Millions of asteroids orbit the sun between Mars and Jupiter, a band known as the asteroid belt. Most of these bodies circle our star peacefully, chugging around the solar system year after year, without incident.
Not all asteroids reside in the belt, however. Some of these rocks hurtle around the sun in orbits that vary wildly from the plane of the planets. If these masses travel close to our orb, we call them near-Earth objects (NEOs). We currently know of more than 29,000 NEOs, of which a little over a hundred are short-period comets. Perhaps the most famous ice ball, Halley’s comet, is a short-period, near-Earth comet. We had observed these cosmic visitors as early as the 16th century and recognized their periodicities by the early 18th century.
Not until 1898, however, did humans detect the first non-comet NEO. German astronomer C.G. Witt noted a body in an eccentric orbit between Mars and Earth. We dubbed it Eros, after the Greek god of love.
Unlike Ceres, the largest asteroid in the belt, Eros is not massive enough to form a sphere. Instead, Eros looks more like a peanut. At its widest point, Eros is 34.4 kilometers wide (just over 21 miles). It is currently the second-largest NEO, behind a rock named Ganymede. Though it pales in comparison to the size of Ceres and other larger asteroids, Eros is not small by any measure. Eros is above five times larger than the impactor that caused the Chickulub crater, the event which spelled extinction for the dinosaurs.
Obviously, Eros smashing into Earth would not be good.
Fortunately, at the moment, that disaster is impossible. Right now, Eros does not cross the orbit of Earth. It does, however, intersect with the elliptical path of Mars. Because of the gravitational dynamics of the solar system, Eros will not always remain only in the realm of Mars. Models predict that one day Eros will become an Earth-crosser, potentially as early as two million years from now. Transiting our orbit would obviously put the planet at risk, so, if life manages to hold on for a few million trips around the sun, one day we’ll need to worry about Eros going from a love god to a war god.
In the final years of the 20th century and the beginning of the 21st, we added to the superlatives of Eros. It was the first near-Earth object we observed from home, so we decided to make it the first studied from close orbit and the first to field a landing spacecraft.
Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker) launched in 1996 with the purpose of visiting Eros. By 2000, the spacecraft reached the asteroid. For 13 months, NEAR Shoemaker went around the sun in an orbit closely matching that of Eros. NASA slowly pushed the probe closer to the asteroid for most of the year. Then, in February 2001, NEAR Shoemaker made a soft landing on Eros, a monumental feat for spacefaring. For more than two weeks, we received data from a rock just 21 miles across at a distance of 196 million miles. Check out the compilation below of images from the craft as it descended on the craggy body.
At the end of February, NASA shut down NEAR Shoemaker. To this day, the craft rests somewhere in the saddle of Eros.
These explorations always evoke two fascinations. The images we snap thanks to the intellect, work, and imagination of our best scientists reflect both physical beauty and engineering ingenuity. Yet, these achievements only exist because the universe is vast and full of ineffable magnificence. How strange and glorious that pretty rocks fill our voids.