Quaoar (50000 Quaoar),
provisional designation
Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been cal ...
, is a
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
in the
Kuiper belt, a region of icy planetesimals beyond
Neptune. A non-resonant object (
cubewano
A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major a ...
), it measures approximately in diameter, about half the diameter of
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...
. The object was discovered by American astronomers
Chad Trujillo
Chadwick A. Trujillo (born November 22, 1973) is an American astronomer, discoverer of minor planets and the co-discoverer of Eris, the most massive dwarf planet known in the Solar System.
Trujillo works with computer software and has examined ...
and
Michael Brown at the
Palomar Observatory on 4 June 2002.
Signs of water ice on the surface of Quaoar have been found, which suggests that
cryovolcanism
A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is know ...
may be occurring on Quaoar.
A small amount of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
is present on its surface, which can only be retained by the largest Kuiper belt objects.
In February 2007,
Weywot
Weywot, officially (50000) Quaoar I Weywot, is the only known moon of the trans-Neptunian planetoid 50000 Quaoar. Discovered by Michael Brown and T.A. Suer using images acquired by the Hubble Space Telescope on 14 February 2006, its existence wa ...
, a synchronous moon in orbit around Quaoar, was discovered by Brown.
Weywot is measured to be across.
Both objects were named after mythological figures from the Native American
Tongva people
The Tongva ( ) are an Indigenous people of California from the Los Angeles Basin and the Southern Channel Islands, an area covering approximately . Some descendants of the people prefer Kizh as an endonym that, they argue, is more historicall ...
in Southern California.
Quaoar is the Tongva creator deity and
Weywot
Weywot, officially (50000) Quaoar I Weywot, is the only known moon of the trans-Neptunian planetoid 50000 Quaoar. Discovered by Michael Brown and T.A. Suer using images acquired by the Hubble Space Telescope on 14 February 2006, its existence wa ...
is his son.
History
Discovery
![Quaoar discovery animation](https://upload.wikimedia.org/wikipedia/commons/2/27/Quaoar_discovery_animation.gif)
Quaoar was discovered on 4 June 2002 by American astronomers
Chad Trujillo
Chadwick A. Trujillo (born November 22, 1973) is an American astronomer, discoverer of minor planets and the co-discoverer of Eris, the most massive dwarf planet known in the Solar System.
Trujillo works with computer software and has examined ...
and
Michael Brown at the
Palomar Observatory in the
Palomar Mountain Range
Palomar Mountain ( ; es, Monte Palomar ) is a mountain ridge in the Peninsular Ranges in northern San Diego County. It is famous as the location of the Palomar Observatory and Hale Telescope, and known for the Palomar Mountain State Park.
Hist ...
in
San Diego County, California.
The discovery formed part of the Caltech Wide Area Sky Survey, which was designed to search for the brightest
Kuiper belt objects using the Palomar Observatory's 1.22-meter
Samuel Oschin telescope
The Samuel Oschin telescope, also called the Oschin Schmidt, is a Schmidt camera at the Palomar Observatory in northern San Diego County, California. It consists of a 49.75-inch Schmidt corrector plate and a 72-inch (f/2.5) mirror. The instrument ...
.
Quaoar was first identified in images by Trujillo on 5 June 2002, when he noticed a dim, 18.6-
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
object slowly moving among the stars of the
constellation Ophiuchus
Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constella ...
.
Quaoar appeared relatively bright for a distant object, suggesting that it could have a size comparable to the diameter of the
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...
.
To ascertain Quaoar's orbit, Brown and Trujillo initiated a search for archival
precovery images. They obtained several precovery images taken by the
Near-Earth Asteroid Tracking
Near-Earth Asteroid Tracking (NEAT) was a program run by NASA and the Jet Propulsion Laboratory, surveying the sky for near-Earth objects. NEAT was conducted from December 1995 until April 2007, at GEODSS on Hawaii (Haleakala-NEAT; 566), as we ...
survey from various observatories in 1996 and 2000–2002.
In particular, they had also found two archival
photographic plates taken by astronomer
Charles T. Kowal in May 1983,
who at the time was searching for the hypothesized
Planet X
Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century and continued at the start of the 20th with Percival Lowell's ...
at the Palomar Observatory.
