View source for Backyard Worlds

{{short description|NASA-funded citizen science project}}
{{Use dmy dates|date=February 2017}}
{{Infobox website
| name = Backyard Worlds: Planet 9
| logo = File:Backyard_Worlds_logo.png
| logo_caption = Logo of Backyard Worlds: Planet 9
| screenshot = 
| caption = Backyard Worlds: Planet 9 logo
| url = {{URL|http://www.backyardworlds.org}}
| commercial = No
| type = [[Citizen science]] project
| language = English
| registration = Optional
| owner = 
| author = 
| launch_date = {{Start date and age|2017|02|15|df=yes|br=yes}}
| current_status = Online
}}
'''Backyard Worlds: Planet 9''' is a [[NASA]]-funded [[citizen science]] project which is part of the [[Zooniverse (citizen science project)|Zooniverse]] [[web portal]].<ref name="nasawantsyou">{{cite news|title=NASA wants you to help find a new planet|url=http://edition.cnn.com/2017/02/16/us/nasa-search-worlds-trnd/index.html|work=[[CNN]]|date=16 February 2017|accessdate=26 December 2017}}</ref> It aims to discover new [[brown dwarf]]s, faint objects that are less massive than stars, some of which might be among the [[List of nearest stars and brown dwarfs|nearest neighbors of the Solar System]], and might conceivably detect the hypothesized [[Planet Nine]]. The project's principal investigator is [[Marc Kuchner]], an astrophysicist at NASA's [[Goddard Space Flight Center]].<ref name="huntforplanet9">{{cite news|title=Hunt for Planet 9: how you can help NASA search for brown dwarfs and low-mass stars|url=https://www.csmonitor.com/Science/Spacebound/2017/0217/Hunt-for-Planet-9-how-you-can-help-NASA-search-for-brown-dwarfs-and-low-mass-stars|work=[[The Christian Science Monitor]]|date=17 February 2017|accessdate=26 December 2017}}</ref>

==Origins==
[[File:Backyard Worlds flipbook.gif|thumb|A typical set of flip book images served up on the Backyard Worlds: Planet 9 website, here displaying the coldest known brown dwarf [[WISE 0855−0714]] as an orange moving spot in the top left-hand corner]]

Backyard Worlds was launched in February 2017, shortly before the 87th anniversary of the discovery of [[Pluto]],<ref>{{cite web|url=https://www.nasa.gov/feature/backyard-worlds-planet-9|title=Backyard Worlds: Planet 9|website=nasa.gov|date=13 March 2017|accessdate=24 December 2017}}</ref> which until [[Pluto#IAU classification|its reclassification]] as a [[dwarf planet]] in 2006 was considered the Solar System's ninth major planet.  Since that reclassification, evidence has come to light that there may be another planet located in the outer region of the Solar System far beyond the [[Kuiper belt]], most commonly referred to as [[Planet Nine]].  This hypothetical new planet would be located so far from the Sun that it would reflect only a very small amount of visible light, rendering it too faint to be detected in most [[astronomical survey]]s conducted to date.<ref name=lurking>{{cite news |last1=Achenbach |first1=Joel |last2=Feltman |first2=Rachel |date=20 January 2016 |title=New evidence suggests a ninth planet lurking at the edge of the solar system |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2016/01/20/new-evidence-suggests-a-ninth-planet-lurking-at-the-edge-of-the-solar-system/ |newspaper=[[The Washington Post]] |access-date=20 January 2016}}</ref><ref name="nasawantsyou"/>  However, models of the conjectured planet's atmosphere suggest that methane condensation could in some cases make it detectable in infrared images captured by the [[Wide-field Infrared Survey Explorer]] (WISE) space telescope.<ref>{{Cite journal |last1=Fortney |first1=Jonathan J. |display-authors=etal |year=2016 |title=The Hunt for Planet Nine: Atmosphere, Spectra, Evolution, and Detectability |journal=The Astrophysical Journal Letters|volume=824 |issue=2 |pages=L25 |arxiv=1604.07424 |bibcode=  2016ApJ...824L..25F|doi=10.3847/2041-8205/824/2/L25|s2cid=119217565 |doi-access=free }}</ref>  Due to the effects of [[proper motion]] and [[parallax]], Planet Nine would appear to move in a distinctive way between images taken of the same patch of sky at different times. In addition to Planet Nine, other objects of interest{{spaced ndash}}such as undiscovered nearby brown dwarfs{{spaced ndash}}would also be seen to move in the project's images.

