# List of minor planets and comets visited by spacecraft

The following tables list all minor planets and comets that have been visited by robotic spacecraft.

## List of minor planets visited by spacecraft

A total of 18 minor planets (asteroids, dwarf planets, and Kuiper belt objects) have been visited by space probes. Moons (not directly orbiting the Sun) and planets are not minor planets and thus are not included in the table below.
* Minor planets and comets visited by spacecraft as of 2019 (except Pluto, Ceres, and Vesta), to scale
* The comparative sizes of the first eight asteroids visited by spacecraft
| Minor planet | Minor planet | Minor planet | Minor planet | Space probe | Space probe | Space probe | Space probe | Space probe |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | Closest approach | Closest approach | Closest approach | Remarks |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | year | in km | in radii$^{(b)}$ | Remarks |
| 951 Gaspra | | 18.2 × 10.5 × 8.9 (12.2 km) | 1916 | Galileo | 1991 | 1,600 | 262 | Flyby; first asteroid visited by a spacecraft. |
| 243 Ida | | 56 × 24 × 21 (28 km) | 1884 | Galileo | 1993 | 2,390 | 152 | Flyby; discovered Dactyl; first asteroid with a moon visited by a spacecraft, largest asteroid visited by spacecraft at the time. |
| 253 Mathilde | | 66 × 48 × 46 (58 km) | 1885 | NEAR Shoemaker | 1997 | 1,212 | 49.5 | Flyby; largest asteroid visited by a spacecraft at the time. |
| 433 Eros | | 34 × 11 × 11 (17 km) | 1898 | NEAR Shoemaker | 1998–2001 | landed | landed | 1998 flyby; 2000 orbited (first asteroid studied from orbit); 2001 landing; first asteroid landing, first asteroid orbited by a spacecraft, first near-Earth asteroid (NEA) visited by a spacecraft. |
| 9969 Braille | | 2.2 × 0.6 (1.6 km) | 1992 | Deep Space 1 | 1999 | 26 | 12.7 | Flyby; followed by flyby of Comet Borrelly; failed to image it during closest approach, only taking images 14,000 km from the asteroid. |
| 5535 Annefrank | | 4.0 | 1942 | Stardust | 2002 | 3,079 | 1,230 | Flyby |
| 25143 Itokawa | | 0.5 × 0.3 × 0.2 (350 meters) | 1998 | Hayabusa | 2005 | landed | landed | Landed; returned dust samples to Earth in 2010 - first sample return mission from asteroid; smallest asteroid visited by a spacecraft, first asteroid visited by a non-NASA spacecraft. |
| 2867 Šteins | | 4.6 | 1969 | Rosetta | 2008 | 800 | 302 | Flyby; first asteroid visited by the ESA. |
| 21 Lutetia | | 120 × 100 × 75 (100 km) | 1852 | Rosetta | 2010 | 3,162 | 64.9 | Flyby on 10 July 2010; largest asteroid visited by a spacecraft at the time. |