From these precovery images, Brown and Trujillo were able to calculate Quaoar's orbit and distance. Additional precovery images of Quaoar have been later identified, with the earliest known found by Edward Rhoads on a photographic plate imaged on 25 May 1954 from the
Palomar Observatory Sky Survey
Palomar may refer to:
Places
* Any of several locations in San Diego County, California:
** Palomar Mountain
** Palomar Observatory, located on Palomar Mountain
** Palomar College in San Marcos, California
** Palomar Medical Center in Escondido, ...
.
Before announcing the discovery of Quaoar, Brown had planned to conduct follow-up observations using the
Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
to measure Quaoar's size.
He had also planned to announce the discovery as soon as possible and found it necessary to keep the discovery information confidential during the follow-up observations.
Rather than submitting his Hubble proposal under
peer review
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer revie ...
, Brown submitted his proposal directly to one of Hubble's operators, who promptly allocated time to Brown.
While setting up the observing algorithm for Hubble, Brown had also planned to use one of the
Keck telescopes in
Mauna Kea, Hawaii, as a part of a study on
cryovolcanism
A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is know ...
on the
moons
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'' ...
of
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
.
This provided him additional time for follow-up observations and took advantage of the whole observing session in July to analyze Quaoar's
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
and characterize its surface composition.
The discovery of Quaoar was formally announced by the
Minor Planet Center in a
Minor Planet Electronic Circular
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
T ...
on 7 October 2002.
It was given the
provisional designation
Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been cal ...
, indicating that its discovery took place during the first half of June 2002.
Quaoar was the 1,512th object discovered in the first half of June, as indicated by the preceding letter and numbers in its provisional designation. On that same day, Trujillo and Brown reported their scientific results from observations of Quaoar at the 34th annual meeting of the
American Astronomical Society's
Division for Planetary Sciences
Division or divider may refer to:
Mathematics
*Division (mathematics), the inverse of multiplication
* Division algorithm, a method for computing the result of mathematical division
Military
*Division (military), a formation typically consisting ...
in
Birmingham, Alabama
Birmingham ( ) is a city in the north central region of the U.S. state of Alabama. Birmingham is the seat of Jefferson County, Alabama's most populous county. As of the 2021 census estimates, Birmingham had a population of 197,575, down 1% fr ...
. They announced Quaoar was the largest Kuiper belt object found yet, surpassing previous record holders
20000 Varuna
20000 Varuna, provisional designation , is a large trans-Neptunian object in the Kuiper belt. It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory. It is na ...
and .
Quaoar's discovery has been cited by Brown as having contributed to the
reclassification of Pluto as a dwarf planet.
Since then, Brown has contributed to the discovery of larger trans-Neptunian objects, including
Haumea
, discoverer =
, discovered =
, earliest_precovery_date = March 22, 1955
, mpc_name = (136108) Haumea
, pronounced =
, adjectives = Haumean
, note = yes
, alt_names =
, named_after = Haumea
, mp_category =
, orbit_ref =
, epoc ...
, ,
Makemake
Makemake (minor-planet designation 136472 Makemake) is a dwarf planet and – depending on how they are defined – the second-largest Kuiper belt object in the classical population, with a diameter approximately 60% that of Pluto. It h ...
and .
Name and symbol
Upon Quaoar's discovery, it was initially given the temporary nickname "Object X" as a reference to Planet X, due to its potentially large size and unknown nature.
At the time, Quaoar's size was uncertain, and its high brightness led the discovery team to speculate that it may be a possible tenth planet. After measuring Quaoar's size with the Hubble Space Telescope in July, the team began considering names for the object, particularly those from
New World
The term ''New World'' is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: Oxford University Press, p. ...
mythologies.
Following the
International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
's (IAU)
naming convention
A naming convention is a convention (generally agreed scheme) for naming things. Conventions differ in their intents, which may include to:
* Allow useful information to be deduced from the names based on regularities. For instance, in Manhatta ...
for
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 ''mino ...
s, non-resonant Kuiper belt objects are to be named after
creation deities.
