594913 ꞌAylóꞌchaxnim ( provisional designation ) is a large

near-Earth asteroid A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit aro ...

discovered by the Zwicky Transient Facility on 4 January 2020. It is the first asteroid discovered to have an orbit completely within

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

's orbit, and is thus the first and only known member of the eponymous ꞌAylóꞌchaxnim (informally named Vatira before its discovery) population of Atira-class asteroids. ꞌAylóꞌchaxnim has the smallest known

aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

and third-smallest known

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 longe ...

among all asteroids. With an absolute magnitude approximately 16.2, the asteroid is expected to be larger than in diameter.

Discovery

ꞌAylóꞌchaxnim was discovered by the Zwicky Transient Facility (ZTF) survey at the

Palomar Observatory The Palomar Observatory is an astronomical research observatory in the Palomar Mountains of San Diego County, California, United States. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

on 4 January 2020, by astronomers Bryce Bolin, Frank Masci, and Quanzhi Ye. The discovery formed part of a campaign for detecting interior-Earth asteroids (Atiras) using the wide-field ZTF camera on the 1.22-meter Samuel Oschin telescope at the Palomar Observatory. The detection of such objects is difficult due to their close proximity to the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

: asteroids within the orbit of

never reach solar elongations greater than 47 degrees, meaning that they are only observable during

twilight Twilight is daylight illumination produced by diffuse sky radiation when the Sun is below the horizon as sunlight from the upper atmosphere is scattered in a way that illuminates both the Earth's lower atmosphere and also the Earth's surf ...

as the Sun is below the Earth's

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

. Because of this, inner-Venusian asteroids could only be observed within a short time frame, hence why the ZTF camera was used since it can effectively detect transient objects. At the time of discovery, ꞌAylóꞌchaxnim was located in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Aquarius, at an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

around 18. The discovery of ꞌAylóꞌchaxnim was reported by astronomer Bryce Bolin, and was subsequently listed on the

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

's Near-Earth Object Confirmation Page (NEOCP) on 4 January 2020. Follow-up observations were then conducted at various observatories in order to determine the asteroid's orbit based on its orbital motion. The discovery of the asteroid was then formally announced 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 ...

issued by the MPC on 8 January 2020. Follow-up observations were later conducted in November 2020 by the Palomar and Xingming observatories, reducing ꞌAylóꞌchaxnim's uncertainty parameter to 5.

Nomenclature

Upon discovery, the asteroid was given the internal designation ZTF09k5. The

(MPC) gave it the provisional designation on 8 January 2020, after follow-up observations sufficiently determined its orbit. After its orbit had been determined to sufficient precision, the MPC assigned it the permanent number 594913 on 20 September 2021 (). Its name was approved on 8 November 2021.WGSBN Bulletin 1, #11
/ref> means 'Venus girl' in the indigenous

Luiseño language The Luiseño language is a Uto-Aztecan language of California spoken by the Luiseño, a Native Americans in the United States, Native American people who at the time of first contact with the Spanish in the 16th century inhabited the coastal ar ...

of southern California. The name celebrates the location of the discovery (Palomar Mountain, which is on ancestral Luiseño land) and the fact that ꞌAylóꞌchaxnim is the first discovered asteroid to orbit entirely within the orbit of Venus. Being the prototype of the informally named Vatira class, its name is expected to be used to refer to this newly confirmed population.

Orbit and classification

ꞌAylóꞌchaxnim is the only asteroid known to have an orbit completely within Venus's orbit. With an

distance of approximately 0.654

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s (AU), it has the smallest known aphelion of all asteroids. In comparison, Venus's average orbital distance from the Sun is 0.723 AU, with a

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

distance of 0.718 AU. ꞌAylóꞌchaxnim is formally classified as an

Atira asteroid Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are Near-Earth objects whose orbits are entirely confined within Earth's orbit; that is, their orbit has an aphelion (farthest point from the Sun) smaller than Ear ...

by the Minor Planet Center due it having an orbit within that of

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. However, unlike previously known Atira asteroids, ꞌAylóꞌchaxnim's orbit is contained within that of Venus, thus it falls into the proposed category of Vatira asteroids—a subclass of Atira asteroids with aphelion distances less than Venus's perihelion distance (hence the name: a

portmanteau In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together.

of 'Venus' and 'Atira'). ꞌAylóꞌchaxnim is technically classified as a

near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

under the Atira classification, though the asteroid's minimum orbit intersection distance from Earth is . The orbit of ꞌAylóꞌchaxnim is well-secured with an uncertainty parameter of 2. The asteroid orbits the Sun in approximately 151 days (0.41 years), with a

of approximately 0.5554 AU. 's orbit is close to a 3:2 mean-motion orbital resonance with Venus, meaning that ꞌAylóꞌchaxnim completes approximately three orbits for every two orbits completed by Venus. The orbit of ꞌAylóꞌchaxnim is moderately eccentric, as it approaches only 0.457 AU from the Sun at perihelion, just within Mercury's aphelion distance of 0.467 AU. ꞌAylóꞌchaxnim's orbit is also moderately inclined to the

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

by approximately 15.9 degrees. ꞌAylóꞌchaxnim has a smaller orbital eccentricity and inclination compared to the generally expected values for typical Vatira asteroids, which were predicted to have an eccentricity around 0.4 and an inclination around 25 degrees. The asteroid's minimum orbit intersection distance from Mercury and Venus is about and , respectively. ꞌAylóꞌchaxnim is approximately tied with (0.5553 AU) as having the second-smallest known orbital period and semi-major axis among all asteroids, though has a slightly smaller semi-major axis. In this case, ꞌAylóꞌchaxnim has the third-smallest known semi-major axis among all asteroids.

