433 Eros

433 Eros
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Name	433 Eros
Caption	Composite image of 433 Eros from the NEAR Shoemaker mission
Discoverer	Gustav Witt
Discovery date	13 August 1898
Mp category	Amor asteroid, Mars-crosser asteroid
Epoch	31 May 2020 (JD 2459000.5)
Semimajor	1.458 AU
Eccentricity	0.2227
Inclination	10.829°
Asc node	304.401°
Arg peri	178.664°
Mean anomaly	320.215°
Period	1.76 yr (643 days)
Dimensions	34.4 × 11.2 × 11.2 km
Rotation	5.270 h
Spectral type	S-type asteroid
Abs magnitude	10.4

433 Eros is a stony asteroid of the Amor group and the first discovered Near-Earth object found to have an orbit that brings it within the path of Mars. It was the first asteroid to be orbited and later landed upon by a spacecraft, the NEAR Shoemaker probe, which provided a wealth of data on its composition and structure. This elongated body, often described as peanut-shaped, has played a pivotal role in understanding the geology of small Solar System bodies and the early history of the planetesimals that formed the terrestrial planets.

Discovery and naming

The asteroid was discovered on 13 August 1898 by the German astronomer Gustav Witt at the Urania Observatory in Berlin. Independently, on the same night, it was observed by the French astronomer Auguste Charlois at the Nice Observatory. Witt is credited with the discovery, and he named the object Eros, after the Greek god of love, a choice that broke the contemporary convention of naming asteroids after female figures from Greek mythology. This discovery was historically significant as it was the first Near-Earth object found, proving that asteroids could exist in orbits that brought them relatively close to Earth.

Physical characteristics

433 Eros is an elongated, peanut-shaped body classified as an S-type asteroid, indicating a composition of silicate minerals and nickel-iron. Measurements from the NEAR Shoemaker mission determined its dimensions to be approximately 34.4 kilometers in length and 11.2 kilometers in width and thickness, making it the second-largest Near-Earth object. Its surface is heavily cratered and covered with a layer of fine, loose regolith, evidenced by the smooth, dust-filled "ponds" observed in some depressions. The asteroid also features several large boulders, notably the house-sized rock nicknamed "The Big Rock", and a prominent saddle-shaped depression named Himeros.

Orbit and rotation

Eros follows an elliptical orbit around the Sun with a semi-major axis of 1.46 astronomical units, taking about 1.76 Earth years to complete one revolution. Its orbit, which crosses that of Mars, classifies it as both a Mars-crosser asteroid and a member of the Amor asteroid group. The asteroid's rotation is prograde, with a period of approximately 5 hours and 16 minutes. Its rotational axis is tilted, and its orbit is subject to perturbations from the gravitational influences of the Sun, Earth, and Mars, causing its trajectory to change over centuries, with calculations by scientists like Andrea Milani showing it can become an Earth-crosser asteroid over long timescales.

Exploration by NEAR Shoemaker

The primary mission to study this asteroid was conducted by NASA's NEAR Shoemaker spacecraft, named in honor of the planetary scientist Eugene Shoemaker. Launched in 1996, the probe entered orbit around the asteroid on 14 February 2000, becoming the first spacecraft to orbit a small body. During its year-long orbital mission, it mapped the surface in unprecedented detail using instruments like the MSI camera and a X-ray spectrometer. In a dramatic conclusion to the mission, the spacecraft was commanded to descend and made a controlled, surviving touchdown on the surface in the region of the Himeros depression on 12 February 2001, returning valuable data during its descent and from the surface.

Scientific importance

The data returned by NEAR Shoemaker transformed the understanding of S-type asteroids, confirming their link to ordinary chondrite meteorites and providing ground truth for Earth-based observations. The mission revealed a homogeneous interior, evidence of a consolidated structure from a larger parent body, and a surface history shaped primarily by impact cratering. Studies of its craters, like the large Shoemaker Crater, helped calibrate the asteroid cratering chronology. Furthermore, its orbit and physical properties make it a key object for studying the dynamical evolution of Near-Earth objects and assessing potential future resource utilization, as proposed by organizations like the Planetary Society.

Category:Amor asteroids Category:Discoveries by Gustav Witt Category:NEAR Shoemaker