| 4 Vesta | | 525.4 | 1807 | Dawn | 2011–2012 | 200 approx. | 0.76 | Space probe broke orbit on 5 September 2012 and headed to Ceres; first "big four" asteroid visited by a spacecraft, largest asteroid visited by a spacecraft at the time. |
| 4179 Toutatis | | 2.45 | 1934 | Chang'e 2 | 2012 | 3.2 | 0.70 | Flyby; closest asteroid flyby, first asteroid visited by a Chinese probe. |
| 1 Ceres | | 939.4 | 1801 | Dawn | 2015–2018 | 35 | 0.07 | First "close up" picture of Ceres taken in December 2014; probe entered orbit in March 2015; first dwarf planet visited by a spacecraft, largest asteroid visited by a spacecraft. |
| 134340 Pluto | | 2376.6 | 1930 | New Horizons | 2015 | 12,500 | 10.5 | Flyby; first trans-Neptunian object visited, most distant object visited by a spacecraft (at the time of the visit). |
| 162173 Ryugu | | 0.896 | 1999 | Hayabusa2 | 2018–2019 | landed | landed | Rendezvoused with asteroid from June 2018 to November 2019. Successful touchdowns to collect a sample in February and July 2019. Three landers and an explosive impactor successfully deployed to the surface. Returned dust samples to Earth in December 2020. |
| 101955 Bennu | | 0.490 | 1999 | OSIRIS-REx | 2018–2020 | landed | landed | Arrived on 3 December 2018; entered lowest orbit on 12 June 2019; smallest object to be orbited by spacecraft and closest ever orbit; touchdown on 20 October 2020 to collect sample. |
| 486958 Arrokoth | | 36 × 18 × 10 | 2014 | New Horizons | 2019 | 3,500 | 380 | Flew by Arrokoth (nicknamed Ultima Thule) on 1 January 2019, currently farthest object to be visited by a spacecraft. |
| 65803 Didymos | | 0.78 | 1996 | DART / LICIACube | 2022 | 1.19 | 3.1 | Asteroid of a near-Earth Apollo group; a flyby target; its moon being the kinetic impact target to test asteroid deflection |
| Dimorphos 65803 Didymos I | | 0.16 | 2003 | DART / LICIACube | 2022 | landed | landed | Moon of a near-Earth asteroid of the Apollo group; flyby target of one and kinetic impact target of another spacecraft to test asteroid deflection |
| 152830 Dinkinesh | | 0.79 | 1999 | Lucy | 2023 | 425 | 1,100 | Flyby; discovered Selam; smallest main-belt asteroid to be visited by a spacecraft |
| Notes: $^a$ A minor planet's dimensions may be described by x, y, and z axes instead of an (average) diameter due to its non-spherical, irregular shape. $^b$ Closest approach given in multiples of the minor planet's mean radius · List ordered in ascending order by a minor planet's first visit. |||||||||

