4337 Arecibo
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4337 Arecibo ( ''prov. designation'': ) is a
binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...
Themistian asteroid The Themis family (''adj. Themistian''; ) is a family of carbonaceous asteroids located in the outer portion of the asteroid belt, at a mean distance of 3.13 AU from the Sun. It is one of the largest families with over 4700 known members, and co ...
from the outer regions of the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
, approximately in diameter. It was discovered on 14 April 1985, by American astronomer
Edward Bowell Edward L. G. "Ted" Bowell (born 1943 in London), is an American astronomer. Bowell was educated at Emanuel School London, University College, London, and the University of Paris. He was principal investigator of the Lowell Observatory Near-Earth ...
at the Anderson Mesa Station near Flagstaff, Arizona, in the United States. It was named after the
Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science ...
in Puerto Rico. It has a relatively large minor-planet moon that was discovered in stellar occultation observations by David Gault and Peter Nosworthy in May 2021, distinguishing it as the first asteroid moon discovered and confirmed solely using the occultation method.


History


Discovery

This asteroid was discovered by American astronomer
Edward Bowell Edward L. G. "Ted" Bowell (born 1943 in London), is an American astronomer. Bowell was educated at Emanuel School London, University College, London, and the University of Paris. He was principal investigator of the Lowell Observatory Near-Earth ...
while measuring a pair of images taken with the
Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...
's 0.33-meter
astrograph An astrograph (or astrographic camera) is a telescope designed for the sole purpose of astrophotography. Astrographs are mostly used in wide-field astronomical surveys of the sky and for detection of objects such as asteroids, meteors, and ...
on 14 April 1985, located at the Anderson Mesa Station near Flagstaff, Arizona, in the United States. The discovery observations were 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. Function ...
on 4 May 1985. In September 1985, astronomers Kiichirō Furukawa and Lutz D. Schmadel both identified the asteroid in prediscovery observations from March and April 1979, while Furukawa independently found earlier prediscovery observations from April 1933. With these prediscovery observations linked, the asteroid's orbit was significantly improved and eventually received its permanent minor planet number of 4337 from the Minor Planet Center on 11 January 1990.


Naming

The asteroid was named after the
Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science ...
in Puerto Rico, home to the world's largest filled-aperature radio telescope in the 20th century. The name was proposed by radar astronomer Steven J. Ostro, in recognition of the observatory's indispensable contributions to the characterization of Solar System bodies including asteroids. The official naming citation was published by the Minor Planet Center on 8 June 1990.


Occultations and satellite discovery

On 19 May 2021, two
amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers ...
s, David Gault and Peter Nosworthy, observed Arecibo passing in front of a magnitude 13.6 star and blocking out its light from New South Wales, Australia. Each observed the stellar occultation using high-speed video cameras attached to their 30-cm aperture telescopes at their home observatories, separated from each other by across (perpendicular) and along (parallel) the path of Arecibo's shadow across Earth. They detected a two-second-long occultation starting at 17:58 UTC, but then unexpectedly detected a secondary, shorter-duration occultation three seconds later. The observed drop in the star's brightness for both events was much greater than would be expected for a
double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...
with one component occulted, leading Gault and Nosworthy to the conclusion that the secondary occultation was more likely caused by a
natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons ...
orbiting Arecibo. Several days after the discovery of Arecibo's satellite, other occultation astronomers were alerted to follow up in another occultation event by Arecibo over North America on 9 June 2021. Richard Nolthenius and Kirk Bender, separated from each other by across and along Arecibo's shadow path, successfully observed the 9 June 2021 occultation from central California. As Arecibo passed in front of a magnitude 12.0 star, they detected the primary two-second-long occultation starting at 10:58 UTC and then the satellite make a secondary occultation three seconds later, confirming the existence of Arecibo's satellite. The satellite discovery and confirmation results from the May and June 2021 occultations were formally published by
Central Bureau for Astronomical Telegrams The Central Bureau for Astronomical Telegrams (CBAT) is the official international clearing house for information relating to transient astronomical events. The CBAT collects and distributes information on comets, natural satellites, novae, su ...
on 20 June 2021. Discoverers Gault and Nosworthy recognize Arecibo's satellite as the first asteroid moon discovered by amateur astronomers, and confirmed using the occultation method. On 30 June 2021, astronomers across the United States prepared for another occultation by Arecibo to further follow up on its satellite, but majority of them experienced technical difficulties and unfavorable weather conditions, resulting in only 5 out of 15 different sites making successful observations. Only 3 of the 5 successful sites reported positive detections (Nolthenius, Bender, and Christopher Kitting of CSU East Bay reported positives) with a single occultation; the other two had misses and did not detect the satellite. It is possible the satellite and main body were a blended image, given the close orbit later determined.


