433 Eros

(Redirected from Eros (asteroid)) Near-Earth asteroid This article is about the asteroid. For the dwarf planet with a similar name, see Eris (dwarf planet).

433 Eros
Discovery
Eros – 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, can be seen snaking diagonally between them. The smaller crater in the foreground is Narcissus. Watters, (2011)
Discovered by	C. G. Witt
Discovery site	Berlin Urania Obs.
Discovery date	13 August 1898
Designations
MPC designation	(433) Eros
Pronunciation	/ˈɪərɒs/
Named after	Ἔρως, Érōs
Alternative designations	1898 DQ 1956 PC
Minor planet category	NEO Amor (I) Mars-crosser
Adjectives	Erotian /ɛˈroʊʃ(i)ən/
Symbol	(astrological)
Orbital characteristics
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	53.89 yr (19,683 days)
Earliest precovery date	29 October 1893
Aphelion	1.7825 AU
Perihelion	1.1334 AU
Semi-major axis	1.4579 AU
Eccentricity	0.2226
Orbital period (sidereal)	1.76 yr (643 days)
Mean anomaly	71.280°
Mean motion	0° 33 35.64 / day
Inclination	10.828°
Longitude of ascending node	304.32°
Argument of perihelion	178.82°
Earth MOID	0.1505 AU (58.6 LD)
Mars MOID	0.2407 AU
Physical characteristics
Dimensions	16.84±0.06 km (mean diameter) 34.4 × 11.2 × 11.2 km
Mass	(6.687±0.003)×10 kg
Mean density	2.67±0.03 g/cm
Synodic rotation period	5.270 h
Geometric albedo	0.25±0.06
Spectral type	S (Tholen) S (SMASS) B–V = 0.921 U–B = 0.531
Apparent magnitude	7.0–15
Absolute magnitude (H)	11.16

433 Eros is a stony asteroid of the Amor group, and the first discovered, and second-largest near-Earth object. It has an elongated shape and a volume-equivalent diameter of approximately 16.8 kilometers (10.4 miles). Visited by the NEAR Shoemaker space probe in 1998, it became the first asteroid ever studied from its own orbit.

The asteroid was discovered by German astronomer C. G. Witt at the Berlin Observatory on 13 August 1898 in an eccentric orbit between Mars and Earth. It was later named after Eros, a god from Greek mythology, the son of Aphrodite. He is identified with the planet Venus.

History

Discovery

Eros was discovered on 13 August 1898 by Carl Gustav Witt at Berlin Urania Observatory and Auguste Charlois at Nice Observatory and temporarily labeled D.Q. Witt was taking a two-hour exposure of beta Aquarii to secure astrometric positions of asteroid 185 Eunike.

Name

Eros is named after the Greek god of love, Erōs. It was the first minor planet to be given a male name; the break with earlier tradition was made because it was the first near-Earth asteroid discovered.

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 and Charles D. Perrine of the Lick Observatory, University of California. Perrine published progress reports in 1906 and 1908. He took 965 photographs with the Crossley Reflector and selected 525 for measurement. A similar program was then carried out, during a closer approach, in 1930–1931 by Harold Spencer Jones. The value of the Astronomical Unit (roughly the Earth-Sun distance) obtained by this program was considered definitive until 1968, when radar and dynamical parallax methods started producing more precise measurements.

Eros was the first asteroid detected by the Arecibo Observatory's radar system.

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.

Mars-crosser

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 system modeling suggests 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 10~10 years. It is a potential Earth impactor, about five times larger than the impactor that created Chicxulub crater and led to the extinction of the non-avian dinosaurs.

NEAR Shoemaker survey and landing

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

This was the first time a Near Earth asteroid was closely visited by a spacecraft.

Animation of NEAR Shoemaker trajectory from 19 February 1996 to 12 February 2001.
- NEAR Shoemaker
- Eros
- Earth
- Mathilde
- Sun
.
Animation of NEAR Shoemaker's trajectory around 433 Eros from 1 April 2000 to 12 February 2001.
NEAR Shoemaker · 433 Eros

Physical characteristics

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 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/cm, about the same as the density of Earth's crust.

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. (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.

It is thought that seismic shockwaves propagate 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. Compression from the same impact is believed to have created the thrust fault Hinks Dorsum.

A phenomenon named dust ponds were discovered in the asteroid in October 2000. Dust ponds are a phenomenon where pockets of dust are seen in airless celestial bodies. These are smooth deposits of dust accumulated in depressions on the surface of the body (like craters), contrasting from the rocky terrain around them. They typically have different color and albedo compared to the surrounding areas. The asteroid contains lots of large craters more than 200 m in diameter. Their number is near to the saturation point of these craters. But craters smaller than that are relatively low. Suggesting that some process of erasure has covered them up. The floors of some craters are covered with smooth and flat areas (less than 10° slope). Such dust ponds are characterized by slightly bluer colour compared to the surrounding terrain. 334 of such ponds are identified, with a diameter of 10m. 255 of these are larger than 30m, and 231 (or 91%) are found within 30° from equator.

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

Visibility from Earth

On 31 January 2012, Eros passed Earth at 0.17867 AU (26,729,000 km; 16,608,000 mi), about 70 times the distance to the Moon, with a visual magnitude of +8.1. During rare oppositions, every 81 years, such as in 1975 and 2056, Eros can reach a magnitude of +7.0, 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.

In popular culture

In the novel and television series The Expanse, a catastrophic science experiment is unleashed on a civilian population living within tunnels cut through Eros. This so-called "Eros Incident" ends with the asteroid mysteriously breaking its usual orbit and crashing into Venus.

It makes an appearance in the novel (and its film adaptation) Ender's Game by Orson Scott Card, serving as a base for humanity and the location of Command School after having been captured from the invading aliens (the Formics) prior to the initial novel who had used the asteroid as their forward operating base in their previous invasion.

In the Space Angel episode 'Visitors from Outer Space' (title text not quite matching narration), Scott McCloud and his crew are forced to destroy Eros by deflecting it into the Sun, after it becomes a hazard to spacecraft navigation.

It is the setting for the entirety of the plot of the novel Captive Universe by Harry Harrison.

Gallery

Animation of the rotation of Eros
View from one end of Eros across the gouge on its side towards the opposite end
First mosaic image of Eros taken from an orbiting spacecraft
Mosaic image of Eros
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 7 May 2013
Orbital diagram of Eros with locations on 1 January 2018
Size comparison of Vesta, Ceres and Eros
Six views of Eros in approximate natural color from NEAR-Shoemaker in February 2000
Stereo image of Eros

Notes

Ratio of mean diameters is 16.84 km/~10 km; the volume ratio is approximately 4.8 (cubed value).

References

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