Asteroid 4660 Nereus Makes Four Close Earth Approaches in 21st Century

Summary: Apollo asteroid 4660 Nereus makes four close Earth approaches in the 21st century as the Earth-crosser intersects Earth’s orbit.

Asteroid 4660 Nereus makes its second close Earth approach of the 21 century on Saturday, Dec. 11, 2021: Courtesy NASA/JPL-Caltech, via NASA JPL Solar System Dynamics

Earth-crossing asteroid 4660 Nereus makes four close Earth approaches in the 21st century as the Apollo asteroid crosses Earth’s orbit at center-to-center distances of less than 0.05 astronomical units.

NASA (National Aeronautics and Space Administration) Jet Propulsion Laboratory’s (JPL) Center for Near Earth Object Studies (CNEOS) calculates four close Earth approaches by asteroid 4660 Nereus between 2002 and 2071.

The asteroid’s first close Earth approach in the 21st century happened Tuesday, Jan. 22, 2002, at approximately 12:23 TDB (Barycentric Dynamical Time; Temps Dynamique Barycentrique). TDB is a relativistic spacetime coordinate time standard that considers the theory of relativity’s time dilation in astronomical calculations.

The close-approach (CA) nominal, or most likely, distance measures Earth’s center to the near Earth object’s (NEO) center. CNEOS calculations for 4660 Nereus are given in astronomical units (au) and in lunar distance (LD).

An astronomical unit approximates the average distance of 150 million kilometers between Earth and the sun. The International Astronomical Union defines an astronomical unit as equating to exactly 149,597,870,700 meters.

Lunar distance, also known as Earth-moon distance, is an astronomical unit of measure expressing the average distance from Earth’s center to the moon’s center. Lunar distance is based on the mean major semi-axis, which is one-half of the longest diameter of the moon’s elliptical orbit. The Center for Near Earth Object Studies places the mean semi-major axis at 384,400 kilometers, or about 0.002570 astronomical units.

The close-approach nominal distance Jan. 22, 2002, was calculated at 0.02902 astronomical units (4,341,330.20 kilometers). The lunar distance was given at 11.30 (4,343,720 kilometers). The CNEOS table placed the asteroid’s velocity relative to Earth at close approach at 5.42 kilometers per second (3.36 miles per second).

Asteroid 4660 Nereus makes a second close-approach in 2021. The event is expected Saturday, Dec. 11, 2021, at approximately 13:51 TDB.

The nominal close-approach distance Dec. 11, 2021, is calculated at 0.02630 astronomical units (3,934,423.99 kilometers). The lunar distance will measure 10.23 (3,932,412 kilometers). The asteroid will be moving at a relative velocity of 6.58 kilometers per second (4.08 miles per second).

The next close approach, the asteroid’s third in the 21st century, is slated for 2060. The close approach will take place Monday, Feb. 14, 2060, at approximately 06:55 TDB.

The nominal close-approach distance Feb. 14, 2060, is calculated at 0.00801 astronomical units (1,198,278.94 kilometers). The lunar distance will measure 3.12 (1,199,328 kilometers). The asteroid’s relative velocity will reach 6.33 kilometers per second (3.93 miles per second).

The fourth and last close approach made in the 21st century by 4660 Nereus will occur in 2071. The close approach is expected Wednesday, Feb. 4, 2071, at approximately 18:32 TDB.

The nominal close-approach distance Feb. 4, 2071, is calculated at 0.01494 astronomical units (2,234,992.18 kilometers). The lunar distance will measure 5.81 (2,233,364 kilometers). The asteroid will achieve a relative velocity of 5.68 kilometers per second (3.52 miles per second).

The first and third close approaches in the 21st century mark the century’s farthest and closest Earth-Nereus distances, respectively, achieved by 4660 Nereus. The asteroid’s Earth-orbit crossing in 2060 will bring Nereus approximately 3,143,051 kilometers (1,953,001 miles) closer to Earth than its Earth-orbit crossing in 2002.

