148780 Altjira

{{Short description|Binary KBO (Kuiper Belt Object)}}

{{Infobox planet

| minorplanet=yes

| background=#C2E0FF

| name=(148780) Altjira

| image=148780-altjira-hubble.jpg

| image_scale=

| caption=Altjira and its companion imaged by the Hubble Space Telescope in 2006

| discoverer=

| discovery_site=Deep Ecliptic Survey at Kitt Peak

| discovered=20 October 2001
August 2006 (secondary)

| mpc_name=(148780) Altjira

| alt_names={{mp|2001 UQ|18}}

| pronounced={{IPAc-en|æ|l|ˈ|tʃ|ɪr|ə}}

| adjective=Altjirian

| mp_category=Cubewano (DES){{cite web

|author=Marc W. Buie

|author-link=Marc W. Buie

|title=Orbit Fit and Astrometric record for 148780

|publisher=SwRI (Space Science Department)

|url=http://www.boulder.swri.edu/~buie/kbo/astrom/148780.html

|accessdate=2011-11-29}}

| orbit_ref = {{cite web

|type=2008-10-02 last obs

|title=JPL Small-Body Database Browser: 148780 Altjira (2001 UQ18)

|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=148780

|accessdate=26 March 2016}}

| epoch=13 January 2016 (JD 2457400.5)

| semimajor={{Convert|44.224|AU|Tm|abbr=on}}

| perihelion={{Convert|41.572|AU|Tm|abbr=on}}

| aphelion={{Convert|46.877|AU|Tm|abbr=on|lk=on}}

| eccentricity=0.059979

| period=294.10 yr (107421 d)

| inclination=5.2056°

| asc_node=2.0132°

| arg_peri=297.71°

| mean_anomaly=124.29°

| avg_speed=

| satellites=1

| mean_diameter={{val|331|51|187|ul=km}} (combined)
{{val|246|38|139|u=km}} (primary)
{{val|221|34|125|u=km}} (secondary)

| mass= 3.952×10¹⁸ kg

| density={{val|0.30|0.50|0.14|u=g/cm³}}

| surface_grav=

| escape_velocity=

| sidereal_day=

| spectral_type = B−V {{=}} {{val|0.91|0.13}}
V−R {{=}} {{val|0.74|0.08}}
V−I {{=}} {{val|1.17|0.09}}

| abs_magnitude=5.7 5.6, 5.4, or 5.1 (primary)
secondary's magnitude difference with primary's: 0.7 ± 0.2

| albedo={{val|0.0430|0.1825|0.0095}}

| single_temperature=

| observation_arc=2539 days (6.95 yr)

| uncertainty=3

| mean_motion=0.0033513°/day

}}

148780 Altjira {{IPAc-en|æ|l|ˈ|tʃ|ɪr|ə}} is a triple or contact-binary double classical Kuiper belt object (cubewano).[http://www.johnstonsarchive.net/astro/astmoons/am-148780.html Johnston's Archive on (148780) Altjira] Retrieved 2011-11-29 The secondary is large compared to the primary, approximately {{convert|246|km|mi}} vs. {{convert|221|km|mi}}. The Altjiran lightcurve is quite flat (Δmag<0.10), which is indicative of a "quasi-spherical body with a homogeneous surface".{{cite journal | arxiv=0910.1472 | doi=10.1051/0004-6361/200912601 | title=Transneptunian objects and Centaurs from light curves | date=2009 | last1=Duffard | first1=R. | last2=Ortiz | first2=J. L. | last3=Thirouin | first3=A. | last4=Santos-Sanz | first4=P. | last5=Morales | first5=N. | journal=Astronomy & Astrophysics | volume=505 | issue=3 | pages=1283–1295 | bibcode=2009A&A...505.1283D }}

The satellite's orbit has the following parameters: semi-major-axis, {{nowrap|9904 ± 56 km}}; period, {{nowrap|139.561 ± 0.047 days}}; eccentricity, {{nowrap|0.3445 ± 0.0045}}; and inclination, {{nowrap|35.19 ± 0.19°}}(retrograde). The total system mass is about 4{{E-sp|18}} kg.{{Cite journal | last1 = Grundy | first1 = W. M. | last2 = Noll | first2 = K. S. | last3 = Nimmo | first3 = F. | last4 = Roe | first4 = H. G. | last5 = Buie | first5 = M. W. | last6 = Porter | first6 = S. B. | last7 = Benecchi | first7 = S. D. | last8 = Stephens | first8 = D. C. | last9 = Levison | first9 = H. F. | doi = 10.1016/j.icarus.2011.03.012 | last10 = Stansberry | first10 = J. A. | title = Five new and three improved mutual orbits of transneptunian binaries | journal = Icarus | volume = 213 | issue = 2 | pages = 678 | date = 2011 | url = http://es.ucsc.edu/~fnimmo/website/Grundy_KBO.pdf|bibcode = 2011Icar..213..678G |arxiv = 1103.2751 | s2cid = 9571163 }}

It was named after the Arrernte creation deity, Altjira, who created the Earth during the Dreamtime and then retired to the sky.

Altjira may be an unresolved hierarchical triple system.{{cite arXiv |last1=Nelsen |first1=Maia A. |title=Beyond Point Masses. IV. TNO Altjira is Likely a Hierarchical Triple Discovered Through Non-Keplerian Motion |date=2024-03-19 |eprint=2403.12786 |last2=Ragozzine |first2=Darin |last3=Proudfoot |first3=Benjamin C. N. |last4=Giforos |first4=William G. |last5=Grundy |first5=Will|class=astro-ph.EP }}