An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian pointsL4 (leading 60°) or L5 (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name "trojan" was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiter's orbit.
The orbit of 2010 TK7, the first Earth trojan to be discovered (left). Lagrangian points L4 and L5. Lines around the blue triangles represent tadpole orbits(right)
(614689) 2020 XL5: Discovered by the Pan-STARRS survey in December 2020 and later recognized as an Earth trojan in January 2021.[4] It is 1.2 km in diameter.
No known objects are currently thought to be L5 trojans of Earth.
Searches
An Earth-based search for L5 objects was conducted in 1994, covering 0.35 square degrees of sky, under poor observing conditions.[5] That search failed to detect any objects:
"The limiting sensitivity of this search was magnitude ~22.8, corresponding to C-type asteroids ~350 m in diameter, or S-type asteroids ~175 m in diameter."[5]
In February 2017, the OSIRIS-REx spacecraft performed a search from within the L4 region on its way to asteroid Bennu.[6] No additional Earth trojans were discovered.[7]
In April 2017, the Hayabusa2 spacecraft searched the L5 region while proceeding to asteroid Ryugu,[8] but did not find any asteroids there.[9]
The orbits of any Earth trojans could make them less energetically costly to reach than the Moon, even though they will be hundreds of times more distant. Such asteroids could one day be useful as sources of elements that are rare near Earth's surface. On Earth, siderophiles such as iridium are difficult to find, having largely sunk to the core of the planet shortly after its formation.
A small asteroid could be a rich source of such elements even if its overall composition is similar to Earth's; because of their small size, such bodies would lose heat much more rapidly than a planet once they had formed, and so would not have melted, a prerequisite for differentiation (even if they differentiated, the core would still be within reach). Their weak gravitational fields also would have inhibited significant separation of denser and lighter material; a mass the size of 2010 TK7 would exert a surface gravitational force of less than 0.00005 times that of Earth (although the asteroid's rotation could cause separation).
Giant-impact hypothesis
A hypothetical planet-sized Earth trojan the size of Mars, given the name Theia, is thought by proponents of the giant-impact hypothesis to be the origin of the Moon. The hypothesis states that the Moon formed after Earth and Theia collided,[10] showering material from the two planets into space. This material eventually accreted around Earth and into a single orbiting body, the Moon.[11]
At the same time, material from Theia mixed and combined with Earth's mantle and core. Supporters of the giant-impact hypothesis theorise that Earth's large core in relation to its overall volume is as a result of this combination.
Continuing interest in near-Earth asteroids
Astronomy continues to retain interest in the subject. A publication[12] describes these reasons thus:
The survival to the present day of an ancient [Earth Trojan] population is reasonably assured provided Earth's orbit itself was not strongly perturbed since its formation. It is therefore pertinent to consider that modern theoretical models of planet formation find strongly chaotic orbital evolution during the final stages of assembly of the terrestrial planets and the Earth–Moon system.
Such chaotic evolution may at first sight appear unfavorable to the survival of a primordial population of [Earth trojans]. However, during and after the chaotic assembly of the terrestrial planets, it is likely that a residual planetesimal population, of a few percent of Earth's mass, was present and helped to damp the orbital eccentricities and inclinations of the terrestrial planets to their observed low values, as well as to provide the so-called "late veneer" of accreting planetesimals to account for the abundance patterns of the highly siderophile elements in Earth's mantle.
Such a residual planetesimal population would also naturally lead to a small fraction trapped in the Earth's Trojan zones as Earth's orbit circularized. In addition to potentially hosting an ancient, long-term stable population of asteroids, Earth's Trojan regions also provide transient traps for NEOs that originate from more distal reservoirs of small bodies in the solar system like the main asteroid belt.
Other companions of Earth
Several other small objects have been found on an orbital path associated with Earth. Although these objects are in 1:1 orbital resonance, they are not Earth trojans, because they do not librate around a definite Sun–Earth Lagrangian point, neither L4 nor L5.
Earth has another noted companion, asteroid 3753 Cruithne. About 5 km across, it has a peculiar type of orbital resonance called an overlapping horseshoe, and is probably only a temporary liaison.[13]
^ Reilly, M. (27 July 2011). "Earth stalker found in eternal twilight". New Scientist. Retrieved 2014-02-21.
^ Choi, C.Q. (27 July 2011). "First asteroid companion of Earth discovered at last". Space.com. Retrieved 2011-07-27.
^ "OSIRIS-REx searches for Earth-trojan asteroids" (Press release). NASA. 9 February 2017.
