We’re here: 433 Eros, the first small body mankind had orbited. Before I go into the NEAR Shoemaker mission, though, let’s remember Eros was one of the best studied small bodies well before NEAR, Galileo, or even all the probes of the “Halley Armada.”
Eros was known almost a century before NEAR even launched. Main Belt asteroids had been found from 1801 to 1898, establishing a curious zone between Mars and Jupiter. All asteroids were being given female names. In 1873, the first Mars-crossing asteroid (132 Aethra) was found, then later 323 Brucia and 391 Ingeborg (hence, their rising numbering). But all these were still predominantly orbiting outside of Mars, and could be thought of as straying inside Mars’ orbit temporarily. In other words, still mostly Belt bodies, just a little weird sometimes.
The 1898 discovery of 433 Eros reordered, and arguably ordered, the Solar System. Eros not only crosses Mars but approaches Earth, and closely- a “Near-Earth Object.” At closest, it comes within 0.1505 astronomical units (or AU, the distance from the Sun to the Earth). At the far point of its orbit (aphelion), Eros doesn’t enter what most would call the inner edge of the Belt, either. Previously, only comets were thought to “pass” Earth via such sweeping orbits. Eros was neither comet, nor quiet resident of the Belt. Yet another blow to the dogma of celestis (the heavens) and mundi (earth) as separate “spheres.” This was dramatic enough that the discovery received the first male name.
Close passes meant that it was easily studied, and useful beyond itself. Perturbations of Eros, timed well enough, gave the mass of the Earth-Moon system. In addition, the size of the Solar System could be taken. Kepler’s 3rd law lets us find the sizes of different orbits, but only as ratios. We know Earth’s year, of course, and we can time the laps of other planets and bodies. But until we numerically measure one orbit (such as Earth’s, let alone another planet’s), we can’t know any other orbit, and thus the Solar System in general. Eros did that where Venus did not. Said Harvard astronomer S. Bailey: “Indeed, Eros, at the most favorable times, is perhaps as good an object as can be desired”