Orbital dynamics

ꞌAylóꞌchaxnim had likely originated from the main

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

, where its orbit was locked in a secular resonance that caused its orbital eccentricity to gradually increase over time, evolving onto an Earth-crossing orbit. Subsequent close encounters with Earth, Venus, and Mercury resulted in gravitational perturbations of the asteroid's orbit, reducing its momentum and causing it to orbit closer to the Sun. Such inward orbital migration is thought to be rare. Near-Earth asteroids transitioning into the Vatira region often have unstable, short-term orbits due to frequent gravitational perturbations by Venus and Mercury. ꞌAylóꞌchaxnim rarely crosses the orbits of Mercury and Venus, which reduces the number of close encounters with either planet that would otherwise perturb ꞌAylóꞌchaxnim's orbit. Nevertheless its orbit is likely to be stable for less than a million years, unless it is on (or enters soon) a nearby 3:2

mean-motion resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

with Venus, which could extend its stability to a few million years. Dynamical modeling of ꞌAylóꞌchaxnim's orbit show that the most likely scenario for its orbital evolution is that ꞌAylóꞌchaxnim's orbit will oscillate for several millions of years before gravitational perturbations lead to the asteroid's eventual collision with a planet, most likely Venus. At 140 thousand years from the present, ꞌAylóꞌchaxnim's aphelion distance will exceed Venus's perihelion distance, as a result of the combined effects of the Kozai resonance and gravitational perturbations. Within the Vatira region, the Kozai resonance causes the orbital inclinations and eccentricities of asteroids to oscillate over several millions of years. As a result, Vatira asteroids can become Atira-class asteroids and vice versa over time, and can cross the orbits of Mercury and Venus during these orbital oscillations. The Kozai resonance often disrupts the orbits of Vatira asteroids, albeit it can also lead to orbital stability for some unperturbed Vatira asteroids. At about 1.2 million years from the present, ꞌAylóꞌchaxnim will leave the Vatira region and will transition onto a Mercury-crossing orbit, with its perihelion oscillating around Mercury's aphelion distance before decoupling from the planet's orbit at about 2.1 million years. After decoupling from Mercury's orbit, ꞌAylóꞌchaxnim was shown to oscillate between an Atira-type orbit ( Q < 0.983 AU) and an Earth-crossing

Aten Aten, also Aton, Atonu, or Itn (, reconstructed ) was the focus of Atenism, the religious system formally established in ancient Egypt by the late Eighteenth Dynasty pharaoh Akhenaten. Exact dating for the Eighteenth Dynasty is contested, thou ...

-type orbit (Q > 0.983 AU), in which the asteroid's aphelion oscillates around Earth's perihelion distance of 0.983 AU. About 740 thousand years afterward, ꞌAylóꞌchaxnim will likely return to its Mercury-crossing orbit, though gravitational perturbations by Mercury and Venus will scatter it onto an Earth-crossing orbit once more before colliding with either planet. After 10 million years from the present, ꞌAylóꞌchaxnim will have most likely collided with Venus. Modeling of the observational selection effects of the Zwicky Transient Facility survey shows a small probability of it detecting ꞌAylóꞌchaxnim based on the current NEO model. The low probability of detection may imply an additional source of ꞌAylóꞌchaxnim asteroids in the inner Solar System such as within the orbit of Mercury.

Physical characteristics

ꞌAylóꞌchaxnim is estimated to have an absolute magnitude (H) of approximately 16.2. The medium diameter of ꞌAylóꞌchaxnim is expected to be larger than . Assuming that the

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

is between 0.25 and 0.05, its diameter should be around , respectively. Near-Earth asteroid population models predict that at least one asteroid of this size has an orbit within that of Venus, implying that ꞌAylóꞌchaxnim could be one of the largest members of the Vatira population. Visible and

near-infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

by the

Roque de los Muchachos Observatory Roque de los Muchachos Observatory (, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated by the Instituto de Astrofísica de Can ...

in 2020 suggests that ꞌAylóꞌchaxnim has a reddish surface that is

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

-rich, based on the presence of a 1 μm absorption feature characteristic of

S-type asteroid S-type (stony-type or silicaceous-type) asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are ...

s. The abundance of olivine in the surface of ꞌAylóꞌchaxnim suggests that it could be a mantle asteroid formed as a fragment from the rocky mantles of large, internally differentiated bodies. The absorption features in ꞌAylóꞌchaxnim's spectrum appear to be intermediate between the S-type and A-type spectral classes, hence it is classified as an Sa-type asteroid. Assuming an average albedo of 0.22 for S-type asteroids, ꞌAylóꞌchaxnim's diameter can be constrained to approximately .

Notes

References

External links

2020 AV2, the first intervenusian asteroid ever discovered
Gianluca Masi, ''The Virtual Telescope Project 2.0'', 9 Jan 2020
Meet 2020 AV2, the first asteroid found that stays inside Venus's orbit!
by Phil Plait, 10 Jan 2020
Meet 2020 AV2, the 1st asteroid entirely within the orbit of Venus
by Gianluca Masi, 10 Jan 2020
First asteroid found within Venus's orbit could be a clue to missing 'mantle' asteroids
Nola Redd, ''

Science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...

'', 1 July 2020 * * {{DEFAULTSORT:594913 Atira asteroids Discoveries by the Zwicky Transient Facility Aylochaxnim # 20200104 20200104