Neptune trojan explained

Neptune trojans are bodies that orbit the Sun near one of the stable Lagrangian points of Neptune, similar to the trojans of other planets. They therefore have approximately the same orbital period as Neptune and follow roughly the same orbital path. Thirty-one Neptune trojans are currently known, of which 27 orbit near the Sun–Neptune Lagrangian point 60° ahead of Neptune and four orbit near Neptune's region 60° behind Neptune. The Neptune trojans are termed 'trojans' by analogy with the Jupiter trojans.

The discovery of in a high-inclination (>25°) orbit was significant, because it suggested a "thick" cloud of trojans[1] (Jupiter trojans have inclinations up to 40°[2]), which is indicative of freeze-in capture instead of in situ or collisional formation.[1] It is suspected that large (radius ≈ 100 km) Neptune trojans could outnumber Jupiter trojans by an order of magnitude.[3] [4]

In 2010, the discovery of the first known Neptune trojan,, was announced.[5] Neptune's trailing region is currently very difficult to observe because it is along the line of sight to the center of the Milky Way, an area of the sky crowded with stars.

Discovery and exploration

In 2001, the first Neptune trojan was discovered,, near Neptune's region, and with it the fifth known populated stable reservoir of small bodies in the Solar System. In 2005, the discovery of the high-inclination trojan has indicated that the Neptune trojans populate thick clouds, which has constrained their possible origins (see below).

On August 12, 2010, the first trojan,, was announced.[5] It was discovered by a dedicated survey that scanned regions where the light from the stars near the Galactic Center is obscured by dust clouds. This suggests that large trojans are as common as large trojans, to within uncertainty, further constraining models about their origins (see below).

It would have been possible for the New Horizons spacecraft to investigate Neptune trojans discovered by 2014, when it passed through this region of space en route to Pluto.[4] Some of the patches where the light from the Galactic Center is obscured by dust clouds are along New Horizonss flight path, allowing detection of objects that the spacecraft could image., the highest-inclination Neptune trojan known, was just bright enough for New Horizons to observe it in end-2013 at a distance of 1.2 AU.[6] However, New Horizons may not have had sufficient downlink bandwidth, so it was eventually decided to give precedence to the preparations for the Pluto flyby.[7] [8]

Dynamics and origin

The orbits of Neptune trojans are highly stable; Neptune may have retained up to 50% of the original post-migration trojan population over the age of the Solar System.[1] Neptune's can host stable trojans equally well as its . Neptune trojans can librate up to 30° from their associated Lagrangian points with a 10,000-year period. Neptune trojans that escape enter orbits similar to centaurs. Although Neptune cannot currently capture stable trojans,[1] roughly 2.8% of the centaurs within 34 AU are predicted to be Neptune co-orbitals. Of these, 54% would be in horseshoe orbits, 10% would be quasi-satellites, and 36% would be trojans (evenly split between the and groups).[9]

The unexpected high-inclination trojans are the key to understanding the origin and evolution of the population as a whole.[10] The existence of high-inclination Neptune trojans points to a capture during planetary migration instead of in situ or collisional formation.[1] The estimated equal number of large and trojans indicates that there was no gas drag during capture and points to a common capture mechanism for both and trojans. The capture of Neptune trojans during a migration of the planets occurs via process similar to the chaotic capture of Jupiter trojans in the Nice model. When Uranus and Neptune are near but not in a mean-motion resonance the locations where Uranus passes Neptune can circulate with a period that is in resonance with the libration periods of Neptune trojans. This results in repeated perturbations that increase the libration of existing trojans causing their orbits to become unstable.[11] This process is reversible allowing new trojans to be captured when the planetary migration continues.[12] For high-inclination trojans to be captured the migration must have been slow,[13] or their inclinations must have been acquired previously.[14]

Colors

The first four discovered Neptune trojans have similar colors.[1] They are modestly red, slightly redder than the gray Kuiper belt objects, but not as extremely red as the high-perihelion cold classical Kuiper belt objects.[1] This is similar to the colors of the blue lobe of the centaur color distribution, the Jupiter trojans, the irregular satellites of the gas giants, and possibly the comets, which is consistent with a similar origin of these populations of small Solar System bodies.[1]

The Neptune trojans are too faint to efficiently observe spectroscopically with current technology, which means that a large variety of surface compositions are compatible with the observed colors.[1]

Several Neptunian Trojans have been observed to have very-red colors similar to cold classical Kuiper belt objects.[15]

Naming

In 2015, the IAU adopted a new naming scheme for Neptune trojans, which are to be named after Amazons, with no differentiation between objects in L4 and L5.[16] The Amazons were an all-female warrior tribe that fought in the Trojan War on the side of the Trojans against the Greeks. As of 2019, the named Neptune trojans are 385571 Otrera (after Otrera, the first Amazonian queen in Greek mythology) and 385695 Clete (after Clete, an Amazon and the attendant to the Amazons' queen Penthesilea, who led the Amazons in the Trojan war).[17] [18]

