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List of Andromeda's satellite galaxies

Collections of galaxies around Messier 31

The Andromeda Galaxy with M110 at the bottom and M32 to the upper left of the core.

The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 35 dwarf galaxies: the brightest and largest is M110, which can be seen with a basic telescope. The second-brightest and closest one to M31 is M32. The other galaxies are fainter, and were mostly discovered starting from the 1970s.

On January 11, 2006, it was announced that Andromeda Galaxy's faint companion galaxies lie on or close to a single plane running through the Andromeda Galaxy's center. This unexpected distribution is not obviously understood in the context of current models for galaxy formation. The plane of satellite galaxies points toward a nearby group of galaxies (M81 Group), possibly tracing the large-scale distribution of dark matter.

It is unknown whether the Triangulum Galaxy is a satellite of Andromeda.

Table of known satellites

Andromeda Galaxy's satellites are listed here by discovery (orbital distance is not known). Andromeda IV is not included in the list, as it was discovered to be roughly 10 times further than Andromeda from the Milky Way in 2014, and therefore a completely unrelated galaxy.

Name	Type	Distance from Sun
(million ly)	Right Ascension**	Declination**	bibcode=2010ApJ...711..671K	title=The SPLASH Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, II, III, VII, X, and XIV Dwarf Spheroidal Galaxies	last1=Kalirai	first1=Jason S.	last2=Beaton	first2=Rachael L.	last3=Geha	first3=Marla C.	author3-link= Marla Geha	last4=Gilbert	first4=Karoline M.	last5=Guhathakurta	first5=Puragra	last6=Kirby	first6=Evan N.	last7=Majewski	first7=Steven R.	last8=Ostheimer	first8=James C.	last9=Patterson	first9=Richard J.	last10=Wolf	first10=Joe	journal=The Astrophysical Journal	year=2010	volume=711	issue=2	pages=671–692	doi=10.1088/0004-637X/711/2/671	arxiv=0911.1998	s2cid=43188686 }}	Apparent magnitude	Mass-to-light ratio	3D distance to M31 (kly)	Year
discovered	Notes
M32	dE2	2.48				+8.1			1749
M110	dE6	2.69			−16.5	+8.5			1773
NGC 185	dE5	2.01				+10.1			1787
NGC 147	dE5	2.2				+10.5			1829
Andromeda I	dSph	2.43			−11.8	+13.6	31 ± 6		1970
Andromeda II***	dSph	2.13			−12.6	+13.5	13 ± 3		1970
Andromeda III	dSph	2.44			−10.2	+15.0	19 ± 12		1970
Andromeda V	dSph	2.52			−9.6	+15.9	bibcode=2011MNRAS.417.1170C	title=The scatter about the 'Universal' dwarf spheroidal mass profile: A kinematic study of the M31 satellites and V and VI	last1=Collins	first1=M. L. M.	last2=Chapman	first2=S. C.	last3=Rich	first3=R. M.	last4=Irwin	first4=M. J.	last5=Peñarrubia	first5=J.	last6=Ibata	first6=R. A.	last7=Arimoto	first7=N.	last8=Brooks	first8=A. M.	last9=Ferguson	first9=A. M. N.	last10=Lewis	first10=G. F.	last11=McConnachie	first11=A. W.	last12=Venn	first12=K.	journal=Monthly Notices of the Royal Astronomical Society	year=2011	volume=417	issue=2	page=1170	doi=10.1111/j.1365-2966.2011.19342.x	doi-access=free	arxiv=1103.2121	s2cid=6345715 }}		1998
Pegasus Dwarf Spheroidal
(Andromeda VI)	dSph	2.55			−11.5	+14.2	12 ± 5		1998
Cassiopeia Dwarf
(Andromeda VII)	dSph	2.49			−13.3	+12.9	7.1 ± 2.8		1998
Andromeda VIII	dSph	2.7	**	**		+9.1			2003	Tidally disrupting; identification unclear
Andromeda IX	dSph	2.5			−8.3	+16.2		127.2	2004
Andromeda X	dSph	2.9			−8.1	+16.1	63 ± 40	332.7	2005
arxiv=astro-ph/0607472	doi=10.1111/j.1365-2966.2006.10823.x	title=Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy	year=2006	last1=Martin	first1=N. F.	last2=Ibata	first2=R. A.	last3=Irwin	first3=M. J.	last4=Chapman	first4=S.	last5=Lewis	first5=G. F.	last6=Ferguson	first6=A. M. N.	last7=Tanvir	first7=N.	last8=McConnachie	first8=A. W.	journal=Monthly Notices of the Royal Astronomical Society	volume=371	issue=4	pages=1983–1991	doi-access=free	bibcode=2006MNRAS.371.1983M	s2cid=20171599 }}	dSph		**	**	−7.3				2006
