4660 Nereus

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4660 Nereus
Nereus.jpg
Asteroid 4660 Nereus (NASA/JPL 2002)
Discovery[1]
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 Apollo
Orbital characteristics[2]
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[3]
Surface area 0.33+0.04
−0.01
km2[3]
Volume 0.019 ± 0.003 km3[3]
Sidereal rotation period 15.16 ± 0.04 h[3]
Pole ecliptic latitude +80°[3]
Pole ecliptic longitude +25°[3]
Albedo 0.54+0.03
−0.09
[3]
Spectral type Xe
Absolute magnitude (H) 18.2 ± 0.7[2]

4660 Nereus (/ˈnɪəriəs/ NEER-ee-əs; Greek: Νηρέας) 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.[1] It is named after Nereus, a Titan in Greek mythology.

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.[4]

Nereus makes seven approaches to Earth of less than 5 million km between 1900 and 2100.[5] The closest will be in February 2060, at 1.2 million km.[5] The next close approach is in December 2021, when it will be 3.9 million km away.[5][6] Its orbital period of 1.82 yr[2] 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.

Spacecraft[edit]

Nereus was scheduled 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. Nonetheless, Nereus may well become a target of future space exploration.[citation needed]

4660 Nereus was considered as a flyby target of the NEAR unmanned robotic spacecraft mission.[7] NEAR eventually launched, but visited 253 Mathilde and 433 Eros.

Physical characteristics[edit]

Nereus has been imaged by radar, revealing a slightly elongated shape which would allow for stable orbits around it.[3] Earlier optical measurements had given an estimated diameter of about 330 ± 50 meters.[8] 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.[3]

External links[edit]

References[edit]

  1. ^ a b Helin, Eleanor F.; Hulkower, Neal D.; Bender, David F. (January 1984). "The discovery of 1982 DB, the most accessible asteroid known". Icarus 57 (1): 42–47. Bibcode:1984Icar...57...42H. doi:10.1016/0019-1035(84)90005-8. 
  2. ^ a b c 4660 Nereus at the JPL Small-Body Database
  3. ^ a b c d e f g h i Brozovic, Marina; et al. (May 2009). "Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target". Icarus 201 (1): 153–156. Bibcode:2009Icar..201..153B. doi:10.1016/j.icarus.2008.12.029. 
  4. ^ "NEA delta_v for spacecraft rendezvous missions". 
  5. ^ a b c "NEODys (4660) Nereus". Department of Mathematics, University of Pisa, ITALY. Retrieved 2009-05-04. 
  6. ^ "Solex". Retrieved 2009-03-03 numbers generated by Solex. 
  7. ^ Extended-mission opportunities for a Discovery-class asteroid rendezvous mission
  8. ^ Delbo, Marco; et al. (November 2003). "Keck observations of near-Earth asteroids in the thermal infrared". Icarus 166 (1): 116–130. Bibcode:2003Icar..166..116D. doi:10.1016/j.icarus.2003.07.002.