==Project description==
Citizen scientists accessing the website search through a [[flip book]]-style animation of specially-processed mid-infrared images captured by WISE known as unWISE coadds,<ref>{{Cite journal|last1=Meisner|first1=A. M.|last2=Lang|first2=D.|last3=Schlafly|first3=E. F|last4=Schlegel|first4=D. J.|title=unWISE Coadds: The Five-year Data Set|journal=Publications of the Astronomical Society of the Pacific|year=2019|language=en|volume=131|issue=1006|pages=1006|doi=10.1088/1538-3873/ab3df4|arxiv=1909.05444|bibcode=2019PASP..131l4504M|s2cid=202566024|doi-access=free}}</ref> taken with filters at the wavelengths of 3.4 and 4.6 [[Micrometre|micrometer]]s. The coadded unWISE images permits fainter objects to be detected than previous processing of WISE imagery allowed. In the flip books these coadds are differenced, a process designed to remove most of signal from stationary objects, leaving moving objects intact.<ref name="Marc J 1705">{{Cite journal |last1=Kuchner |first1=Marc J. |display-authors=etal |year=2017 |title=The First Brown Dwarf Discovered by the Backyard Worlds: Planet 9 Citizen Science Project |journal=The Astrophysical Journal |volume=841 |issue=2 |pages=L19 |arxiv=1705.02919 |bibcode=  2017ApJ...841L..19K|doi=10.3847/2041-8213/aa7200|s2cid=119087928 |doi-access=free }}</ref> The aim is to identify points of light that move between the flip book frames, including slower-moving "dipoles". Citizen scientists who spot a moving object are encouraged to fill out a "Think You've Got One" form which the project scientists review to confirm if there is motion. The images contain [[Artifact (error)|instrumental artifacts]] and are [[image noise|noisy]], which hampers the use of automated [[image processing]] software and makes the task ideal for exploiting human visual recognition capabilities.<ref name="nasawantsyou"/><ref name="huntforplanet9"/> Additionally, to improve the ability to detect objects some participants have created their own tools such as ''Wiseview'', a web-based animation visualization tool.<ref name="spitzer"/>

Once candidates have been identified the science team follow-up the most scientifically interesting objects using ground-based telescopes (at sites such as [[Mont Mégantic Observatory]], [[Apache Point Observatory]], [[W. M. Keck Observatory]], [[Las Campanas Observatory]], [[Gemini Observatory]] and the [[NASA Infrared Telescope Facility]]) and space telescopes (principally the [[Spitzer Space Telescope]] and the [[Hubble Space Telescope]]), in order to clarify their nature and assign a spectral type if possible.

The project has been awarded a grant from NASA's Astrophysics Data Analysis Program which will fund it until 2020.<ref name="blogpost20180214"/>

In November 2018, the project was "rebooted", with new images and reduced noise.<ref name="blogpost20181116">{{cite web|url=https://blog.backyardworlds.org/2018/11/16/the-reboot-is-here/|title=The Reboot Is Here!|date=16 November 2018|website=Blog.backyardworlds.org|accessdate=22 February 2019}}</ref>  By August 2020, more than 100,000 citizen scientists worldwide had taken part in the project.<ref>{{cite web|url=https://edition.cnn.com/2020/08/19/world/sun-cool-brown-dwarf-neighbors-scn-trnd/index.html|title=Citizen scientists help discover 95 brown dwarfs that are neighbors of our sun|date=19 August 2020|accessdate=21 August 2020|website=cnn.com}}</ref>

=== Cool Neighbors project ===
In June 2023 the project "Backyard Worlds: Cool Neighbors" was launched.<ref>{{Cite web |last=gradyrobbins |date=2023-06-27 |title=Backyard Worlds: Cool Neighbors – Explore the Mysteries of Extreme Brown Dwarfs |url=https://blog.backyardworlds.org/2023/06/27/backyard-worlds-cool-neighbors-explore-the-mysteries-of-extreme-brown-dwarfs/ |access-date=2023-07-21 |website=Backyard Worlds: Planet 9 |language=en}}</ref> The "Planet 9" predecessor was focused on finding a hypothesised outer planet, which is not ideal in finding faint brown dwarfs. The new project has switched to focus on searching for faint and cool Y-dwarfs. The new "Cool Neighbors" project pre-selects its images with the help of [[machine learning]].<ref>{{Cite web |title=Backyard Worlds: Cool Neighbors - FAQ |url=https://www.zooniverse.org/projects/coolneighbors/backyard-worlds-cool-neighbors/about/faq |access-date=2023-07-21 |website=www.zooniverse.org}}</ref>

