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Voyager 1

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Voyager 1
Model of a small-bodied spacecraft with a large, central dish and many arms and antennas extending from it
Model of the Voyager spacecraft design
Mission typeOuter planetary, heliosphere, and interstellar medium exploration
OperatorNASA / Jet Propulsion Laboratory
COSPAR ID1977-084A[1]
SATCAT no.10321[2]
Websitevoyager.jpl.nasa.gov
Mission duration
  • 41 years, 2 months and 24 days elapsed
  • Planetary mission: 3 years, 3 months, 9 days
  • Interstellar mission: 37 years, 11 months and 15 days elapsed (continuing)
Spacecraft properties
ManufacturerJet Propulsion Laboratory
Launch mass825.5 kg (1,820 lb)
Power470 watts (at launch)
Start of mission
Launch dateSeptember 5, 1977, 12:56:00 (1977-09-05UTC12:56Z) UTC
RocketTitan IIIE
Launch siteCape Canaveral Launch Complex 41
Flyby of Jupiter
Closest approachMarch 5, 1979
Distance349,000 km (217,000 mi)
Flyby of Saturn
Closest approachNovember 12, 1980
Distance124,000 km (77,000 mi)
Flyby of Titan (atmosphere study)
Closest approachNovember 12, 1980
Distance6,490 km (4,030 mi)

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 41 years, 2 months and 24 days as of November 29, 2018, the spacecraft still communicates with the Deep Space Network to receive routine commands and return data. At a distance of 142.31 astronomical units (2.1289×1010 km; 1.3229×1010 mi) (21.289 billion kilometers; 13.229 billion miles) from the Sun as of June 4, 2018,[3] it is the most distant man-made object from Earth.[4]

The probe's objectives included flybys of Jupiter, Saturn, and Saturn's largest 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.[5][6][7] 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 12, 1980, Voyager 1 became the third of five artificial objects to achieve the escape velocity that will allow them to leave the Solar System. On August 25, 2012, Voyager 1 became the first spacecraft to cross the heliopause and enter the interstellar medium.[8]

In a further testament to the robustness of Voyager 1, the Voyager team completed a successful test of the spacecraft's trajectory correction maneuver (TCM) thrusters on November 28, 2017. The last time these backup thrusters were fired up was in November 1980. Voyager project manager Suzanne Dodd anticipates that successful use of the TCM thrusters will extend the Voyager mission by an additional "two to three years".[9]

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 its scientific instruments.

Mission background[edit]

History[edit]

In the 1960s, a Grand Tour to study the outer planets was proposed which prompted NASA to begin work on a mission in the early 1970s.[10] Information gathered by the Pioneer 10 spacecraft helped Voyager's engineers design Voyager to cope more effectively with the intense radiation environment around Jupiter.[11]

Initially, 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.[12]

Spacecraft components[edit]

Main article: Voyager program § Spacecraft design
The 3.7 m (12 ft) diameter high gain dish antenna used on the Voyager craft

Voyager 1 was constructed by the Jet Propulsion Laboratory.[13][14][15] 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.[16]

Communication system[edit]

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-meter (12 ft) diameter high gain Cassegrain antenna to send and receive radio waves via the three Deep Space Network stations on the Earth.[17] The craft normally transmits data to Earth over Deep Space Network Channel 18, using a frequency of either 2.3 GHz or 8.4 GHz, while signals from Earth to Voyager are transmitted at 2.1 GHz.[18]

When Voyager 1 is unable to communicate directly with the Earth, its digital tape recorder (DTR) can record about 64 kilobytes of data for transmission at another time.[19] Signals from Voyager 1 take over 19 hours to reach Earth.[3]

Power[edit]

Voyager 1 has three radioisotope thermoelectric generators (RTGs) mounted on a boom. Each MHW-RTG contains 24 pressed plutonium-238 oxide spheres.[20] The RTGs generated about 470 W of electric power at the time of launch, with the remainder being dissipated as waste heat.[21] The power output of the RTGs declines over time (due to the 87.7-year half-life of the fuel and degradation of the thermocouples), but the craft's RTGs will continue to support some of its operations until 2025.[16][20]

As of November 29, 2018, Voyager 1 has 72.19% of the plutonium-238 that it had at launch. By 2050, it will have 56.5% left.

