The tale of the Trojan War, as told by Homer, is a tale of intrigue and heroes. And, as with characters from Greek mythology, many of the names end up being concerned with things in the sky.
In the early twentieth century, when astrophotography became good enough to see such things, it became clear that Jupiter, the largest planet in the solar system, was accompanied not only by its own system of moons, but also by two groups of distant assistants. These were groups of asteroids that precisely followed the giant planet’s orbit, but either led or followed Jupiter itself by about 60 degrees of arc.
These groups are concentrated in places called the L4 and L5 Lagrange points, after the mathematician who predicted their existence. L4 and L5 are traps in space caused by the interaction of the gravitational fields of Jupiter and the Sun. Once in one of them, an asteroid generally got stuck there. As these captured asteroids were divided into two camps, their early discoverers enjoyed recalling the bodies discovered in L4, which leads Jupiter, after the Greek war heroes, and those in L5, which follow that planet, after the Trojans (although each camp has also a spy from the other in the middle).
Siege of Troy
The most famous asteroids lie in a belt between the orbits of Mars and Jupiter. Spectral analysis of sunlight reflected from these, and comparisons with bits of space rock that fell to Earth as meteorites, suggest that some are bits of dwarf planets that later collided with each other (although a few, like Ceres, remain intact. ), while the rest are clumps of material from the early solar nebula, often including pebbles of once molten rock called chondrules. Many asteroids based on agglomeration are rich in carbon, which makes them dark in color and opaque to reddish. In particular, their spectra are similar to those of cartilage-bearing meteorites called carbonaceous chondrites.