Editing Planetary system (section)

===Components===

====Planets and stars====
{{main|Planet-hosting stars}}

[[Image:Morgan-Keenan spectral classification.svg|300px|thumb|right|The Morgan-Keenan spectral classification]]
Most known exoplanets orbit stars roughly similar to the [[Sun]]: that is, [[main sequence|main-sequence stars]] of [[stellar classification|spectral categories]] F, G, or K. One reason is that planet-search programs have tended to concentrate on such stars. In addition, statistical analyses indicate that lower-mass stars ([[red dwarf]]s, of [[stellar classification|spectral category]] M) are less likely to have planets massive enough to be detected by the [[radial-velocity method]].<ref name="cumming08">{{Cite journal| author=Andrew Cumming|date=2008|title=The Keck Planet Search: Detectability and the Minimum Mass and Orbital Period Distribution of Extrasolar Planets|journal=Publications of the Astronomical Society of the Pacific|volume=120| issue=867|pages=531–554| arxiv=0803.3357|doi=10.1086/588487| bibcode=2008PASP..120..531C| author2=R. Paul Butler| author3=Geoffrey W. Marcy| last4=Vogt| first4=Steven S.| last5=Wright| first5=Jason T.| last6=Fischer| first6=Debra A.|s2cid=10979195| author-link3=Debra Fischer | display-authors=3}}</ref><ref name="bonfils05">{{Cite journal |doi=10.1051/0004-6361:200500193 |title=The HARPS search for southern extra-solar planets VI: A Neptune-mass planet around the nearby M dwarf Gl 581 |journal=Astronomy and Astrophysics |volume=443 |issue=3 |pages=L15–L18 |year=2005 |last1=Bonfils |first1=Xavier |last2=Forveille |first2=Thierry |last3=Delfosse |first3=Xavier |last4=Udry |first4=Stéphane |last5=Mayor |first5=Michel |last6=Perrier |first6=Christian |last7=Bouchy |first7=François |last8=Pepe |first8=Francesco |last9=Queloz |first9=Didier |last10=Bertaux |first10=Jean-Loup |bibcode=2005A&A...443L..15B |arxiv=astro-ph/0509211 |s2cid=59569803 }}</ref> Nevertheless, several tens of planets around red dwarfs have been discovered by the [[Kepler space telescope]] by the [[transit method]], which can detect smaller planets.

====Circumstellar disks and dust structures====
{{main|Circumstellar disk}}
[[File:NASA-14114-HubbleSpaceTelescope-DebrisDisks-20140424.jpg|thumb|250px|right|[[Debris disks]] detected in [[Hubble Space Telescope|HST]] archival images of young stars, ''HD 141943'' and ''HD 191089'', using improved imaging processes (April 24, 2014).]]
After planets, circumstellar disks are one of the most commonly-observed properties of planetary systems, particularly of young stars. The Solar System possesses at least four major circumstellar disks (the [[asteroid belt]], [[Kuiper belt]], [[scattered disc]], and [[Oort cloud]]) and clearly-observable disks have been detected around nearby solar analogs including [[Epsilon Eridani]] and [[Tau Ceti]]. Based on observations of numerous similar disks, they are assumed to be quite common attributes of stars on the [[main sequence]].

