Editing AU Microscopii (section)

== Planetary system ==
AU Microscopii's debris disk has an asymmetric structure and an inner gap or hole cleared of debris, which has led a number of astronomers to search for planets orbiting AU Microscopii.  By 2007, no searches had led to any detections of planets.<ref name = "METCHEVETAL05" /><ref name = "MASCIADRIETAL05"/> However, in 2020 the discovery of a Neptune-sized planet was announced based on [[astronomical transit|transit]] observations by [[Transiting Exoplanet Survey Satellite|TESS]].<ref name=PlavchanNature_2020/> Its rotation axis is well aligned with the rotation axis of the parent star, with the misalignment being equal to 5{{±|16|15}}°.<ref name=Duncan2020/>

Since 2018, a second planet, AU Microscopii c, was suspected to exist. It was confirmed in December 2020, after additional transit events were documented by the TESS observatory.<ref name=Martioli2020/> A 2024 study which performed measurements of [[Rossiter–McLaughlin effect]] for the planet c revealed that the planet is possibly misaligned with the star's rotation axis, returning a poorly constrained value of projected [[Axial tilt#Extrasolar planets|obliquity]] ''λ''<sub>c</sub> = {{val|67.8|31.7|49.0|u=deg}}.<ref name=Yu2024 />

A third planet in the system was suspected since 2022 based on [[transit-timing variation]]s,<ref name=Wittrock2022/> and "validated" in 2023, although several possible orbital periods of planet d cannot be ruled out yet. This planet has a mass comparable to that of Earth.<ref name=Wittrock2023/> [[Doppler spectroscopy|Radial velocity]] observations have also found evidence for a fourth, outer planet as of 2023.<ref name="Donati2023"/> Observations of the AU Microscopii system with the [[James Webb Space Telescope]] were unable to confirm the presence of previously unknown companions.<ref name="Joshua E 2308">{{Cite journal |last1=Lawson |first1=Kellen |last2=Schlieder |first2=Joshua E. |last3=Leisenring |first3=Jarron M. |last4=Bogat |first4=Ell |last5=Beichman |first5=Charles A. |last6=Bryden |first6=Geoffrey |last7=Gáspár |first7=András |last8=Groff |first8=Tyler D. |last9=McElwain |first9=Michael W. |last10=Meyer |first10=Michael R. |last11=Barclay |first11=Thomas |last12=Calissendorff |first12=Per |last13=De Furio |first13=Matthew |last14=Ygouf |first14=Marie |last15=Boccaletti |first15=Anthony |date=2023-10-01 |title=JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii |journal=The Astronomical Journal |volume=166 |issue=4 |pages=150 |doi=10.3847/1538-3881/aced08 |doi-access=free |arxiv=2308.02486 |bibcode=2023AJ....166..150L |issn=0004-6256}}</ref> Observations with [[CHEOPS]] also detected strong TTVs of AU Mic c, which can be explained with planet d on a 12.6 day orbit. The mass of planet d is found to be only about 20% of the mass of earth (or two [[Mars]] masses) according to this study.<ref name="Boldog2025">{{Cite journal |arxiv=2501.09058 |last1=Matrà |first1=L. |title=REsolved ALMA and SMA Observations of Nearby Stars (REASONS): A population of 74 resolved planetesimal belts at millimetre wavelengths |date=2025-01-15 |last2=Marino |first2=S. |last3=Wilner |first3=D. J. |last4=Kennedy |first4=G. M. |last5=Booth |first5=M. |last6=Krivov |first6=A. V. |last7=Williams |first7=J. P. |last8=Hughes |first8=A. M. |last9=Burgo |first9=C. del|journal=Astronomy and Astrophysics |volume=693 |doi=10.1051/0004-6361/202451397 |bibcode=2025A&A...693A.151M }}</ref>