Members

The amount of high-inclination objects in such a small sample, in which relatively fewer high-inclination Neptune trojans are known due to observational biases,[1] implies that high-inclination trojans may significantly outnumber low-inclination trojans.[10] The ratio of high- to low-inclination Neptune trojans is estimated to be about 4:1.[1] Assuming albedos of 0.05, there are an expected Neptune trojans with radii above 40 km in Neptune's .[1] This would indicate that large Neptune trojans are 5 to 20 times more abundant than Jupiter trojans, depending on their albedos.[1] There may be relatively fewer smaller Neptune trojans, which could be because these fragment more readily.[1] Large trojans are estimated to be as common as large trojans.

and display significant dynamical instability.[10] This means they could have been captured after planetary migration, but may as well be a long-term member that happens not to be perfectly dynamically stable.[10]

As of September 2023, 31 Neptune trojans are known, of which 27 orbit near the SunNeptune Lagrangian point 60° ahead of Neptune, 4 orbit near Neptune's region 60° behind Neptune, and one orbits on the opposite side of Neptune but frequently changes location relative to Neptune to L4 and L5. These are listed in the following table. It is constructed from the list of Neptune trojans maintained by the IAU Minor Planet Center[19] and with diameters from Sheppard and Trujillo's paper on,[20] unless otherwise noted.

NameProv.
designation
Lagrangian
point
q Q ei (°)Abs. magDiameter
(km)
NotesMPC
scope=row style=text-align:center colspan=2 21.109 40.613 0.310 19.2 7.2 2010 Jumping trojan
scope=row style=text-align:center scope=row29.318 30.942 0.031 1.4 8.8 2004 First Neptune trojan numbered and named
scope=row style=text-align:center scope=row28.469 31.771 0.052 5.3 8.3 2005
scope=row style=text-align:center colspan=2 28.130 32.028 0.065 28.1 8.5 2007
scope=row style=text-align:center colspan=2 29.622 30.503 0.009 9.6 7.8 2016
scope=row style=text-align:center colspan=2 29.064 30.878 0.025 22.3 7.3 2016
scope=row style=text-align:center colspan=2 29.404 31.011 0.031 1.3 8.1 2001 First Neptune trojan discovered, unstable Trojan
scope=row style=text-align:center colspan=2 29.077 31.014 0.028 8.2 7.6 2006
scope=row style=text-align:center colspan=2 24.553 35.851 0.183 13.6 8.7 2011 Temporary Neptune trojan
scope=row style=text-align:center colspan=2 28.092 32.162 0.067 25.0 9.0 2005 First high-inclination trojan discovered
scope=row style=text-align:center colspan=2 27.365 32.479 0.079 27.6 8.2 2008 First trojan discovered
scope=row style=text-align:center colspan=2 28.608 31.253 0.048 6.6 8.1 2016
scope=row style=text-align:center colspan=2 27.913 32.189 0.070 4.3 7.8 2016
scope=row style=text-align:center colspan=2 27.662 32.455 0.083 29.4 8.1 2012
scope=row style=text-align:center colspan=2 27.806 32.259 0.072 20.8 9.3 [21] 2014
scope=row style=text-align:center colspan=2 28.794 31.538 0.042 28.4 7.6 2019
scope=row style=text-align:center colspan=2 26.624 34.084 0.124 6.6 6.8 2016 Stability uncertain
scope=row style=text-align:center colspan=2 29.366 30.783 0.028 10.1 8.8 2020
scope=row style=text-align:center colspan=2 28.611 31.784 0.053 7.5 8.9 2021
scope=row style=text-align:center colspan=2 28.092 32.135 0.066 13.1 8.2 2020
scope=row style=text-align:center colspan=2 27.787 32.683 0.081 18.6 9.6 2021
scope=row style=text-align:center colspan=2 27.563 32.525 0.087 31.3 8.3 2018
scope=row style=text-align:center colspan=2 26.961 33.215 0.101 18.8 8.3 2014 Most eccentric stable Neptune trojan[22]
scope=row style=text-align:center colspan=2 28.137 31.971 0.067 19.4 9.3 2015
scope=row style=text-align:center colspan=2 28.426 31.614 0.050 29.5 8.4 2020
scope=row style=text-align:center colspan=2 27.038 33.060 0.096 33.7 8.2 2020
scope=row style=text-align:center colspan=2 28.661 31.457 0.045 35.8 8.2 2018
scope=row style=text-align:center colspan=2 27.309 33.243 0.098 30.8 8.6 2021
scope=row style=text-align:center colspan=2 27.742 32.236 0.074 30.8 10.2 2018
scope=row style=text-align:center colspan=2 27.513 32.497 0.086 16.9 9.0 2018
scope=row style=text-align:center colspan=2 28.488 31.488 0.049 5.0 8.4 2018
scope=row style=text-align:center colspan=2 27.612 32.327 0.073 17.2 9.2 2018
scope=row style=text-align:center colspan=2 29.211 31.174 0.033 38.9 7.3 2021 Highest known inclination