[[Interplanetary dust cloud]]s have been studied in the Solar System and analogs are believed to be present in other planetary systems. Exozodiacal dust, an [[exoplanet]]ary analog of [[zodiacal dust]], the 1–100 micrometre-sized grains of [[amorphous carbon]] and [[silicate]] dust that fill the plane of the Solar System<ref>{{cite journal
 |author1=Stark, C. |author2=Kuchner, M. | title=The Detectability of Exo-Earths and Super-Earths Via Resonant Signatures in Exozodiacal Clouds
 | journal=The Astrophysical Journal | year=2008 | volume=686
 | issue = 1
 | pages=637–648
 | bibcode=2008ApJ...686..637S
 | doi = 10.1086/591442 |arxiv = 0810.2702 |s2cid=52233547 }}</ref> has been detected around the [[51 Ophiuchi]], [[Fomalhaut]],<ref>{{cite journal
|author1=Lebreton, J. |author2=van Lieshout, R. |author3=Augereau, J.-C. |author4=Absil, O. |author5=Mennesson, B. |author6=Kama, M. |author7=Dominik, C. |author8=Bonsor, A. |author9=Vandeportal, J. |author10=Beust, H. |author11=Defrère, D. |author12=Ertel, S. |author13=Faramaz, V. |author14=Hinz, P. |author15=Kral, Q. |author16=Lagrange, A.-M. |author17=Liu, W. |author18=Thébault, P. | title= An interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin 
 | journal=Astronomy and Astrophysics | year=2013 | volume=555
 | pages=A146
 | bibcode=2013A&A...555A.146L
 | doi = 10.1051/0004-6361/201321415 |arxiv = 1306.0956 |s2cid=12112032 }}</ref><ref name="VLTI/PIONIER">{{cite journal
|author1=Absil, O. |author2=Le Bouquin, J.-B. |author3=Berger, J.-P. |author4=Lagrange, A.-M. |author5=Chauvin, G. |author6=Lazareff, B. |author7=Zins, G. |author8=Haguenauer, P. |author9=Jocou, L. |author10=Kern, P. |author11=Millan-Gabet, R. |author12=Rochat, S. |author13=Traub, W. | title= Searching for faint companions with VLTI/PIONIER. I. Method and first results  
 | journal=Astronomy and Astrophysics   | year=2011 | volume=535
 | pages=A68
 | bibcode=2011A&A...535A..68A
 | doi = 10.1051/0004-6361/201117719 |arxiv = 1110.1178 |s2cid=13144157 }}</ref> [[Tau Ceti]],<ref name="VLTI/PIONIER" /><ref>{{cite journal
 |author1=di Folco, E. |author2=Absil, O. |author3=Augereau, J.-C. |author4=Mérand, A. |author5=Coudé du Foresto, V. |author6=Thévenin, F. |author7=Defrère, D. |author8=Kervella, P. |author9=ten Brummelaar, T. A. |author10=McAlister, H. A. |author11=Ridgway, S. T. |author12=Sturmann, J. |author13=Sturmann, L. |author14=Turner, N. H. | title=A near-infrared interferometric survey of debris disk stars
 | journal=Astronomy and Astrophysics | year=2007 | volume=475
 | issue = 1
 | pages=243–250
 | bibcode=2007A&A...475..243D
 | doi = 10.1051/0004-6361:20077625 |arxiv = 0710.1731 |s2cid=18317389 }}</ref> and [[Vega]] systems.

