4660 Nereus,

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calcu ...

1982 DB, is a small (about ) asteroid. It was discovered by

Eleanor F. Helin Eleanor Francis "Glo" Helin (née Francis, 19 November 1932 – 25 January 2009) was an American astronomer. She was principal investigator of the Near-Earth Asteroid Tracking (NEAT) program of NASA's Jet Propulsion Laboratory. (Some sources gi ...

on 28 February 1982, approximately a month after it passed from Earth. Nereus is potentially an important

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

with a high

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

. It is an

Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...

and

Mars-crosser A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. Some Mars-crossers numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and . Many databases, for i ...

, with an

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

that frequently comes close to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, and because of this it is exceptionally accessible to spacecraft. Indeed, because of its small size and close orbit, its

delta-V Delta-''v'' (more known as "change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as ...

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 on 14 February 2060, at 1.2 million km. The most recent closest approach was on 11 December 2021, when it was 3.9 million km away. During the 2021 approach, the asteroid peaked around

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

12.6, requiring a telescope with around a 100mm

objective lens In optical engineering, the objective is the optical element that gathers light from the object being observed and Focus (optics), focuses the ray (optics), light rays to produce a real image. Objectives can be a single Lens (optics), lens or mirr ...

to be visually seen. Its orbital period of 1.82 yr also puts it somewhat near a 2:1

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...

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. Nereus is classified as a

potentially hazardous asteroid A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...

(PHA), due to both its

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

and its

minimum orbit intersection distance Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits of ...

. The asteroid is classified as E-type, so it could be potentially associated with

aubrite Aubrites are a group of meteorites named for Aubres, a small achondrite meteorite that fell near Nyons, France, in 1836. They are primarily composed of the orthopyroxene enstatite and are often called enstatite achondrites. Their igneous origin ...

meteorites (

enstatite Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and m ...

achondrite An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystalliz ...

s).

Spacecraft

Nereus was proposed for visitation by both the private

Near Earth Asteroid Prospector Asteroid mining is the hypothetical exploitation of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification of asteroids ...

(NEAP) probe, and the Japanese

sample return mission A sample-return mission is a spacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as lo ...

Hayabusa was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis. ''Hayabusa'', formerly known as MUSES-C ...

. 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 25143 Itokawa (provisional designation ) is a sub-kilometer near-Earth object of the Apollo group and a potentially hazardous asteroid. It was discovered by the LINEAR program in 1998 and later named after Japanese rocket engineer Hideo Itokawa ...

. 4660 Nereus was considered as a flyby target of the

NEAR NEAR or Near may refer to: People * Thomas J. Near, US evolutionary ichthyologist * Near, a developer who created the higan emulator Science, mathematics, technology, biology, and medicine * National Emergency Alarm Repeater (NEAR), a form ...

robotic spacecraft mission.Extended-mission opportunities for a Discovery-class asteroid rendezvous mission
/ref> NEAR was eventually launched, but visited

253 Mathilde Mathilde (minor planet designation: 253 Mathilde) is an asteroid in the intermediate asteroid belt, approximately 50 kilometers in diameter, that was discovered by Austrian astronomer Johann Palisa at Vienna Observatory on 12 November 1885. It h ...

and

433 Eros Eros (minor planet designation: (433) Eros), provisional designation is a stony asteroid of the Amor group and the first discovered and second-largest near-Earth object with an elongated shape and a mean diameter of approximately . Visi ...

Physical characteristics

Nereus has been imaged by

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

, revealing a slightly elongated shape which would allow for stable orbits around it. Earlier optical measurements had given an estimated diameter of about 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 . 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 The Planetary Society is an American internationally-active non-governmental nonprofit organization. It is involved in research, public outreach, and political space advocacy for engineering projects related to astronomy, planetary science, and ...

which organized a naming contest.Helin, Eleanor F. (Jan/Feb 1991), "Eureka! The Recovery of 1982DB," pp. 12–16, Planetary Report, Planetary Society, Pasadena, CA. The winner, Robert M. Cutler, then an employee of NASA contractor The MITRE Corporation, named the asteroid after the ancient Greek proto-god

Nereus In Greek mythology, Nereus ( ; ) was the eldest son of Pontus (the Sea) and Gaia (the Earth), with Pontus himself being a son of Gaia. Nereus and Doris became the parents of 50 daughters (the Nereids) and a son ( Nerites), with whom Nereus liv ...

who had characteristics later attributed to Apollo (prophecy) and

Poseidon Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...

(a sea god similar to Nereus but with legs rather than a fish tail).

References

External links

IAUC 3675

* * * {{DEFAULTSORT:Nereus 004660 Discoveries by Eleanor F. Helin Named minor planets 004660 004660 2021211 19820228

Spacecraft

Physical characteristics

Name

See also

References

External links