Numbers and Mass
Estimates of the total number of Trojans are based on deep surveys of limited areas of the sky. The L4 swarm is believed to hold between 160–240,000 asteroids with diameters larger than 2 km and about 600,000 with diameters larger than 1 km. If the L5 swarm contains a comparable number of objects, there are more than 1 million Trojans 1 km in size or larger. For the objects brighter than absolute magnitude 9.0 the population is probably complete. These numbers are similar to that of comparable asteroids in the asteroid belt. The total mass of the Trojans is estimated at 0.0001 of the mass of Earth or one-fifth of the mass of the asteroid belt.
Two more recent studies indicate, however, that the above numbers may overestimate the number of Trojans by several-fold. This overestimate is caused by (1) the assumption that all Trojans have a low albedo of about 0.04, whereas small bodies may actually have an average albedo as high as 0.12; (2) an incorrect assumption about the distribution of Trojans in the sky. According to the new estimates, the total number of Trojan asteroids with a diameter larger than 2 km is 6.3 ± 1.0×104 and 3.4 ± 0.5×104 in the L4 and L5 swarms, respectively. These numbers would be reduced by a factor of 2 if small Trojans are more reflective than large ones.
The number of Trojans observed in the L4 swarm is slightly larger than that observed in L5; however, since the brightest Trojans show little variation in numbers between the two populations, this disparity is probably due to observational bias. However, some models indicate that the L4 swarm may be slightly more stable than the L5 swarm.
The largest of the Trojans is 624 Hektor, which has an average diameter of 203 ± 3.6 km. There are few large Trojans in comparison to the overall population. With decreasing size, the number of Trojans grows very quickly down to 84 km, much more so than in the asteroid belt. A diameter of 84 km corresponds to an absolute magnitude of 9.5, assuming an albedo of 0.04. Within the 4.4–40 km range the Trojans' size distribution resembles that of the main-belt asteroids. An absence of data means that nothing is known about the masses of the smaller Trojans. The size distribution suggests that the smaller Trojans are the products of collisions by larger Trojans.
Read more about this topic: Jupiter Trojan
Famous quotes containing the words numbers and/or mass:
“Out of the darkness where Philomela sat,
Her fairy numbers issued. What then ailed me?
My ears are called capacious but they failed me,
Her classics registered a little flat!
I rose, and venomously spat.”
—John Crowe Ransom (1888–1974)
“Where mass opinion dominates the government, there is a morbid derangement of the true functions of power. The derangement brings about the enfeeblement, verging on paralysis, of the capacity to govern. This breakdown in the constitutional order is the cause of the precipitate and catastrophic decline of Western society. It may, if it cannot be arrested and reversed, bring about the fall of the West.”
—Walter Lippmann (1889–1974)