{{OrbitboxPlanet begin
| name = AU Microscopii
| table_ref = <ref name=Martioli2020/><ref name="Cale2021"/><ref name=Wittrock2023/><ref name="Donati2023"/><ref name="Boldog2025"/>
}}
{{OrbitboxPlanet
| exoplanet = b
| mass_earth = {{val|10.2|3.9|2.7}}
| radius_earth = {{val|4.07|0.17}}
| semimajor = {{val|0.0645|0.0013}}
| period = {{val|8.4630351|0.0000003}}
| eccentricity = {{val|0.00021|0.00006}}
| inclination = {{val|89.9904|0.0036|0.0019}}
}}
{{OrbitboxPlanet
| exoplanet = d
| mass_earth = {{val|1.014|0.146}} or<br />{{val|0.203|0.022|0.024}}
| radius_earth = 
| semimajor = 
| period = {{val|12.73812|0.00128}}
| eccentricity = {{val|0.00097|0.00042}}
| inclination = {{val|88.10|0.43}}
}}
{{OrbitboxPlanet
| exoplanet = c
| mass_earth = {{val|14.2|4.8|3.5}}
| radius_earth = {{val|3.24|0.16}}
| semimajor = {{val|0.1101|0.0020}}
| period = {{val|18.85901|0.00009}}
| eccentricity = {{val|0.01056|0.00089}}
| inclination = {{val|89.589|0.058|0.068}}
}}
{{OrbitboxPlanet hypothetical
| exoplanet = e
| mass_earth = {{val|35.2|6.7|5.4}}
| radius_earth = 
| semimajor = 
| period = {{val|33.39|0.10}}
| eccentricity = 
| inclination = 
}}
{{OrbitboxPlanet disk
| disk = Debris disk
| periapsis =<50
| apoapsis =>150
| inclination = <!--Inclination from the plane of the sky, in degrees-->
}}
{{Orbitbox end}}

===Debris disk===
[[Image:Debris disk AU Mic HST.jpg|left|thumb|[[Hubble Space Telescope]] image of the debris disk around AU Microscopii.]]
[[File:Mysterious ripples moving through the disc of AU Microscopii.webm|thumb|left|This short time lapse sequence shows images of the debris disk's "fast-moving features".]]

[[File:Dusty Debris Disk Around AU Mic (au-mic1).jpeg|thumb|left|300px|[[James Webb Space Telescope]] has imaged (Au Mic) the inner workings of a dusty disk surrounding a nearby red dwarf star.<ref>{{cite news |date=October 18, 2023 |title=Dusty Debris Disk Around AU Mic6 |url=https://esawebb.org/images/au-mic1/}}</ref> ]]

All-sky observations with the [[IRAS|Infrared Astronomy Satellite]] revealed faint infrared emission from AU Microscopii.<ref>{{Cite web |title=IRASFSC - IRAS Faint Source Catalog, Version 2.0 |url=https://heasarc.gsfc.nasa.gov/W3Browse/all/irasfsc.html |access-date=2024-05-10 |website=heasarc.gsfc.nasa.gov}}</ref><ref>{{Cite journal |last=Moshir |first=M. |display-authors=etal |date=1990-01-01 |title=IRAS Faint Source Catalogue, version 2.0. |url=https://ui.adsabs.harvard.edu/abs/1990IRASF.C......0M |journal=IRAS Faint Source Catalogue |pages=0|bibcode=1990IRASF.C......0M }}</ref> This emission is due to a circumstellar [[Debris disk|disk of dust]] which first resolved at optical wavelengths in 2003 by [[Paul Kalas]] and collaborators using the [[UH88|University of Hawaii 2.2-m telescope]] on [[Mauna Kea]], Hawaii.<ref name="KALASETAL04" />  This large debris disk faces the earth edge-on at nearly 90 degrees,<ref>{{cite journal|author = Paul Kalas, James R. Graham and Mark Clampin|title = A planetary system as the origin of structure in Fomalhaut's dust belt|journal = Nature|date = 23 June 2005|pages = 1067–1070|bibcode = 2005Natur.435.1067K|doi = 10.1038/nature03601|issue = 7045|volume = 435|pmid = 15973402|arxiv = astro-ph/0506574 |s2cid = 4406070}}</ref> and measures at least 200 [[Astronomical unit|AU]] in radius.  At these large distances from the star, the lifetime of dust in the disk exceeds the age of AU Microscopii.<ref name="KALASETAL04" />  The disk has a gas to dust mass ratio of no more than 6:1, much lower than the usually assumed primordial value of 100:1.<ref name="ROBERGEETAL05" />  The debris disk is therefore referred to as "gas-poor", as the primordial gas within the circumstellar system has been mostly depleted.<ref>{{Cite journal |last1=Roberge |first1=Aki |last2=Weinberger |first2=Alycia J. |last3=Redfield |first3=Seth |last4=Feldman |first4=Paul D. |date=2005-06-01 |title=Rapid Dissipation of Primordial Gas from the AU Microscopii Debris Disk |url=https://ui.adsabs.harvard.edu/abs/2005ApJ...626L.105R |journal=The Astrophysical Journal |volume=626 |issue=2 |pages=L105–L108 |doi=10.1086/431899 |arxiv=astro-ph/0505302 |bibcode=2005ApJ...626L.105R |issn=0004-637X}}</ref>  The total amount of dust visible in the disk is estimated to be at least a lunar mass, while the larger [[planetesimal]]s from which the dust is produced are inferred to have at least six lunar masses.<ref>{{cite journal|author1=C. H. Chen |author2=B. M. Patten |author3=M. W. Werner |author4=C. D. Dowell |author5=K. R. Stapelfeldt |author6=I. Song |author7=J. R. Stauffer |author8=M. Blaylock |author9=K. D. Gordon |author10=V. Krause  |name-list-style=amp |title = A Spitzer Study of Dusty Disks around Nearby, Young Stars|journal = The Astrophysical Journal|date = December 1, 2005|issue = 2|pages = 1372–1384|bibcode = 2005ApJ...634.1372C|doi = 10.1086/497124|volume = 634|doi-access=free }}</ref>

