21601 Aias

Aias is a dark Jovian asteroid orbiting in the leading Greek camp at Jupiter's {{L4}} Lagrangian point, 60° ahead of the Gas Giant's orbit in a 1:1 resonance {{crossreference|(see Trojans in astronomy)}}. It is also a non-family asteroid in the Jovian background population.

It orbits the Sun at a distance of 5.0–5.4 AU once every 11 years and 11 months (4,356 days; semi-major axis of 5.22 AU). Its orbit has an eccentricity of 0.04 and an inclination of 19° with respect to the ecliptic. The body's observation arc begins with a precovery published by the Digitized Sky Survey and taken at the Siding Spring Observatory in March 1991, more than 7 years prior to its official discovery observation at Socorro.

This minor planet was numbered on 8 February 2001 ({{small|M.P.C. 22480}}). It was named in April 2025 after Aias, also known as Ajax the Lesser, the leader of the Locrians who fought with the Acheans.

Aias is an assumed C-type asteroid. Its V–I color index of 0.97 is typical for that of D-type asteroids, the dominant spectral type among the Jupiter trojans.

In April 2013, a rotational lightcurve of Aias was obtained from photometric observations by Robert Stephens at the Center for Solar System Studies (CS3) in California. Lightcurve analysis gave a rotation period of {{val|12.65|0.01}} hours and a brightness variation of 0.30 magnitude ({{small|U=2+}}). Observations by his college Brian Warner at CS3 in July 2017, gave a similar period of 12.530 hours with an amplitude of 0.25 magnitude ({{small|U=2+}}).{{efn|name=Lightcurve-plots-CS3}}{{efn|name=lcdb-Stephens-2018a}}

According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Aias measures 54.91 and 56.08 kilometers in diameter and its surface has an albedo of 0.064 and 0.100, respectively. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 55.67 kilometers based on an absolute magnitude of 10.0.

{{Largest Jupiter trojans}}

{{notelist|refs=

{{efn|name=lcdb-Stephens-2018a|1=Unpublished /Not available at ADS: observations from July 2017 by Brian Warner / Robert Stephens. Rotation period {{val|12.530|0.005}} hours with a brightness amplitude of {{val|0.25|0.02}} mag. Quality code of 2+. Summary figures for (21601) 1998 XO89 at the [http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=21601%7C1998+XO89 LCDB]}}

{{efn|name=Lightcurve-plots-CS3|1=Lightcurve plots of (21601) 1998 XO89 from [http://www.planetarysciences.org/plots/RDS/21601_1998XO89_2013-04-05.PNG 2013] and [http://www.planetarysciences.org/plots/BDW/21601_1998XO89_20170714.PNG 2017] by Robert Stephens and Brian Warner at the Center for Solar System Studies {{Obscode|U81}}, Landers. Quality code is n.a/2+ (lightcurve rating at CS3). Summary figures at the [http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=21601%7C1998+XO89 LCDB] and [http://www.planetarysciences.org/PHP/CS3_Lightcurves.php CS3] website}}

}}

{{reflist|30em|refs=

{{cite web

|type = 2017-11-25 last obs.

|title = JPL Small-Body Database Browser: 21601 (1998 XO89)

|url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2021601

|publisher = Jet Propulsion Laboratory

|access-date = 19 June 2018}}

{{cite web

|title = 21601 (1998 XO89)

|work = Minor Planet Center

|url = https://www.minorplanetcenter.net/db_search/show_object?object_id=21601

|access-date = 19 June 2018}}

{{cite web

|title = List of Jupiter Trojans

|work = Minor Planet Center

|date = 1 June 2018

|url = https://www.minorplanetcenter.net/iau/lists/JupiterTrojans.html

|access-date = 19 June 2018}}

{{cite web

|title = MPC/MPO/MPS Archive

|work = Minor Planet Center

|url = https://www.minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html

|access-date = 19 June 2018}}

{{cite journal

|first1 = T. |last1 = Grav

|first2 = A. K. |last2 = Mainzer

|first3 = J. M. |last3 = Bauer

|first4 = J. R. |last4 = Masiero

|first5 = C. R. |last5 = Nugent

|date = November 2012

|title = WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy

|url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2012ApJ...759...49G

|journal = The Astrophysical Journal

|volume = 759

|issue = 1

|page = 10

|bibcode = 2012ApJ...759...49G

|doi = 10.1088/0004-637X/759/1/49

|arxiv = 1209.1549

|s2cid = 119101711

|access-date= 19 June 2018}} ([http://vizier.cfa.harvard.edu/viz-bin/VizieR-6?-source=J/ApJ/759/49/table1&MPC=21601 online catalog])