The team settled on selecting names from
Native American mythologies local to the Palomar Mountain region, the location where they discovered Quaoar. Through
Internet search
A search engine is a software system designed to carry out web searches. They search the World Wide Web in a systematic way for particular information specified in a textual web search query. The search results are generally presented in a ...
ing, the team eventually decided upon the name ''
Kwawar'', the creator god of the
Tongva people
The Tongva ( ) are an Indigenous people of California from the Los Angeles Basin and the Southern Channel Islands, an area covering approximately . Some descendants of the people prefer Kizh as an endonym that, they argue, is more historicall ...
indigenous to the area around
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
.
The Tongva were the first inhabitants of the
Los Angeles Basin
The Los Angeles Basin is a sedimentary Structural basin, basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an wikt:anomalous, anomalous group of east-west trending chains of mountai ...
, where Michael Brown's institute, the
California Institute of Technology
The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
, is located.
According to Brown, the name "Quaoar" is pronounced with three syllables, and Trujillo's website on Quaoar gives a three-syllable pronunciation, , as an approximation of the Tongva pronunciation .
The name can be also pronounced as two syllables, , reflecting the usual English spelling and pronunciation of the deity Kwawar.
In Tongva mythology, Kwawar (or Quaoar) is the creation force of the universe, singing and dancing deities into existence.
Quaoar has no form or gender, although the deity is generally referred to with masculine pronouns.
He first sings and dances to create Weywot (Sky Father), then they sing Chehooit (Earth Mother) and Tamit (Grandfather Sun) into existence. As they sang and danced deities into existence, the creation force became more complex as each joined the singing and dancing. Eventually, after reducing chaos to order, they created the great seven giants that upheld the world.
They then gave rise to the lower animals and eventually the first man and woman, Tobohar and Pahavit.
Upon their investigation of names from Tongva mythology, Brown and Trujillo realized that there were existing members of the Tongva and considered contacting them for permission.
They consulted tribal historian Marc Acuña, who suggested that the name ''Kwawar'' was appropriate for the newly discovered object.
The name was then changed to ''Qua-o-ar'' as this spelling was preferred among the Tongva.
However, the name's spelling was later reconsidered by Brown due to its ambiguous pronunciation resulting from the four-vowel combination ''uaoa''—no other word in the English language has this particular combination of vowels.
(Indeed, even if one takes the ''u'' to be part of the initial consonant ''qu'', it then only appears at
Kaoani but it also appears in proper nouns such as
Laoag
Laoag, officially the City of Laoag ( ilo, Siudad ti Laoag; fil, Lungsod ng Laoag), is a 1st class component city and capital of the province of Ilocos Norte, Philippines. According to the 2020 census, it has a population of 111,651 people. ...
and
Paraoa
Paraoa, Tohora, or Hariri is a small atoll of the central Tuamotus, Tuamotu Archipelago in French Polynesia. It is located 76 km south of Hao (French Polynesia), Hao Atoll's westernmost point. The closest land is Manuhangi Atoll, 52 km t ...
) Regardless, the name and discovery of Quaoar were publicly announced in October, though Brown had not sought approval of the name by the IAU's
Committee on Small Body Nomenclature
In ancient times, only the Sun and Moon, a few stars, and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are discovered e ...
(CSBN).
Quaoar's name was announced before the official numbering of the object, which
Brian Marsden—the head of the Minor Planet Center—remarked in 2004 to be a violation of the protocol during the time that the name of —another large trans-Neptunian object discovered by Brown—was announced.
Despite this, the name was approved by the CSBN, and the naming citation, along with Quaoar's official numbering, was published in a
Minor Planet Circular
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 20 November 2002.
Quaoar was given the
minor planet number
A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog or ...
50000, which was not by coincidence but to commemorate its large size, being that it was found in the search for a Pluto-sized object in the Kuiper belt.
The large Kuiper belt object 20000 Varuna was similarly numbered for a similar occasion.
However, subsequent even larger discoveries such as
136199 Eris
Eris (minor-planet designation 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high- eccentricity orbit. Eris was discovered i ...
were simply numbered according to the order in which their orbits were confirmed.