==Project status==
In December 2017, seven new brown dwarfs were confirmed, as well as two [[Subdwarf#Cool subdwarfs|cool subdwarf]]s. The spectral types of the new brown dwarfs were T0, T2.8, T5, T6, T6.5, and two of type T8. In addition, there were 337 brown dwarf candidates awaiting [[Astronomical spectroscopy|spectra]] for confirmation.<ref name="blogpost20171222">{{cite web|url=https://blog.backyardworlds.org/2017/12/22/snow-white-and-the-seven-new-confirmed-brown-dwarfs/|title=Snow White and the Seven New Confirmed Brown Dwarfs|date=22 December 2017|website=Blog.backyardworlds.org|accessdate=31 December 2017}}</ref>

As of the first anniversary of the project in February 2018, the project had discovered 17 brown dwarfs and two cool subdwarfs. The coldest object discovered is of spectral type T9, which raises hopes of discovering type Y dwarfs in the future. In addition, a spectrum was also taken of one possibly variable object of unknown type that does not actually exhibit proper motion. There are 432 objects of interest awaiting verification, of which 38 are Y dwarf candidates.<ref name="blogpost20180214">{{cite web|url=https://blog.backyardworlds.org/2018/02/14/we-love-you-and-happy-anniversary/|title=We Love You! And Happy Anniversary!|date=14 February 2018|website=Blog.backyardworlds.org|accessdate=14 February 2018}}</ref>

In July 2018 an update on the project's blog stated that in total 42 brown dwarfs had been spectroscopically confirmed from a list of 879 candidates.  Fourteen of those confirmed are closer to the solar system than {{convert|20|pc|ly|abbr=off}}.<ref name="blogpost20180711">{{cite web|url=https://blog.backyardworlds.org/2018/07/11/42-confirmed-brown-dwarfs-and-counting/|title=42 Confirmed Brown Dwarfs and Counting
|date=11 July 2018|website=Blog.backyardworlds.org|accessdate=13 July 2018}}</ref>

As of July 2019, there are 1305 candidate objects to be followed up, of which there are 131 confirmed objects: 70 dwarfs of type T and 61 dwarfs of type L. Of the candidate and confirmed brown dwarfs, 55 of them are closer to the solar system than 20 parsecs. There are also roughly 100 Y dwarf candidates.<ref name="blogpost20190715">{{cite web|url=https://blog.backyardworlds.org/2019/07/15/one-hundred-thirty-one-brown-dwarfs/|title=One Hundred Thirty-One Brown Dwarfs|date=15 July 2019|website=Blog.backyardworlds.org|accessdate=24 July 2019}}</ref>

At the 235th meeting of the American Astronomical Society in January 2020 a summary of the current status of the project was presented and this included 1503 L, T and Y dwarf candidates. In total 221 spectra have been taken of candidate objects.<ref>{{Cite web|url=https://twitter.com/astrogrecoj/status/1214715443992092672|title=Awesome talk by @jfaherty about the results from the Backyard Worlds project! Lots of new brown dwarfs being discovered! #AAS235pic.twitter.com/U2t2KxQvuf|last=Greco|first=Jennifer|date=2020-01-07|website=@astrogrecoj|language=en|access-date=2020-01-08}}</ref>

==Published discoveries==

===WISEA 1101+5400===
{{main|WISEA 1101+5400}}
In June 2017, it was announced that Backyard Worlds had made its first official discovery: a brown dwarf designated [[WISEA 1101+5400]], of [[spectral type]] T5.5 and located 34 parsecs (111 light years) from Earth. A paper announcing the discovery was accepted for publication in ''[[Astrophysical Journal Letters]]'', and Backyard Worlds now holds the record among all Zooniverse projects as having the shortest time from project launch to first publication.<ref name="blogpost20170608">{{cite web|url=https://blog.backyardworlds.org/2017/06/08/our-first-paper-the-discovery-of-brown-dwarf-wisea-11015400/|title=Our First Paper: the Discovery of Brown Dwarf WISEA 1101+5400|date=8 June 2017|website=Blog.backyardworlds.org|accessdate=6 October 2017}}</ref><ref name="Marc J 1705"/>

