Voyager 1 & 2: The Children of the Unknown and the Silence

The Voyager missions are perhaps the most poetic form of science ever created by human intellect. Two small spacecraft, twin in construction but not in course, originally designed for a four-year mission to the outer planets, and finally, nearly half a century later, still continue to travel through interstellar space — silently, yet still “active.”

Voyager 2 was launched first, on August 20, 1977, and Voyager 1 followed on September 5, 1977 — and yet the second launch was named “1,” because its trajectory made it reach Jupiter and Saturn first. The planning was masterful: a rare alignment of the planets that occurs every 176 years allowed a journey from Jupiter to Saturn, Uranus, and Neptune using successive gravity assists. A chain of cosmic “slingshots” that hurled the Voyagers out of the Solar System.

Each Voyager has a mass of about 825 kilograms (including fuel and the RTG*), and carries a 3.7-meter high-gain** antenna (that parabolic “dish” that still sends radio signals to Earth with only 23 watts of power). By analogy, it’s like spotting a bicycle headlight from the far edge of the Solar System.

*RTG stands for Radioisotope Thermoelectric Generator — the radioisotopic thermoelectric generator. It is the device that converts heat from radioactive decay (usually plutonium-238) into electrical energy. The Voyagers, Pioneers, and Cassini, because they travel far from the Sun, cannot operate with solar panels and therefore rely on RTGs for decades of steady power.

**High-Gain Antenna is the spacecraft’s large parabolic antenna that sends and receives data to/from Earth. “High gain” means it concentrates the signal into a narrow beam, increasing communication efficiency — essential when the signal must cross billions of kilometers.

The spacecraft’s power comes from three radioisotope thermoelectric generators (RTGs) containing plutonium-238, initially producing around 470 watts. Today, after almost 48 years, Voyager 1 operates on less than 250 watts and continues… Some instruments have already been turned off to conserve power, but its pulse remains.

Its scientific instruments include cosmic-ray detectors, magnetometers, wide- and narrow-angle cameras, plasma detectors, and radio-wave instruments. It was the first time humanity saw up close planets that until then were merely “faint balls” in telescopes.

There was also a Greek “representation” on the mission. The Greek physicist involved was Stamatios Krimigis, one of NASA’s top space scientists. He led the charged-particle detection experiment, which for the first time recorded the boundaries of the Solar System and the transition to interstellar space. His contribution is considered fundamental and thanks to him a piece of Greek science travels forever among the stars.

Encounters with the giants

Voyager 1

It approached Jupiter in March 1979. Its images changed forever our knowledge of the Solar System: Jupiter’s moons proved to be worlds with active geology. Io, for example, exhibits volcanic activity — the first active volcano observed beyond Earth. Europa appeared to have an icy shell hiding an ocean beneath.

In November 1980, Voyager 1 passed Saturn, photographing its rings in detail and revealing Titan’s haze. There it was decided not to continue to other planets but to head out of the ecliptic — a course toward the galactic north to exit the Solar System.

Voyager 2

This one followed a slower but spectacular journey. After Jupiter (July 1979) and Saturn (August 1981), it continued to Uranus (January 1986) — the first and only visit by a human spacecraft there. We saw a cold blue world with winds reaching 700 km/h.

The final stop was Neptune, in August 1989. Its images revealed the “Great Dark Spot”: a storm the size of Earth, and its moons, most notably Triton, covered in nitrogen and featuring active plumes. From there, the gravity assist launched it out of the ecliptic, on a path opposite to Voyager 1’s, toward the galactic south.

Voyagers 1 and 2 are the only missions that have explored all the outer planets. No other program has achieved anything comparable, nor will it anytime soon.

Exit into interstellar space

Voyager 1 is today the most distant object ever made by humans. In 2012 it officially crossed the heliopause, at roughly 121 AU from the Sun, and is moving at 17 km/s (about 61,200 km/h). If you were on it, each second you would be moving away from Earth by six times the distance Athens–Patras.