Planetary symbol
A planet symbol (or ''planetary symbol'') is a graphical symbol used in astrology and astronomy to represent a classical planet (including the Sun and the Moon) or one of the modern planets. The symbols were also used in alchemy to represent the me ...
s are no longer much used in astronomy, so Quaoar never received a symbol in the astronomical literature. A Quaoar symbol (
![Quaoar symbol (fixed width)](https://upload.wikimedia.org/wikipedia/commons/5/58/Quaoar_symbol_%28fixed_width%29.svg)
), mostly used among astrologers,
is included in
Unicode
Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, wh ...
as U+1F77E.
Proposed New Characters: The Pipeline
/ref> The symbol was designed by Denis Moskowitz, a software engineer in Massachusetts; it combines the letter Q (for 'Quaoar') with a canoe, and is stylized to recall angular Tongva rock art.
Orbit and classification
Quaoar orbits the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
at an average distance of , taking 288.8 years to complete one full orbit around the Sun. With an orbital eccentricity of 0.04, Quaoar follows a nearly circular orbit, only slightly varying in distance from 42 AU at perihelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any elli ...
to 45 AU at aphelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any ell ...
. At such distances, light from the Sun takes more than 5 hours to reach Quaoar. Quaoar has last passed aphelion in late 1932 and is currently approaching the Sun at a rate of 0.035 AU per year, or about . Quaoar will reach perihelion around February 2075.
Because Quaoar has a nearly circular orbit, it does not approach close to Neptune such that its orbit can become significantly perturbed under the gravitational influence of Neptune. Quaoar's minimum orbit intersection distance
Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits o ...
from Neptune is only 12.3 AU—it does not approach Neptune within this distance over the course of its orbit, as it is not in a mean-motion orbital resonance with Neptune. Simulations by the Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis.
Since 1998 through the end of 2003, the ...
show that the perihelion and aphelion distances of Quaoar's orbit do not change significantly over the next 10 million years; Quaoar's orbit appears to be stable over the long term.
Quaoar is generally classified as a trans-Neptunian object or distant minor planet
A distant minor planet, or ''distant object'', is any minor planet found beyond Jupiter in the outer Solar System that is not commonly thought of as an "asteroid". The umbrella term is used by IAU's Minor Planet Center (MPC), which is responsibl ...
by the Minor Planet Center since it orbits in the outer Solar System beyond Neptune. Since Quaoar is not in a mean-motion resonance with Neptune, it is also classified as a classical Kuiper belt object
A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major a ...
(cubewano) by the Minor Planet Center and Deep Ecliptic Survey. Quaoar's orbit is moderately inclined 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 agains ...
plane by 8 degrees, relatively high when compared to the inclinations of Kuiper belt objects within the dynamically cold population. Because Quaoar's orbital inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
For a satellite orbiting the Earth ...
is greater than 4 degrees, it is part of the dynamically hot population of high-inclination classical Kuiper belt objects. The high inclinations of hot classical Kuiper belt objects such as Quaoar are thought to have resulted from gravitational scattering by Neptune during its outward migration
Migration, migratory, or migrate may refer to: Human migration
* Human migration, physical movement by humans from one region to another
** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
in the early Solar System.
Physical characteristics
Quaoar's albedo
Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...
or reflectivity could be as low as 0.1, similar to 's albedo of 0.127. This may indicate that fresh ice has disappeared from Quaoar's surface. The surface is moderately red, meaning that Quaoar is relatively more reflective in the red and near-infrared spectrum than in the blue. The Kuiper belt objects Varuna and are also moderately red in the spectral class. Larger Kuiper belt objects are often much brighter because they are covered in more fresh ice and have a higher albedo, and thus they present a neutral color. A 2006 model of internal heating via radioactive decay suggested that Quaoar may not be capable of sustaining an internal ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the worl ...
of liquid water at the mantle–core boundary.
The presence of methane and other volatiles
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
On planet Earth, the term ...
on Quaoar's surface suggest that it may support a tenuous atmosphere produced from the sublimation of volatiles. With a measured mean temperature of ~ , the upper limit of Quaoar's atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...
is expected to be in the range of a few microbars. Due to Quaoar's small size and mass, the possibility of Quaoar having an atmosphere of nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
has been ruled out, since the gases would escape from Quaoar. The possibility of a methane atmosphere, with the upper limit being less than 1 microbar, was considered until 2013, when Quaoar occulted a 15.8-magnitude star and revealed no sign of a substantial atmosphere, placing an upper limit to at least 20 nanobars, under the assumption that Quaoar's mean temperature is and that its atmosphere consists of mostly methane. The upper limit of atmosphere pressure was tightened to 10 nanobars after another stellar occultation in 2019.
