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2685 Masursky, provisional designation 1981 JN, is a stony Eunomian asteroid from the central regions of the asteroid belt, approximately 11 kilometers (6.8 miles) in diameter. It was discovered on 3 May 1981, by American astronomer Edward Bowell at the Anderson Mesa Station near Flagstaff, Arizona, and named after American planetary geologist Harold Masursky.[1] In January 2000, the Cassini space probe observed the S-type asteroid from afar during its coast to Saturn.[7]

2685 Masursky
Asteroid 2685Masurky.png
Masursky imaged by Cassini–Huygens in January 2000
Discovery [1]
Discovered byE. Bowell
Discovery siteAnderson Mesa Stn.
Discovery date3 May 1981
MPC designation(2685) Masursky
Named after
Harold Masursky[1]
(American planetary geologist)
1981 JN · 1950 VO
1973 QF · 1975 XJ5
1977 KU
main-belt[1][2] · (middle)
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc44.58 yr (16,282 d)
Aphelion2.8522 AU
Perihelion2.2874 AU
2.5698 AU
4.12 yr (1,505 d)
0° 14m 21.48s / day
Physical characteristics
Mean diameter
10.744±0.170 km[4]

Orbit and classificationEdit

Masursky is a member of the Eunomia family (502),[3] a prominent family of stony asteroids and the largest one in the intermediate main belt with more than 5,000 members.[8]

It orbits the Sun in the central main-belt at a distance of 2.3–2.9 AU once every 4 years and 1 month (1,505 days; semi-major axis of 2.57 AU). Its orbit has an eccentricity of 0.11 and an inclination of 12° with respect to the ecliptic.[2] The asteroid was first observed as 1950 VO at McDonald Observatory in November 1950. The body's observation arc begins with its observation as 1973 QF at Cerro El Roble Observatory in August 1973, nearly 8 years prior to its official discovery observation at Anderson Mesa.[1]

Cassini–Huygens flybyEdit

Little was known about Masursky until the Cassini–Huygens space probe, en route to Jupiter and Saturn, flew past it on 23 January 2000. Because Cassini passed the asteroid at a distance of 1.6 million kilometers (approximately 4 lunar distances), the images it returned showed nothing more than a dot.[7]

Physical characteristicsEdit

Cassini's observations had cast some doubt on its composition,[7] but later ground-based spectroscopy has confirmed its stony S-type spectrum,[6] which is also the Eunomia family's overall spectral type.[8]:23

Diameter and albedoEdit

During its flyby in January 2000, Cassini–Huygens estimated a mean-diameter of approximately 15–20 kilometers, based on an angular diameter of 0.81–1.08 arcseconds just hours before its closest approach.[7] According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Masursky measures 10.744 kilometers in diameter and its surface has an albedo of 0.114.[4][5]

Rotation periodEdit

As of 2018, no rotational lightcurve of Masursky has been obtained from photometric observations. The body's rotation period, spin-axis and shape remain unknown.[2]


This minor planet was named after Harold Masursky (1923–1990), a planetary geologist at the USGS Astrogeology Science Center of the U.S. Geological Survey, in Flagstaff, Arizona. Masursky worked on numerous space missions and programs including Ranger, Surveyor, Lunar Orbiter, Apollo, Mariner 9, Viking, Pioneer Venus, Voyager, as well as on the Galileo and Magellan spacecrafts.[1] The official naming citation was published by the Minor Planet Center on 4 August 1982 (M.P.C. 7158).[9]


  1. ^ a b c d e f "2685 Masursky (1981 JN)". Minor Planet Center. Retrieved 7 April 2018.
  2. ^ a b c d e "JPL Small-Body Database Browser: 2685 Masursky (1981 JN)" (2018-03-27 last obs.). Jet Propulsion Laboratory. Retrieved 7 April 2018.
  3. ^ a b "Asteroid 2685 Masursky – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 26 October 2019.
  4. ^ a b Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121.
  5. ^ a b Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8.
  6. ^ a b Lazzaro, Daniela; Mothé-Diniz, Thaís.; Carvano, Jorge M.; Angeli, Cláudia A.; Betzler, Alberto S.; Florczak, Marcos; et al. (December 1999). "The Eunomia Family: A Visible Spectroscopic Survey". Icarus. 142 (2): 445–453. Bibcode:1999Icar..142..445L. doi:10.1006/icar.1999.6213.
  7. ^ a b c d "PIA02449: Masursky". NASA/JPL – Photojournal. 11 February 2000. Retrieved 7 April 2018.
  8. ^ a b Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). Identification and Dynamical Properties of Asteroid Families. Asteroids IV. pp. 297–321. arXiv:1502.01628. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.
  9. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 7 April 2018.

External linksEdit