4660 Nereus

4660 Nereus

Asteroid 4660 Nereus (NASA/JPL 2002)
Discovery
Discovered by	Eleanor F. Helin
Discovery site	1.22 m Samuel Oschin telescope
Discovery date	1982-02-28
Designations
MPC designation	4660 Nereus
Named after	Nereus
Minor planet category	Apollo
Orbital characteristics
Epoch 2455000.5 (2009-Jun-18.0)
Aphelion	2.024728773 ± 5.2857e-09 AU
Perihelion	.952348940 ± 4.6552e-09 AU
Semi-major axis	1.488538857 ± 3.8859e-09 AU
Eccentricity	.360212240 ± 3.6302e-09
Orbital period	1.82 ± 7.112e-09 year
Mean anomaly	31.478023 ± 5.8909e-06°
Inclination	1.432741 ± 2.915e-06°
Longitude of ascending node	314.50349 ± 3.3535e-05°
Argument of perihelion	157.97882 ± 3.4694e-05°
Physical characteristics
Dimensions	X = 510 ± 20 m Y = 330 ± 20 m Z = 241+80 −10 m
Surface area	0.33+0.04 −0.01 km2
Volume	0.019 ± 0.003 km3
Sidereal rotation period	15.16 ± 0.04 h
Pole ecliptic latitude	+80°
Pole ecliptic longitude	+25°
Albedo	0.54+0.03 −0.09
Spectral type	Xe
Absolute magnitude (H)	18.2 ± 0.7

4660 Nereus (/ˈnɪəriəs/ NEER-ee-əs; Greek: Νηρέας, provisional designation 1982 DB) is a small (about 0.33 kilometres (0.21 mi)) asteroid. It was discovered by Eleanor F. Helin on February 28, 1982, approximately 1 month after a near pass by the Earth.

Nereus is potentially a very important asteroid. It is an Apollo and Mars-crosser, with an orbit that frequently comes very close to Earth, and because of this it is exceptionally accessible to spacecraft. Indeed, because of its small size and close orbit, its delta-V for rendezvous of ~5 km/s is smaller than the Moon's, which is about 6.3 km/s.

Nereus makes seven approaches to Earth of less than 5 million km between 1900 and 2100. The closest will be in February 2060, at 1.2 million km. The next close approach is in December 2021, when it will be 3.9 million km away. Its orbital period of 1.82 yr also puts it somewhat near a 2:1 orbital resonance with Earth, which means that an approximately 4-year mission could depart for and return from the asteroid on relatively near passes to the Earth.

The asteroid is classified as E-type, so it could be potentially associated with aubrite meteorites (enstatite achondrites).

Spacecraft

Nereus was proposed for visitation by both the private Near Earth Asteroid Prospector (NEAP) probe, and the Japanese sample return mission Hayabusa. However, the NEAP probe was not realized, and the Hayabusa's launch was delayed by 10 months and the probe had to be redirected to 25143 Itokawa.

4660 Nereus was considered as a flyby target of the NEAR unmanned robotic spacecraft mission. NEAR eventually launched, but visited 253 Mathilde and 433 Eros.

Physical characteristics

Nereus has been imaged by radar, revealing a slightly elongated shape which would allow for stable orbits around it. Earlier optical measurements had given an estimated diameter of about 330 ± 50 meters. More recent work on the analysis of the radar data gives a much more detailed shape for Nereus as well as a fairly detailed terrain map of the surface.

Nereus has a generally ellipsoidal shape with dimensions of 510 x 330 x 241 m. On the ends of its longest axis, one end appears narrower and rounder than the other, larger end, making it more of an egg shape. The larger end also appears to have a flatter region on one side of it. Nereus rotates about an axis roughly perpendicular to its longest axis much like a silver spoon spinning on a table.

Name

Although the discoverer is given the opportunity to name the asteroid, Helin donated naming rights to the Planetary Society which organized a naming contest. The winner, Robert M. Cutler, then an employee of NASA contractor The MITRE Corporation, named the asteroid after the ancient Greek proto-god Nereus who had characteristics later attributed to Apollo (prophecy) and Poseidon (a sea god similar to Nereus but with legs rather than a fish tail).

External links

• 4660 Nereus at the JPL Small-Body Database

• Discovery · Orbit diagram · Orbital elements · Physical parameters

• IAUC 3675
• IAUC 3677
• IAUC 3686
• IAUC 5092