433 Eros

433 Eros is an S-type near-Earth asteroid approximately 34.4×11.2×11.2 kilometres (21.4×7.0×7.0 mi) in size, the second-largest near-Earth asteroid after 1036 Ganymed. It was discovered in 1898 and was the first near-Earth asteroid discovered. It was the first asteroid orbited by an Earth probe (in 2000). It belongs to the Amor group.

Eros is a Mars-crosser asteroid, the first known to come within the orbit of Mars. Objects in such an orbit can remain there for only a few hundred million years before the orbit is perturbed by gravitational interactions. Dynamical integrations suggest that Eros may evolve into an Earth-crosser within as short an interval as two million years, and has a roughly 50% chance of doing so over a time scale of 10⁸–10⁹ years.^[5] It is a potential Earth impactor,^[5] about five times larger than the impactor that created Chicxulub crater and led to the extinction of the dinosaurs.^{[lower-alpha 1]}

The NEAR Shoemaker probe visited Eros twice, first with a 1998 flyby, and then by orbiting it in 2000 when it extensively photographed its surface. On February 12, 2001, at the end of its mission, it landed on the asteroid's surface using its maneuvering jets.

History

Animation of the rotation of Eros.

View from one end of Eros across the gouge on its side towards the opposite end.

At 4.8 km (3.0 mi) across, the crater Psyche is Eros's second largest.

Regolith of Eros, seen during NEAR's descent; area shown is about 12 meters (40 feet) across

Orbital diagram of Eros with locations on May 7, 2013

Discovery

Eros was discovered on 13 August 1898 by Gustav Witt in Berlin and Auguste Charlois at Nice.^[6] Witt was taking a 2-hour exposure of Beta Aquarii to secure astrometric positions of asteroid 185 Eunike.^[7]

Later studies

During the opposition of 1900–1901, a worldwide program was launched to make parallax measurements of Eros to determine the solar parallax (or distance to the Sun), with the results published in 1910 by Arthur Hinks of Cambridge.^[8] A similar program was then carried out, during a closer approach, in 1930–1931 by Harold Spencer Jones.^[9] The value obtained by this program was considered definitive until 1968, when radar and dynamical parallax methods became more important.

Eros was the first asteroid detected by the Arecibo Observatory's radar system.^[10][11]

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

Name

Eros is named after the Greek god of love, Erōs. It is pronounced /ˈɪərɒs/ EER-os or sometimes /ˈɛrɒs/ ERR-os. The rarely used adjectival form of the name is Erotian /ᵻˈroʊʃən/. Eros is also the first masculine name for an asteroid.^[12]

Physical characteristics

A composite image of the north polar region, with the craters Psyche above and Himeros below. The long ridge Hinks Dorsum, believed to be a thrust fault,^[13] can be seen snaking diagonally between them. The smaller crater in the foreground is Narcissus.

Size comparison of Vesta, Ceres and Eros.

Surface gravity depends on the distance from a spot on the surface to the center of a body's mass. Eros's surface gravity varies greatly because 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 (373 K) at perihelion. Nighttime measurements fall near −150 °C (123 K). Eros's density is 2.67 g/cm³, 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 an impact approximately 1 billion years ago.^[14] (The crater involved was proposed to be named "Shoemaker", but is not recognized as such by the International Astronomical Union (IAU), and has been formally designated Charlois Regio.) This event 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.^[15]

It is theorized that seismic shockwaves propagated through the asteroid, shaking smaller craters into rubble. Since Eros is irregularly shaped, parts of the surface antipodal to the point of impact can be within 9 kilometres of the impact point (measured in a straight line through the asteroid) even though some intervening parts of the surface are more than 9 kilometres away in straight-line distance. A suitable analogy would be the distance from the top centre of a bun to the bottom centre as compared to the distance from the top centre to a point on the bun's circumference: top-to-bottom is a longer distance than top-to-periphery when measured along the surface but shorter than it in direct straight-line terms.^[15]

Compression from the same impact is believed to have created the thrust fault Hinks Dorsum.^[13]

Data from the Near Earth Asteroid Rendezvous spacecraft collected on Eros in December 1998 suggests that it could contain 20,000 billion kilograms of aluminum and similar amounts of metals that are rare on Earth, such as gold and platinum.^[16]

Visibility from Earth

On January 31, 2012, Eros passed Earth at 0.17867 AU (26,729,000 km; 16,608,000 mi),^[17][18] about 70 times the distance to the Moon, with a visual magnitude of +8.1.^[19] During rare oppositions, every 81 years, such as in 1975 and 2056, Eros can reach a magnitude of +7.0,^[4] which is brighter than Neptune and brighter than any main-belt asteroid except 1 Ceres, 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 Earth, its retrograde motion is very small. For example, in January and February 2137, it moves retrograde only 34 minutes in right ascension.^[1]

See also

• Eros in fiction
• List of geological features on 433 Eros

Notes and references

External links

Wikimedia Commons has media related to (433) Eros.

Wikimedia Commons has media related to Photos of 433 Eros by NEAR.

• NEAR Shoemaker spacecraft
• NEAR image of the day archive
  • The Subtle Colors of Eros
  • The Color of Regolith
  • Color View of the Saddle
  • Creating Color Images of Eros
  • Eros Color at Higher Resolution
  • Eros' colors
  • Eros in color
• Movie: NEAR Shoemaker spacecraft landing
• The Eros Project (OrbDev's attempts at litigation over their property claim)
• 3D VRML 433 Eros Model
• 3D shape model of Eros (requires WebGL)
• 433 Eros at the JPL Small-Body Database
  
  • Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
• NEODys (saved output file from 2007) showing distance and magnitude Ephemerides for Eros during rare oppositions
• The Chicxulub Debate In relation to the K-T extinction.
• Dearborn Observatory Records, Northwestern University Archives, Evanston, Illinois Notations as to historical archived work on asteroid 433 Eros.
• Eros at Opposition in 2012 (Royal Astronomical Society of New Zealand)
• NEAR database by ASU (Image search) (Example)
• Eros nomenclature and Eros map with feature names from the USGS planetary nomenclature page

Further reading

• Clark, C. S.; Clark, P. E (March 13–17, 2006). "Using Boundary-based Mapping Projections to Reveal Patterns in Depositional and Erosional Features on 433 Eros". 37th Annual Lunar and Planetary Science Conference. 37: 1189. Bibcode:2006LPI....37.1189C. 
• Riner, M. A.; et al. (November 2008). "Global survey of color variations on 433 Eros: Implications for regolith processes and asteroid environments". Icarus. 198 (1): 67–76. Bibcode:2008Icar..198...67R. doi:10.1016/j.icarus.2008.07.007.