Comets and Asteroids
433 Eros is a large near-Earth object which may one day get very up close and personal
Minor planet 433 Eros is a siliceous or S-type asteroid, which means it has a stony composition. At 34.4x11.2x11.2km its elongated body is the second largest near-Earth object known. It belongs to a group of objects called the Amor asteroids, named after 1221 Amor. All the asteroids in this family have orbits that remain outside Earth’s orbit.
Eros was the first asteroid to be orbited and landed on by a spacecraft. The craft in question was NEAR Shoemaker, which entered its orbit in 2000 and soft landed the following year.
Like most Amor asteroids, Eros’s orbit crosses Mars’s. At aphelion it is 1.78 AU from the Sun and at perihelion comes as close as 1.13 AU. At favourable oppositions – which occur every 81 years – Eros can appear as bright as mag. +7.0. This year, though, when Eros reaches opposition on 7 December, it will appear as a mag. +9.7 object in the ill-defined constellation of Camelopardalis. Its distance from Earth will be about 40.5 million km, which may sound close but is significantly further than our 26.7 million km close encounter with it on 31 January 2012.
It’s thought that gravitational perturbations could alter Eros’s orbit from a Mars-crosser to an Earth-crosser within a couple of million years. Eros is classed as a potential Earth impactor; worryingly it is five times the size of the asteroid that caused the extinction of the dinosaurs.
At the start of December, 433 Eros is located 2.5° east of the eastern end of the asterism Kemble’s Cascade in Camelopardalis. It then arcs west as it heads south. Its distance from Earth continues to decrease during December, and so its apparent brightness increases. On 1 December, when Eros is 2.9 AU from Earth, it shines at mag. +9.9. By the end of the month its distance will drop to 2.2 AU and its magnitude will rise to +9.2.