^ Hui, Man-To; Wiegert, Paul A.; Tholen, David J.; Föhring, Dora (November 2021). "The second Earth trojan 2020 XL5". The Astrophysical Journal Letters. 922 (2): L25. arXiv:2111.05058. Bibcode:2021ApJ...922L..25H. doi:10.3847/2041-8213/ac37bf. S2CID 243860678.
^ ab Whiteley, Robert J.; Tholen, David J. (1998). "CCD search for Lagrangian asteroids of the Earth–Sun system". Icarus. 136 (1): 154–167. Bibcode:1998Icar..136..154W. doi:10.1006/icar.1998.5995. article no. IS985995A. Received 24 November 1997; revised 13 April 1998.
^ "NASA mission to search for rare asteroids" (Press release). NASA. Retrieved 2017-03-01.
^ "OSIRIS-REx asteroid search tests instruments". NASA. Retrieved 2017-03-24.
^Mission status of Hayabusa2(PDF). 49th Lunar and Planetary Science Conference 2018. Retrieved 2018-08-10.
^Knapton, Sarah (29 January 2016). "Earth is actually two planets, scientists conclude". The Telegraph.
^ "The Theia hypothesis: New evidence emerges that Earth and Moon were once the same". The Daily Galaxy. 2007-07-05. Retrieved 2013-11-13.
^ Malhotra, Renu (February 18, 2019). "The case for a deep search for Earth's Trojan asteroids". Nature Astronomy. 3 (3): 193–194. arXiv:1903.01922. Bibcode:2019NatAs...3..193M. doi:10.1038/s41550-019-0697-z. S2CID 119333756.
^ Murray, C. (1997). "The Earth's secret companion". Nature. 387 (6634): 651–652. Bibcode:1997Natur.387..651M. doi:10.1038/42585.
^ Agle, D.C.; Brown, Dwayne; Cantillo, Laurie (15 June 2016). "Small asteroid is Earth's constant companion". NASA / JPL. Retrieved 15 June 2016.
^"Data from NSF's NOIRLab Show Earth Trojan Asteroid Is the Largest Found". Retrieved 27 January 2023.
earth, trojan, asteroid, that, orbits, vicinity, earth, lagrangian, points, leading, trailing, thus, having, orbit, similar, earth, only, have, been, discovered, name, trojan, first, used, 1906, jupiter, trojans, asteroids, that, were, observed, near, lagrangi. An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth Sun Lagrangian points L4 leading 60 or L5 trailing 60 thus having an orbit similar to Earth s Only two Earth trojans have so far been discovered The name trojan was first used in 1906 for the Jupiter trojans the asteroids that were observed near the Lagrangian points of Jupiter s orbit The orbit of 2010 TK7 the first Earth trojan to be discovered left Lagrangian points L4 and L5 Lines around the blue triangles represent tadpole orbits right Contents 1 Members 1 1 L4 leading 1 2 L5 trailing 2 Searches 3 Significance 4 Giant impact hypothesis 5 Continuing interest in near Earth asteroids 6 Other companions of Earth 7 Gallery 8 See also 9 ReferencesMembers Edit 2010 TK7 one of the two known Earth trojans is located at the lower right circled by a small green ring L4 leading Edit 2010 TK7 A 300 metre diameter asteroid discovered using the Wide field Infrared Survey Explorer WISE satellite in January 2010 1 2 3 614689 2020 XL5 Discovered by the Pan STARRS survey in December 2020 and later recognized as an Earth trojan in January 2021 4 It is 1 2 km in diameter L5 trailing Edit No known objects are currently thought to be L5 trojans of Earth Searches EditAn Earth based search for L5 objects was conducted in 1994 covering 0 35 square degrees of sky under poor observing conditions 5 That search failed to detect any objects The limiting sensitivity of this search was magnitude 22 8 corresponding to C type asteroids 350 m in diameter or S type asteroids 175 m in diameter 5 In February 2017 the OSIRIS REx spacecraft performed a search from within the L4 region on its way to asteroid Bennu 6 No additional Earth trojans were discovered 7 In April 2017 the Hayabusa2 spacecraft searched the L5 region while proceeding to asteroid Ryugu 8 but did not find any asteroids there 9 Significance Edit The template below Unreferenced is being considered for merging See templates for discussion to help reach a consensus This section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed July 2013 Learn how and when to remove this template message The orbits of any Earth trojans could make them less energetically costly to reach than the Moon even though they will be hundreds of times more distant Such asteroids could one day be useful as sources