433 Eros

433 Eros

This picture of Eros shows the view looking from one end of the asteroid across the gouge on its underside and toward the opposite end.
Discovery
Discovered by	Carl Gustav Witt
Discovery date	August 13, 1898
Designations
Alternative names	1898 DQ; 1956 PC
Minor planet category	Amor, Mars-crosser asteroid
Orbital characteristics
Epoch October 22, 2004 (JD 2453300.5)
Aphelion	266.762 Gm (1.783 AU)
Perihelion	169.548 Gm (1.133 AU)
Semi-major axis	218.155 Gm (1.458 AU)
Eccentricity	0.223
Orbital period	643.219 d (1.76 a)
Average orbital speed	24.36 km/s
Mean anomaly	320.215°
Inclination	10.829°
Longitude of ascending node	304.401°
Argument of perihelion	178.664°
Physical characteristics
Dimensions	13×13×33 km
Mass	7.2×1015 kg
Mean density	2.4 g/cm³
Surface gravity	0.0059 m/s²
Escape velocity	0.0103 km/s
Rotation period	0.2194 d (5 h 16 min)
Albedo	0.16
Temperature	~227 K
Spectral type	S
Apparent magnitude	+7.1 to +15
Absolute magnitude (H)	11.16

433 Eros is the first found Near-Earth asteroid named after the Greek god of love, Eros (Greek Ἔρως). It is an S-type asteroid about 13 × 13 × 33 km in size, the second-biggest 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 higher than 10km. It is thought to be bigger than the impactor that created Chicxulub Crater in the Yucatán, which has been linked to the extinction of the dinosaurs.

On January 31, 2012, Eros is expected to pass Earth at 0.1787 astronomical units (16.6 million miles) with a visual magnitude of +8.1. 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, not usually, 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 biggest of any body in the Solar System.

Eros was visited by the NEAR Shoemaker probe, which orbited it, taking many pictures 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 (Michel et al., 1996).

The adjectival form which is not used a lot 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 changes a lot, since Eros is not a sphere but a stretched peanut-shaped (or potato- or shoe-shaped) object. The daytime temperature on Eros hovers at about 100 °C and nighttime measurements at −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 bigger rocks strewn across Eros were blown off 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 first 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.

History

As one of the bigger Near Earth Asteroids (NEAs), Eros has played a significant role in history. It was found 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 Aquarius to secure astrometric positions of asteroid 185 Eunike.

In 1975, Eros became the first asteroid to be detected by radar.

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.

References and Notes

• Thomas PC, Robinson MS (1970). "Seismic resurfacing by a single impact on the asteroid 433 Eros". Nature. 436 (7049): 366–9. PMID 16034412

Other websites

• NEAR Shoemaker spacecraft
• NEAR image of the day archive
• Movie: NEAR Shoemaker spacecraft landing
• The Eros Project (OrbDev's attempts at litigation over their property claim)
• Orbital simulation from JPL (Java)
• NEODys (saved output file) showing distance and magnitude Ephemerides for Eros during rare oppositions