Jupiter trojan

The asteroids of the inner Solar System and Jupiter
  Jupiter trojans
  Hilda asteroids 		  Asteroid belt
  Orbits of planets
The Jupiter trojans are divided into two groups: The Greek camp in front of and the Trojan camp trailing behind Jupiter in their orbit.

The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange points: either L4, existing 60° ahead of the planet in its orbit, or L5, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU.[1]

The first Jupiter trojan discovered, 588 Achilles, was spotted in 1906 by German astronomer Max Wolf.[2] More than 9,800 Jupiter trojans have been found as of May 2021.[3] By convention, they are each named from Greek mythology after a figure of the Trojan War, hence the name "trojan". The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million,[1] approximately equal to the number of asteroids larger than 1 km in the asteroid belt.[4] Like main-belt asteroids, Jupiter trojans form families.[5]

As of 2004, many Jupiter trojans showed to observational instruments as dark bodies with reddish, featureless spectra. No firm evidence of the presence of water, or any other specific compound on their surface has been obtained, but it is thought that they are coated in tholins, organic polymers formed by the Sun's radiation.[6] The Jupiter trojans' densities (as measured by studying binaries or rotational lightcurves) vary from 0.8 to 2.5 g·cm−3.[5] Jupiter trojans are thought to have been captured into their orbits during the early stages of the Solar System's formation or slightly later, during the migration of giant planets.[5]

The term "Trojan Asteroid" specifically refers to the asteroids co-orbital with Jupiter, but the general term "trojan" is sometimes more generally applied to other small Solar System bodies with similar relationships to larger bodies: Mars trojans, Neptune trojans, Uranus trojans and Earth trojans are known to exist.[7][8][9] Temporary Venus trojans and Saturn trojans exist, as well as for 1 Ceres and 4 Vesta. The term "Trojan asteroid" is normally understood to specifically mean the Jupiter trojans because the first Trojans were discovered near Jupiter's orbit and Jupiter currently has by far the most known Trojans.[3]

  1. ^ a b Cite error: The named reference Yoshida2005 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Nicholson1961 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference MPC-Trojan-count was invoked but never defined (see the help page).
  4. ^ Tedesco, E. F.; Desert, F.-X. (2002). "The Infrared Space Observatory Deep Asteroid Search". The Astronomical Journal. 123 (4): 2070–2082. Bibcode:2002AJ....123.2070T. doi:10.1086/339482.
  5. ^ a b c Cite error: The named reference Jewitt2004 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Dotto2006 was invoked but never defined (see the help page).
  7. ^ Sheppard, S. S.; C. A. Trujillo (28 July 2006). "A thick cloud of Neptune Trojans and their colors" (PDF). Science. 313 (5786). New York: 511–514. Bibcode:2006Sci...313..511S. doi:10.1126/science.1127173. OCLC 110021198. PMID 16778021. S2CID 35721399. Archived from the original (PDF) on 12 April 2020.
  8. ^ "NASA's WISE Mission Finds First Trojan Asteroid Sharing Earth's Orbit 27 July 2011". Archived from the original on 2 May 2017. Retrieved 29 July 2011.
  9. ^ Connors, Martin; Wiegert, Paul; Veillet, Christian (28 July 2011). "Earth's Trojan asteroid". Nature. 475 (7357): 481–483. Bibcode:2011Natur.475..481C. doi:10.1038/nature10233. PMID 21796207. S2CID 205225571.