The primary mission of NEAR is to orbit asteroid Eros for approximately 1 year. During that time it will conduct a variety of measurements designed to help understand the composition, mineralogy, and overall characteristics of Eros. If all works out after its baseline mission is completed, NEAR will circle in closer and closer until mission controllers may actually attempt a quasi-soft landing (i.e. a slow motion collision) on Eros itself.

NEAR was originally scheduled to enter orbit around Eros in late 1998. However, software problems caused an aborted firing of the spacecraft's engine and the mission had to be re-planned. Luckily, it was possible to perform subsequent engine firings to cause NEAR and Eros to meet up again. Curiously, NEAR will enter orbit around an asteroid named after the Greek god of love on St. Valentines Day.

NEAR has had two practice encounters with asteroids thus far - one expected, the other unexpected. NEAR passed by asteroid 253 Mathilde in 1997 on its way to Eros and gathered a series of pictures and measurements. Mathilde was found to have a number of immense craters and a rather low density for its size lending support to the idea that it may actually be a loose collection of smaller pieces - a rubble pile of sorts. Then, In 1998, even after NEAR's engine mishap, images and data were obtained from an unplanned flyby of Eros albeit at a distance.

Eros was discovered in 1898 and is one of the largest asteroids known. Eros has an elongated peanut-like shape measuring 40 x 14 x 14 kilometers and rotates once every 5.27 hours. Eros is classified as an Earth Approaching Asteroid. Specifically it is placed in the Amor category of asteroids. Amors have orbits that bring them to within 1.3 AU of the sun (1.3 times Earth's average distance from the sun). Eros orbits around the Sun with a perihelion (closest approach) of 1.13 AU (169,045,593 km) and an aphelion (greatest distance) of 1.78 AU (266,284,209 km).

Eros is classified as being an S type asteroid, one which has a composition of iron- and magnesium-bearing silicates such as pyroxene and olivine mixed together with metals such as nickel and iron. Asteroids with this mixed composition are thought to be remnants of larger asteroids that were originally large enough to have differentiated into different layers as they formed. Over time, these larger asteroids were broken into pieces by repeated impacts.

While the orbit of Eros currently does not cross that of Earth, some data have shown the orbits of objects such as Eros to "wander" over time with a slight, but not negligible chance that it might hit Earth one day. While the chance that Eros itself might strike Earth is small, the chance that another object may do so is greater - hence the intense interest in these objects.