### Incidental flybys

In addition to the above listed objects, three asteroids have been imaged by spacecraft at distances too large to resolve features (over 100,000 km).
| Minor planet | Minor planet | Minor planet | Minor planet | Space probe | Space probe | Space probe | Space probe | Space probe |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | Closest approach | Closest approach | Closest approach | Remarks |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | year | in km | in radii$^{(b)}$ | Remarks |
| 2685 Masursky | | 10.7 | 1981 | Cassini–Huygens | 2000 | 1,600,000 | 297,840 | Distant incidental flyby. |
| 132524 APL | | 2.5 | 2002 | New Horizons | 2006 | 101,867 | 81,493 | Distant incidental flyby. |
| (668956) 2012 PM35 | | 0.9-2.5 | 2012 | Dawn | 2017 | 200,000 | 130,000 | Distant incidental flyby; approached Ceres to 200,000 km in September 2017 while Dawn was in orbit. |

## List of comets visited by spacecraft

| Comet | Comet | Comet | Comet | Space probe | Space probe | Space probe | Space probe | Space probe |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | Closest approach | Closest approach | Closest approach | Remarks |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | year | in km | in radii$^{(b)}$ | Remarks |
| 21P/Giacobini–Zinner | | 2 | 1900 | ICE | 1985 | 7,800 | 7,800 | First flyby of a comet |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | Vega 1 | 1986 | 8,889 | 1,620 | flyby |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | Vega 2 | 1986 | 8,030 | 1,460 | flyby |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | Suisei | 1986 | 151,000 | 27,450 | distant flyby |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | Sakigake | 1986 | 6,990,000 | 1,270,747 | distant flyby |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | Giotto | 1986 | 596 | 108 | flyby; first direct images of a comet nucleus |
| 1P/Halley | | 15×9 | Known since 1759 (Precovered to 240 BCE) | ICE | 1986 | 31,000,000 | 5,647,000 | distant flyby |
| 26P/Grigg–Skjellerup | | 2.6 | 1902 | Giotto | 1992 | 200 | 154 | flyby |
| 19P/Borrelly | | 8×4×4 | 1904 | Deep Space 1 | 2001 | 2,171 | 814 | flyby; closest approach in September 2001 when probe entered the comet's coma |
| 81P/Wild | | 5.5×4.0×3.3 | 1978 | Stardust | 2004 | 240 | 113 | flyby; first sample return mission from comet to Earth (2006) |
| 9P/Tempel | | 7.6×4.9 | 1867 | Deep Impact | 2005 | 500 | 80 | flyby; delivered an impactor |
| 9P/Tempel | | 7.6×4.9 | 1867 | Deep Impact's impactor vehicle | 2005 | landed | landed | first landing on a comet (blasted a crater) |
| 9P/Tempel | | 7.6×4.9 | 1867 | Stardust | 2011 | 181 | 57.9 | flyby; imaged the crater created by Deep Impact |
| 103P/Hartley | | 1.4 | 1986 | EPOXI (Deep Impact) | 2010 | 700 | 1,000 | flyby; smallest comet visited |
| 67P/Churyumov–Gerasimenko | | 4.1×3.3×1.8 | 1969 | Rosetta | 2016 | landed | landed | first orbiter of comet (November 2014); impacted surface as of 2016; OSIRIS captured image with 11 cm/px-resolution in Spring 2015 |
| 67P/Churyumov–Gerasimenko | | 4.1×3.3×1.8 | 1969 | Philae (Rosetta's lander) | 2014 | landed | landed | first soft landing on a comet (November 2014) |
| Notes: $^{(a)}$Due to a non-spherical, irregular shape, a comet's x, y, and z axes instead of an (average) diameter are often used to describe its dimensions. $^{(b)}$Closest approach given in multiples of the comet's (average mean) radius · List ordered in ascending order by a comet's first visit. |||||||||

### Incidental flybys

| Comet | Comet | Comet | Comet | Space probe | Space probe | Space probe | Space probe | Space probe |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | Closest approach | Closest approach | Closest approach | Remarks |
| Name | Image | Dimensions (km)$^{(a)}$ | Discovery year | Name | year | in km | in radii$^{(b)}$ | Remarks |
| D/1895 Q1 (Swift) | | unknown | 1895 | Mariner 4 | 1967 | 20,000,000 | unknown | Unconfirmed. Reanalysis of the probe's trajectory in 2005 speculated the probe might've approached the comet's shattered nucleus, explaining the "meteor storm" it encountered |

### Spacecraft visited by comets

Comet C/2013 A1 passed close by planet Mars in October 2014, closer than the Moon is to Earth. As of early 2014 it was calculated to pass as close as 0.00087 AU (130,000 km; 81,000 mi). This was so close that the event was deemed dangerous to spacecraft in orbit around Mars. Spacecraft that were active at that time included 2001 Mars Odyssey, Mars Express, MAVEN, Mars Orbiter Mission, and Mars Reconnaissance Orbiter in Mars orbit – and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity.

