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433 Eros

433 Eros (irr'-os) is the first discovered Near-Earth asteroid, named after the Greek god of love, Eros (Greek Ἔρως). It is an S-type asteroid approximately 13 × 13 × 33 km in size, the second-largest near-Earth asteroid (NEA) after 1036 Ganymed, belonging to the Amors. It is a Mars-crosser asteroid and was the first asteroid that was known to come within the orbit of Mars. Eros is one of the few NEAs with a maximum diameter greater than 10 km. It is believed to be larger than the impactor that created Chicxulub Crater in the Yucatán, which has been linked to the extinction of the dinosaurs.

Eros was visited by the NEAR Shoemaker probe, which orbited it, taking extensive photographs of its surface, and, on February 12 2001, at the end of its mission, landed on the asteroid's surface using its maneuvering jets.

Objects in an orbit like Eros can exist for only a few hundred million years before the orbit is perturbed by gravitational interactions. Simulations suggest that Eros may evolve into an Earth-crosser within 2 million years.

The rarely-used adjectival form of the name Eros is Erotian ().

Physical characteristics

Surface gravity depends on the distance from a spot on the surface to the center of a body's mass. The Erotian surface gravity varies greatly, since Eros is not a sphere but an elongated peanut-shaped (or potato- or shoe-shaped) object. The daytime temperature on Eros can reach about 100 °C at perihelion. Nighttime measurements fall near −150 °C. Eros's density is 2,400 kg/m³, about the same as the density of Earth's crust. It rotates once every 5.27 hours.

NEAR scientists have found that most of the larger rocks strewn across Eros were ejected from a single crater in a meteorite collision approximately 1 billion years ago. This impact may also be responsible for the 40 percent of the Erotian surface that is devoid of craters smaller than 0.5 kilometers across. It was originally thought that the debris thrown up by the collision filled in the smaller craters. An analysis of crater densities over the surface indicates that the areas with lower crater density are within 9 kilometers of the impact point. Some of the lower density areas were found on the opposite side of the asteroid but still within 9 kilometers.

It is theorized that seismic shockwaves propagated through the asteroid, shaking smaller craters into rubble. Since Eros is irregularly shaped, a 9 kilometer straight line through the asteroid can reach locations that would be further away if travelling across the surface, thus leading to the uneven pattern of crater density on the surface.

Eros contains more gold than the total amount of gold ever extracted on Earth.

History

As one of the larger Near Earth Asteroids (NEAs), Eros has played a significant role in history. It was discovered on the same night (13 August 1898) by Gustav Witt in Berlin and Auguste Charlois at Nice. Witt was taking a 2 hour exposure of Beta Aquarii to secure astrometric positions of asteroid 185 Eunike.

During the opposition of 1900-1901, a world-wide program was launched to make parallax measurements of the asteroid to determine the solar parallax (or distance to the sun), with the results published in 1910 by Arthur Hinks of Cambridge. A similar program was then carried out, during a closer approach, in 1930-1931 by Harold Spencer Jones. The value obtained by this program was considered definitive until 1968, when greater faith was placed in radar and dynamical parallax methods.

Eros was one of the first asteroids to be visited by a spacecraft, and the first to be orbited and soft-landed on. NASA spacecraft NEAR Shoemaker entered orbit around Eros in 2000, and came to rest on its surface in 2001.

Visibility from Earth

On January 31, 2012, Eros is expected to pass Earth at 0.179 astronomical units (16.6 million miles) with a visual magnitude of +8.5. But during rare oppositions, every 81 years, such as in 1975 and 2056, Eros can reach a magnitude of +7.1, which is brighter than Neptune and brighter than any main belt asteroid except 4 Vesta and, rarely, 2 Pallas and 7 Iris. Under this condition, the asteroid actually appears to stop, but unlike the normal condition for a body in heliocentric conjunction with the Earth, it never appears to be retrograde. Its synodic period of over 846 Earth days is among the largest of any body in the Solar System.

Legal controversy

In an experimental legal case, Eros was claimed as property by Gregory W. Nemitz of OrbDev. According to the Homestead principle, Nemitz argued that he had the right to claim ownership of any celestial body that he made use of; he claimed he had designated Eros a spacecraft parking facility and wished to charge NASA a parking and storage fee of twenty cents per year for NEAR Shoemaker. Nemitz's case was dismissed and an appeal denied.