Mass and density
Because Quaoar 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 ...
object, the mass of the system can be calculated from the orbit of the secondary. Quaoar's estimated density of around and estimated size of suggests that it is a dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
. American astronomer Michael Brown estimates that rocky bodies around in diameter relax into hydrostatic equilibrium
In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary ...
, and that icy bodies relax into hydrostatic equilibrium somewhere between and . With an estimated mass greater than , Quaoar has the mass and diameter "usually" required for being in hydrostatic equilibrium according to the 2006 IAU draft definition of a planet (5 kg, 800 km), and Brown states that Quaoar "must be" a dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
. Light-curve-amplitude analysis shows only small deviations, suggesting that Quaoar is indeed a spheroid with small albedo spots and hence a dwarf planet.
Planetary scientist Erik Asphaug has suggested that Quaoar may have collided with a much larger body, stripping the lower-density mantle from Quaoar, and leaving behind the denser core. He envisioned that Quaoar was originally covered by a mantle of ice that made it to bigger than its present size, and that it collided with another Kuiper belt object about twice its size—an object roughly the diameter of Pluto, or even approaching the size of Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. This model was made assuming Quaoar actually had a density of 4.2 g/cm3, but more recent estimates have given it a more Pluto-like density of only 2 g/cm3, with no further need for the collision theory.
Size
Quaoar is thought to be an oblate spheroid around in diameter, being slightly flattened in shape. The estimates come from observations of stellar occultation
Stellar means anything related to one or more stars (''stella''). The term may also refer to:
Arts, entertainment, and media
* ''Stellar'' (magazine), an Irish lifestyle and fashion magazine
* Stellar Loussier, a character from ''Mobile Suit Gu ...
s by Quaoar, in which it passes in front of a star, in 2013 and 2019. Given that Quaoar has an estimated oblateness of and a measured equatorial diameter of , Quaoar is believed to be in hydrostatic equilibrium, being described as a Maclaurin spheroid. Quaoar is about as large and massive as (if somewhat smaller than) Pluto's moon Charon. Quaoar is roughly half the size of Pluto.
Quaoar was the first trans-Neptunian object
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically ...
to be measured ''directly'' from Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
images, using a method comparing images with the Hubble point spread function (PSF). In 2004, Quaoar was estimated to have a diameter of with an uncertainty of , using Hubble's measurements. Given its distance Quaoar is on the limit of Hubble's resolution of 40 milliarcseconds
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 n ...
and its image is consequently "smeared" on a few adjacent pixels. By comparing carefully this image with the images of stars in the background and using a sophisticated model of Hubble optics (PSF), Brown and Trujillo were able to find the best-fit disk size that would give a similar blurred image. This method was also applied by the same authors to measure the size of the dwarf planet Eris.
At the time of its discovery in 2002, Quaoar was the largest object found in the Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
since the discovery of Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...
. Quaoar's size was subsequently revised downward and was later superseded in size as larger objects (, , and ) were discovered. The uncorrected 2004 Hubble estimates only marginally agree with the 2007 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 around ...
measurements by the Spitzer Space Telescope that suggest a higher albedo
Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...
(0.19) and consequently a smaller diameter (). Adopting a Uranian satellite limb darkening
Limb darkening is an optical effect seen in stars (including the Sun), where the central part of the disk appears brighter than the edge, or ''limb''. Its understanding offered early solar astronomers an opportunity to construct models with such ...
profile suggests that the 2004 Hubble size estimate for Quaoar was approximately 40 percent too large, and that a more proper estimate would be about 900 km. In 2010, Quaoar was estimated to be about in diameter, using a weighted average of Spitzer and corrected Hubble estimates. In observations of the object's shadow as it occulted an unnamed 16th-magnitude star on 4 May 2011, Quaoar was estimated to be in diameter. Measurements from the Herschel Space Observatory in 2013 suggested that Quaoar has a diameter of . In that same year, Quaoar occulted a 15.8-magnitude star, yielding a chord length of , consistent with the Herschel estimate. Another occultation by Quaoar in June 2019 also yielded a similar chord length of .