## Future visits
### Planned
#### Legend

Enroute  In development
| Name | Diameter$^{(a)}$ (km) | Year of discovery | Spacecraft | Year of visit | Notes |
| 16 Psyche | 186 | 1852 | Psyche | 2029 | Large metallic main-belt asteroid |
| 617 Patroclus-Menoetius | 141 | 1906 | Lucy | 2033 | Binary Jupiter trojan, Trojan camp, 5th-largest Jupiter trojan |
| 3200 Phaethon | 5 | 1983 | DESTINY$^+$ | 2030 | Active near-Earth asteroid and parent body of Geminids meteor shower |
| 3548 Eurybates | 72 | 1973 | Lucy | 2027 | Jupiter trojan with satellite, Greek camp |
| 11351 Leucus | 42 | 1997 | Lucy | 2028 | Jupiter trojan, Greek camp, a slow rotator |
| 15094 Polymele | 21 | 1999 | Lucy | 2027 | Jupiter trojan with satellite, Greek camp |
| 21900 Orus | 53 | 1999 | Lucy | 2028 | Jupiter trojan, Greek camp |
| 52246 Donaldjohanson | 3.9 | 1981 | Lucy | 2025 | Main-belt asteroid and member of the Erigone family |
| 65803 Didymos | 0.8 | 1996 | Hera | 2026 | Probe will study the results obtained by the NASA's DART impactor 4 years after its mission. |
| Dimorphos 65803 Didymos I | 0.16 | 2003 | Hera | 2026 | Probe will study the results obtained by the NASA's DART impactor 4 years after its mission. |
| 98943 Torifune | 0.5 | 2001 | Hayabusa2# | 2026 | Near-Earth asteroid of the Apollo group; extended mission target |
| 99942 Apophis | 0.370 | 2004 | OSIRIS-APEX | 2029 | Extended mission after sample delivery |
| 10253 Westerwald | 2.3 | 1973 | MBR Explorer | 2030 | Flyby |
| 623 Chimaera | 22 | 1907 | MBR Explorer | 2030 | Flyby |
| 13294 Rockox | 5.2 | 1998 | MBR Explorer | 2031 | Flyby |
| (88055) 2000 VA$_{28}$ | 5.4 | 2000 | MBR Explorer | 2032 | Flyby |
| (23871) 1998 RC$_{76}$ | 6.7 | 1998 | MBR Explorer | 2032 | Flyby |
| (59980) 1999 SG$_6$ | 8.0 | 1999 | MBR Explorer | 2033 | Flyby |
| 269 Justitia | 53.62 | 1887 | MBR Explorer | 2034 | Orbit and Landing |
| 469219 Kamoʻoalewa | 0.041 | 2016 | Tianwen-2 | 2026 | Co-orbital near-Earth asteroid; sample return target |
| 1998 KY26 | 0.030 | 1998 | Hayabusa2# | 2031 | Near-Earth asteroid of the Apollo group; extended mission target |
| 2015 XF261 | 0.03 | 2015 | Unnamed CNSA mission | 2029 | Near-Earth asteroid of the Aten group, will be visited by an orbiter and impactor for an asteroid deflection test. |
| 311P/PanSTARRS | 0.48 | 2013 | Tianwen-2 | 2034 | Active main-belt asteroid |
| $^{(a)}$ given diameters are estimates ||||||

### Proposals

The following table lists minor planets that are proposed to be visited by spacecraft missions that have not yet been approved.
| Name | Diameter (km) | Year of discovery | Spacecraft | Proposed dates | Notes |
| 50000 Quaoar | 1086 | 2002 | Interstellar Express | Launch: 2024 Flyby: 2030s | A Voyager-like mission proposed to be launched in 2024 by the CNSA. A pair of probes would flyby Neptune, Quaoar, and one other KBO. |
| (153591) 2001 SN263 | 2.6 | 2001 | ASTER | Launch: 2025 Flyby: 2027 | Brazilian Space Agency mission to triple near-Earth asteroid system of the Amor group |
| 99942 Apophis | 0.370 | 2004 | Ramses | Launch: 2028 Flyby: 2029 | ESA proposal |