[23] and [24] were thought to be Neptune trojans at the time of their discovery, but further observations have disconfirmed their membership. is currently thought to be in a 3:5 resonance with Neptune.[25] is currently following a quasi-satellite loop around Neptune.[26]

See also

External links

Notes and References

  1. Sheppard . Scott S. . Trujillo, Chadwick A. . A Thick Cloud of Neptune Trojans and Their Colors . 10.1126/science.1127173 . Science . 313 . 5786 . 511–514 . June 2006 . 2008-02-26 . 16778021 . 2006Sci...313..511S . 35721399 . live . https://web.archive.org/web/20100716005454/http://www.dtm.ciw.edu/users/sheppard/pub/Sheppard06NepTroj.pdf . 2010-07-16.
  2. Jewitt . David C. . Trujillo, Chadwick A. . Luu, Jane X. . Population and size distribution of small Jovian Trojan asteroids. 2000. The Astronomical Journal . 120 . 2 . 1140–7 . 10.1086/301453 . 2000AJ....120.1140J. astro-ph/0004117 . 119450236 .
  3. E. I. Chiang and Y. LithwickNeptune Trojans as a Testbed for Planet Formation,The Astrophysical Journal, 628, pp. 520–532 Preprint
  4. Web site: 30 January 2007 . Neptune May Have Thousands of Escorts . David Powell . Space.com . 2007-03-08 . live . https://web.archive.org/web/20080815161200/http://www.space.com/scienceastronomy/070130_st_neptune_trojans.html . 15 August 2008.
  5. Web site: 2010-08-12 . Trojan Asteroid Found in Neptune's Trailing Gravitational Stability Zone . Carnegie Institution of Washington . Scott S. Sheppard . 2007-12-28 . live . https://web.archive.org/web/20100815095616/http://www.dtm.ciw.edu/users/sheppard/L5trojan/ . 2010-08-15.
  6. Web site: Parker . Alex . Citizen "Ice Hunters" help find a Neptune Trojan target for New Horizons . www.planetary.org/blogs . . 2012-10-09 . 2012-10-09 . live . https://web.archive.org/web/20121101020405/http://www.planetary.org/blogs/guest-blogs/20121009-parker-neptune-trojan-ice-hunters.html . 2012-11-01.
  7. Web site: Stern, Alan. May 1, 2006. Where Is the Centaur Rocket?. The PI's Perspective. Johns Hopkins APL. June 11, 2006. https://web.archive.org/web/20060901204154/http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_5_1_2006_2.php. September 1, 2006. dead.
  8. News: Parker . Alex . 2011 HM102: A new companion for Neptune . The Planetary Society . April 30, 2013 . October 7, 2014 . dead . https://web.archive.org/web/20141009183627/http://www.planetary.org/blogs/guest-blogs/2013/0430-2011hm102-new-neptune-companion.html . October 9, 2014 .
  9. Alexandersen . M. . Gladman . B. . Greenstreet . S. . Kavelaars . J. J. . Petit . J. -M. . Gwyn . S. . 10.1126/science.1238072 . A Uranian Trojan and the Frequency of Temporary Giant-Planet Co-Orbitals . Science . 341 . 6149 . 994–997 . 2013 . 23990557. 1303.5774. 2013Sci...341..994A . 39044607 .
  10. Horner, J., Lykawka, P. S., Bannister, M. T., & Francis, P. 2008 LC18: a potentially unstable Neptune Trojan Accepted to appear in Monthly Notices of the Royal Astronomical Society
  11. Kortenkamp. Stephen J.. Malhotra. Renu. Michtchenko. Tatiana. Survival of Trojan-type companions of Neptune during primordial planet migration. Icarus. 2004. 167. 2. 347–359. 10.1016/j.icarus.2003.09.021. astro-ph/0305572. 2004Icar..167..347K . 2046901.
  12. Nesvorný. David. Vokrouhlický. David. Chaotic Capture of Neptune Trojans. The Astronomical Journal. 2009. 137. 6. 5003–5011. 10.1088/0004-6256/137/6/5003. 2009AJ....137.5003N . 10.1.1.693.4387. 54186674 .
  13. Gomes. R.. Nesvorny. D.. Neptune trojan formation during planetary instability and migration. Astronomy & Astrophysics. 2016. 592. A146. 10.1051/0004-6361/201527757. 2016A&A...592A.146G. free.
