4660 Nereus
Encyclopedia
4660 Nereus is a small (about 0.33 kilometre (0.205053003094436 mi)) asteroid. It was discovered by Eleanor F. Helin
on February 28, 1982, approximately 1 month after a near pass by the Earth. 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.
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.
probe, and the Japanese Hayabusa
probe. However, the former project is defunct, and Hayabusa's delay in launching caused it to be redirected to 25143 Itokawa
. Nonetheless, Nereus may well become a target of future space exploration.
, 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 an egg spinning on a table.
Eleanor F. Helin
Eleanor Francis "Glo" Helin was an American astronomer. She was principal investigator of the Near Earth Asteroid Tracking program of NASA's Jet Propulsion Laboratory. Some sources give her name as Eleanor Kay Helin...
on February 28, 1982, approximately 1 month after a near pass by the Earth. It is named after Nereus
Nereus
In Greek mythology, Nereus was the eldest son of Pontus and Gaia , a Titan who with Doris fathered the Nereids, with whom Nereus lived in the Aegean Sea. In the Iliad the Old Man of the Sea is the father of Nereids, though Nereus is not directly named...
, a Titan
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....
in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
.
Nereus is potentially a very important asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
. It is an Apollo
Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth...
and Mars-crosser
Mars-crosser asteroid
A Mars-crosser is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here. They include the two numbered Mars trojans 5261 Eureka and ....
, with an orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
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
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....
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
Year
A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....
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
Nereus was scheduled for visitation by both the private Near Earth Asteroid ProspectorNear Earth Asteroid Prospector
The Near Earth Asteroid Prospector, or NEAP, was a concept for a small innovative commercial spacecraft mission by the private company SpaceDev. The goal was to fly NEAP to a targeted near Earth asteroid residing beyond the Earth's orbit, successfully land one or more scientific instruments on the...
probe, and the Japanese Hayabusa
Hayabusa
was an unmanned spacecraft developed by the Japan Aerospace Exploration Agency to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis....
probe. However, the former project is defunct, and Hayabusa's delay in launching caused it to be redirected to 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
. Nonetheless, Nereus may well become a target of future space exploration.
Physical characteristics
Nereus has been imaged by radarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
, 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 an egg spinning on a table.