of elements that are rare near Earth s surface On Earth siderophiles such as iridium are difficult to find having largely sunk to the core of the planet shortly after its formation A small asteroid could be a rich source of such elements even if its overall composition is similar to Earth s because of their small size such bodies would lose heat much more rapidly than a planet once they had formed and so would not have melted a prerequisite for differentiation even if they differentiated the core would still be within reach Their weak gravitational fields also would have inhibited significant separation of denser and lighter material a mass the size of 2010 TK7 would exert a surface gravitational force of less than 0 00005 times that of Earth although the asteroid s rotation could cause separation Giant impact hypothesis EditA hypothetical planet sized Earth trojan the size of Mars given the name Theia is thought by proponents of the giant impact hypothesis to be the origin of the Moon The hypothesis states that the Moon formed after Earth and Theia collided 10 showering material from the two planets into space This material eventually accreted around Earth and into a single orbiting body the Moon 11 At the same time material from Theia mixed and combined with Earth s mantle and core Supporters of the giant impact hypothesis theorise that Earth s large core in relation to its overall volume is as a result of this combination Continuing interest in near Earth asteroids EditAstronomy continues to retain interest in the subject A publication 12 describes these reasons thus The survival to the present day of an ancient Earth Trojan population is reasonably assured provided Earth s orbit itself was not strongly perturbed since its formation It is therefore pertinent to consider that modern theoretical models of planet formation find strongly chaotic orbital evolution during the final stages of assembly of the terrestrial planets and the Earth Moon system Such chaotic evolution may at first sight appear unfavorable to the survival of a primordial population of Earth trojans However during and after the chaotic assembly of the terrestrial planets it is likely that a residual planetesimal population of a few percent of Earth s mass was present and helped to damp the orbital eccentricities and inclinations of the terrestrial planets to their observed low values as well as to provide the so called late veneer of accreting planetesimals to account for the abundance patterns of the highly siderophile elements in Earth s mantle Such a residual planetesimal population would also naturally lead to a small fraction trapped in the Earth s Trojan zones as Earth s orbit circularized In addition to potentially hosting an ancient long term stable population of asteroids Earth s Trojan regions also provide transient traps for NEOs that originate from more distal reservoirs of small bodies in the solar system like the main asteroid belt Other companions of Earth EditSeveral other small objects have been found on an orbital path associated with Earth Although these objects are in 1 1 orbital resonance they are not Earth trojans because they do not librate around a definite Sun Earth Lagrangian point neither L4 nor L5 Earth has another noted companion asteroid 3753 Cruithne About 5 km across it has a peculiar type of orbital resonance called an overlapping horseshoe and is probably only a temporary liaison 13 469219 Kamoʻoalewa an asteroid discovered on 27 April 2016 is possibly the most stable quasi satellite of Earth 14 Known and suspected companions of Earth vte Name Eccentricity Diameter m Discoverer Date of Discovery Type Current TypeMoon 0 055 3474800 Prehistory Natural satellite Natural satellite1913 Great Meteor Procession 1913 02 09 Possible Temporary satellite Destroyed3753 Cruithne 0 515 5000 Duncan Waldron 1986 10 10 Quasi satellite Horseshoe orbit1991 VG 0 053 5 12 Spacewatch 1991 11 06 Temporary satellite Apollo asteroid 85770 1998 UP1 0 345 210 470 Lincoln Lab s ETS 1998 10 18 Horseshoe orbit Horseshoe orbit54509 YORP 0 230 124 Lincoln Lab s ETS 2000 08 03 Horseshoe orbit Horseshoe orbit2001 GO2 0 168 35 85 Lincoln Lab s ETS 2001 04 13 Possible Horseshoe orbit