Editing Jupiter trojan (section)

== Numbers and mass ==
[[File:Lagrange points.jpg|thumb|right|A [[gravitational potential]] contour plot showing Earth's Lagrangian points; {{L4|nolink=yes}} and {{L5|nolink=yes}} are ahead (above) and behind (below) the planet, respectively. Jupiter's Lagrangian points are similarly situated in its much larger orbit.]]

Estimates of the total number of Jupiter trojans are based on deep surveys of limited areas of the sky.<ref name=Yoshida2005/> The {{L4|nolink=yes}} swarm is believed to hold between 160,000 and 240,000 asteroids with diameters larger than 2&nbsp;km and about 600,000 with diameters larger than 1&nbsp;km.<ref name=Yoshida2005/><ref name=Jewitt2000/> If the {{L5|nolink=yes}} swarm contains a comparable number of objects, there are more than {{Nowrap|1 million}} Jupiter trojans 1&nbsp;km in size or larger. For the objects brighter than [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] 9.0 the population is probably complete.<ref name=Fernandes2003/> These numbers are similar to that of comparable asteroids in the asteroid belt.<ref name=Yoshida2005/> The total mass of the Jupiter trojans is estimated at 0.0001 of the mass of Earth or one-fifth of the mass of the asteroid belt.<ref name=Jewitt2000/>

Two more recent studies indicate that the above numbers may overestimate the number of Jupiter trojans by several-fold. This overestimate is caused by (1) the assumption that all Jupiter trojans have a low [[albedo]] of about 0.04, whereas small bodies may have an average albedo as high as 0.12;<ref name=Fernandes2009/> (2) an incorrect assumption about the distribution of Jupiter trojans in the sky.<ref name=Nakamura2008/> According to the new estimates, the total number of Jupiter trojans with a diameter larger than 2&nbsp;km is {{nowrap|6,300 ± 1,000}} and {{nowrap|3,400 ± 500}} in the L<sub>4</sub> and L<sub>5</sub> swarms, respectively.<ref name=Nakamura2008/> These numbers would be reduced by a factor of 2 if small Jupiter trojans are more reflective than large ones.<ref name=Fernandes2009/>

The number of Jupiter trojans observed in the {{L4|nolink=yes}} swarm is slightly larger than that observed in {{L5|nolink=yes}}. Because the brightest Jupiter trojans show little variation in numbers between the two populations, this disparity is probably due to observational bias.<ref name=Jewitt2004/> Some models indicate that the {{L4|nolink=yes}} swarm may be slightly more stable than the {{L5|nolink=yes}} swarm.<ref name=Marzari2002/>

The largest Jupiter trojan is [[624 Hektor]], which has a mean diameter of 203&nbsp;±&nbsp;3.6&nbsp;km.<ref name=Fernandes2003/> There are few large Jupiter trojans in comparison to the overall population. With decreasing size, the number of Jupiter trojans grows very quickly down to 84&nbsp;km, much more so than in the asteroid belt. A diameter of 84&nbsp;km corresponds to an absolute magnitude of 9.5, assuming an [[albedo]] of 0.04. Within the 4.4–40&nbsp;km range the Jupiter trojans' size distribution resembles that of the main-belt asteroids. Nothing is known about the masses of the smaller Jupiter trojans.<ref name=Marzari2002/> The size distribution suggests that the smaller Trojans may be the products of collisions by larger Jupiter trojans.<ref name=Jewitt2004/>

{{JPL SBDB Jupiter Trojans}}