===LSPM J0207+3331===
[[File:White Dwarf Disk.jpg|thumb|Artist's impression of the white dwarf LSPM J0207+3331 surrounded by a long-lived system of dust rings]]
{{main|LSPM J0207+3331}}
In October 2018, a participant in the project discovered [[LSPM J0207+3331]]{{spaced ndash}}the oldest and coldest [[white dwarf]] known to host a [[circumstellar disc|circumstellar disk]], despite being 3 billion years old. The time since this star became a white dwarf is far longer than the expected timescale for such disks to be cleared from a system. The disk consists of two rings at different temperatures. This star has been studied with the [[W. M. Keck Observatory|Keck telescope]] and is the subject of ongoing research.<ref name="blogpost20190219">{{cite web|url=https://blog.backyardworlds.org/2019/02/19/the-crystal-ball-white-dwarf/|title=The Crystal Ball White Dwarf|date=19 February 2019|website=Blog.backyardworlds.org|accessdate=22 February 2019}}</ref><ref>{{cite web|url=https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=13147|title=Volunteer Discovers Record-Setting White Dwarf Star|date=19 February 2019|website=NASA.gov|accessdate=22 February 2019}}</ref>

===W2150AB===
[[File:W2150AB.jpg|thumb|Image of [[W2150AB]] taken with the [[Spitzer Space Telescope]]. This binary brown dwarf system was discovered by volunteers of the project]]
{{main|W2150AB}}
At the 235th meeting of the [[American Astronomical Society]] in January 2020 the discovery of the wide brown dwarf binary [[W2150AB]] was presented by [[Jacqueline Faherty]]. The L1+T8 co-moving system is separated by 341&nbsp;[[Astronomical unit|au]], being one of three brown dwarf binary systems where both objects are easily resolved by ground-based telescopes. The system has the lowest [[gravitational binding energy]] for a brown dwarf binary that is not young and with the primary being a [[L dwarf|L-dwarf]] or later.<ref>{{Cite journal|last1=Faherty|first1=J.|last2=Goodman|first2=S.|last3=Caselden|first3=D.|last4=Colin|first4=G.|last5=Kuchner|first5=M.|last6=Meisner|first6=A.|last7=Gagné|first7=J.|last8=Schneider|first8=A.|last9=Gonzales|first9=E.|last10=Bardalez Gagliuffi|first10=D.|last11=Logsdon|first11=S.| last12=Allers|first12=K.|last13=Burgasser|first13=A.|last14=The Backyard Worlds: Planet 9 Collaboration|date=January 2020|title=Citizen Scientists discover a very low mass, wide co-moving brown dwarf system|journal=AAS|language=en|volume=52|pages=352.07|bibcode=2020AAS...23535207F}}</ref><ref>{{cite journal|last1=Faherty|first1=Jacqueline K.|last2=Goodman|first2=Sam|last3=Caselden|first3=Dan|last4=Colin|first4=Guillaume|last5=Kuchner|first5=Marc J.|last6=Meisner|first6=Aaron M.|last7=Gagné|first7=Jonathan|last8=Schneider|first8=Adam C.|last9=Gonzales|first9=Eileen C.|last10=Gagliuffi|first10=Daniella C. Bardalez|last11=Logsdon|first11=Sarah E.|first12=Katelyn |last12=Allers|first13=Adam J. |last13=Burgasser|last14=The Backyard Worlds Planet 9 Collaboration|title=WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9|journal=[[Astrophysical Journal]]|year=2020|volume=889|issue=2|page=176|doi=10.3847/1538-4357/ab5303|arxiv=1911.04600|bibcode=2020ApJ...889..176F|s2cid=207863267 |doi-access=free }}</ref>

===WISE J0830+2837===
The discovery of [[WISE J0830+2837]], the first [[Y dwarf|Y-dwarf]] discovered by volunteers was also presented at the 235th meeting by project scientist [[Daniella Bardalez Gagliuffi]]. The Y-dwarf was not detected by the [[Hubble Space Telescope]], but the [[Spitzer Space Telescope]] did detect this object due to it observing at longer wavelengths of light. It is about 11.2 parsec (36.5 light years) distant and has a temperature of about 350&nbsp;[[Kelvin|K]] (77&nbsp;[[Celsius|°C]] or 170&nbsp;[[Fahrenheit|°F]]).  This estimated temperature would place it between the majority of the Y-dwarf population so far identified and [[WISE 0855−0714]], the coldest object of this type known.<ref>{{Cite journal|last1=Bardalez Gagliuffi|first1=Daniella C.|last2=Faherty|first2=Jacqueline K.|last3=Schneider|first3=Adam C.|last4=Meisner|first4=Aaron|last5=Caselden|first5=Dan|last6=Colin|first6=Guillaume|last7=Goodman|first7=Sam|last8=Kirkpatrick|first8=J. Davy|last9=Kuchner|first9=Marc|last10=Gagné|first10=Jonathan|last11=Logsdon|first11=Sarah E.|last12=Burgasser|first12=Adam J.|last13=Allers|first13=Katelyn|last14=Debes|first14=John|last15=Wisniewski|first15=John|last16=Rothermich|first16=Austin|last17=Andersen|first17=Nikolaj Stevnbak|last18=Thevenot|first18=Melina |last19=Walla|first19=Jim|last20=Collaboration|first20=Backyard Worlds: Planet 9 Citizen Science|date=Jun 2020|title=WISEA J083011.95+283716.0: A Missing Link Planetary-mass Object|journal=[[Astrophysical Journal]]|language=en|volume=895|issue=2|pages=145|doi=10.3847/1538-4357/ab8d25|bibcode=2020ApJ...895..145B|arxiv=2004.12829|s2cid=216553879 |doi-access=free }}</ref>