American astronomer Eleanor Helin (Nov. 19, 1932-Jan. 25, 2009) discovered asteroid 4660 Nereus during an observing weekend at northern San Diego County’s Palmor Observatory in 1982 with American astrogeologist and comet and minor planet discoverer Eugene Merle “Gene” Shoemaker (April 28, 1928-July 19, 1997). She noted the asteroid on a plate they obtained Sunday, Feb. 28, 1982, with Palomar’s 48-inch (1.22-meter) Samuel Oschin telescope.

NASA Jet Propulsion Laboratory’s Solar System Dynamics website classifies 4660 Nereus (1982 DB) as an Apollo asteroid and as a potentially hazardous asteroid (PHA). CNEOS defines Apollo asteroids as Earth-crossing near-Earth asteroids (NEAs) with major semi-axes that are larger than Earth’s major semi-axes of 1.0 astronomical units. Also, Apollo asteroids have perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”) distances that are less than Earth’s aphelion (Ancient Greek: ἀπό, apó, “from” + ἥλιος, hḗlios, “sun”) distance of 1.017 astronomical units.

Potentially hazardous asteroids have an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 astronomical units or less and an absolute magnitude (H) of 22.0 or brighter. NASA JPL Solar System Dynamics website profiles Nereus with an Earth MOID of 0.00315334 astronomical units and an absolute magnitude value of 18.2. CNEOS explains an asteroid’s absolute magnitude as the visual magnitude recorded by an observer for the asteroid’s placement one astronomical unit away from both the observer and the sun and at zero, or full, phase angle.

The takeaways for four close Earth approaches made by asteroid 4660 Nereus in the 21st century are that the closest approach will occur Monday, Feb. 14, 2060, the farthest close approach happened Tuesday, Jan. 22, 2002, and that the next close approach will take place Saturday, Dec. 11, 2021.

porkchop plot of mission options from Earth to 4660 Nereus between Jan. 1, 2019, and Dec. 26, 2023; for example, three hypothetical missions departing in 2021 (April 20, Aug. 28, Nov. 26, respectively), have short flight times (230 days, 120 days, 10 days, respectively) and arrive in December (Dec. 6, Dec. 26, Dec. 6, respectively), the month of Nereus’ second close approach in the 21st century: Courtesy NASA/JPL-Caltech, via NASA JPL Solar System Dynamics

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Asteroid 4660 Nereus makes its second close Earth approach of the 21 century on Saturday, Dec. 11, 2021: Courtesy NASA/JPL-Caltech, via NASA JPL Solar System Dynamics @ https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=4660%20nereus;old=0;orb=1

porkchop plot of mission options from Earth to 4660 Nereus between Jan. 1, 2019, and Dec. 26, 2023; for example, three hypothetical missions departing in 2021 (April 20, Aug. 28, Nov. 26, respectively), have short flight times (230 days, 120 days, 10 days, respectively) and arrive in December (Dec. 6, Dec. 26, Dec. 6, respectively), the month of Nereus’ second close approach in the 21st century: Courtesy NASA/JPL-Caltech, via NASA JPL Solar System Dynamics @ https://ssd.jpl.nasa.gov/?mdesign_server&des=4660

For further information:

Chodas, Paul. “4660 Nereus (1982 DB).” NASA Jet Propulsion Laboratory Center for Near Earth Object Studies > Close Approaches > NEOs.
Available @ https://cneos.jpl.nasa.gov/ca/

Chodas, Paul. “NEO Basics.” NASA Jet Propulsion Laboratory Center for Near Earth Object Studies > About.
Available @ https://cneos.jpl.nasa.gov/about/neo_groups.html

Green, Daniel W.E. “1982 DB.” Central Bureau for Astronomical Telegrams > IAU Circular No. 5092. Sept. 18, 1990.
Available @ http://www.cbat.eps.harvard.edu/iauc/05000/05092.html#Item1

Helin, Eleanor F. “Discovering an Asteroid.” The Planetary Report, vol. II, no. 4 (July/August 1982): 4-6.
Available @ https://planetary.s3.amazonaws.com/assets/tpr/pdf/tpr-1982-v02n4.pdf

Helin, Eleanor F. “Eureka! The Recovery of 1982DB.” The Planetary Report, vol. XI, no. 1 (January/February 1991): 16.
Available @ https://planetary.s3.amazonaws.com/assets/tpr/pdf/tpr-1991-v11n1.pdf

Helin, Eleanor F. “Help Name 1982DB.” The Planetary Report, vol. XI, no. 1 (January/February 1991): 17.
Available @ https://planetary.s3.amazonaws.com/assets/tpr/pdf/tpr-1991-v11n1.pdf

Helin, Eleanor F.; Neal D. Hulkower; and David F. Bender. “The Discovery of 1982 DB, the Most Accessible Asteroid Known.” Icarus, vol. 57, issue 1 (January 1984): 42-47.