The [[Astronomical spectroscopy|spectral energy distribution]] of AU Microscopii's debris disk at [[Submillimetre astronomy|submillimetre]] wavelengths indicate the presence of an inner hole in the disk extending to 17 AU,<ref>{{cite journal|title = A Submillimeter Search of Nearby Young Stars for Cold Dust: Discovery of Debris Disks around Two Low-Mass Stars|author1=Michael C. Liu |author2=Brenda C. Matthews |author3=Jonathan P. Williams |author4=Paul G. Kalas  |name-list-style=amp |journal = [[The Astrophysical Journal]]|date = June 10, 2004|volume = 608|issue = 1|pages = 526–532|bibcode = 2004ApJ...608..526L|doi = 10.1086/392531|arxiv = astro-ph/0403131 |s2cid=9178164 }}</ref> while scattered light images estimate the inner hole to be 12 AU in radius.<ref name="KIRSTETAL05" />  Combining the spectral energy distribution with the surface brightness profile yields a smaller estimate of the radius of the inner hole, 1 - 10 AU.<ref name="METCHEVETAL05" /> The inner part of the disk is [[asymmetry|asymmetric]] and shows structure in the inner 40 AU.<ref name="LIU04" />  The inner structure has been compared with that expected to be seen if the disk is influenced by larger bodies or has undergone recent planet formation.<ref name="LIU04" /> The [[surface brightness]] (brightness per area) of the disk in the near infrared <math style="vertical-align:+0em">\scriptstyle I</math> as a function of projected distance <math style="vertical-align:+0em">\scriptstyle r</math> from the star follows a characteristic shape.  The inner <math style="vertical-align:+0em">\scriptstyle r\,<\,15 AU</math> of the disk appear approximately constant in density and the brightness is unchanging, more-or-less flat.<ref name="KIRSTETAL05" />  Around  <math style="vertical-align:-0.07em">\scriptstyle r\, \approx\, 15 AU</math> the density and surface brightness begins to decrease: first it decreases slowly in proportion to distance as <math style="vertical-align:+0em">\scriptstyle I\, \propto \,  r^{-1.8}</math>; then outside <math style="vertical-align:+0em">\scriptstyle r\, \approx\, 43 AU</math>, the density and brightness drops much more steeply, as <math style="vertical-align:+0em">\scriptstyle I\, \propto \, r^{-4.7}</math>.<ref name="KIRSTETAL05" />  This "broken power-law" shape is similar to the shape of the profile of β Pic's disk.