Computers[edit]

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). Since the 1990s, space probes usually have completely autonomous cameras.[22]

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 1970s Viking orbiters.[23] 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.[citation needed]

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.[24][25]

Scientific instruments[edit]

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[26]
Name Wavelength Spectrum Sensitivity
Clear 280–640 nm
Voyager - Filters - Clear.png
UV 280–370 nm
Voyager - Filters - UV.png
Violet 350–450 nm
Voyager - Filters - Violet.png
Blue 430–530 nm
Voyager - Filters - Blue.png
⋮
Green 530–640 nm
Voyager - Filters - Green.png
⋮
Orange 590–640 nm
Voyager - Filters - Orange.png
⋮
Wide-angle camera[27]
Name Wavelength Spectrum Sensitivity
Clear 280–640 nm
Voyager - Filters - Clear.png
⋮
Violet 350–450 nm
Voyager - Filters - Violet.png
Blue 430–530 nm
Voyager - Filters - Blue.png
CH4-U 536–546 nm
Voyager - Filters - CH4U.png
Green 530–640 nm
Voyager - Filters - Green.png
Na-D 588–590 nm
Voyager - Filters - NaD.png
Orange 590–640 nm
Voyager - Filters - Orange.png
CH4-JST 614–624 nm
Voyager - Filters - CH4JST.png
  • Principal investigator: Bradford Smith / University of Arizona (PDS/PRN website)
  • Data: PDS/PDI data catalog, PDS/PRN data catalog
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
  • Principal investigator: G. Tyler / Stanford University PDS/PRN overview
  • Data: PDS/PPI data catalog, PDS/PRN data catalog (VG_2803), NSSDC data archive
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
  • Principal investigator: Rudolf Hanel / NASA Goddard Space Flight Center (PDS/PRN website)
  • Data: PDS/PRN data catalog, PDS/PRN expanded data catalog (VGIRIS_0001, VGIRIS_002), NSSDC Jupiter data archive
Ultraviolet Spectrometer
(disabled) 		UVS Designed to measure atmospheric properties, and to measure radiation. More
  • Principal investigator: A. Broadfoot / University of Southern California (PDS/PRN website)
  • Data: PDS/PRN data catalog
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. More
  • Principal investigator: Norman F. Ness / NASA Goddard Space Flight Center (website)
  • Data: PDS/PPI data catalog, NSSDC data archive
Plasma Spectrometer
(defective) 		PLS Investigates the microscopic properties of the plasma ions and measures electrons in the energy range from 5 eV to 1 keV. More
  • Principal investigator: John Richardson / MIT (website)
  • Data: PDS/PPI data catalog, NSSDC data archive
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
  • Principal investigator: Stamatios Krimigis / JHU / APL / University of Maryland (JHU/APL website / UMD website / KU website)
  • Data: UMD data plotting, PDS/PPI data catalog, NSSDC data archive
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
  • Principal investigator: Edward Stone / Caltech / NASA Goddard Space Flight Center (website)
  • Data: PDS/PPI data catalog, NSSDC data archive
Planetary Radio Astronomy Investigation
(disabled) 		PRA Utilizes a sweep-frequency radio receiver to study the radio-emission signals from Jupiter and Saturn. More
  • Principal investigator: James Warwick / University of Colorado
  • Data: PDS/PPI data catalog, NSSDC data archive
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
  • Principal investigator: Arthur Lane / JPL (PDS/PRN website)
  • Data: PDS/PRN data catalog
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
  • Principal investigator: Donald Gurnett / University of Iowa (website)
  • Data: PDS/PPI data catalog

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[edit]

Timeline of travel[edit]

Voyager 1 skypath 1977-2030.png
Voyager 1's trajectory from the earth, diverging from the ecliptic in 1981 at Saturn and now heading into the constellation Ophiuchus
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 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 at 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 interstellar space.
2014-07-07 Further confirmation probe is in interstellar space.
2016-04-19 Terminated Ultraviolet Spectrometer operations.
2017-11-28 "Trajectory correction maneuver" (TCM) thrusters are tested in their first use since November 1980.[28]

