Astronomy:4660 Nereus

From HandWiki
Short description: Near-Earth asteroid
4660 Nereus
Nereus Goldstone PIA24566 animated.gif
Nereus imaged by NASA's Goldstone Solar System Radar on its close approach in 2021
Discovery[1]
Discovered byEleanor F. Helin
Discovery site1.22-m Samuel Oschin telescope
Discovery date28 February 1982
Designations
(4660) Nereus
Pronunciation/ˈnɪəriəs/ NEER-ee-əs[3]
Named afterΝηρεύς Nēreús
Minor planet categoryApollo Apollo
PHA[2]
Orbital characteristics[2]
Epoch 2021-Jul-01 (JD 2459396.5)
Uncertainty parameter 0
Observation arc14647 days (40.10 yr)
|{{{apsis}}}|helion}}2.0250 astronomical unit|AU (303 million km)
|{{{apsis}}}|helion}}0.95287 AU (143 million km)
1.4889 AU (223 million km)
Eccentricity0.36004
Orbital period1.82 yr (663.62 d)
Mean anomaly256.71°
Mean motion0° 32m 33.371s / day
Inclination1.4316°
Longitude of ascending node314.41°
158.12°
Earth MOID0.0031 AU (460 thousand km)
Physical characteristics
Dimensions
  • X = 510±20 m
  • Y = 330±20 m
  • Z = 241+80
    −10
     m
    [4]
Mean radius0.165 km
Surface area0.33+0.04
−0.01
 km2
[4]
Volume0.019±0.003 km3[4]
Rotation period15.1 h (0.63 d)
Sidereal rotation period15.16[4]
Pole ecliptic latitude+80°[4]
Pole ecliptic longitude+25°[4]
Geometric albedo0.54+0.03
−0.09
[4]
Xe
Apparent magnitude12.6 (2021 peak)
9.8 (2060 peak)
Absolute magnitude (H)18.2±0.7[2]


4660 Nereus, provisional designation 1982 DB, is a small (about 0.33 kilometres (0.21 mi)) asteroid. It was discovered by Eleanor 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 important asteroid with a high albedo. It is an Apollo and Mars-crosser, with an orbit that frequently comes 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.[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 around apparent magnitude 12.6, requiring a telescope with around a 100mm objective lens to be visually seen. 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.[citation needed]

Nereus is classified as a potentially hazardous asteroid (PHA),[2] due to both its absolute magnitude (H ≤ 22) and its minimum orbit intersection distance (MOID ≤ 0.05 AU).[7]

Close approaches[2]
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 as E-type, so it could be potentially associated with aubrite meteorites (enstatite achondrites).[4]

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.[9] 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).

Physical characteristics

Collage of Nereus radar images from Goldstone in November 2021

Nereus has been imaged by radar, revealing a slightly elongated shape which would allow for stable orbits around it.[4] Earlier optical measurements had given an estimated diameter of about 330±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 of 510 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]

Exploration

Nereus imaged by the Goldstone radar in 2002

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 robotic spacecraft mission.[11] NEAR was eventually launched, but visited 253 Mathilde and 433 Eros.

See also

  • List of minor planets and comets visited by spacecraft

References

  1. 1.0 1.1 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. doi:10.1016/0019-1035(84)90005-8. Bibcode1984Icar...57...42H. 
  2. 2.0 2.1 2.2 2.3 2.4 2.5 "JPL Small-Body Database Browser: 4660 Nereus (1982 DB)". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=4660&view=OPC. 
  3. "Nereus". Merriam-Webster Dictionary. https://www.merriam-webster.com/dictionary/Nereus. 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Brozovic, Marina (May 2009). "Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target". Icarus 201 (1): 153–156. doi:10.1016/j.icarus.2008.12.029. Bibcode2009Icar..201..153B. http://echo.jpl.nasa.gov/asteroids/4660_Nereus/brozovic.etal.2009.nereus.pdf. 
  5. "NEA delta_v for spacecraft rendezvous missions". http://echo.jpl.nasa.gov/~lance/delta_v/delta_v.rendezvous.html. 
  6. 6.0 6.1 6.2 "NEODys (4660) Nereus". Department of Mathematics, University of Pisa, ITALY. https://newton.spacedys.com/neodys/index.php?pc=1.1.8&n=Nereus. 
  7. "NEO Groups". NASA. Archived from the original on November 2, 2016. https://web.archive.org/web/20161102020040/http://neo.jpl.nasa.gov/neo/groups.html. 
  8. "Horizons Batch for 2166-Feb-03 09:09 UT". JPL Horizons. https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%274660%27&START_TIME=%272166-Feb-03%2009:09%27&STOP_TIME=%272166-Feb-04%27&STEP_SIZE=%271+day%27&QUANTITIES=%2720,39%27. Retrieved 2021-11-08. 
  9. Helin, Eleanor F. (Jan/Feb 1991), "Eureka! The Recovery of 1982DB," pp. 12–16, Planetary Report, Planetary Society, Pasadena, CA.
  10. Delbo, Marco (November 2003). "Keck observations of near-Earth asteroids in the thermal infrared". Icarus 166 (1): 116–130. doi:10.1016/j.icarus.2003.07.002. Bibcode2003Icar..166..116D. 
  11. Extended-mission opportunities for a Discovery-class asteroid rendezvous mission

External links