{{cite web

|title = Asteroid (21601) 1998 XO89 – Proper Elements

|publisher = AstDyS-2, Asteroids – Dynamic Site

|url = https://newton.spacedys.com/astdys/index.php?n=21601&pc=1.1.6

|access-date= 19 June 2018}}

{{cite web

|title = LCDB Data for (21601)

|publisher = Asteroid Lightcurve Database (LCDB)

|url = http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=21601%7C

|access-date = 19 June 2018}}

{{cite journal

|display-authors = 6

|first1 = Fumihiko |last1 = Usui

|first2 = Daisuke |last2 = Kuroda

|first3 = Thomas G. |last3 = Müller

|first4 = Sunao |last4 = Hasegawa

|first5 = Masateru |last5 = Ishiguro

|first6 = Takafumi |last6 = Ootsubo

|first7 = Daisuke |last7 = Ishihara

|first8 = Hirokazu |last8 = Kataza

|first9 = Satoshi |last9 = Takita

|first10 = Shinki |last10 = Oyabu

|first11 = Munetaka |last11 = Ueno

|first12 = Hideo |last12 = Matsuhara

|first13 = Takashi |last13 = Onaka

|date = October 2011

|title = Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey

|journal = Publications of the Astronomical Society of Japan

|volume = 63

|issue = 5

|pages = 1117–1138

|bibcode = 2011PASJ...63.1117U

|doi = 10.1093/pasj/63.5.1117

|doi-access=

}} ([http://vizier.cfa.harvard.edu/viz-bin/VizieR-5?-source=J/PASJ/63/1117/acua_v1&Num=21601 online], [https://core.ac.uk/download/pdf/43545172.pdf AcuA catalog p. 153])

{{Cite journal

|first1 = Linda M. |last1 = French

|first2 = Robert D. |last2 = Stephens

|first3 = Daniel R. |last3 = Coley

|first4 = Lawrence H. |last4 = Wasserman

|first5 = Faith |last5 = Vilas

|first6 = Daniel |last6 = La Rocca

|date = October 2013

|title = A Troop of Trojans: Photometry of 24 Jovian Trojan Asteroids

|url = http://adsabs.harvard.edu/cgi-bin/bib_query?bibcode=2013MPBu...40..198F

|journal = The Minor Planet Bulletin

|volume = 40

|issue = 4

|pages = 198–203

|issn = 1052-8091

|bibcode = 2013MPBu...40..198F

|access-date= 19 June 2018}}

{{cite journal

|title = WGSBN Bulletin 5, #5

|url = https://wgsbn-iau.org/files/Bulletins/V005/WGSBNBull_V005_005.pdf

|journal = WGSBN Bulletin

|publisher = International Astronomical Union

|volume = 5

|issue = 5

|date = 7 April 2025

|accessdate = 7 April 2025}}

}}

• [http://www.minorplanet.info/PHP/lcdbsummaryquery.php Asteroid Lightcurve Database (LCDB)], query form ([http://www.minorplanet.info/lightcurvedatabase.html info] {{Webarchive|url=https://web.archive.org/web/20171216050541/http://www.minorplanet.info/lightcurvedatabase.html |date=16 December 2017 }})
• [https://books.google.com/books?id=aeAg1X7afOoC&pg Dictionary of Minor Planet Names], Google books
• [https://www.minorplanetcenter.net/iau/lists/NumberedMPs020001.html Discovery Circumstances: Numbered Minor Planets (20001)-(25000)] – Minor Planet Center
• [https://sbntools.psi.edu/ferret/SimpleSearch/results.action?targetName=21601 Small Bodies Data Ferret] at the Asteroid (21601) 1998 XO89
• {{AstDys|21601}}
• {{JPL small body}}

{{Minor planets navigator | |number=21601 |21602 Ialmenus }}

{{Small Solar System bodies}}

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