List of artificial objects leaving the Solar System

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The red and green arrows indicate the positions of Voyager 1 and Pioneer 10 respectively at the end of 2008; the blue shell indicates the estimated size of the termination shock they have entered, whereas the grey annulus shows the Kuiper belt. The yellow shell indicates one light-day distance from the Sun. Click on image for larger view and links to other scales.

Below is a list of artificial objects leaving the Solar System. All of these objects are space probes and their upper stages launched by NASA.

Planetary exploration probes[edit]

  • Pioneer 10 – Launched in 1972, flew past Jupiter in 1973 and is heading in the direction of Aldebaran (65 light years away) in the constellation of Taurus. Contact was lost in January 2003.
  • Pioneer 11 – Launched in 1973, flew past Jupiter in 1974 and Saturn in 1979. Contact was lost in November 1995. The spacecraft is headed toward the constellation of Aquila (The Eagle), northwest of the constellation of Sagittarius. Barring an incident, Pioneer 11 will pass near one of the stars in the constellation in about 4 million years.[1]
  • Voyager 2 – Launched in August 1977, flew past Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. Although it entered the heliosheath, it is debated whether it has passed the heliopause. Voyager 2 is still active.
  • Voyager 1 – Launched in September 1977, flew past Jupiter in 1979 and Saturn in 1980, making a special close approach to Saturn's moon Titan. The probe passed the heliopause on 25 August 2012 to enter interstellar space,[2] and is still active. It is headed towards an encounter with a star called AC +79 3888, which lies 17.6 light-years from Earth, in about 40,000 years.[3]
  • New Horizons – Launched in 2006, the probe flew past Jupiter in 2007 and Pluto on 14 July 2015. It is currently headed towards a flyby of the Kuiper belt object (486958) 2014 MU69, nicknamed Ultima Thule, on January 1, 2019 as part of the Kuiper Belt Extended Mission (KEM).[4]

Although other probes were launched first, Voyager 1 has achieved a higher speed and overtaken all others. Voyager 1 overtook Voyager 2 a few months after launch, on 19 December 1977.[5] It overtook Pioneer 11 in 1983,[6] and then Pioneer 10—becoming the probe farthest from Earth—on February 17, 1998.[7]

Voyager 2 is also moving faster than the probes launched earlier: having overtaken Pioneer 11 by March 1988,[6] it will overtake Pioneer 10 in April 2019.[8]

Depending on how the "Pioneer anomaly" impacts it, New Horizons will also probably pass the Pioneer probes, but will need many years to do so. It will not overtake Pioneer 11 until the 22nd Century and will not overtake Pioneer 10 until the end of that century, and it will never overtake the Voyagers.[6]

Distance and speed from the Sun[edit]

Name Launched Distance (AU) Speed (km/s)
Voyager 1 1977 141 17
Pioneer 10 1972 120 12
Voyager 2 1977 116 15
Pioneer 11 1973 99 11
New Horizons 2006 40 14

Source : heavens above[9] and JPL[10]

Propulsion stages[edit]

A Star-48 rocket motor like the one used to launch the New Horizons probe

Every planetary probe was placed into its escape trajectory by a multistage rocket, the last stage of which ends up on nearly the same trajectory as the probe it launched. Because these stages cannot be actively guided, their trajectories are now different from the probes they launched (the probes were guided with small thrusters that allow course changes). However, in cases where the spacecraft acquired escape velocity because of a gravity assist, the stages may not have a similar course and there is the remote possibility that they collided with something. Some objects in heliocentric orbit have been reidentified with a telescope, and so it can be confirmed that they are still there. The stages on an escape trajectory are:

  • Pioneer 10 third stage, a TE364-4 variant of the Star-37 solid fuel rocket.[11]
  • Voyager 1 third stage, a Star 37E solid fuel rocket.[12]
  • Voyager 2 third stage, a Star 37E solid fuel rocket.[12]
  • New Horizons third stage, a Star-48 solid fuel rocket, is on a similar escape trajectory out of the Solar System as New Horizons, even arriving at Jupiter by 6 hours before New Horizons. On Oct 15, 2015 it passed through Pluto's orbit at a distance of 213 million kilometers (over 1 AU) distant from Pluto.[13][14] This was nearly four months after the New Horizons probe did.[15]

In addition, two small yo-yo de-spin weights on wires were used to reduce the spin of the New Horizons probe prior to its release from the third-stage rocket. Once the spin rate was lowered, these masses and the wires were released, and so are also on an escape trajectory out of the Solar System.[16][17] None of these objects are trackable (they have no power or radio antennae, spin uncontrollably, and are too small to be detected), and their exact positions are unknowable beyond their projected Solar System escape trajectories.

The third stage of Pioneer 11 is thought to be in solar orbit because its encounter with Jupiter would not have resulted in escape from the Solar System. Pioneer 11 gained the required velocity to escape the Solar System in its subsequent encounter with Saturn.[12]

The only objects to date to be launched directly into a solar escape trajectory were the New Horizons spacecraft, its third stage, and the two de-spin masses. The New Horizons Centaur (second) stage is not escaping; it is in a 2.83-year heliocentric (solar) orbit.[13]

The Pioneer 10 and 11, and Voyager 1 and 2 Centaur (second) stages are also in heliocentric orbits.[17][18]

In order to leave the Solar System, the probe needs to reach the escape velocity. After leaving Earth, the Sun's escape velocity is 42.1 km/s. In order to reach this speed, it is highly advantageous to utilize the orbital speed of the Earth around the Sun, which is 29.78 km/s. By passing near a planet, a probe can gain extra speed.


See also[edit]


  1. ^ "The Pioneer Missions". NASA. 
  2. ^ Harwood, William (September 12, 2013). "Voyager 1 finally crosses into interstellar space". CBS News. 
  3. ^ Wall, Mike (13 September 2015). "Interstellar Traveler: NASA's Voyager 1 Probe On 40,000-Year Trek to Distant Star". Retrieved 4 June 2018. 
  4. ^ Brown, Dwayne (2016-07-01). "New Horizons Receives Mission Extension to Kuiper Belt, Dawn to Remain at Ceres" (Press release). Washington, DC. NASA. Retrieved 2016-10-06. 
  5. ^ Gebhardt, Chris; Goldader, Jeff. "Thirty-four years after launch, Voyager 2 continues to explore". Retrieved 15 July 2015. 
  6. ^ a b c Cranor, David. "When the Voyagers passed the Pioneers". Nothing More Powerful. Retrieved 4 December 2017. 
  7. ^ "Voyager - The Interstellar Mission". Jet Propulsion Laboratory. NASA. 
  8. ^ Chris Gebhardt, Pioneer 10: first probe to leave the inner solar system & precursor to Juno, in "" website, July 15, 2017
  9. ^ Spacecraft escaping the Solar System, 2018
  10. ^ "Voyager – Mission Status". Jet Propulsion Laboratory. NASA. Retrieved January 2, 2018. 
  11. ^ "NASA - NASA Glenn Pioneer Launch History". NASA. 
  12. ^ a b c "rockets - Where are the upper stages for the Voyager/Pioneer stages? - Space Exploration Stack Exchange". 
  13. ^ a b Stern, Alan; Guo, Yanping (October 28, 2010). "Where Is the New Horizons Centaur Stage?". Johns Hopkins University Applied Physics Laboratory. 
  14. ^ "Star 48b Third-stage Motor - Unmanned". 
  15. ^ "Derelict Booster to Beat Pluto Probe to Jupiter". 
  16. ^ Pierre Bauduin. "New Horizons". 
  17. ^ a b "Deep space probes and other manmade objects beyond near Earth space". 
  18. ^[permanent dead link]

External links[edit]