Atira asteroid#ꞌAylóꞌchaxnim asteroids

There is no official name for the class commonly referred as Atira asteroids. The term "Apohele asteroids" was proposed by the discoverers of {{mpl|1998 DK|36}}, after the Hawaiian word for orbit, from apo {{IPA|haw|ˈɐpo|}} 'circle' and hele {{IPA|haw|ˈhɛlɛ|}} 'to go'.[https://wehewehe.org/gsdl2.85/cgi-bin/hdict?a=d&d=D1434&l=en (Ulukau Hawaiian Electronic Library)] This was suggested partly because of its similarity to the words aphelion (apoapsis) and helios.{{efn|name=Tholen-CCC}} Other authors adopted the designation "Inner Earth Objects" (IEOs). Following the general practice to name a new class of asteroids for the first recognized member of that class, which in this case was 163693 Atira, the designation of "Atira asteroids" was largely adopted by the scientific community, including by NASA.{{cite journal |last1=Ribeiro |first1=Anderson O. |display-authors=et al|title=Dynamical study of the Atira group of asteroids |journal=Monthly Notices of the Royal Astronomical Society |date=1 June 2016 |volume=458 |issue=4 |pages=4471–4476 |doi=10.1093/mnras/stw642|doi-access=free }}

Their location inside the Earth's orbit makes Atiras very difficult to observe, as from Earth's perspective they are close to the Sun and therefore 'drowned out' by the Sun's overpowering light. This means that Atiras can usually only be seen during twilight. The first documented twilight searches for asteroids inside Earth's orbit were performed by astronomer Robert Trumpler over the early 20th century, but he failed to find any.

The first confirmed Atira asteroid was 163693 Atira in 2003, discovered by the Lincoln Laboratory Near Earth Asteroid Research Team.{{cite web |title=Minor Planet Circular 61768|url=https://minorplanetcenter.net/iau/ECS/MPCArchive/2008/MPC_20080122.pdf|publisher=Minor Planet Center|access-date=2024-08-22}} {{As of|January 2025}}, there are 34 known Atiras, two of which are named, nine of which have received a numbered designation, and seven of which are potentially hazardous objects.{{cite web |title=Small-Body Database Query |url=https://ssd.jpl.nasa.gov/tools/sbdb_query.html#!#results |website=Solar System Dynamics – Jet Propulsion Laboratory |publisher=NASA – California Institute of Technology |access-date=2025-01-17}}

Most Atira asteroids originated in the asteroid belt and were driven to their current locations as a result of gravitational perturbation, as well as other causes such as the Yarkovsky effect.{{cite journal|title=A Twilight Search for Atiras, Vatiras, and Co-orbital Asteroids: Preliminary Results|journal=The Astronomical Journal|publisher=IOP Publishing|year=2020 |doi=10.3847/1538-3881/ab629c |last1=Ye |first1=Quanzhi |display-authors=et al|volume=159 |issue=2 |page=70 |arxiv=1912.06109 |bibcode=2020AJ....159...70Y |s2cid=209324310 |doi-access=free }} A number of known Atiras could be fragments or former moons of larger Atiras as they exhibit an unusually high level of orbital correlation.{{Cite journal

|first1 = Carlos |last1 = de la Fuente Marcos

|first2 = Raúl |last2 = de la Fuente Marcos

|date = 20 December 2023

|title = Baked before Breaking into Bits: Evidence for Atira-type Asteroid Splits

|journal = Research Notes of the American Astronomical Society

|volume = 7

|issue = 12

|pages = 278 (3 pages)

