 1 has three radioisotope thermoelectric generators (RTGs) mounted on a boom. Each MHW-RTG contains 24 pressed plutonium-238 oxide spheres. The RTGs generated about 470 watts of electric power at the time of launch, with the remainder being dissipated as waste heat.[27] The power output of the RTGs does decline over time (due to the short 87.7 yr half-life of the fuel and degradation of the thermocouples), but the RTGs of Voyager 1 will continue to support some of its operations until 2025.[23][28]

Computers

Voyager spacecraft diagram

Unlike the other onboard instruments, the operation of the cameras for visible light is not autonomous, but rather it is controlled by an imaging parameter table contained in one of the on-board digital computers, the Flight Data Subsystem (FDS). More recent space probes, since about 1990, usually have completely autonomous cameras.

The computer command subsystem (CCS) controls the cameras. The CCS contains fixed computer programs such as command decoding, fault detection, and correction routines, antenna pointing routines, and spacecraft sequencing routines. This computer is an improved version of the one that was used in the Viking orbiter.[29] The hardware in both custom-built CCS subsystems in the Voyagers is identical. There is only a minor software modification for one of them that has a scientific subsystem that the other lacks.

The Attitude and Articulation Control Subsystem (AACS) controls the spacecraft orientation (its attitude). It keeps the high-gain antenna pointing towards the Earth, controls attitude changes, and points the scan platform. The custom-built AACS systems on both Voyagers are the same.

Scientific instruments

Main article: Voyager program
Instrument Name Abr. Description
Imaging Science System
(disabled) 		(ISS) Utilized a two-camera system (narrow-angle/wide-angle) to provide imagery of Jupiter, Saturn and other objects along the trajectory. More
Filters
Narrow Angle Camera Filters[30]
Name Wavelength Spectrum Sensitivity
Clear 280–640 nm
UV 280–370 nm
Violet 350–450 nm
Blue 430–530 nm
' '
'
Green 530–640 nm
' '
'
Orange 590–640 nm
' '
'
Wide Angle Camera Filters[31]
Name Wavelength Spectrum Sensitivity
Clear 280–640 nm
' '
'
Violet 350–450 nm
Blue 430–530 nm
CH4-U 536–546 nm
Green 530–640 nm
Na-D 588–590 nm
Orange 590–640 nm
CH4-JST 614–624 nm
Radio Science System
(disabled) 		(RSS) Utilized the telecommunications system of the Voyager spacecraft to determine the physical properties of planets and satellites (ionospheres, atmospheres, masses, gravity fields, densities) and the amount and size distribution of material in Saturn's rings and the ring dimensions. More
Infrared Interferometer Spectrometer
(disabled) 		(IRIS) Investigates both global and local energy balance and atmospheric composition. Vertical temperature profiles are also obtained from the planets and satellites as well as the composition, thermal properties, and size of particles in Saturn's rings. More
Ultraviolet Spectrometer
(active) 		(UVS) Designed to measure atmospheric properties, and to measure radiation. More
Triaxial Fluxgate Magnetometer
(active) 		(MAG) Designed to investigate the magnetic fields of Jupiter and Saturn, the interaction of the solar wind with the magnetospheres of these planets, and the magnetic field of interplanetary space out to the boundary between the solar wind and the magnetic field of interstellar space, if crossed. More
Plasma Spectrometer
(defective) 		(PLS) Investigates the macroscopic properties of the plasma ions and measures electrons in the energy range from 5 eV to 1 keV. More
Low Energy Charged Particle Instrument
(active) 		(LECP) Measures the differential in energy fluxes and angular distributions of ions, electrons and the differential in energy ion composition. More
Cosmic Ray System
(active) 		(CRS) Determines the origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, the nucleosynthesis of elements in cosmic-ray sources, the behavior of cosmic rays in the interplanetary medium, and the trapped planetary energetic-particle environment. More
Planetary Radio Astronomy Investigation
(disabled) 		(PRA) Utilizes a sweep-frequency radio receiver to study the radio-emission signals from Jupiter and Saturn. More
Photopolarimeter System
(defective) 		(PPS) Utilized a telescope with a polarizer to gather information on surface texture and composition of Jupiter and Saturn and information on atmospheric scattering properties and density for both planets. More
Plasma Wave System
(active) 		(PWS) Provides continuous, sheath-independent measurements of the electron-density profiles at Jupiter and Saturn as well as basic information on local wave-particle interaction, useful in studying the magnetospheres. More

For more details on the Voyager space probes' identical instrument packages, see the separate article on the overall Voyager Program.