Orbit and classification

Arecibo is a Themistian asteroid that belongs to the
Themis family The Themis family (''adj. Themistian''; ) is a family of carbonaceous asteroids located in the outer portion of the asteroid belt, at a mean distance of 3.13 AU from the Sun. It is one of the largest families with over 4700 known members, and cons ...
(), a very large
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
aceous asteroids named after their
parent body In meteoritics, a parent body is the celestial body from which originates a meteorite or a class of meteorites. Identification The easiest way to correlate a meteorite with a parent body is when the parent body still exists. This is the case fo ...
24 Themis. Arecibo orbits the Sun in the outer main-belt at a distance of 3.0–3.6  AU once every 5 years and 11 months (2,156 days;
semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the lo ...
of 3.27 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- center, in geometry * Eccentricity (graph theory) of a ...
of 0.09 and an
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
of 2 ° with respect to the
ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agai ...
. Because of its low orbital inclination, Arecibo is visible along the ecliptic at
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 ...
s 16–18. Arecibo is too faint to be seen with the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
, even when at its peak brightness of magnitude 16 at
opposition Opposition may refer to: Arts and media * ''Opposition'' (Altars EP), 2011 EP by Christian metalcore band Altars * The Opposition (band), a London post-punk band * '' The Opposition with Jordan Klepper'', a late-night television series on Com ...
—a telescope of at least in
aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...
size is required to see it.


Physical characteristics

The
spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting th ...
of Arecibo is unknown, but it can be assumed to be a carbonaceous C-type, similar to most members of the Themis family. Like most members of the Themis family, Arecibo likely has a highly
porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
internal structure with a low density below , which is indeed implied by its mass determined from the satellite's orbital motion.


Diameter and albedo

Based on occultation observations from 9 June 2021, the primary body of the Arecibo system measures in diameter, assuming that it has a spherical shape. On the other hand,
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
thermal emission measurements by the
Japan Aerospace Exploration Agency The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...
's '' Akari'' and
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...
's
Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2 ...
(WISE) determined smaller diameters of , respectively, with corresponding
geometric albedo In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle) to that of an ''idealized'' flat, fully reflecting, diffusively scattering ( Lambertian) disk w ...
s of 0.10 and 0.08. The discrepancy between the occultation and infrared measurements may be caused by a highly flattened shape for both components of the Arecibo system; in this case the occultation-derived primary diameter would represent the maximum extent of its shape. WISE's estimates for Arecibo's
absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it we ...
range from 11.9 to 12.6, with an average of 12.4 assumed by the Collaborative Asteroid Lightcurve Link. The Minor Planet Center and
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA ...
's Small-Body Database both determine an absolute magnitude of 12.5 based on visible photometry only.


Rotation

In July 2021, a preliminary rotational
lightcurve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
of Arecibo was obtained from photometric observations by Swiss astronomer Raoul Behrend at
Geneva Observatory The Geneva Observatory (french: Observatoire de Genève, german: Observatorium von Genf) is an astronomical observatory at Sauverny (CH) in the municipality of Versoix, Canton of Geneva, in Switzerland. It shares its buildings with the astronomy ...
in Switzerland. Lightcurve analysis gave an approximate
rotation period The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...
of hours with a brightness amplitude of 0.17 magnitude ( U=2). High-precision photometry and
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...
from the ''
Gaia In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthe ...
'' spacecraft confirmed this period and showed that it is equal to the satellite's orbital period, suggesting that the Arecibo primary is in synchronous rotation with the satellite's orbital period. Based on ''Gaia'' photometry, Arecibo's north pole points in the direction of
ecliptic longitude The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System b ...
271° and ecliptic latitude 68°. ''Gaia'' astrometry for the satellite's orbit yields a pole orientation of ecliptic longitude and ecliptic latitude , in agreement with the photometry-derived pole orientation. This suggests the
axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...
of Arecibo primary is aligned with the satellite's orbital inclination at 30° with respect to the ecliptic.