Possible Horseshoe orbit2002 AA29 0 013 20 100 LINEAR 2002 01 09 Quasi satellite Horseshoe orbit2003 YN107 0 014 10 30 LINEAR 2003 12 20 Quasi satellite Horseshoe orbit 164207 2004 GU9 0 136 160 360 LINEAR 2004 04 13 Quasi satellite Quasi satellite 277810 2006 FV35 0 377 140 320 Spacewatch 2006 03 29 Quasi satellite Quasi satellite2006 JY26 0 083 6 13 Catalina Sky Survey 2006 05 06 Horseshoe orbit Horseshoe orbit2006 RH120 0 024 2 3 Catalina Sky Survey 2006 09 13 Temporary satellite Apollo asteroid 419624 2010 SO16 0 075 357 WISE 2010 09 17 Horseshoe orbit Horseshoe orbit2010 TK7 0 191 150 500 WISE 2010 10 01 Earth trojan Earth trojan2013 BS45 0 083 20 40 Spacewatch 2010 01 20 Horseshoe orbit Horseshoe orbit2013 LX28 0 452 130 300 Pan STARRS 2013 06 12 Quasi satellite temporary Quasi satellite temporary2014 OL339 0 461 70 160 EURONEAR 2014 07 29 Quasi satellite temporary Quasi satellite temporary2015 SO2 0 108 50 110 Crni Vrh Observatory 2015 09 21 Quasi satellite Horseshoe orbit temporary2015 XX169 0 184 9 22 Mount Lemmon Survey 2015 12 09 Horseshoe orbit temporary Horseshoe orbit temporary2015 YA 0 279 9 22 Catalina Sky Survey 2015 12 16 Horseshoe orbit temporary Horseshoe orbit temporary2015 YQ1 0 404 7 16 Mount Lemmon Survey 2015 12 19 Horseshoe orbit temporary Horseshoe orbit temporary469219 Kamoʻoalewa 0 104 40 100 Pan STARRS 2016 04 27 Quasi satellite stable Quasi satellite stableDN16082203 2016 08 22 Possible Temporary satellite Destroyed2020 CD3 0 017 1 6 Mount Lemmon Survey 2020 02 15 Temporary satellite Temporary satellite2020 PN1 0 127 10 50 ATLAS HKO 2020 08 12 Horseshoe orbit temporary Horseshoe orbit temporary2020 PP1 0 074 10 20 Pan STARRS 2020 08 12 Quasi satellite stable Quasi satellite stable2020 XL5 0 387 1100 1260 Pan STARRS 2020 12 12 Earth trojan Earth trojan2022 NX1 0 025 5 15 Moonbase South Observatory 2020 07 02 Temporary satellite Apollo asteroid2023 FW13 0 177 10 20 Pan STARRS 2023 03 28 Quasi satellite Quasi satelliteGallery Edit Illustration of Trojan Asteroid 2020 XL5 15 See also Edit2003 YN107 2006 RH120 3753 Cruithne 6Q0B44E Claimed moons of Earth Kordylewski cloud Natural satellite Quasi satellite Theia giant impact hypothesisReferences Edit Reilly M 27 July 2011 Earth stalker found in eternal twilight New Scientist Retrieved 2014 02 21 Choi C Q 27 July 2011 First asteroid companion of Earth discovered at last Space com Retrieved 2011 07 27 OSIRIS REx searches for Earth trojan asteroids Press release NASA 9 February 2017 Hui Man To Wiegert Paul A Tholen David J Fohring Dora November 2021 The second Earth trojan 2020 XL5 The Astrophysical Journal Letters 922 2 L25 arXiv 2111 05058 Bibcode 2021ApJ 922L 25H doi 10 3847 2041 8213 ac37bf S2CID 243860678 a b Whiteley Robert J Tholen David J 1998 CCD search for Lagrangian asteroids of the Earth Sun system Icarus 136 1 154 167 Bibcode 1998Icar 136 154W doi 10 1006 icar 1998 5995 article no IS985995A Received 24 November 1997 revised 13 April 1998 NASA mission to search for rare asteroids Press release NASA Retrieved 2017 03 01 OSIRIS REx asteroid search tests instruments NASA Retrieved 2017 03 24 太陽 地球系のL5点付近の観測について JAXA 2017 04 11 Retrieved 2017 04 18 Mission status of Hayabusa2 PDF 49th Lunar and Planetary Science Conference 2018 Retrieved 2018 08 10 Knapton Sarah 29 January 2016 Earth is actually two planets scientists conclude The Telegraph The Theia hypothesis New evidence emerges that Earth and Moon were once the same The Daily Galaxy 2007 07 05 Retrieved 2013 11 13 Malhotra Renu February 18 2019 The case for a deep search for Earth s Trojan asteroids Nature Astronomy 3 3 193 194 arXiv 1903 01922 Bibcode 2019NatAs 3 193M doi 10 1038 s41550 019 0697 z S2CID 119333756 Murray C 1997 The Earth s secret companion Nature 387 6634 651 652 Bibcode 1997Natur 387 651M doi 10 1038 42585 Agle D C Brown Dwayne Cantillo Laurie 15 June 2016 Small asteroid is Earth s constant companion NASA JPL Retrieved 15 June 2016 Data from NSF s NOIRLab Show Earth Trojan Asteroid Is the Largest Found Retrieved 27 January 2023 Portals Stars Spaceflight Outer space Science Retrieved from https en wikipedia org w index php title Earth trojan amp oldid 1167256891, wikipedia, wiki, book, books, library,
