2685 Masursky, provisional designation , is a stony Eunomian

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

from the central regions of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

, approximately 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. In January 2000, the Cassini space probe observed the S-type asteroid from afar during its coast to Saturn.

Orbit and classification

''Masursky'' is a member of the Eunomia family (), a prominent

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of stony asteroids and the largest one in the intermediate main belt with more than 5,000 members. 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 Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.11 and an inclination of 12 ° with respect to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

. The asteroid was first observed as at McDonald Observatory in November 1950. The body's observation arc begins with its observation as at Cerro El Roble Observatory in August 1973, nearly 8 years prior to its official discovery observation at Anderson Mesa.

Cassini–Huygens flyby

Little was known about ''Masursky'' until the Cassini–Huygens space probe, en route to

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

and

Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...

, 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.

Physical characteristics

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

Diameter and albedo

During its flyby in January 2000, Cassini–Huygens estimated a mean diameter of approximately 15–20 kilometers, based on an

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

of 0.81–1.08 arcseconds just hours before its closest approach. 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 Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

of 0.114.

Rotation period

As of 2018, no rotational

lightcurve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

of ''Masursky'' has been obtained from photometric observations. The body's

rotation period In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...

, spin-axis and shape remain unknown.

Naming

This

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

was named after Harold Masursky (1922–1990), 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 Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...

Mariner 9 Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971, from Spaceport Florida Launch Comp ...

Viking Vikings were seafaring people originally from Scandinavia (present-day Denmark, Norway, and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded, and settled throughout parts of Europe.Roesdahl, pp. 9� ...

, Pioneer Venus, Voyager, as well as on the ''

Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

'' and '' Magellan'' spacecraft. The official naming citation was published by the

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Funct ...

on 4 August 1982 ().