Voyager 2 crossed into interstellar space in 2018, at about 119 AU, providing the first direct measurements of how the Sun’s influence ends. Since then, both spacecraft sail through the “void,” still sending data. Their signals now take over 22 hours to reach Earth.

The Golden Record

Like Pioneer, the Voyagers carry their own message. Not a plaque, but a golden record: the Voyager Golden Record. Carl Sagan, Ann Druyan, and their team assembled a collection of 116 images, 90 minutes of music (from Bach to Chuck Berry), natural sounds of Earth (thunder, laughter, waves, whale song) and 55 greetings in different languages.

The record is gold-plated and protected with an aluminum cover, and it bears engraved instructions for how an extraterrestrial civilization could play it. It also includes a pulsar map showing Earth’s position in the Galaxy, similar to Pioneer’s but more refined. It is perhaps the most beautiful “human imprint” ever to leave the planet.

Ann Druyan has said that her heartbeat — recorded while she was thinking of Sagan — is included on the record. In other words, literally the pulse of a human love is on that record.

The record is like a time capsule of humanity, divided into sections: sounds, music, images, greetings, and scientific data.

1. Greetings from Earth

Each greeting is brief, about 20–30 seconds, saying “hello, we are the inhabitants of Earth.”

A. Ancient / Historical Languages

1. Sumerian

2. Akkadian

3. Ancient Greek

4. Latin

5. Hittite

These are considered “historical” and are not included in the list of 55 modern languages.

B. Modern Languages

1. Amoy (Fujian dialect, China)

2. Armenian

3. Arabic

4. Aramaic

5. Bengali

6. Burmese

7. Cantonese

8. Czech

9. Dutch

10. English

11. French

12. German

13. Gujarati (India)

14. Hebrew

15. Hindi

16. Hungarian

17. Ilocano (Philippine dialect)

18. Indonesian

19. Italian

20. Japanese

21. Kannada (India)

22. Korean

23. Luganda (Uganda)

24. Marathi (India)

25. Nepali

26. Nguni (South African language family related to Zulu)

27. Nyanja (Malawian language)

28. Oriya (Odia, India)

29. Persian (Farsi)

30. Polish

31. Portuguese

32. Punjabi

33. Quechua (Central South America, Inca language)

34. Rajasthani (India)

35. Romanian

36. Russian

37. Serbian

38. Sinhalese (Sri Lanka)

39. Sotho (Southern African)

40. Spanish

41. Swedish

42. Tamil

43. Telugu

44. Thai

45. Turkish

46. Ukrainian

47. Urdu

48. Vietnamese

49. Welsh

50. Wu (Shanghai dialect, China)

51. Greek (Modern Greek)

52. French Creole (e.g., Haitian)

53. Hawaiian

54. Malagasy

55. Fijian

    
    

These 55 are the modern greetings.

The only language with double representation is Greek.

2. Sounds of Earth

Includes natural sounds and human activity:

Natural sounds

• Thunder

• Rain

• Wind

• Ocean waves

• Earthquake, volcano

• Heartbeat

• Human laughter

Animal life

• Birdsong

• Rattlesnakes, dogs, cats, whales, dolphins

Human activity

• Sounds of tools and machinery

• Farming, factories, vehicles

• Spoken human voices (other than the greetings)

  
  

3. Music

Contains 90 minutes of music from different cultures and eras:

• Western classical: Bach, Beethoven, Stravinsky

• Indian music: Ravi Shankar (sitar)

• African music: male and female songs

• Asian music: Chinese guqin, Japanese gagaku

• Native musical traditions: Native American, Cherokee, Navajo, Appalachian, Blues, Jazz, Rock (Chuck Berry)

• Music from the Middle East, Southeast Asia, South America (Quechua)

The aim is to show variety of cultures, rhythms, and eras.

4. Images

There are 116 images with graphic and photographic representations:

Human life and society

• Human bodies (man, woman)

• Families, children, communities

• Activities: work, education, religion, arts

Earth and the natural environment

• Landscapes: mountains, rivers, forests, oceans

• Animals, plants

• Human technology: buildings, bridges, machines

Science and mathematics

• Human anatomical diagrams

• Numeric systems and mathematical symbols

• Elements of the Solar System (Sun, planets, orbits)

A chart showing Earth’s position relative to 14 pulsars to indicate where we are in the Galaxy.

