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433 Eros

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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.
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.
Discovered byCarl Gustav Witt
Discovery timeAugust 13, 1898
Other names1898 DQ; 1956 PC
Mars-crosser asteroid
Reference date October 22, 2004 (JD 2453300.5)
Longest distance from the Sun266.762 Gm (1.783 AU)
Shortest distance from the Sun169.548 Gm (1.133 AU)
Longest distance from the center of its orbital path
("semi-major axis")
218.155 Gm (1.458 AU)
How egg-shaped its orbit is
How long it takes to complete an orbit643.219 d (1.76 a)
Average speed24.36 km/s
Mean anomaly320.215°
Angle above the reference plane
Longitude of where it comes up through the reference plane304.401°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
Size and Other Qualities
Measures13×13×33 km
Mass7.2×1015 kg
Average density2.4 g/cm³
Gravity at its surface0.0059 m/s²
Slowest speed able to escape into space
("escape velocity")
0.0103 km/s
How long it takes to turn around one time0.2194 d (5 h 16 min)
How much light it reflects0.16
Avg. surface temp.~227 K
Light-band group
("spectral type")
Seeming brightness
("apparent magnitude")
+7.1 to +15
True brightness
("absolute magnitude")

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 10 km. 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.[1]

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.


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.[2] Witt was taking a 2 hour exposure of beta Aquarius to secure astrometric positions of asteroid 185 Eunike.[3]

In 1975, Eros became the first asteroid to be detected by radar.[4]

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
  1. Dividing the mass of 433 Eros by its density gives a volume of 3000 km3, while the estimated 5 km radius of the (assumed spherical) Chicxulub Crater impactor yields a volume of only about 520 km3.
  2. Scholl, Hans and Lutz D. Schmadel, "Discovery Circumstances of the First Near-Earth Asteroid (433) Eros", Beiträge zur Astronomiegeschichte, vol. 5, p. 210-220 (2002)

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