Satellite

Arecibo hosts a relatively large minor-planet moon with a size about half its diameter, forming a binary system. This unnamed satellite orbits closely at an orbital radius of from the primary body of the Arecibo system, completing a full revolution in about . It was discovered by Australian amateur astronomers David Gault and Peter Nosworthy while observing Arecibo occulting a star on 19 May 2021, and was confirmed in another occultation on 9 June 2021.


Orbit

The observed
angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...
between the satellite and primary body in the 19 May and 9 June 2021 occultations were and
milliarcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The nau ...
s, respectively. In July 2021, Nolthenius presented a preliminary analysis suggesting that the satellite's orbital radius should lie in the range of , based on an assumed system density of and an outer orbital stability limit set by
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...
's gravitational influence. Because no photometric measurements of Arecibo's rotation period were available at that time, constraints on the satellite's orbital period were solely limited to the three occultations observed in 2021, which suggested periods of 20 days and its shorter-period aliases of 10 days, 5 days, and 2.5 days. On 13 June 2022, a team of European astronomers led by Paolo Tanga, on behalf of the
European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (120 ...
, published a proof-of-concept analysis of the Arecibo system using high-precision astrometry and photometry from the ''
Gaia In Greek mythology, Gaia (; from Ancient Greek , a poetical form of , 'land' or 'earth'),, , . also spelled Gaea , is the personification of the Earth and one of the Greek primordial deities. Gaia is the ancestral mother—sometimes parthe ...
'' mission, as part of its third data release. They found that Arecibo exhibits periodic oscillations in brightness and position that are both compatible with a period of , consistent with earlier ground-based photometry from July 2021 and establishing the satellite's orbital period. They determined a smaller orbital radius of and an inclination of with respect to the ecliptic, precisely coinciding with the satellite's positions observed in the May and June 2021 occultations. Given the satellite's close proximity to the primary body and coincidence of brightness and position oscillation periods, the satellite is likely in
synchronous orbit A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. Simplified meanin ...
with the primary's rotation period.


Physical characteristics

The initial detection of the satellite in the 19 May 2021 occultation provided poor constraints on its size due to close spacing between the observers' sites. The 9 June 2021 occultation proved to be more reliable with wider spacing between observer sites, providing a best-fit satellite diameter of for an assumed spherical shape for the satellite. Given this diameter estimate, this makes the satellite about half the size of the primary body in the Arecibo system. The satellite is massive enough to induce measurable positional wobbling of the Arecibo primary, although with an unexpectedly low amplitude of up to 2.7 milliarcseconds from ''Gaias view, or 8.5% of the maximum observed angular separation between the satellite and primary. This small positional wobbling of the Arecibo primary implies a very low satellite-to-primary mass ratio relative to the satellite-to-primary diameter ratio, which could either be explained by a highly flattened shape or a very low density for the satellite. Tanga and collaborators favor the high flattening scenario as it yields more realistic density values and can explain the infrared underestimation of the primary's diameter. In this case, the occultation-derived satellite diameter would represent its maximum shape extent and its minimum possible density would be , expected for a highly porous Themistian asteroid.


Notes


References


External links

* Barry, Tony.
4337 Arecibo - a possible binary asteroid?
. Western Sydney Amateur Astronomy Group. 20 May 2021. * Johnston, Wm. Robert.

''Asteroids with Satellites Database''. Johnston's Archive. 30 April 2022. * * {{DEFAULTSORT:Arecibo 004337 Discoveries by Edward L. G. Bowell Named minor planets 004337 004337 19850414