===T subdwarfs===
A paper was published in [[the Astrophysical Journal]] in July 2020 reporting the discovery of two unusual brown dwarfs; [[WISEA J041451.67-585456.7]] was discovered by Backyard Worlds volunteers and [[WISEA 1810−1010|WISEA J181006.18-101000.5]] by the NEOWISE Proper Motion Survey, also with the aid of a Backyard Worlds citizen scientist.<ref>{{Cite journal|title = WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?|last1=Schneider|first1=Adam C.|last2=Burgasser|first2=Adam J.|last3=Gerasimov|first3=Roman|last4=Marocco|first4=Federico|last5=Gagné|first5=Jonathan|last6=Goodman|first6=Sam|last7=Beaulieu|first7=Paul|last8=Pendrill|first8=William|last9=Rothermich|first9=Austin|last10=Sainio|first10=Arttu |last11=Kuchner|first11=Marc J.|last12=Caselden|first12=Dan|last13=Meisner|first13=Aaron M.|last14=Faherty|first14=Jacqueline K.|last15=Mamajek|first15=Eric E.|last16=Hsu|first16=Chih-Chun|last17=Greco|first17=Jennifer J.|last18=Cushing|first18=Michael C.|last19=Kirkpatrick|first19=J. Davy|last20=Bardalez-Gagliuffi|first20=Daniella|last21=Logsdon|first21=Sarah E.|last22=Allers|first22=Katelyn|last23=Debes|first23=John H.|last24=Collaboration|first24=Backyard Worlds: Planet 9|date=July 2020|journal=[[Astrophysical Journal]]|language=en|volume=898|issue=1|pages=77|arxiv=2007.03836|doi=10.3847/1538-4357/ab9a40|bibcode=2020ApJ...898...77S|s2cid=220403370 |doi-access=free }}</ref> These high-proper motion objects display unique [[Color index|colors]] and near-infrared spectra that do not fully match current models. The models producing the best matches to the spectra imply the brown dwarfs have [Fe/H] ≤ -1, meaning they have extremely sub-solar [[metallicity]], containing far lower amounts of elements heavier than hydrogen or helium compared to the Sun. The estimates from the model spectra suggest that these objects have up to 30 times less iron than typical for known brown dwarfs.<ref>{{Cite web|title=Two Bizarre Brown Dwarfs Found With Citizen Scientists' Help|url=https://www.nasa.gov/feature/goddard/2020/two-bizarre-brown-dwarfs-found-with-citizen-scientists-help/|website=NASA.gov|date=10 July 2020|accessdate=11 August 2020}}</ref> The authors argue that the spectral properties combined with the estimated low temperatures of approximately 1200-1400 [[Kelvin|K]] make these brown dwarfs likely the first extreme [[Subdwarf#Cool subdwarfs|subdwarf]]s of the T spectral class (esdTs) to be identified.  The extremely low metallicity implies these brown dwarfs are very old, approximately 10 billion years, as the galaxy at this time would have featured lower quantities of heavy elements. This provides evidence that [[substellar objects]] were able to form in the low metallicity environment of the [[Milky Way]]'s past.<ref>{{Cite web|title=Citizen Scientists Help Discover "Weird" Brown Dwarfs|url=https://skyandtelescope.org/astronomy-news/citizen-scientists-help-discover-weird-brown-dwarfs/|website=Skyandtelescope.org|date=20 July 2020|accessdate=11 August 2020}}</ref>

