Short answers, pulled from the story.
An asteroid is a minor planet, an object larger than a meteoroid that is neither a planet nor an identified comet, orbiting within the inner Solar System or co-orbital with Jupiter as a Trojan. Asteroids are rocky, metallic, or icy bodies with no atmosphere, broadly classified as C-type, M-type, or S-type.
Giuseppe Piazzi, a Catholic priest at the Academy of Palermo in Sicily, discovered the first asteroid, Ceres, on the 1st of January 1801. He first reported it as a comet, then suspected it might be something better than a comet.
Roughly one million asteroids are known, and the greatest number lie in the main asteroid belt between the orbits of Mars and Jupiter, approximately 2 to 4 astronomical units from the Sun. Despite their numbers, their combined mass is only 3% that of Earth's Moon.
A body is classified as a comet rather than an asteroid if it shows a coma, or tail, when warmed by solar radiation, caused by sublimation of its near-surface ices. Comets also typically have more eccentric orbits, though recent observations suggest a continuum between the two types of bodies.
NASA's Double Asteroid Redirection Test deliberately crashed into Dimorphos, the moon of the double asteroid Didymos, in September 2022 to test planetary defense. The impact shortened Dimorphos's orbital period by about 32 minutes, made it an active asteroid, and produced a dust tail 10000 km long.
The largest asteroid is Ceres, a dwarf planet with a diameter of 940 km, followed by 4 Vesta and 2 Pallas, both just over 500 km across, and then Hygiea. These four largest objects make up about five-eighths of the asteroid belt's mass, with Ceres and Vesta alone accounting for half.
Once an asteroid's orbit is confirmed, it receives a catalogue number, and the discoverer of the first apparition with a calculated orbit may propose a name, subject to approval by the International Astronomical Union. A simple chronological numbering system was established in 1925, replacing earlier letter-based schemes.