## Past proposals
### Failed missions

Former targets for launched spacecraft.
Key :
* spacecraft failure
* mission planning decisions
| Name | Diameter (km) | Date of discovery | Spacecraft | Year | Notes |
| 2P/Encke | 4.8 | January 17, 1786 | CONTOUR | 1998 | Spacecraft lost while leaving Earth orbit |
| 2P/Encke | 4.8 | January 17, 1786 | NEAR | 1998 | Target changed before launch |
| 4 Vesta | 525 | March 29, 1807 | NEAR | 1998 | Target changed before launch |
| 6P/d'Arrest | 3.2 | June 28, 1851 | CONTOUR | 2008 | Spacecraft lost while leaving Earth orbit |
| 7P/Pons–Winnecke | 5.2 | June 12, 1819 | Mariner 5 | 1969 | Target changed to Venus before launch |
| 21P/Giacobini–Zinner | 2 | December 20, 1900 | Suisei | 1998 | Extended mission, spacecraft ran out of fuel en route. |
| 29 Amphitrite | 204 | March 1, 1854 | Galileo | 1986 | Target changed due to launch postponement |
| 46P/Wirtanen | 1.2 | January 17, 1948 | Rosetta | 2011 | Initial target, was changed due to delay. |
| 73P/Schwassmann–Wachmann | 1.1 (before breakup) | May 2, 1930 | CONTOUR | 2006 | Spacecraft lost while leaving Earth orbit |
| 76P/West–Kohoutek–Ikemura | 0.66 | January 1975 | Deep Space 1 | 2000 | Target changed due to launch postponement |
| 85D/Boethin | | January 4, 1975 | EPOXI (Deep Impact) | 2007 | Astronomers were unable to locate the comet, which is too faint to be observed. |
| 140 Siwa | 103 | October 13, 1874 | Rosetta | 2007 | Target changed due to launch postponement |
| 145 Adeona | 151 | June 3, 1875 | Dawn | 2016 | Abandoned target (not seriously considered) |
| 223 Rosa | 82.7 | March 9, 1882 | JUICE | 2029 | Secondary target; abandoned to conserve fuel for primary Jupiter orbiter mission. |
| 1036 Ganymed | 35 | October 23, 1924 | NEAR | 1998 | Target changed before launch |
| 1620 Geographos | 5.1×1.8 | September 14, 1951 | Clementine | 1995 | Mission failed before retargeting |
| 2019 van Albada | 7.5-9.4 | September 28, 1935 | NEAR | 1998 | Target changed before launch |
| 2101 Adonis | 0.6 | February 12, 1936 | Vega 2 | 1987 | Secondary target; insufficient fuel |
| 2530 Shipka | 12.4 | July 9, 1978 | Rosetta | 2007 | Secondary target; changed for better trajectory |
| 2703 Rodari | 9 | March 29, 1979 | Rosetta | 2007 | Target in early mission planning, but not chosen |
| 3352 McAuliffe | 2–5 | February 6, 1981 | Deep Space 1 | 1998 | Target changed due to launch postponement |
| 3840 Mimistrobell | 5.2 | October 9, 1980 | Rosetta | 2007 | Target changed |
| 4015 Wilson–Harrington | 4 | November 19, 1949 | NEAR | 1998 | Target changed before launch |
| 4015 Wilson–Harrington | 4 | November 19, 1949 | Deep Space 1 | 2001 | Secondary target; abandoned due to instrument failure |
| 4660 Nereus | ~1 | February 28, 1982 | NEAR | 1997 | Target changed before launch |
| 4660 Nereus | ~1 | February 28, 1982 | Hayabusa | 2002 | Target changed due to launch postponement |
| 4979 Otawara | 5.5 | August 2, 1949 | Rosetta | 2007 | Target changed due to launch postponement |
| (5604) 1992 FE | 0.6 | March 26, 1992 | OSIRIS-REx | 2018 | Secondary target abandoned in 2010 during early mission planning |
| (10302) 1989 ML | 0.6 | June 29, 1989 | Hayabusa | 2002 | Target changed due to launch postponement |
| (163249) 2002 GT | 0.35-0.5 | April 3, 2002 | EPOXI (Deep Impact) | 2020 | Communications with spacecraft lost |
| (172034) 2001 WR1 | 0.66 | November 17, 2001 | Hayabusa2 | 2023 | Target proposed for extended mission but not selected. |
| (185851) 2000 DP107 | ~0.8 | February 29, 2000 | PROCYON | 2016 | Ion engine failure in heliocentric orbit |
| 1991 VG | 0.005-0.012 | November 6, 1991 | NEA Scout | 2022 | Target changed due to launch postponement |
| 2001 AV43 | 0.03 | January 5, 2001 | Hayabusa2 | 2029 | Target proposed but not selected |
| 2020 GE | 0.018 | 2020 | NEA Scout | 2023 | Communications with spacecraft lost |
| 2022 OB5 | 0.004–0.010 | 2022 | Odin | 2025 | Communications with spacecraft lost |