Andromeda XII	dSph		**	**	−6.4				2006
Andromeda XIII (Pisces III)	dSph				−6.9				2006
Andromeda XIV (Pisces IV)	dSph				−8.3		102 ± 71		2007
Andromeda XV	dSph		**	**	−9.4				2007
Andromeda XVI (Pisces V)	dSph	doi=10.3847/0004-637X/819/2/147	title=The Islands Project. I. Andromeda Xvi, an Extremely Low Mass Galaxy Not Quenched by Reionization	year=2016	last1=Monelli	first1=Matteo	last2=Martínez-Vázquez	first2=Clara E.	last3=Bernard	first3=Edouard J.	last4=Gallart	first4=Carme	last5=Skillman	first5=Evan D.	last6=Weisz	first6=Daniel R.	last7=Dolphin	first7=Andrew E.	last8=Hidalgo	first8=Sebastian L.	last9=Cole	first9=Andrew A.	last10=Martin	first10=Nicolas F.	last11=Aparicio	first11=Antonio	last12=Cassisi	first12=Santi	last13=Boylan-Kolchin	first13=Michael	last14=Mayer	first14=Lucio	last15=McConnachie	first15=Alan	last16=McQuinn	first16=Kristen B. W.	last17=Navarro	first17=Julio F.	journal=The Astrophysical Journal	volume=819	issue=2	page=147	arxiv=1603.00625	bibcode=2016ApJ...819..147M	s2cid=32263075	doi-access=free }}	−9.2	580.6	2007
Andromeda XVII	dSph		**	**	−8.5			313.1	2008
Andromeda XVIII	dSph/Sm							515.3	2008
Andromeda XIX	dSph		**	**	−9.3				2008
Andromeda XX	dSph				−6.3			512.1	2008
Andromeda XXI	dSph		**	**	−9.9			472.9	2009
Andromeda XXII	dSph		**	**	−7.0			910	2009
Andromeda XXIII	dIrr							427.3	2011
Andromeda XXIV			**	**				401.2	2011
Andromeda XXV			**	**				319.6	2011
Andromeda XXVI								489.2	2011
Andromeda XXVII			**	**					2011	Tidally disrupted
last=Moore	first=Nicole Casal	date=7 Nov 2011	title=Newly found dwarf galaxies could help reveal the nature of dark matter	work=News Service	publisher=University of Michigan	url=http://www.ns.umich.edu/new/releases/20040-newly-found-dwarf-galaxies-could-help-reveal-the-nature-of-dark-matter	access-date=10 Dec 2011 }} (reprinted in R&D Magazine)	dSph				−8.8				2011
Andromeda XXIX	dIrr							636	2011
last1=McConnachie	first1=Alan W.	year=2012	title=The observed properties of dwarf galaxies in and around the Local Group	journal=The Astronomical Journal	volume=144	issue=1	pages=4	arxiv=1204.1562	doi=10.1088/0004-6256/144/1/4	bibcode=2012AJ....144....4M	s2cid=118515618	url=http://www.astro.uvic.ca/~alan/Nearby_Dwarf_Database.html }}	dSph?
Andromeda XXXI (Lacerta I)	dSph?								2013
Andromeda XXXII (Cassiopeia III)	dSph?	2.74						doi=10.3847/1538-3881/acf859	doi-access=free	title=Exploring the Structures and Substructures of the Andromeda Satellite Dwarf Galaxies Cassiopeia III, Perseus I, and Lacerta I	date=2023	last1=Rhode	first1=Katherine L.	last2=Smith	first2=Nicholas J.	last3=Crnojevic	first3=Denija	last4=Sand	first4=David J.	last5=Lambert	first5=Ryan A.	last6=Vesperini	first6=Enrico	last7=Smith	first7=Madison V.	last8=Janowiecki	first8=Steven	last9=Salzer	first9=John J.	last10=Karunakaran	first10=Ananthan	last11=Spekkens	first11=Kristine	journal=The Astronomical Journal	volume=166	issue=5	page=180	arxiv=2309.01045	bibcode=2023AJ....166..180R }}	2013
Andromeda XXXIII (Perseus I)	dSph?	2.41						1,140	2013
Tidal Stream Northwest
(Tidal Stream E and F)			**	**					2009
Tidal Stream Southwest			**	**					2009
Pegasus V galaxy (Peg V, Andromeda XXXIV)	d	682 kpc	±0.1	±3	−6.3			245 kpc	2022	url= http://www.sci-news.com/astronomy/pegasus-v-10960.html	title= Pegasus V: New Ultra-Faint Dwarf Galaxy Spotted in Outskirts of Andromeda	date= 1 July 2022	publisher= Sci-News }}
Andromeda XXXV		3.02			-5.2			158 kpc	2025
Triangulum Galaxy*
(M33)	SA(s)cd	2.59				+6.27		750	1654?	Its relation to Andromeda is uncertain.

