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|Discovered by||G. Witt|
|Discovery site||Berlin Urania Obs.|
|Discovery date||13 August 1898|
|Eros (Greek mythology)|
|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|
|1.76 yr (643 days)|
|0° 33m 35.64s / day|
|Earth MOID||0.1505 AU (58.6 LD)|
|Mars MOID||0.2407 AU|
Eros (minor planet designation: 433 Eros), provisional designation 1898 DQ, is a stony and elongated asteroid of the Amor group and the first discovered and second-largest near-Earth object with a mean diameter of approximately 16.8 kilometers. Visited by the NEAR Shoemaker space probe in 1998, it became the first asteroid ever studied from orbit.
The eccentric asteroid was discovered by German astronomer Carl Gustav Witt at the Berlin Observatory on 13 August 1898, and later named after Eros, a god from Greek mythology; the son of Aphrodite who is identified with the planet Venus.
Eros was discovered on 13 August 1898 by Carl Gustav Witt at Berlin Urania Observatory and Auguste Charlois at Nice Observatory. Witt was taking a two-hour exposure of Beta Aquarii to secure astrometric positions of asteroid 185 Eunike.
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. 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 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.
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. It is a potential Earth impactor, about five times larger than the impactor that created Chicxulub crater and led to the extinction of the dinosaurs.[b]
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 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.
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. (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 theorized 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.
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.
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