====Comets====
{{main|Comet}}
{{As of|2014|11}} there are 5,253 known Solar System comets<ref>{{cite web |last=Johnston |first=Robert |title=Known populations of solar system objects |url=http://www.johnstonsarchive.net/astro/sslist.html |date=August 2, 2014 |access-date=January 19, 2015 |archive-date=June 9, 2019 |archive-url=https://web.archive.org/web/20190609054832/http://www.johnstonsarchive.net/astro/sslist.html |url-status=dead }}</ref> and they are thought to be common components of planetary systems. The first exocomets were detected in 1987<ref name="Ferlet et al.1987">{{cite journal | bibcode=1987A&A...185..267F |title=The Beta Pictoris circumstellar disk. V - Time variations of the CA II-K line|author1=Ferlet, R. |author2=Vidal-Madjar, A. |author3=Hobbs, L. M.|year=1987|journal=[[Astronomy and Astrophysics]]|volume=185|pages=267–270}}</ref><ref name="Beust1990">{{cite journal |bibcode=1990A&A...236..202B |title=The Beta Pictoris circumstellar disk. X - Numerical simulations of infalling evaporating bodies |last1=Beust |first1=H. |last2=Lagrange-Henri |first2=A.M. |last3=Vidal-Madjar |first3=A. |last4=Ferlet |first4=R. |volume=236 |year=1990 |pages=202–216 |journal=[[Astronomy and Astrophysics]]}}</ref> around [[Beta Pictoris]], a very young [[A-type main-sequence star]]. There are now a total of 11 stars around which the presence of exocomets have been observed or suspected.<ref name="Lagrange-Henri et al.1990">{{cite journal| bibcode=1990A&A...227L..13L |title=HR 10 - A new Beta Pictoris-like star?|author1=Lagrange-Henri, A. M. |author2=Beust, H. |author3=Ferlet, R. |author4=Vidal-Madjar, A. |author5=Hobbs, L. M.|year=1990|journal=[[Astronomy and Astrophysics]]|volume=227|pages=L13–L16}}</ref><ref name="Lecavelier Des Etangs et al.1997">{{cite journal| bibcode=1997A&A...325..228L |title=HST-GHRS observations of candidate β Pictoris-like circumstellar gaseous disks.|author=Lecavelier Des Etangs, A.|display-authors=etal|year=1997|journal=[[Astronomy and Astrophysics]]|volume=325|pages=228–236}}</ref><ref name="Welsh et al.2013">{{cite journal| bibcode=2013PASP..125..759W |title=Circumstellar Gas-Disk Variability Around A-Type Stars: The Detection of Exocomets?|author1=Welsh, B. Y. |author2=Montgomery, S. |name-list-style=amp |year=2013|journal=[[Publications of the Astronomical Society of the Pacific]]|volume=125|issue=929|pages=759–774|doi=10.1086/671757|doi-access=free}}</ref><ref name="Kiefer et al.2014">{{cite journal| bibcode=2014A&A...561L..10K |title=Exocomets in the circumstellar gas disk of HD 172555|author1=Kiefer, F. |author2=Lecavelier Des Etangs, A.|display-authors=etal|year=2014|journal=[[Astronomy and Astrophysics]]|volume=561|pages=L10|doi=10.1051/0004-6361/201323128|arxiv = 1401.1365 |s2cid=118533377}}</ref> All discovered exocometary systems ([[Beta Pictoris]], [[HR 10]],<ref name="Lagrange-Henri et al.1990"/> [[51 Ophiuchi]], [[HR 2174]],<ref name="Lecavelier Des Etangs et al.1997"/> [[49 Ceti]], [[5 Vulpeculae]], [[2 Andromedae]], [[HD 21620]], [[HD 42111]], [[HD 110411]],<ref name="Welsh et al.2013" /><ref name="Space-20130107">{{cite web |title='Exocomets' Common Across Milky Way Galaxy |url=http://www.space.com/19156-exocomets-alien-solar-systems.html |date=January 7, 2013 |publisher=Space.com |access-date=January 8, 2013 }}</ref> and more recently [[HD 172555]]<ref name="Kiefer et al.2014" />) are around very young [[Stellar classification#Class A|A-type stars]].

====Other components====
{{Further|Circumplanetary disk}}
Computer modelling of an impact in 2013 detected around the star [[2MASS J08090250-4858172|NGC 2547-ID8]] by the [[Spitzer Space Telescope]], and confirmed by ground observations, suggests the involvement of large asteroids or [[protoplanet]]s similar to the events believed to have led to the formation of terrestrial planets like the Earth.<ref>{{Cite web |title=NASA's Spitzer Telescope Witnesses Asteroid Smashup |url=https://www.jpl.nasa.gov/news/nasas-spitzer-telescope-witnesses-asteroid-smashup/ |access-date=2025-05-17 |website=NASA Jet Propulsion Laboratory (JPL) |language=en-US}}</ref>

Based on observations of the Solar System's large collection of natural satellites, they are believed common components of planetary systems; however, the existence of [[exomoons]] has not yet been confirmed. The star [[1SWASP J140747.93-394542.6]], in the constellation [[Centaurus]], is a strong candidate for a natural satellite.<ref>{{Cite web |title=Saturn-like ring system eclipses Sun-like star |url=https://www.sciencedaily.com/releases/2012/01/120109115830.htm |access-date=2025-05-17 |website=ScienceDaily |language=en |quote=Mamajek thinks his team could be either observing the late stages of planet formation if the transiting object is a star or brown dwarf, or possibly moon formation if the transiting object is a giant planet.}}</ref> Indications suggest that the confirmed extrasolar planet [[WASP-12b]] also has at least one satellite.<ref>[http://www.ria.ru/science/20120206/558647431.html Российские астрономы впервые открыли луну возле экзопланеты] (in Russian) – "Studying of a curve of change of shine of WASP-12b has brought to the Russian astronomers unusual result: regular splashes were found out.<...> Though stains on a star surface also can cause similar changes of shine, observable splashes are very similar on duration, a profile and amplitude that testifies for benefit of exomoon existence."</ref>