|bibcode = 2023RNAAS...7..278D

|doi = 10.3847/2515-5172/ad16de

|arxiv =

|doi-access = free

}}

Atiras do not cross Earth's orbit and are not immediate impact event threats, but their orbits may be perturbed outward by a close approach to either Mercury or Venus and become Earth-crossing asteroids in the future. The dynamics of many Atira asteroids resemble the one induced by the Kozai-Lidov mechanism,{{efn|Namely, they have coupled oscillations in orbital eccentricity and inclination}} which contributes to enhanced long-term orbital stability, since there is no libration of the perihelion.{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=11 June 2018 |title=Kozai--Lidov Resonant Behavior Among Atira-class Asteroids |journal=Research Notes of the AAS |volume=2 |issue=2 |pages=46 |arxiv=1806.00442 |bibcode=2018RNAAS...2...46D |doi=10.3847/2515-5172/aac9ce|s2cid=119239031 |doi-access=free }}{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=1 August 2019 |title=Understanding the evolution of Atira-class asteroid 2019 AQ₃, a major step towards the future discovery of the Vatira population|journal=Monthly Notices of the Royal Astronomical Society |volume= 487|issue= 2|pages= 2742–2752|url = https://academic.oup.com/mnras/article-abstract/487/2/2742/5498309|arxiv=1905.08695|bibcode=2019MNRAS.487.2742D|doi=10.1093/mnras/stz1437|doi-access=free |s2cid=160009327 }}

A 2017 study published in the journal Advances in Space Research proposed a low-cost space probe be sent to study Atira asteroids, citing the difficulty in observing the group from Earth as a reason to undertake the mission.{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S0273117717300236|title=Optimised low-thrust mission to the Atira asteroids|journal=Advances in Space Research|publisher=Elsevier|last1=Di Carlo|first1=Marilena|last2=Martin|first2=Juan Manuel Romero|last3=Gomez|first3=Natalia Ortiz|last4=Vasile|first4=Massimiliano|date=1 April 2017|accessdate=February 9, 2023|doi=10.1016/j.asr.2017.01.009|volume=59|issue=7|pages=1724–1739|bibcode=2017AdSpR..59.1724D |s2cid=116216149 }} The study proposed that the mission would be powered by spacecraft electric propulsion and would follow a path designed to flyby as many Atira asteroids as possible. The probe would also attempt to discover new NEO's that may pose a threat to Earth.

ꞌAylóꞌchaxnim asteroids, which had been provisionally nicknamed "Vatira" asteroids before the first was discovered,{{efn|The nickname "Vatira" combined "Venus" with "Atira".}} are a subclass of Atiras that orbit entirely interior to the orbit of Venus, aka 0.718 AU. Despite their orbits placing them at a significant distance from Earth, they are still classified as near-Earth objects.{{cite web|title= JPL Small-Body Database Browser: 2020 AV2|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3985571|website=Jet Propulsion Laboratory|publisher=NASA|access-date= 9 January 2020|archive-url=https://web.archive.org/web/20200111003446/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3985571|archive-date=11 January 2020|url-status=live}} Observations suggest that ꞌAylóꞌchaxnim asteroids frequently have their orbits altered into Atira asteroids and vice versa.{{cite journal|url=https://academic.oup.com/mnras/article-abstract/517/4/5921/6815743?login=false|title=The orbital evolution of Atira asteroids|journal=Monthly Notices of the Royal Astronomical Society|last1=Lai|first1=H.T.|last2=Ip|first2=W.H.|date=4 December 2022|accessdate=February 9, 2023|volume=517|issue=4|pages=5921–5929|doi=10.1093/mnras/stac2991|doi-access=free |arxiv=2210.09652}}