Launch and trajectory[edit]

Voyager 1 lifted off atop a Titan IIIE.
Animation of Voyager 1's trajectory from September 1977 to 31 December 1981
   Voyager 1  ·   Earth ·   Jupiter ·   Saturn ·   Sun

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[29] and Saturn sooner, following a shorter trajectory.[30]

The trajectory of Voyager 1 through the Jupiter system

Flyby of Jupiter[edit]

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.[29] 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 moon 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.[29]

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 (full-size video)

  • The Great Red Spot as seen from Voyager 1

    Jupiter's Great Red Spot, an anti-cyclonic 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 un-cratered 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

Flyby of Saturn[edit]

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 encountered Saturn 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.[31]

Voyager 1 found that about seven per cent 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 mph). The wind blows mostly in an easterly direction.[30]

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 the 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.[31]

Voyager 1's mission included a flyby of Titan, Saturn's largest moon, which had long been known to have an atmosphere. Images taken by Pioneer 11 in 1979 had indicated the atmosphere was substantial and complex, further increasing interest. The Titan flyby occurred as the spacecraft entered the system to avoid any possibility of damage closer to Saturn compromising observations, and approached to within 6,400 km (4,000 mi), passing behind Titan as seen from Earth and the Sun. Voyager's measurement of the atmosphere's effect on sunlight and Earth-based measurement of its effect on the probe's radio signal were used to determine the atmosphere's composition, density, and pressure. Titan's mass was also measured by observing its effect on the probe's trajectory. The thick haze prevented any visual observation of the surface, but the measurement of the atmosphere's composition, temperature, and pressure led to speculation that lakes of liquid hydrocarbons could exist on the surface.[32]

Because observations of Titan were considered vital, the trajectory chosen for Voyager 1 was designed around the optimum Titan flyby, which took it below the south pole of Saturn and out of the plane of the ecliptic, ending its planetary science mission.[33] Had Voyager 1 failed or been unable to observe Titan, Voyager 2's trajectory would have been altered to incorporate the Titan flyby,[32]:94 precluding any visit to Uranus and Neptune.[5] The trajectory Voyager 1 was launched into would not have allowed it to continue on to Uranus and Neptune,[33]:155 but could have been altered to avoid a Titan flyby and travel from Saturn to Pluto, arriving in 1986.[7]

Media related to the Voyager 1 Saturn encounter at Wikimedia Commons

Exit from the heliosphere[edit]

A set of grey squares trace roughly left to right. A few are labeled with single letters associated with a nearby colored 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 center of each colored square
The Family Portrait of the Solar System acquired by Voyager 1
Position of Voyager 1 above the plane of the ecliptic on February 14, 1990

On February 14, 1990, Voyager 1 took the first ever "family portrait" of the Solar System as seen from outside,[34] which includes the image of planet Earth known as Pale Blue Dot. Soon afterwards its cameras were deactivated to conserve energy and computer resources for other equipment. The camera software has been removed from the spacecraft, so it would now be complex to get them working again. Earth-side software and computers for reading the images are also no longer available.[5]

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.[35][36] Travelling at about 17 kilometers per second (11 mi/s)[37] it has the fastest heliocentric recession speed of any spacecraft.[38]

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.[39] As of 2013, the probe was moving with a relative velocity to the Sun of about 17,030 meters per second (55,900 ft/s).[40] With the velocity the probe is currently maintaining, Voyager 1 is traveling about 325 million miles (523×10^6 km) per year,[41] or approximately half a light-year per ten millennia.

Termination shock[edit]

Close flybys of gas giants gave gravity assists to both Voyagers

Scientists at the Johns Hopkins University Applied Physics Laboratory think that Voyager 1 entered the termination shock in February 2003.[42] 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.[43] 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.[44][45][46]

In May 2005, a NASA press release said that the consensus was that Voyager 1 was then in the heliosheath.[47] 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 the craft crossed the termination shock in late 2004.[48] This event is estimated to have occurred on December 15, 2004 at a distance of 94 AU from the Sun.[48][49]

Heliosheath[edit]

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.[50] This seems to be the first such amateur tracking of Voyager 1.[50]