### Cancelled or not developed missions

| Name | Diameter (km) | Date of discovery | Spacecraft | Year | Notes |
| 1 Ceres | 939 | January 1, 1801 | Ceres Polar Lander | | |
| 1 Ceres | 939 | January 1, 1801 | Calathus | | |
| 2 Pallas | 512 | March 28, 1802 | Athena | 2024 | |
| 4 Vesta | 525 | March 29, 1807 | AGORA | 1990-1994 | |
| 4 Vesta | 525 | March 29, 1807 | MAOSEP | 1990s | |
| 4 Vesta | 525 | March 29, 1807 | Vesta | 1994 | |
| 22P/Kopff | 3.0 | August 23, 1906 | CRAF | 2001 | |
| 29P/Schwassmann–Wachmann | 65 | 1927 | Centaurus | Launch: 2026 Flyby: 2030s | not selected |
| 46P/Wirtanen | 1.2 | January 17, 1948 | Comet Hopper | 2022 | |
| 50 Virginia | 99.8 | 1857 | MANTIS | Launch: 2020s Flyby: 2020s | A flyby proposal of 14 asteroids, the largest being 50 Virginia. |
| 67P/Churyumov–Gerasimenko | 4.1×3.3×1.8 | September 20, 1969 | CAESAR | 2024 | |
| 67P/Churyumov–Gerasimenko | 4.1×3.3×1.8 | September 20, 1969 | CONDOR | 2024 | Proposed comet sample-return mission. |
| 88P/Howell | 4.4 | 1981 | CORSAIR | 2024 | Proposed comet sample-return mission. |
| 433 Eros | 34 × 11 × 11 | 1898 | Clementine 2 | 1996 | |
| 449 Hamburga | 86 | October 31, 1899 | CRAF | 1998 | |
| 2060 Chiron | 271 | 1977 | Centaurus | Launch: 2026 Flyby: 2030s | A flyby proposal. |
| 4015 Wilson–Harrington | 4 | November 19, 1949 | Marco Polo/Hayabusa Mk2 | 2022 | |
| 4179 Toutatis | 2.45 | 1934 | Clementine 2 | 1996 | |
| 4660 Nereus | ~1 | February 28, 1982 | NEAP | 1997 | |
| 7968 Elst–Pizarro or 133P/Elst–Pizarro | ~0.6 | July 24, 1979 | Castalia | 2028 | |
| 10199 Chariklo | 260.35 | 1997 | Camilla | Launch: 2026 Flyby: 2039 | A mission concept for a flyby and impactor. |
| 25143 Itokawa | 0.5 × 0.3 × 0.2 | 1998 | Asteroid Redirect Mission | 2021 | |
| (35107) 1991 VH | 1.04 | November 9, 1991 | Janus | 2026 | Launch delayed, target not available |
| 47171 Lempo | 0.272 | October 1, 1999 | New Horizons 2 | | |
| (55637) 2002 UX25 | ~0.69 | October 30, 2002 | New Horizons 2 | | |
| (65679) 1989 UQ | | | Marco Polo | 2018-2020 | |
| 66652 Borasisi | ~0.1 | September 8, 1999 | New Horizons 2 | | |
| 99942 Apophis | 0.37 | June 19, 2004 | Don Quijote | 2015 | |
| 101955 Bennu | 0.490 | 1999 | Asteroid Redirect Mission | 2021 | |
| 101955 Bennu | 0.490 | 1999 | HAMMER | | |
| 134340 Pluto | 2376 | February 18, 1930 | Pluto Kuiper Express | 2004 | |
| 162173 Ryugu | 0.9 | May 10, 1999 | Marco Polo | 2018-2020 | |
| 162173 Ryugu | 0.9 | May 10, 1999 | Asteroid Redirect Mission | 2021 | |
| (162998) 2001 SK162 | | | Marco Polo | 2018-2020 | |
| (175706) 1996 FG3 | 1.69 | March 24, 1996 | Janus | 2026 | Launch delayed, target not available |
| (175706) 1996 FG3 | 1.7 | March 24, 1996 | Marco Polo | 2018-2020 | |
| (341843) 2008 EV5 | 0.4 | March 4, 2008 | Marco Polo | 2018-2020 | |
| (341843) 2008 EV5 | 0.4 | March 4, 2008 | Asteroid Redirect Mission | 2021 | |
| (612267) 2001 SG286 | | | Marco Polo | 2018-2020 | |
| (612600) 2003 SM84 | 0.086-0.16 | September 20, 2003 | Don Quijote | 2015 | |
| Trojan asteroids | | 1906 | OKEANOS | Launch: 2026 | Proposed multiple flyby mission to Jupiter's Trojan asteroids using solar sail propulsion. |