A study by Lodieu et al.<ref>{{Cite journal |last1=Lodieu |first1=N. |last2=Zapatero Osorio |first2=M. R. |last3=Martin |first3=E. L. |last4=Rebolo Lopez |first4=R. |last5=Gauza |first5=B. |date=2022-06-01 |title=Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3 |journal=Astronomy and Astrophysics |volume=663 |page=663 |doi=10.1051/0004-6361/202243516 |arxiv=2206.13097 |bibcode=2022A&A...663A..84L |s2cid=249836684 |url=https://ui.adsabs.harvard.edu/abs/2022arXiv220613097L}}</ref> observed WISE1810 with a range of ground-based telescopes, using imaging and spectroscopy. They find a closer distance of {{Val|8.9|0.7|0.6}} parsec, a radius of {{Val|0.67|0.32|0.20}} {{Jupiter radius}} and a mass of {{Val|17|56|12}} {{Jupiter mass}}. This makes WISE1810 the closest extreme [[Ultra-cool dwarf|ultra-cool]] subdwarf and the closest extreme metal-poor brown dwarf known to science, as of June 2022. The optical and infrared spectrum does not show any methane or [[carbon monoxide]] absorption, which is expected at these temperatures of about 800 K, and the WISE photometry suggest a depleted methane atmosphere. Only [[Collision-induced absorption and emission#Other cool stars|H<sub>2</sub> CIA]] and [[water vapor]] absorption is detected, suggesting a [[carbon]]-deficient and metal-poor atmosphere, or alternatively an [[oxygen]]-enhanced atmosphere.

A study in 2024 discovered three additional T-type subdwarfs and introduced a new classification system for T subdwarfs. This system classified WISE 1810 as a esdT3: and WISE 0414 as a esdT6:. The study also found L and T dwarfs with unusual galactic orbits. [[2MASS J05325346+8246465|2MASS J053253.46+824646.5]] (previous known L subdwarf) and [[CWISE J113010.07+313944.7]] (mild T-subdwarf) were identified as possible members of the Thamnos [[Stellar stream|stellar streams]]. These two brown dwarfs are on a [[Retrograde and prograde motion|retrograde]] Galactic orbit. [[CWISE J155349.96+693355.2]] was found to be a possible member of the [[Helmi stream]] (prograde galactic orbit). Three T dwarfs (SDSS J014016.89+015054.1, CWISEP J111055.12-174738.2, and CWISEP J145837.91+173450.1) are found to have high metallicity and might be part of the high velocity [[thick disk]]. This population originates from the inner Milky Way and was scattered outwards.<ref name="Burgasser2024">{{Cite arXiv |eprint=2411.01378 |class=astro-ph |first1=Adam J. |last1=Burgasser |first2=Adam C. |last2=Schneider |title=New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs |date=2 Nov 2024 |last3=Meisner |first3=Aaron M. |last4=Caselden |first4=Dan |last5=Hsu |first5=Chih-Chun |last6=Gerasimov |first6=Roman |last7=Aganze |first7=Christian |last8=Softich |first8=Emma |last9=Karpoor |first9=Preethi |first10=Christopher A. |last10=Theissen |first11=Hunter |last11=Brooks |first12=Thomas P. |last12=Bickle |first13=Jonathan |last13=Gagné |first14=Étienne |last14=Artigau |first15=Michaël |last15=Marsset |first16=Austin |last16=Rothermich |first17=Jacqueline K. |last17=Faherty |first18=J. Davy |last18=Kirkpatrick |first19=Marc J. |last19=Kuchner |first20=Nikolaj Stevnbak |last20=Andersen |first21=Paul |last21=Beaulieu |first22=Guillaume |last22=Colin |first23=Jean Marc |last23=Gantier |first24=Leopold |last24=Gramaize |first25=Les |last25=Hamlet |first26=Ken |last26=Hinckley |first27=Martin |last27=Kabatnik |first28=Frank |last28=Kiwy |first29=David W. |last29=Martin |first30=Diego H. |last30=Massat |first31=William |last31=Pendrill |first32=Arttu |last32=Sainio |first33=Jörg |last33=Schümann |first34=Melina |last34=Thévenot |first35=Jim |last35=Walla |first36=Zbigniew |last36=Wędracki |last37=the Backyard Worlds: Planet 9 Collaboration}}</ref>

