 Nereus imaged byNASA'sGoldstone Solar System Radar on its close approach in 2021 | |
| Discovery[1] | |
|---|---|
| Discovered by | Eleanor F. Helin |
| Discovery site | 1.22-mSamuel Oschin telescope |
| Discovery date | 28 February 1982 |
| Designations | |
| (4660) Nereus | |
| Pronunciation | /ˈnɪəriəs/NEER-ee-əs[2] |
Named after | ΝηρεύςNēreús |
Apollo PHA[3] | |
| Orbital characteristics[3] | |
| Epoch 2021-Jul-01 (JD 2459396.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 14647 days (40.10 yr) |
| Aphelion | 2.0250 AU (303 million km) |
| Perihelion | 0.95287 AU (143 million km) |
| 1.4889 AU (223 million km) | |
| Eccentricity | 0.36004 |
| 1.82 yr (663.62 d) | |
| 256.71° | |
| 0° 32m 33.371s / day | |
| Inclination | 1.4316° |
| 314.41° | |
| 158.12° | |
| Earth MOID | 0.0031 AU (460 thousand km) |
| Physical characteristics | |
| Dimensions |
|
| 0.165 km | |
| 0.33+0.04 −0.01 km2[4] | |
| Volume | 0.019±0.003 km3[4] |
| 15.1 h (0.63 d) | |
| 15.16[4] | |
| +25°[4] | |
| +80°[4] | |
| 0.54+0.03 −0.09[4] | |
| Xe | |
| 12.6(2021 peak) 9.8(2060 peak) | |
| 18.2±0.7[3] | |
4660 Nereus (provisional designation1982 DB) is a small (about 0.33 kilometres (0.21 mi)) asteroid. It was discovered byEleanor F. Helin on 28 February 1982, approximately a month after it passed 4.1 million km (11 LD) from Earth.[1]
Nereus is potentially an importantasteroid with a highalbedo. It is anApollo andMars-crosser, with anorbit that frequently comes close toEarth, and because of this it is exceptionally accessible to spacecraft. Indeed, because of its small size and close orbit, itsdelta-V for rendezvous of ~5 km/s is smaller than the Moon's, which is about 6.3 km/s.[5]
Nereus makes seven approaches to Earth of less than 5 million km between 1900 and 2100.[6] The closest will be on 14 February 2060, at 1.2 million km.[6] The most recent closest approach was on 11 December 2021, when it was 3.9 million km away.[6] During the 2021 approach, the asteroid peaked aroundapparent magnitude 12.6, requiring a telescope with around a 100mmobjective lens to be visually seen. Its orbital period of 1.82yr[3] also puts it somewhat near a 2:1orbital 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.[citation needed]
Nereus is classified as apotentially hazardous asteroid (PHA),[3] due to both itsabsolute magnitude(H ≤ 22) and itsminimum orbit intersection distance(MOID ≤ 0.05 AU).[7]
| Date | JPL SBDB nominal geocentric distance | uncertainty region (3-sigma) |
|---|---|---|
| 2021-12-11 | 3934242 km | ± 3 km |
| 2060-02-14 | 1198007 km | ± 234 km |
| 2166-02-03 | 2800000 km | ± 261 thousand km[8] |
The asteroid is classified asE-type, so it could be potentially associated withaubrite meteorites (enstatiteachondrites).[4]
Although the discoverer is given the opportunity to name the asteroid, Helin donated naming rights to thePlanetary Society which organized a naming contest.[9]
The winner, Robert M. Cutler, then an employee of NASA contractor The MITRE Corporation, named the asteroid after the ancient Greek proto-godNereus who had characteristics later attributed to Apollo (prophecy) andPoseidon (a sea god similar to Nereus but with legs rather than a fish tail).
Nereus has been imaged byradar, revealing a slightly elongated shape which would allow for stable orbits around it.[4] Earlier optical measurements had given an estimated diameter of about330±50 meters.[10] 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 of510 m × 330 m × 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.[4]
Nereus was proposed for visitation by both the privateNear Earth Asteroid Prospector (NEAP) probe, and the Japanesesample return missionHayabusa. However, the NEAP probe was not realized, and the Hayabusa's launch was delayed by 10 months and the probe had to be redirected to25143 Itokawa.
4660 Nereus was considered as a flyby target of theNEAR robotic spacecraft mission.[11] NEAR was eventually launched, but visited253 Mathilde and433 Eros.
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