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.[51][52] On this date, the spacecraft was approximately 116 AU or 10.8 billion miles (17.3 billion kilometers) from the Sun.[53]

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 (~33yr 6mo from launch). 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.[5]

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 AU from the Sun.[57]

Heliopause[edit]

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.[58] 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.[59]

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.[60][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 (less than 30 times the brightness of the full moon).[65] The spacecraft was traveling at 17.043 km/s (10.590 mi/s) relative to the Sun. It would need about 17,565 years at this speed to travel a light-year.[65] To compare, Proxima Centauri, the closest star to the Sun, is about 4.2 light-years (2.65×105 AU) distant. Were the spacecraft traveling in the direction of that star, 73,775 years would pass before Voyager 1 reaches it. (Voyager 1 is heading in the direction of the constellation Ophiuchus.[65])

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 thought 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.[66] 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."[66] 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."[67] 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.[68][69][70]

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.[71] [72]

In 2013 Voyager 1 was exiting the solar system at a speed of about 3.6 AU per year, while Voyager 2 is going slower, leaving the solar system at 3.3 AU per year.[73] Each year Voyager 1 increases its lead over Voyager 2.

Voyager 1 reached a distance of 135 AU from the Sun on May 18, 2016.[3] By September 5, 2017, that had increased to about 139.64 AU from the Sun, or just over 19 light-hours, and at that time Voyager 2 was 115.32 AU from the Sun.[3]

Its progress can be monitored at NASA's website (see: External links).[3]

Voyager 1 and the other probes that are in or on their way to interstellar space, except New Horizons.

Interstellar medium[edit]

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 (~10d short of 34yrs since launch), the date durable changes in the density of energetic particles were first detected.[62][63][64] By this point most space scientists had abandoned the hypothesis 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.[74] 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[60] (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[72][75] 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.[76]

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][72]

Future of the probe[edit]

Image of Voyager 1's radio signal on February 21, 2013[77]
Simulated view of Voyager 1 relative to the solar system on August 2, 2018.
Simulated view of the Voyager probes relative to the solar system and heliopause on August 2, 2018.

Voyager 1 is expected to reach the theorized Oort cloud in about 300 years[78][79] and take about 30,000 years to pass through it.[61][72] 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.[80] That star is generally moving towards the Solar System at about 119 km/s (430,000 km/h; 270,000 mph).[80] NASA says that "The Voyagers are destined—perhaps eternally—to wander the Milky Way."[81]

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. The Voyager spacecraft benefited from multiple planetary flybys to increase their heliocentric velocities, whereas New Horizons received only a single such boost, from its Jupiter flyby. As of 2018, New Horizons is traveling at about 14 km/s, 3 km/s slower than Voyager 1, and is still slowing down.[82]

In December 2017 it was announced that NASA had successfully fired up all four of Voyager 1's trajectory correction maneuver (TCM) thrusters. The TCM thrusters will be used in the place of a degraded set of jets which were used to help keep the probe's antenna pointed towards the Earth. Use of the TCM thrusters will allow Voyager 1 to continue to transmit data to NASA for two to three more years.[83][84]

Year End of specific capabilities as a result of the available electrical power limitations[85]
2007 Termination of plasma subsystem (PLS)
2008 Power off Planetary Radio Astronomy Experiment (PRA)
2016[86] Termination of scan platform and Ultraviolet Spectrometer (UVS) observations
2018 approx. 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)
2019–2020 approx. Termination of gyroscopic operations (previously 2017, but backup thrusters active for continuation of gyroscopic operations.)
2020 Start shutdown of science instruments (as of October 18, 2010 the order is undecided, however the Low-Energy Charged Particles, Cosmic Ray Subsystem, Magnetometer, and Plasma Wave Subsystem instruments are expected to still be operating)[87]
2025–2030 Will no longer be able to power even a single instrument.

Golden record[edit]

A child's greeting in English recorded on the Voyager Golden Record
Voyager Golden Record
Main article: Voyager Golden Record

Each Voyager space probe carries a gold-plated audio-visual disc, should the spacecraft ever be found by intelligent life forms from other planetary systems.[88] The disc carries 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 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.[89]

See also[edit]

References[edit]

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External links[edit]

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