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Malik, Tariq. “NASA Maps Dangerous Asteroids That May Threaten Earth (Photos).” Space.com > Science & Astronomy. Aug. 14, 2013.
Available @ https://www.space.com/22369-nasa-asteroid-threat-map.html

Marriner, Derdriu. “Eleanor Helin Discovered Asteroid 4660 Nereus in February 1982.” Earth and Space News. Wednesday, Feb. 26, 2020.
Available @ https://earth-and-space-news.blogspot.com/2020/02/eleanor-helin-discovered-asteroid-4660.html

Marriner, Derdriu. “Robert Cutler Named Helin 1982 Asteroid Discovery 4660 Nereus in 1991.” Earth and Space News. Wednesday, March 4, 2020.
Available @ https://earth-and-space-news.blogspot.com/2020/03/robert-cutler-named-helin-1982-asteroid.html

Marsden, Brian G. “1982 DB.” Central Bureau for Astronomical Telegrams > IAU Circular No. 3675. March 5, 1982.
Available @ http://www.cbat.eps.harvard.edu/iauc/03600/03675.html

Marsden, Brian G. “1982 DB.” Central Bureau for Astronomical Telegrams > IAU Circular No. 3677. March 10, 1982.
Available @ http://www.cbat.eps.harvard.edu/iauc/03600/03677.html

Minor Planet Center. “(4660) 1982 DB.” Minor Planet Circular 17416. Dec. 2, 1990.
Available @ https://www.minorplanetcenter.net/iau/ECS/MPCArchive/1990/MPC_19901202.pdf

Minor Planet Center. “(4660) Nereus = 1982 DB.” Minor Planet Circular 19338. Nov. 21, 1991.
Available @ https://www.minorplanetcenter.net/iau/ECS/MPCArchive/1991/MPC_19911121.pdf

NASA JPL Solar Systems Dynamics. "4660 Nereus (1982 DB) Orbital Elements." NASA Jet Propulsion Laboratory (JPL) Solar System Dynamics (SSD) > NASA JPL Small-Body Database Browser.
Available @ https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=nereus;old=0;orb=1;cov=0;log=0;cad=0#elem

NASA JPL Solar Systems Dynamics. "4660 Nereus (1982 DB) Mission Design." NASA Jet Propulsion Laboratory (JPL) Solar System Dynamics (SSD) > JPL Small-Body Database Browser > JPL Small-Body Mission-Design Tool.
Available @ https://ssd.jpl.nasa.gov/?mdesign_server&des=4660

NEODyS. “(4660) Nereus: Close Approaches.” NEODyS-2 > Objects.
Available @ https://newton.spacedys.com/neodys/index.php?pc=1.1.8&n=nereus

Ostro, Steven J., Dr. “4660_Nereus Planning.” Asteroid Radar Research > 1010 Radar-Detected Asteroids and Comets > 851 Near-Earth Asteroids.
Available @ https://echo.jpl.nasa.gov/asteroids/Nereus/4660_Nereus_planning.html

van der Hucht, Karel A. “2021, Dec 11 Asteroid 4660 Nereus.” IAU International Astronomical Union > IAU for the Public > Themes > Near Earth Asteroids (NEAs): A Chronology of Milestones -- Page 3: 2011-2880. Last updated Oct. 7, 2013.
Available @ https://www.iau.org/public/themes/neo/nea3/

Yeomans, Donald K. “Naming an Asteroid.” The Planetary Report, vol. XI, no. 6 (November/December 1991): 6.
Available @ https://planetary.s3.amazonaws.com/assets/tpr/pdf/tpr-1991-v11n6.pdf