First formally theorised to exist by William F. Bottke and Gianluca Masi in 2002 and 2003,{{cite journal |last1=Bottke |first1=William F. |display-authors=et al|date=April 2002 |title=Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects

|journal=Icarus |volume=156 |issue=2 |pages=399–433 |doi= 10.1006/icar.2001.6788 |doi-access=free |bibcode=2002Icar..156..399B }}{{cite journal |last1=Masi |first1=Gianluca |date=June 2003 |title=Searching for inner-Earth objects: a possible ground-based approach

|journal=Icarus |volume=163 |issue=2 |pages=389–397 |doi= 10.1016/S0019-1035(03)00082-4 |doi-access=free |bibcode=2003Icar..163..389M }} the first and to date only such asteroid found is 594913 ꞌAylóꞌchaxnim,{{cite news |title=2020 AV2, the first intervenusian asteroid ever discovered: an image – 08 Jan. 2020 |url=https://www.virtualtelescope.eu/2020/01/09/2020-av2-the-first-intervenusian-asteroid-ever-discovered-an-mage-08-jan-2020/ |first=Gianluca|last=Masi |publisher=Virtual Telescope Project |date=9 January 2020 |access-date=9 January 2020}} which was discovered on 4 January 2020 by the Zwicky Transient Facility. As the archetype, it subsequently gave its name to the class.{{cite journal |last1=Bolin |first1=Bryce T. |display-authors=et al|date=November 2022 |title=The discovery and characterization of (594913) 'Ayló'chaxnim, a kilometre sized asteroid inside the orbit of Venus |url=https://authors.library.caltech.edu/records/4fewd-rff56/files/slac089.pdf?download=1 |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=517 |issue=1 |pages=L49–L54 |doi=10.1093/mnrasl/slac089 |access-date=1 October 2022|doi-access=free }} It has an aphelion of only 0.656 AU, the smallest of any known asteroid.

{{main|Vulcanoid}}

No asteroids have yet been discovered to orbit entirely inside the orbit of Mercury (q = 0.307 AU). Such hypothetical asteroids would likely be termed vulcanoids, although the term often refers to asteroids which more specifically have remained in the intra-Mercurian region over the age of the Solar System.

The following table lists the known and suspected Atiras {{as of|November 2024|lc=y}}. 594913 ꞌAylóꞌchaxnim, due to its unique classification, has been highlighted in pink. The interior planets Mercury and Venus have been included for comparison as grey rows.

:^(A) All diameter estimates are based on an assumed albedo of 0.14 (except 163693 Atira, for which the size has been directly measured)

:^(B) Binary asteroid

• List of minor planet groups
• List of minor planets

{{notelist|refs=

{{efn|name=Tholen-CCC|1={{URL|1=http://abob.libs.uga.edu/bobk/ccc/cc070998.html |2=Cambridge Conference Correspondence, (2)}}: WHAT'S IN A NAME: APOHELE = APOAPSIS & HELIOS – from Dave Tholen, Cambridge Conference Network (CCNet) DIGEST, 9 July 1998
Benny,
Duncan Steel has already brought up the subject of a class name for objects with orbits interior to the Earth's. To be sure, we've already given that subject some thought. I also wanted a word that begins with the letter "A", but there was some desire to work Hawaiian culture into it. I consulted with a friend of mine that has a master's degree in the Hawaiian language, and she recommended "Apohele", the Hawaiian word for "orbit". I found that an interesting suggestion, because of the similarity to fragments of "apoapsis" and "helios", and these objects would have their apoapsis closer to the Sun than the Earth's orbit. By the way, the pronunciation would be like "ah-poe-hey-lay". Rob Whiteley has suggested "Ali{{okina}}i", which refers to the Hawaiian elite,

which provides a rich bank of names for discoveries in this class, such as Kuhio, Kalakaua, Kamehameha, Liliuokalani, and so on. Unfortunately, I think the okina (the reverse apostrophe) would be badly treated by most people.
I wasn't planning to bring it up at this stage, but because Duncan has

already done so, here's what we've got on the table so far. I'd appreciate some feedback on the suggestions.
--Dave}}

}}

{{reflist|refs=

{{cite web|title = Near-Earth Asteroid Discovery Statistics|url = https://cneos.jpl.nasa.gov/stats/totals.html|date = 14 May 2019|access-date = 25 May 2019|website=Jet Propulsion Laboratory|publisher=NASA|last1=Chodas|first1=Paul|last2=Khudikyan|first2=Shakeh|last3=Chamberlin|first3=Alan}}

