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 The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calc ...
, 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
The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 tim ...
, a region of icy planetesimals beyond
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...
. 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 axe ...
), 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 trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. The object was discovered by American astronomers
Chad Trujillo and
Michael Brown at the
Palomar Observatory
Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...
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 known ...
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 ...
is present on its surface, which can only be retained by the largest Kuiper belt objects.
In February 2007,
Weywot, 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
Quaoar (50000 Quaoar), provisional designation , is a dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. A non-resonant object ( cubewano), it measures approximately in diameter, about half the diameter of Pluto. Th ...
is the Tongva creator deity and
Weywot 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 and
Michael Brown at the
Palomar Observatory
Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...
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
San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the f ...
.
The discovery formed part of the Caltech Wide Area Sky Survey, which was designed to search for the brightest
Kuiper belt
The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 tim ...
objects using the Palomar Observatory's 1.22-meter
Samuel Oschin telescope.
Quaoar was first identified in images by Trujillo on 5 June 2002, when he noticed a dim, 18.6-
magnitude object slowly moving among the stars of the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the earliest 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 trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
.
To ascertain Quaoar's orbit, Brown and Trujillo initiated a search for archival
precovery
In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of an object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This happens mos ...
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 plate
Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...
s taken by astronomer
Charles T. Kowal
Charles Thomas Kowal (November 8, 1940 – November 28, 2011) was an American astronomer known for his observations and discoveries in the Solar System. As a staff astronomer at Caltech's Mount Wilson and Palomar Mountain observatories between ...
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.
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
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when co ...
in
Mauna Kea
Mauna Kea ( or ; ; abbreviation for ''Mauna a Wākea''); is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii and second-highest peak of an island on Earth. The peak ...
, 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 known ...
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
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 ...
in a
Minor Planet Electronic Circular 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 calc ...
, 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
The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...
's
Division for Planetary Sciences 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% f ...
. They announced Quaoar was the largest Kuiper belt object found yet, surpassing previous record holders
20000 Varuna 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 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 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 ''minor ...
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 largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world ...
.
The Tongva were the first inhabitants of the
Los Angeles Basin
The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east-west trending chains of mountains collectively known as the ...
, 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
Kaoani comes from the Japanese and . Kaoanis are small animated smilies that usually bounce up and down to look like they are floating. Kaoani originate in Japan and are also known as puffs, anime blobs, anikaos or anime emoticons.
Kaoani can ...
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) 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 (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 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 were simply numbered according to the order in which their orbits were confirmed.
Planetary symbols 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, ...
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 at an average distance of , taking 288.8 years to complete one full orbit around the Sun. With an orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values bet ...
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
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...
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 su ...
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 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 Ea ...
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 refle ...
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
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 consid ...
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
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
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 microbar
The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa (100 kPa), or slightly less than the current average atmospheric pressure on Earth at sea l ...
s. 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 simpl ...
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 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 planeta ...
, 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
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has ci ...
around in diameter, being slightly flattened in shape. The estimates come from observations of stellar occultations by Quaoar, in which it passes in front of a star, in 2013 and 2019. Given that Quaoar has an estimated oblateness
Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is ...
of and a measured equatorial diameter of , Quaoar is believed to be in hydrostatic equilibrium, being described as a Maclaurin spheroid
A Maclaurin spheroid is an oblate spheroid which arises when a self-gravitating fluid body of uniform density rotates with a constant angular velocity. This spheroid is named after the Scottish mathematician Colin Maclaurin, who formulated it for t ...
. Quaoar is about as large and massive as (if somewhat smaller than) Pluto's moon Charon
In Greek mythology, Charon or Kharon (; grc, Χάρων) is a psychopomp, the ferryman of Hades, the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the ...
. 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 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 trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. 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 Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
measurements by the Spitzer Space Telescope
The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, ...
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 refle ...
(0.19) and consequently a smaller diameter (). Adopting a Uranian satellite limb darkening 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
The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...
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 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 known ...
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 ...
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
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding env ...
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 trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
, 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 (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 (LORRI) aboard the ''New Horizons
''New Horizons'' is an interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a ...
'' 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 would potentially fly by Quaoar in the 2030s before continuing to the interstellar medium
In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
, and the first of China National Space Administration
China National Space Administration (CNSA; ) is the government agency of the People's Republic of China that is responsible for civil space administration and international space cooperation, including organizing or leading foreign exchanges ...
's proposed '' Interstellar Express'' 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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050000
Discoveries by Michael E. Brown
Discoveries by Chad Trujillo
Named minor planets
50000 Quaoar,
Dwarf planets
Binary trans-Neptunian objects
Objects observed by stellar occultation, 050000
Astronomical objects discovered in 2002, 20020604