Cryovolcanism
In 2004, signs of crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
line ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaqu ...
were found on Quaoar, indicating that the temperature rose to at least sometime in the last ten million years. Speculation began as to what could have caused Quaoar to heat up from its natural temperature of . Some have theorized that a barrage of mini-meteor
A meteoroid () is a small rocky or metallic body in outer space.
Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...
s may have raised the temperature, but the most discussed theory speculates that cryovolcanism
A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is know ...
may be occurring, spurred by the decay of radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
elements within Quaoar's core. Since then (2006), crystalline water ice was also found on , but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7). More precise observations of Quaoar's near infrared spectrum
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 around ...
in 2007 indicated the presence of small quantities (5%) of solid methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
and ethane
Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
. Given its boiling point of , methane is a volatile ice at average surface temperatures of Quaoar, unlike water ice or ethane. Both models and observations suggest that only a few larger bodies (Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...
, and ) can retain the volatile ices whereas the dominant population of small trans-Neptunian object
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically ...
s lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.
Rotation
Quaoar's rotation period is uncertain, and two possible rotation periods of Quaoar are given (8.64 hours or 17.68 hours). Derived from the rotational light curves of Quaoar observed on March through June 2003, its rotation period is measured to be 17.6788 hours.
Satellite
Quaoar has one known moon, Weywot
Weywot, officially (50000) Quaoar I Weywot, is the only known moon of the trans-Neptunian planetoid 50000 Quaoar. Discovered by Michael Brown and T.A. Suer using images acquired by the Hubble Space Telescope on 14 February 2006, its existence wa ...
(full designation ''(50000) Quaoar I Weywot''), discovered in 2006. It is thought to be somewhere around in diameter.
Exploration
It was calculated that a flyby mission to Quaoar could take 13.57 years using a Jupiter gravity assist, based on launch dates of 25 December 2016, 22 November 2027, 22 December 2028, 22 January 2030 or 20 December 2040. Quaoar would be 41 to 43 AU from the Sun when the spacecraft arrives. In July 2016, the Long Range Reconnaissance Imager
Long Range Reconnaissance Imager (LORRI) is a telescope aboard the ''New Horizons'' spacecraft for imaging. LORRI has been used to image Jupiter, its moons, Pluto and its moons, and Arrokoth since its launch in 2006. LORRI is a reflecting telescope ...
(LORRI) aboard the '' New Horizons'' spacecraft took a sequence of four images of Quaoar from a distance of about 14 AU. ''Interstellar Probe
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar space, which is typically defined as the region beyond the heliopause. It also refers to probes capable of reaching other s ...
'', a concept by Pontus Brandt and his colleagues at Johns Hopkins Applied Physics Laboratory
The Johns Hopkins University Applied Physics Laboratory (Applied Physics Laboratory, or APL) is a not-for-profit university-affiliated research center (UARC) in Howard County, Maryland. It is affiliated with Johns Hopkins University and emplo ...
would potentially fly by Quaoar in the 2030s before continuing to the interstellar medium, and the first of China National Space Administration's proposed ''Interstellar Express
''Interstellar Express'' or ''Interstellar Heliosphere Probe'' (), is the current name for a proposed Chinese National Space Administration program designed to explore the heliosphere and interstellar space. The program will feature two space ...
'' probe designed to explore the heliosphere has it considered as a potential flyby target. Quaoar has been chosen as a flyby target for missions like these particularly for its escaping methane atmosphere and possible cryovolcanism, as well as its close proximity to the heliospheric nose.
Notes
References
External links
Frequently Asked Questions About Quaoar
Quaoar could have hit a bigger Pluto-sized body at high speeds
(Video Credit: Craig Agnor, E. Asphaug)
– Nature.com article
– SPACE.com article by Elizabeth Howell
Beyond Jupiter – (50000) Quaoar
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Discoveries by Michael E. Brown
Discoveries by Chad Trujillo
Named minor planets
Dwarf planets
Binary trans-Neptunian objects
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