List of artificial objects leaving the Solar System

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 torus 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. It does not include those missions that went into orbit around planets, or into orbit around the Sun because they are not leaving the Solar System.

List

Planetary exploration probes

• Pioneer 10 – Launched in 1972, flew past Jupiter in 1973. Contact lost in January 2003 and is heading in the direction of Aldebaran (65 light years away) in Taurus.
• Pioneer 11 – Launched in 1973, flew past Jupiter in 1974 and Saturn in 1979. Contact lost in November 1995. The spacecraft is headed toward the constellation of Aquila (The Eagle), northwest of the constellation of Sagittarius. Barring 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. Probe has (depending on the source) not passed the heliosheath, but 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. Probe passed the heliopause on 25 August 2012 to enter interstellar space,^[2] and is still active.
• New Horizons – Launched in 2006, probe made flyby of Jupiter in 2007, made a flyby of Pluto on 14 July 2015. Flyby of Pluto may be followed by a flyby of a trans-Neptunian object in the Kuiper belt.

Although other probes were launched first, Voyager 1 was able to achieve a higher speed and has overtaken all others. Voyager 1 overtook Voyager 2 a few months after launch, on 19 December 1977.^[3] It overtook Pioneer 11 some time in the late 1980s, and then Pioneer 10—becoming the probe farthest from Earth—on February 17, 1998.^[4]

Voyager 2 is also moving faster than the probes launched before it, and thus overtook Pioneer 11 in 1997 and will overtake Pioneer 10 sometime in 2021.

New Horizons will also likely pass the Pioneer probes, but will need many years to do so. It will not overtake Pioneer 11 until ~2082 and will not overtake Pioneer 10 until ~2130. Barring some unforeseen gravity assist it will never overtake the Voyagers.

Boosters

Every planetary probe was placed into its escape orbit by a rocket booster. These rockets are themselves on nearly the same trajectory as the probes they launched. Because they 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 boosters 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 boosters on an escape trajectory are:

• Pioneer 10 third stage, a TE364-4 variant of the Star-37 solid fuel rocket.^[5]
• Voyager 1 third stage, a Star 37E solid fuel rocket.^[6]
• Voyager 2 third stage, a Star 37E solid fuel rocket.^[6]
• New Horizons third stage, a Star-48 solid fuel booster, is on a similar escape trajectory out of the Solar System as New Horizons, even arriving at Jupiter by 6 hours before New Horizons. It will pass 213 million kilometers (over 1 AU) distant from Pluto.^[7][8] It had crossed Pluto's orbit in late 2015.^[9]
• In addition, two small yo-yo de-spin weights on wires were used to reduce the spin of the New Horizons probe prior its release from the third-stage booster. 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.^[10][11]

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.^[6]

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.^[7]

The Pioneer 10 and 11, and Voyager 1 and 2 Centaur (second) stages are also in heliocentric orbits.^[11][12]

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 necessary to take advantage to 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.

Gallery

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  Photograph of Voyager 1 / Voyager 2

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  Artist's concept of Pioneer 10 / Pioneer 11

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  Artist's concept of Pioneer 10 near Jupiter

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  Artist's concept of New Horizons approaching Pluto.

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  Artist's concept of New Horizons near Pluto.

See also

• List of artificial objects in heliocentric orbit

References

1. "The Pioneer Missions". NASA.
2. Harwood, William (September 12, 2013). "Voyager 1 finally crosses into interstellar space". CBS News.
3. Gebhardt, Chris; Goldader, Jeff. "Thirty-four years after launch, Voyager 2 continues to explore". nasaspaceflight.com. Retrieved 15 July 2015.
4. "Voyager - The Interstellar Mission". Jet Propulsion Laboratory. NASA.
5. "NASA - NASA Glenn Pioneer Launch History". NASA.
6. "rockets - Where are the upper stages for the Voyager/Pioneer stages? - Space Exploration Stack Exchange". stackexchange.com.
7. Stern, Alan; Guo, Yanping (October 28, 2010). "Where Is the New Horizons Centaur Stage?". Johns Hopkins University Applied Physics Laboratory.
8. "Star 48b Third-stage Motor - Unmanned Spaceflight.com". unmannedspaceflight.com.
9. "Derelict Booster to Beat Pluto Probe to Jupiter". Space.com.
10. Pierre Bauduin. "New Horizons". weebau.com.
11. "Deep space probes and other manmade objects beyond near Earth space". johnstonsarchive.net.
12. https://usspaceobjectsregistry.state.gov/Lists/SpaceObjects/DispFormaspx?ID=3348.html

External links

• Spacecraft escaping the Solar System in heavens-above.com