Images of the spacecraft
Media related to the Voyager spacecraft at Wikimedia Commons

Mission profile

Timeline of travel
Date Event
1977-09-05 Spacecraft launched at 12:56:00 UTC.
1977-12-10 Entered asteroid belt.
1977-12-19 Voyager 1 overtakes Voyager 2. (see diagram)
1978-09-08 Exited asteroid belt.
1979-01-06 Start Jupiter observation phase.
1980-08-22 Start Saturn observation phase.
1980-12-14 Begin Voyager Extended Mission.
Extended Mission
1990-02-14 Final images of the Voyager Program acquired by Voyager 1 to create the Solar System "Family Portrait".
1998-02-17 Voyager 1 overtakes Pioneer 10 as the most distant spacecraft from the Sun, at 69.419 AU. Voyager 1 is moving away from the Sun over 1 AU per year faster than Pioneer 10.
2004-12-17 Passed the termination shock at 94 AU and entered the heliosheath.
2007-02-02 Terminated plasma subsystem operations.
2007-04-11 Terminated plasma subsystem heater.
2008-01-16 Terminated planetary radio astronomy experiment operations.
2012-08-25 Crossed the heliopause at 121 AU and entered the interstellar medium.

Launch and trajectory

The Voyager 1 probe was launched on September 5, 1977, from Launch Complex 41 at the Cape Canaveral Air Force Station, aboard a Titan IIIE launch vehicle. The Voyager 2 probe had been launched two weeks earlier, on August 20, 1977. Despite being launched later, Voyager 1 reached both Jupiter[32] and Saturn sooner, following a shorter trajectory.[33]

Voyager 1 lifted off with a Titan IIIE

Encounter with Jupiter

Main article: Exploration of Jupiter

Voyager 1 began photographing Jupiter in January 1979. Its closest approach to Jupiter was on March 5, 1979, at a distance of about 349,000 kilometers (217,000 miles) from the planet's center.[32] Because of the greater photographic resolution allowed by a closer approach, most observations of the moons, rings, magnetic fields, and the radiation belt environment of the Jovian system were made during the 48-hour period that bracketed the closest approach. Voyager 1 finished photographing the Jovian system in April 1979.

Discovery of active volcanic activity on the satellite Io was probably the greatest surprise. It was the first time active volcanoes had been seen on another body in the Solar System. It appears that activity on Io affects the entire Jovian system. Io appears to be the primary source of matter that pervades the Jovian magnetosphere - the region of space that surrounds the planet influenced by the planet's strong magnetic field. Sulfur, oxygen, and sodium, apparently erupted by Io's volcanoes and sputtered off the surface by impact of high-energy particles, were detected at the outer edge of the magnetosphere of Jupiter.[32]

The two Voyager space probes made a number of important discoveries about Jupiter, its satellites, its radiation belts, and its never-before-seen planetary rings.

  • Voyager 1 time-lapse movie of Jupiter approach. (Link to full size video)
  • The Great Red Spot as seen from Voyager 1.
    Jupiter's Great Red Spot, an anticyclonic storm larger than Earth, as seen from Voyager 1.
  • View of lava flows radiating from the volcano Ra Patera on Io.
    View of sulfur-rich lava flows radiating from the volcano Ra Patera on Io.
  • A volcanic eruption plume rises over the limb of Io.
    The eruption plume of the volcano Loki rises 160 km (100 mi) over the limb of Io.
  • Europa as seen from Voyager 1 at a distance of 2.8 million km.
    Europa's lineated but uncratered face, evidence of currently active geology, at a distance of 2.8 million km.
  • Icy surface of Ganymede as photographed from 253,000 km.
    Ganymede's tectonically disrupted surface, marked with bright impact sites, from 253,000 km.
Media related to the Voyager 1 Jupiter encounter at Wikimedia Commons

Encounter with Saturn

Main article: Exploration of Saturn

The gravitational assist trajectories at Jupiter were successfully carried out by both Voyagers, and the two spacecraft went on to visit Saturn and its system of moons and rings. Voyager 1's Saturnian flyby occurred in November 1980, with the closest approach on November 12, 1980, when the space probe came within 124,000 kilometers (77,000 mi) of Saturn's cloud-tops. The space probe's cameras detected complex structures in the rings of Saturn, and its remote sensing instruments studied the atmospheres of Saturn and its giant moon Titan.[34]

Voyager 1 found that about 7 percent of the volume of Saturn's upper atmosphere is helium (compared with 11 percent of Jupiter's atmosphere), while almost all the rest is hydrogen. Since Saturn's internal helium abundance was expected to be the same as Jupiter's and the Sun's, the lower abundance of helium in the upper atmosphere may imply that the heavier helium may be slowly sinking through Saturn's hydrogen; that might explain the excess heat that Saturn radiates over energy it receives from the Sun. Winds blow at high speeds in Saturn. Near the equator, the Voyagers measured winds about 500 m/s (1,100 mi/hr). The wind blows mostly in an easterly direction.