===95 cold brown dwarfs observed with Spitzer===
[[File:WISEU0503 JWST.png|thumb|[[WISEU 0503−5648]], as seen by JWST [[Mid-Infrared Instrument|MIRI]]. This object (likely a Y-dwarf) was first published in 2020]]
In August 2020, the Backyard Worlds team published a paper in the Astrophysical Journal detailing follow-up conducted using the Spitzer Space Telescope on a sample of the coldest discoveries that had been made before the telescope was decommissioned. 95 had Spitzer mid-infrared colors consistent with being a cold brown dwarf, with 75 of these having their proper motion confirmed by comparison to their position in WISE images.  Among the discoveries highlighted as most significant were; 3 possible T subdwarfs based on high [[Proper motion|tangential velocity]] estimates, a rare widely separated T8 companion to the white dwarf [[LSPM J0055+5948]], and 5 new Y dwarfs, four of which (including the previously published [[#WISE J0830+2837|WISE J0830+2837]]) where Spitzer colors indicate they have spectral types Y1 or later, with only at most 6 of these coldest set of brown dwarfs previously being known. The T8 companion to the white dwarf LSPM J0055+5948 could be the oldest (7-13 billion years old) brown dwarf known to science, together with [[Wolf 1130|Wolf 1130C]] (>10 billion years old).<ref name="spitzer">{{Cite journal|title = Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project|last1=Meisner|first1=Aaron M.|last2=Faherty|first2=Jacqueline K.|last3=Kirkpatrick|first3=J. Davy|last4=Schneider|first4=Adam C.|last5=Caselden|first5=Dan|last6=Gagné|first6=Jonathan|last7=Kuchner|first7=Marc J.|last8=Burgasser|first8=Adam J.|last9=Casewell|first9=Sarah L.|last10=Debes|first10=John H.|last11=Artigau|first11=Etienne|last12=Bardalez-Gagliuffi|first12=Daniella|last13=Logsdon|first13=Sarah E.|last14=Kiman|first14=Rocia|last15=Allers|first15=Katelyn|last16=Hsu|first16=Chih-Chun|last17=Wisniewski|first17=John P.|last18=Allen|first18=Michaela B.|last19=Beaulieu|first19=Paul|last20=Colin|first20=Guillaume|last21=Durantini Luca|first21=Hugo A.|last22=Goodman|first22=Sam|last23=Gramaize|first23=Leopold|last24=Hamlet|first24=Leslie K.|last25=Hinckley|first25=Ken|last26=Kiwy|first26=Frank|last27=Martin|first27=David W.|last28=Pendrill|first28=William|last29=Rothermich|first29=Austin|last30=Sainio|first30=Arttu|last31=Schumann|first31=Jorg|last32=Stevnbak Andersen|first32=Nikolaj|last33=Tanner|first33=Christopher|last34=Thakur|first34=Vinod|last35=Thevenot|first35=Melina|last36=Walla|first36=Jim|last37=Wedracki|first37=Zbigniew|last38=Aganze|first38=Christian|last39=Gerasimov|first39=Roman|last40=Theissen|first40=Christopher|last41=Collaboration|first41=Backyard Worlds: Planet 9|date=August 2020|journal=[[Astrophysical Journal]]|volume=899|issue=2|page=123|language=en|arxiv=2008.06396|doi=10.3847/1538-4357/aba633|bibcode=2020ApJ...899..123M|s2cid=221135837 |doi-access=free }}</ref>