It is uncertain whether it is a companion galaxy of the Andromeda Galaxy.

** RA/DEC values marked in Italics are rough estimates.

*** Martin et al. (2009) gave aliases to several satellite galaxies of the Andromeda Galaxy that are located in Pisces. However, the name Pisces II was later used for a different galaxy that is a satellite of the Milky Way, so it is not used here.

References

(2025-02-27). "NASA's Hubble Provides Bird's-Eye View of Andromeda Galaxy's Ecosystem - NASA Science".
(2010). "The SPLASH Survey: Internal Kinematics, Chemical Abundances, and Masses of the Andromeda I, II, III, VII, X, and XIV Dwarf Spheroidal Galaxies". The Astrophysical Journal.
(2011). "The scatter about the 'Universal' dwarf spheroidal mass profile: A kinematic study of the M31 satellites and V and VI". Monthly Notices of the Royal Astronomical Society.
(2006). "Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy". Monthly Notices of the Royal Astronomical Society.
[http://spider.seds.org/spider/LG/Add/lg_dis.html Discovery of the Local Group Galaxies]
(2016). "The Islands Project. I. Andromeda Xvi, an Extremely Low Mass Galaxy Not Quenched by Reionization". The Astrophysical Journal.
(2019). "A dwarf disrupting - Andromeda XXVII and the North West Stream". Monthly Notices of the Royal Astronomical Society.
Moore, Nicole Casal. (7 Nov 2011). "Newly found dwarf galaxies could help reveal the nature of dark matter". University of Michigan.
(2024). "Stellar Metallicities and Gradients in the Faint M31 Satellites Andromeda XVI and Andromeda XXVIII". The Astrophysical Journal.
(2012). "The observed properties of dwarf galaxies in and around the Local Group". The Astronomical Journal.
(2023). "Exploring the Structures and Substructures of the Andromeda Satellite Dwarf Galaxies Cassiopeia III, Perseus I, and Lacerta I". The Astronomical Journal.
[http://www.ucolick.org/~raja/aas_prs_rls_010610/ New tidal streams found in Andromeda reveal history of galactic mergers]
(1 July 2022). "Pegasus V: New Ultra-Faint Dwarf Galaxy Spotted in Outskirts of Andromeda". Sci-News.
University of Surrey. (30 June 2022). "New fossil galaxy discovery could answer important questions about the history of the universe". AAAS.
(2022). "Pegasus V/Andromeda XXXIV–a newly discovered ultrafaint dwarf galaxy on the outskirts of Andromeda". Monthly Notices of the Royal Astronomical Society: Letters.
(2025-03-11). "Andromeda XXXV: The Faintest Dwarf Satellite of the Andromeda Galaxy". The Astrophysical Journal Letters.
"Messier Object 33".
Martin, Nicolas F.. (1 November 2009). "PAndAS' CUBS: Discovery of Two New Dwarf Galaxies in the Surroundings of the Andromeda and Triangulum Galaxies". The Astrophysical Journal.
(2010). "Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way". The Astrophysical Journal.

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