The Voyagers found aurora-like ultraviolet emissions of hydrogen at mid-latitudes in the atmosphere, and auroras at polar latitudes (above 65 degrees). The high-level auroral activity may lead to formation of complex hydrocarbon molecules that are carried toward the equator. The mid-latitude auroras, which occur only in sunlit regions, remain a puzzle, since bombardment by electrons and ions, known to cause auroras on Earth, occurs primarily at high latitudes.

Both Voyagers measured the rotation of Saturn (the length of a day) at 10 hours, 39 minutes, 24 seconds.[34]

Because Pioneer 11 had one year earlier detected a thick, gaseous atmosphere over Titan, the Voyager space probes' controllers at the Jet Propulsion Laboratory elected for Voyager 1 to make a close approach of Titan. Its trajectory with a close fly-by of Titan caused a gravitational deflection that sent Voyager 1 out of the plane of the ecliptic, thus ending its planetary science mission. Voyager 1 could have been directed to visit Uranus and Neptune (later accomplished by Voyager 2). Also, Voyager 1 could have been commanded onto a different trajectory, whereby the gravitational slingshot effect of Saturn's mass would have steered and boosted it out to a fly-by of Pluto. However, this Plutonian option was not exercised, because the close fly-by of Titan was determined to have more scientific value and less risk.[35]

Media related to the Voyager 1 Saturn encounter at Wikimedia Commons

Exit from the heliosphere

A set of grey squares trace roughly left to right. A few are labeled with single letters associated with a nearby coloured square. J is near to a square labeled Jupiter; E to Earth; V to Venus; S to Saturn; U to Uranus; N to Neptune. A small spot appears at the centre of each coloured square
The "family portrait" of the Solar System taken by Voyager 1

Voyager 1, on February 14, 1990, took the first ever "family portrait" of the Solar System as seen from outside,[36] which includes the image of planet Earth known as "Pale Blue Dot". Soon afterwards its cameras were deactivated to conserve power and computer resources for other equipment. Camera software have been removed from the spacecraft, so it now would be complex to get them working again (also Earth-side software and computers for reading the images are no longer available).[35]

The pale blue dot image showing Earth from 6 billion kilometers appearing as a tiny dot (the blueish-white speck approximately halfway down the brown band to the right) within the darkness of deep space

On February 17, 1998, Voyager 1 reached a distance of 69 AU from the Sun and overtook Pioneer 10 as the most distant spacecraft from Earth.[37] Travelling at about 17 kilometers per second (11 mi/s)[38] it has the fastest heliocentric recession speed of any spacecraft.[39]

As Voyager 1 headed for interstellar space, its instruments continued to study the Solar System. Jet Propulsion Laboratory scientists used the plasma wave experiments aboard Voyager 1 and 2 to look for the heliopause, the boundary at which the solar wind transitions into the interstellar medium.[40]

Termination shock

File:Tour.gif
Close flybys of gas giants gave gravity assists to both Voyagers

Scientists at the Johns Hopkins University Applied Physics Laboratory believed that Voyager 1 had entered the termination shock in February 2003.[41] This marks the point where the solar wind slows down to subsonic speeds. Some other scientists expressed doubt, discussed in the journal Nature of November 6, 2003.[42] The issue would not be resolved until other data became available, since Voyager 1's solar-wind detector ceased functioning in 1990. This failure meant that termination shock detection would have to be inferred from the data from the other instruments on board.[43][44][45]

In May 2005, a NASA press release said that the consensus was that Voyager 1 was then in the heliosheath.[46] In a scientific session at the American Geophysical Union meeting in New Orleans on the morning of May 25, 2005, Dr. Ed Stone presented evidence that Voyager 1 crossed the termination shock in late 2004.[47] This event is believed to have occurred on December 15, 2004 at a distance of 94 AU from the Sun.[47][48]

Heliosheath

On March 31, 2006, amateur radio operators from AMSAT in Germany tracked and received radio waves from Voyager 1 using the 20-meter (66 ft) dish at Bochum with a long integration technique. Retrieved data was checked and verified against data from the Deep Space Network station at Madrid, Spain.[49] This is believed to be the first such amateur tracking of Voyager 1.[49]