{{Cite journal

|first1 = David J. |last1 = Tholen

|author-link1 = David J. Tholen

|first2 = Robert J. |last2 = Whiteley

|date = September 1998

|title = Results From NEO Searches At Small Solar Elongation

|journal = American Astronomical Society

|volume = 30

|page = 1041

|bibcode = 1998DPS....30.1604T

}}

{{Cite journal

|first1 = Patrick |last1 = Michel

|author-link1 = Patrick Michel

|first2 = Vincenzo |last2 = Zappalà

|author-link2 = Vincenzo Zappalà

|first3 = Alberto |last3 = Cellino

|first4 = Paolo |last4 = Tanga

|date = February 2000

|title = NOTE: Estimated Abundance of Atens and Asteroids Evolving on Orbits between Earth and Sun

|journal = Icarus

|publisher = Harcourt

|volume = 143

|issue = 2

|pages = 421–424

|bibcode = 2000Icar..143..421M

|doi = 10.1006/icar.1999.6282

}}

{{cite web|title = Near-Earth Object Groups|website = Jet Propulsion Laboratory|publisher = NASA|url = http://neo.jpl.nasa.gov/neo/groups.html|archive-url = https://web.archive.org/web/20020202160655/http://neo.jpl.nasa.gov/neo/groups.html|url-status = dead|archive-date = 2 February 2002|last1=Baalke|first1=Ron|access-date= 11 November 2016}}

{{cite web

|title = JPL Small-Body Database Search Engine: Q < 0.983 (AU)

|website = JPL Solar System Dynamics

|publisher = NASA

|url = http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;OBJ_field=0;ORB_field=0;c1_group=ORB;c1_item=Bn;c1_op=%3C;c1_value=0.983;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBiBhBnBgBjBrCkAiAp;.cgifields=format_option;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=com_orbit_class&query=1&c_sort=CkA |access-date =30 December 2017}}

{{cite journal

|title = The orbital distribution of Near-Earth Objects inside Earth's orbit

|url = https://static1.squarespace.com/static/5743c691d51cd42eed1e15ea/t/57451dc89f72665be88257b5/1464147402569/Greenstreetetal2012_NEOSSat1model.pdf

|first1 = Sarah |last1 = Greenstreet

|first2 = Henry |last2 = Ngo

|first3 = Brett |last3 = Gladman

|date = January 2012

|journal = Icarus

|publisher = Elsevier

|volume = 217

|issue = 1

|pages = 355–366

|doi = 10.1016/j.icarus.2011.11.010

|bibcode = 2012Icar..217..355G

|hdl = 2429/37251

|quote = We have provisionally named objects with 0.307 < Q < 0.718 AU Vatiras, because they are Atiras which are decoupled from Venus. Provisional because it will be abandoned once the first discovered member of this class will be named.|hdl-access= free

}}

{{cite journal

|title = Physical characterization of 2020 AV₂, the first known asteroid orbiting inside Venus orbit

|url = https://academic.oup.com/mnras/article-abstract/496/3/3572/5859506

|first1 = Marcel M. |last1 = Popescu

|display-authors = et al

|date = 11 August 2020

|access-date = 8 July 2020

|journal = Monthly Notices of the Royal Astronomical Society

|volume = 496

|issue = 3

|pages = 3572–3581

|doi = 10.1093/mnras/staa1728

|doi-access = free

|bibcode = 2020MNRAS.496.3572P

|arxiv = 2006.08304|s2cid = 219687045

}}

}}

• [http://www.minorplanetcenter.org/iau/lists/Atensq.html List Of Aten Minor Planets], Minor Planet Center

{{Small Solar System bodies}}

{{DEFAULTSORT:Apohele Asteroid}}

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Category:Lists of asteroids