In October 2015 it was reported that astronomers using the [[Very Large Telescope]] (VLT) had detected very unusual outward-moving features in the disk. By comparing the VLT images with those taken by the [[Hubble Space Telescope]] in 2010 and 2011 it was found that the wave-like structures are moving away from the star at speeds of up to 10 kilometers per second (22,000 miles per hour). The waves farther away from the star seem to be moving faster than those close to it, and at least three of the features are moving fast enough to escape the gravitational pull of the star.<ref name="Ripples">{{cite web|title=Mysterious Ripples Found Racing Through Planet-Forming Disk |url=http://hubblesite.org/newscenter/archive/releases/2015/36/ |website=Hubblesite |access-date=8 October 2015 |archive-url=https://web.archive.org/web/20151011023230/http://hubblesite.org/newscenter/archive/releases/2015/36/full/ |archive-date=11 October 2015 |url-status=live }}</ref> Follow-up observations with the [[VLT-SPHERE|SPHERE]] instrument on the [[Very Large Telescope]] were able to confirm the presence of the fast-moving features,<ref>{{Cite journal |last1=Boccaletti |first1=A. |last2=Sezestre |first2=E. |last3=Lagrange |first3=A.-M. |last4=Thébault |first4=P. |last5=Gratton |first5=R. |last6=Langlois |first6=M. |last7=Thalmann |first7=C. |last8=Janson |first8=M. |last9=Delorme |first9=P. |last10=Augereau |first10=J.-C. |last11=Schneider |first11=G. |last12=Milli |first12=J. |last13=Grady |first13=C. |last14=Debes |first14=J. |last15=Kral |first15=Q. |date=2018-06-01 |title=Observations of fast-moving features in the debris disk of AU Mic on a three-year timescale: Confirmation and new discoveries |url=https://www.aanda.org/articles/aa/abs/2018/06/aa32462-17/aa32462-17.html |journal=Astronomy & Astrophysics |language=en |volume=614 |pages=A52 |doi=10.1051/0004-6361/201732462 |arxiv=1803.05354 |bibcode=2018A&A...614A..52B |issn=0004-6361}}</ref> and James Webb Space Telescope observations found similar features within the disk in two NIRCam filters;<ref name="Joshua E 2308"/> however, these features have not been detected in the radio with [[Atacama Large Millimeter Array]] observations.<ref>{{Cite journal |last1=Daley |first1=Cail |last2=Hughes |first2=A. Meredith |last3=Carter |first3=Evan S. |last4=Flaherty |first4=Kevin |last5=Lambros |first5=Zachary |last6=Pan |first6=Margaret |last7=Schlichting |first7=Hilke |last8=Chiang |first8=Eugene |last9=Wyatt |first9=Mark |last10=Wilner |first10=David |last11=Andrews |first11=Sean |last12=Carpenter |first12=John |date=2019-04-01 |title=The Mass of Stirring Bodies in the AU Mic Debris Disk Inferred from Resolved Vertical Structure |journal=The Astrophysical Journal |volume=875 |issue=2 |pages=87 |doi=10.3847/1538-4357/ab1074 |doi-access=free |arxiv=1904.00027 |bibcode=2019ApJ...875...87D |issn=0004-637X}}</ref><ref name="Evan S 2207">{{Cite journal |last1=Vizgan |first1=David |last2=Meredith Hughes |first2=A. |last3=Carter |first3=Evan S. |last4=Flaherty |first4=Kevin M. |last5=Pan |first5=Margaret |last6=Chiang |first6=Eugene |last7=Schlichting |first7=Hilke |last8=Wilner |first8=David J. |last9=Andrews |first9=Sean M. |last10=Carpenter |first10=John M. |last11=Moór |first11=Attila |last12=MacGregor |first12=Meredith A. |date=2022-08-01 |title=Multiwavelength Vertical Structure in the AU Mic Debris Disk: Characterizing the Collisional Cascade |journal=The Astrophysical Journal |volume=935 |issue=2 |pages=131 |doi=10.3847/1538-4357/ac80b8 |doi-access=free |arxiv=2207.05277 |bibcode=2022ApJ...935..131V |issn=0004-637X}}</ref> These fast-moving features have been described as "dust avalanches", where dust particles catastrophically collide into planetesimals within the disk.<ref>{{Cite journal |last1=Chiang |first1=Eugene |last2=Fung |first2=Jeffrey |date=2017-10-05 |title=Stellar Winds and Dust Avalanches in the AU Mic Debris Disk |journal=The Astrophysical Journal |volume=848 |issue=1 |pages=4 |doi=10.3847/1538-4357/aa89e6 |doi-access=free |arxiv=1707.08970 |bibcode=2017ApJ...848....4C |issn=0004-637X}}</ref><ref name="Evan S 2207"/>