It was confirmed on December 13, 2010 that Voyager 1 had passed the reach of the radial outward flow of the solar wind, as measured by the Low Energy Charged Particle device. It is suspected that solar wind at this distance turns sideways because of interstellar wind pushing against the heliosphere. Since June 2010, detection of solar wind had been consistently at zero, providing conclusive evidence of the event.[50][51][52] On this date, the spacecraft was approximately 17.3 billion kilometers (116 AU or 10.8 billion miles) from the Sun.[53]

a Bow Shock appears to wrap around the heliosphere that encompasses the Solar System
Voyager 1 passed through the heliosheath en route to interstellar space

Voyager 1 was commanded to change its orientation to measure the sideways motion of the solar wind at that location in space on March 2011. A test roll done in February had confirmed the spacecraft's ability to maneuver and reorient itself. The course of the spacecraft was not changed. It rotated 70 degrees counterclockwise with respect to Earth to detect the solar wind. This was the first time the spacecraft had done any major maneuvering since the family portrait photograph of the planets was taken in 1990. After the first roll the spacecraft had no problem in reorienting itself with Alpha Centauri, Voyager 1's guide star, and it resumed sending transmissions back to Earth. Voyager 1 was expected to enter interstellar space "at any time". Voyager 2 was still detecting outward flow of solar wind at that point but it was estimated that in the following months or years it would experience the same conditions as Voyager 1.[54][55]

The spacecraft was reported at 12.44° declination and 17.163 hours right ascension, and at an ecliptic latitude of 34.9° (the ecliptic latitude changes very slowly), placing it in the constellation Ophiuchus as observed from the Earth on May 21, 2011.[35]

On December 1, 2011, it was announced that Voyager 1 had detected the first Lyman-alpha radiation originating from the Milky Way galaxy. Lyman-alpha radiation had previously been detected from other galaxies, but because of interference from the Sun, the radiation from the Milky Way was not detectable.[56]

NASA announced on December 5, 2011 that Voyager 1 had entered a new region referred to as a "cosmic purgatory". Within this stagnation region, charged particles streaming from the Sun slow and turn inward, and the Solar System's magnetic field is doubled in strength as interstellar space appears to be applying pressure. Energetic particles originating in the Solar System decline by nearly half, while the detection of high-energy electrons from outside increases 100-fold. The inner edge of the stagnation region is located approximately 113 astronomical units from the Sun.[57][58]

Heliopause

Plot showing a dramatic increase in the rate of cosmic ray particle detection by the Voyager 1 spacecraft (October 2011 through October 2012)
Plot showing a dramatic decrease in the rate of solar wind particle detection by Voyager 1 (October 2011 through October 2012)

NASA announced in June 2012 that the probe was detecting changes in the environment that were suspected to correlate with arrival at the heliopause.[59] Voyager 1 had reported a marked increase in its detection of charged particles from interstellar space, which are normally deflected by the solar winds within the heliosphere from the Sun. The craft thus began to enter the interstellar medium at the edge of the Solar System.[60]

Voyager 1 became the first spacecraft to cross the heliopause in August 2012, then at a distance of 121 AU from the Sun, although this was not confirmed for another year.[8][61][62][63][64]

As of September 2012, sunlight took 16.89 hours to get to Voyager 1 which was at a distance of 121 AU. The apparent magnitude of the Sun from the spacecraft was −16.3.[3] Voyager 1 was traveling at 17,043 m/s (38,120 mph) relative to the Sun (about 3.595 AU per year). It would need about 17,565 years at this speed to travel a complete light year.[3] To compare, Proxima Centauri, the closest star to the Sun, is about 4.2 light-years (or 2.65×105 AU) distant. Were the spacecraft traveling in the direction of that star, 73,775 years would pass before reaching it. (Voyager 1 is heading in the direction of the constellation Ophiuchus.[3])