  14. Parker. Alex. The intrinsic Neptune Trojan orbit distribution: Implications for the primordial disk and planet migration. Icarus. 2015. 247. 112–125. 10.1016/j.icarus.2014.09.043. 1409.6735. 2015Icar..247..112P . 119203006.
  15. Keck, gemini, and palomar 200-inch visible photometry of red and very-red neptunian trojans . etal . B. T. . Bolin . C. . Fremling . A. . Morbidelli . K. S. . Noll . J. . van Roestel . E. K. . Deibert . February 2023 . . 521 . 1 . L29–L33 . 10.1093/mnrasl/slad018 . free . 2302.04280.
  16. Web site: DIVISION F / Working Group for Small Body Nomenclature Working Group for Small Body Nomenclature. THE TRIENNIAL REPORT (2015 Sept 1 - 2018 Feb 15). 10 April 2018. 25 August 2018. IAU. Ticha, J.. etal.
  17. Web site: 385571 Otrera (2004 UP10). Minor Planet Center. 30 November 2015. 4 August 2017.
  18. Web site: 385695 Clete (2005 TO74). Minor Planet Center. 18 May 2019. 10 June 2019.
  19. Web site: List Of Neptune Trojans . Minor Planet Center . 2012-08-09 . live . https://archive.today/20120525133119/http://www.minorplanetcenter.org/iau/lists/NeptuneTrojans.html . 2012-05-25.
  20. Sheppard . Scott S. . Scott S. Sheppard . Trujillo, Chadwick A. . Detection of a Trailing (L5) Neptune Trojan . . 329 . 5997 . 1304 . . 2010-08-12 . 10.1126/science.1189666 . 20705814 . 2010Sci...329.1304S. 7657932 . free .
  21. Web site: Conversion of Absolute Magnitude to Diameter. www.physics.sfasu.edu. 29 April 2018. live. https://web.archive.org/web/20100323180835/http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html. 23 March 2010.
  22. Observation of Two New L4 Neptune Trojans in the Dark Energy Survey Supernova Fields. D. W.. Gerdes. R. J.. Jennings. G. M.. Bernstein. M.. Sako. F.. Adams. D.. Goldstein. R.. Kessler. T.. Abbott. F. B.. Abdalla. S.. Allam. A.. Benoit-Lévy. E.. Bertin. D.. Brooks. E.. Buckley-Geer. Elizabeth Buckley-Geer. D. L.. Burke. D.. Capozzi. A. Carnero. Rosell. M. Carrasco. Kind. J.. Carretero. C. E.. Cunha. C. B.. D'Andrea. L. N.. da Costa. D. L.. DePoy. S.. Desai. J. P.. Dietrich. P.. Doel. T. F.. Eifler. A. Fausti. Neto. B.. Flaugher. Brenna Flaugher . J.. Frieman. E.. Gaztanaga. D.. Gruen. R. A.. Gruendl. G.. Gutierrez. K.. Honscheid. D. J.. James. K.. Kuehn. N.. Kuropatkin. O.. Lahav. T. S.. Li. M. A. G.. Maia. M.. March. P.. Martini. C. J.. Miller. R.. Miquel. R. C.. Nichol. B.. Nord. R.. Ogando. A. A.. Plazas. A. K.. Romer. A.. Roodman. E.. Sanchez. B.. Santiago. M.. Schubnell. I.. Sevilla-Noarbe. R. C.. Smith. M.. Soares-Santos. Marcelle Soares-Santos. F.. Sobreira. E.. Suchyta. M. E. C.. Swanson. G.. Tarlé. J.. Thaler. A. R.. Walker. W.. Wester. Y.. Zhang. 28 January 2016. The Astronomical Journal. 151. 2. 39. 10.3847/0004-6256/151/2/39. 1507.05177. 2016AJ....151...39G. 55326461 . free .
  23. http://www.minorplanetcenter.net/iau/mpec/K05/K05U97.html MPEC 2005-U97 : 2005 TN74, 2005 TO74
  24. Web site: Distant EKOs, 55 . 2012-07-24 . live . https://web.archive.org/web/20130525030402/http://www.boulder.swri.edu/ekonews/issues/past/n055/html/index.html . 2013-05-25 .
  25. Web site: Orbit and Astrometry for 05TN74. www.boulder.swri.edu. 29 April 2018. live. https://web.archive.org/web/20180429165723/http://www.boulder.swri.edu/~buie/kbo/astrom/05TN74.html. 29 April 2018.
  26. de la Fuente Marcos . de la Fuente Marcos . (309239) 2007 RW10: a large temporary quasi-satellite of Neptune . Astronomy and Astrophysics Letters . 545 . L9 . 2012 . 10.1051/0004-6361/201219931 . 1209.1577 . 2012A&A...545L...9D. 118374080 .