5. Technical characteristics

The main recognizable elements we see:

1. Hydrogen atom symbol

2. Solar System + pulsars

3. Lines for images

4. Turntable instructions

5. Binary numbers and logarithmic scales

   
   

1. Hydrogen atom symbol

Shows the electron transition in hydrogen (21 cm wavelength). It is used as a unit of measurement of length and time for all the other diagrams.

Elements:

• Two circles (high/low energy states)

• Arrow indicating the transition

• Small lines as a wavelength reference

  
  

2. Solar System + 14 pulsars

Diagram: Sun at the center with 14 lines pointing to pulsars.

• Lines = direction to each pulsar.

• Line endpoints = pulse frequency in Hz expressed in binary.

• Distances = logarithmic, to show Earth’s position in the Galaxy.

  Purpose: To locate Earth and the moment the record was created.

  
  

List of pulsars:

1. CP 1919 (B1919+21)

2. B0329+54

3. B0355+54

4. B0531+21 (Crab)

5. B0833−45 (Vela)

6. B1509−58

7. B1642−03

8. B1706−44

9. B1749−28

10. B1815−14

11. B1915+13

12. B1937+21

13. B1952+29

14. B2016+28

    
    

3. Instructions to play the record

Schematic arrows and circles show:

• How to place the disk (turntable)

• Rotational speed

• How to read the voltage/format signalPurpose: To convert the signal into sound or image.

  
  

4. Lines and dots for images

There is a raster scheme that shows:

• Number of lines per image

• Line-to-column ratio

• Order of image playback (116 photographs)Purpose: To reconstruct the images from the record’s data.

  
  

5. Mathematics and physical constants

Diagrams show:

• Numbers in binary

• Ratios and units of measurement

• Logarithmic scales for length and distance

Used to understand the rest of the symbols by extraterrestrials.

6. Temporal signals

The record contains marks and timing code that show:

• Duration of each image or sound

• Playback rate

• Where each item starts and ends

  
  

NASA still maintains contact with both spacecraft. Each command now takes almost two days to go and return. The communication delay is so large that every message is like a letter to time.

Power is decreasing, temperatures drop, and each year the team decides which instrument will be turned off next. It is estimated that around 2035–2040 the spacecraft will become completely silent, without enough energy for a transmitter. But they will continue to travel for millions of years — cold, but intact.

The next destinations

Voyager 1

It is currently heading toward the constellation Ophiuchus.

In about 40,000 years it will pass at approximately 1.6 light-years from Gliese 445, a red dwarf. After 2 million years it will have moved deep into interstellar space, not approaching any particular star closely — it will drift toward the Galactic Northern Crown (Corona Borealis).

Voyager 2

It is heading toward Sagittarius, a little “below” the plane of the ecliptic. In roughly 40,000 years it will be near Ross 248, another red dwarf, at a distance of about 1.7 light-years. Approximately 296,000 years from now it will pass relatively close to Sirius, the brightest star in our sky.

In 1.7–2 million years it will have entered the region of the Galactic Center, into completely unknown terrains of interstellar matter.

Both will have switched off long before then; from that point on they will continue silently. Literally the oldest ambassadors of humanity that will still exist when perhaps we no longer do. Neither will ever truly “arrive” anywhere, but both will wander eternally among the stars — carriers of data from an era that, for us, will be prehistory.

The legacy

If Pioneer 10 was the first to break the Sun’s bonds, the Voyagers were the ones that threw the gates wide open. They show that science is not only calculation — it is an act of faith. Faith that it is worth sending something into the dark simply because someone, somewhere, sometime might find it.

These two spacecraft are our most distant ambassadors. They carry sounds, images, words, emotions, and the silence of an entire humanity. Whatever happens, even if all traces of us on Earth vanish, out there two small messengers will continue to travel, holding the message that once there was life that looked up at the sky and wanted to touch it.