In late 2012, researchers reported that particle data from the spacecraft suggested that the probe had passed through the heliopause. Measurements from the spacecraft revealed a steady rise since May in collisions with high energy particles (above 70 MeV), which are believed to be cosmic rays emanating from supernova explosions far beyond the Solar System, with a sharp increase in these collisions in late August. At the same time, in late August, there was a dramatic drop in collisions with low-energy particles, which are thought to originate from the Sun.[65] Ed Roelof, space scientist at Johns Hopkins University and principal investigator for the Low-Energy Charged Particle instrument on the spacecraft declared that "Most scientists involved with Voyager 1 would agree that [these two criteria] have been sufficiently satisfied."[65] However, the last criterion for officially declaring that Voyager 1 had crossed the boundary, the expected change in magnetic field direction (from that of the Sun to that of the interstellar field beyond), had not been observed (the field had changed direction by only 2 degrees[61]), which suggested to some that the nature of the edge of the heliosphere had been misjudged. On December 3, 2012, Voyager project scientist Ed Stone of the California Institute of Technology said, "Voyager has discovered a new region of the heliosphere that we had not realized was there. We're still inside, apparently. But the magnetic field now is connected to the outside. So it's like a highway letting particles in and out."[66] The magnetic field in this region was 10 times more intense than Voyager 1 encountered before the termination shock. It was expected to be the last barrier before the spacecraft exited the Solar System completely and entered interstellar space.[67][68][69]

In March 2013, it was announced that Voyager 1 might have become the first spacecraft to enter interstellar space, having detected a marked change in the plasma environment on August 25, 2012. However, until September 12, 2013, it was still an open question as to whether the new region was interstellar space or an unknown region of the Solar System. At that time, the former alternative was officially confirmed.[11][70][71]

Voyager 1 reached a distance of 125 AU from the Sun on August 2, 2013.[72]

Position of Voyager 1 on a logarithmic distance scale as of August 2013

Interstellar medium

On September 12, 2013, NASA officially confirmed that Voyager 1 had reached the interstellar medium in August 2012 as previously observed, with a generally accepted date of August 25, 2012, the date durable changes in the density of energetic particles were first detected.[8][61][62][63][64] By this point most space scientists had abandoned the belief that a change in magnetic field direction must accompany crossing of the heliopause;[63] a new model of the heliopause predicted that no such change would be found.[73] A key finding that persuaded many scientists that the heliopause had been crossed was an indirect measurement of an 80-fold increase in electron density, based on the frequency of plasma oscillations observed beginning on April 9, 2013,[63] triggered by a solar outburst that had occurred in March 2012[8] (Electron density is expected to be two orders of magnitude higher outside the heliopause than within.[62]) Weaker sets of oscillations measured in October and November 2012[10][70] provided additional data. An indirect measurement was required because Voyager 1's plasma spectrometer had stopped working in 1980.[64] In September 2013, NASA released audio renditions of these plasma waves. The recordings represent the first sounds to be captured in interstellar space.[74][75]

While Voyager 1 is commonly spoken of as having left the Solar System simultaneously with having left the heliosphere, the two are not the same. The Solar System is usually defined as the vastly larger region of space populated by bodies that orbit the Sun. The craft is presently less than one seventh the distance to the aphelion of Sedna, and it has not yet entered the Oort cloud, the source region of long-period comets, regarded by astronomers as the outermost zone of the Solar System.[61][70][71]

Future of the probe

Image of Voyager 1's radio signal on February 21, 2013

Voyager 1 will reach the Oort cloud in about 300 years[76][77] and take about 30,000 years to pass through it.[61][70][71] Though it is not heading towards any particular star, in about 40,000 years, it will pass within 1.6 light years of the star Gliese 445, which is at present in the constellation Camelopardalis.[78] That star is generally moving towards the Solar System at about 119 km/s (430,000 km/h; 270,000 mph).[78] The Voyagers are destined—perhaps eternally—to wander the Milky Way.[79]

Provided Voyager 1 does not collide with anything and is not retrieved, the New Horizons space probe will never pass it, despite being launched from Earth at a faster speed than either Voyager spacecraft. New Horizons is traveling at about 15 km/s, 2 km/s slower than Voyager 1, and is still slowing down. When New Horizons reaches the same distance from the Sun as Voyager 1 is now, its speed will be about 13 km/s (8 mi/s).[80]

Year End of specific capabilities as a result of the available electrical power limitations
2007 Termination of plasma subsystem (PLS)
2008 Power off Planetary Radio Astronomy Experiment (PRA)
2010 Terminate scan platform and Ultraviolet spectrometer (UVS) observations
2015 Termination of Data Tape Recorder (DTR) operations (limited by ability to capture 1.4 kbit/s data using a 70 m/34 m antenna array. This is the minimum rate at which the DTR can read-out data.)
2016 approx Termination of gyroscopic operations
2020 Start shutdown of science instruments (as of October 18, 2010 the order is undecided but the Low-Energy Charged Particles, Cosmic Ray Subsystem, Magnetometer, and Plasma Wave Subsystem instruments are expected to still be operating)[81]
2025–2030 Will no longer be able to power any single instrument.

See also

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