=== Co-moving benchmark systems ===
The backyard worlds project found additional co-moving systems. 34 low-mass co-moving companions were discovered in 2022 with the NOIRLab Source Catalog DR2.<ref>{{Cite journal |last1=Kiwy |first1=Frank |last2=Faherty |first2=Jacqueline K. |author-link2=Jackie Faherty|last3=Meisner |first3=Aaron |last4=Schneider |first4=Adam C. |last5=Kirkpatrick |first5=J. Davy |author-link5=J. Davy Kirkpatrick|last6=Kuchner |first6=Marc J. |author-link6=Marc Kuchner|last7=Burgasser |first7=Adam J. |last8=Casewell |first8=Sarah |last9=Kiman |first9=Rocio |last10=Calamari |first10=Emily |last11=Aganze |first11=Christian |last12=Hsu |first12=Chih-Chun |last13=Sainio |first13=Arttu |last14=Thakur |first14=Vinod |last15=Backyard Worlds: Planet 9 Collaboration |date=2022-07-01 |title=Discovery of 34 Low-mass Comoving Systems Using NOIRLab Source Catalog DR2 |journal=The Astronomical Journal |volume=164 |issue=1 |pages=3 |arxiv=2204.09739 |bibcode=2022AJ....164....3K |doi=10.3847/1538-3881/ac68e7 |doi-access=free |issn=0004-6256}}</ref> Later in March 2024 an additional 89 ultracool dwarf companions were identified. This study increased the number of ultracool companions to FGK stars by about 42%. These benchmark system represent a wide variety of systems, including six systems with white dwarf hosts, systems with binary hosts or companions that are binaries, systems with old or young ages, systems with red or blue spectral types and systems with a wide separation of >1000 astronomical units (AU). One young co-moving system consists of [[GJ 900]], a K7+M4+M6 triple star system and the T9-dwarf [[CW2335+0142]], which is a [[planetary-mass object]] (~10.5 {{Jupiter mass}}). Another notable system is [[CW0627−0028AB]], which is a wide T0blue+T3 dwarf system or a possible triple (L5+T2.5)+T3 system. If the distance is confirmed, it would be the widest substellar binary discovered at a separation of about 860 AU. The brown dwarf companion [[CWISE J060202.17-462447.8]] (~52 {{Jupiter mass}}) to the white dwarf [[WD J060159.98-462534.40]] is an additional contender for the oldest brown dwarf with an age of {{val|10.9|2.6|2.0}} billion years.<ref>{{Cite journal |last1=Rothermich |first1=Austin |last2=Faherty |first2=Jacqueline K. |author-link2=Jackie Faherty |last3=Bardalez-Gagliuffi |first3=Daniella |last4=Schneider |first4=Adam C. |last5=Kirkpatrick |first5=J. Davy |author-link5=J. Davy Kirkpatrick |last6=Meisner |first6=Aaron M. |last7=Burgasser |first7=Adam J. |last8=Kuchner |first8=Marc |author-link8=Marc Kuchner |last9=Allers |first9=Katelyn |last10=Gagné |first10=Jonathan |last11=Caselden |first11=Dan |last12=Calamari |first12=Emily |last13=Popinchalk |first13=Mark |last14=Gerasimov |first14=Roman |last15=Aganze |first15=Christian |last16=Softich |first16=Emma |last17=Hsu | first17=Chin-Chun |last18=Karpoor |first18=Preethi |last19=Theissen|first19=Christopher A.|last20=Rees|first20=Jon|last21=Cecilio-Flores-Elie|first21=Rosario|last22=Cushing|first22=Michael C.|last23=Marocco|first23=Federico|last24=Casewell|first24=Sarah|last25=Hamlet|first25=Les|last26=Allen|first26=Michaela B.|last27=Beaulieu|first27=Paul|first28=Guillaume |last28=Colin |first29=Jean Marc |last29=Gantier |first30=Leopold |last30=Gramaize |first31=Peter |last31=Jałowiczor |first32=Martin |last32=Kabatnik |first33=Frank |last33=Kiwi |first34=David W. |last34=Martin |first35=Billy |last35=Pendrill |first36=Ben |last36=Pumphrey |first37=Arttu |last37=Sainio |first38=Jörg |last38=Schümann |first39=Nikolaj |last39=Stevnbak |first40=Guoyou |last40=Sun |first41=Christopher |last41=Tanner |first42=Vinod |last42=Thakur |first43=Melina |last43=Thévenot |first44=Zbigniew |last44=Wedracki|date=7 Mar 2024 |title=89 New Ultracool Dwarf Co-Moving Companions Identified With The Backyard Worlds: Planet 9 Citizen Science Project |journal=AJ |volume=167 |issue=6 |page=253 |doi=10.3847/1538-3881/ad324e |doi-access=free |arxiv=2403.04592|bibcode=2024AJ....167..253R }}</ref> Additional M+T co-moving systems were discovered in April 2024 in a collaborative work together with the CatWISE team. 13 new systems were discovered, representing a 60% increase of the number of M+T systems. The sample includes young and old objects, including the candidate planetary-mass companion [[2MASS J05581644–4501559]] B and [[UCAC3 52–1038]] B, which is on a wide 7100 AU orbit.<ref>{{Cite journal |last1=Marocco |first1=Federico |last2=Kirkpatrick |first2=J. Davy |last3=Schneider |first3=Adam C. |last4=Meisner |first4=Aaron M. |last5=Popinchalk |first5=Mark |last6=Gelino |first6=Christopher R. |last7=Faherty |first7=Jacqueline K. |last8=Burgasser |first8=Adam J. |last9=Caselden |first9=Dan |last10=Gagné |first10=Jonathan |last11=Aganze |first11=Christian |last12=Bardalez-Gagliuffi |first12=Daniella C. |last13=Casewell |first13=Sarah L. |last14=Hsu |first14=Chih-Chun |last15=Kiman |first15=Rocio |date=2024-04-22 |title=Thirteen New M Dwarf + T Dwarf Pairs Identified with WISE/NEOWISE |journal= The Astrophysical Journal|arxiv=2404.14324 |first16=Peter R. M. |last16=Eisenhardt |first17=Marc J. |last17=Kuchner |first18=Daniel |last18=Stern |first19=Léopold |last19=Gramaize |first20=Arttu |last20=Sainio |first21=Thomas P. |last21=Bickle |first22=Austin |last22=Rothermich |first23=William |last23=Pendrill |first24=Melina |last24=Thévenot |first25=Martin |last25=Kabatnik |first26=Giovanni |last26=Colombo |first27=Hiro |last27=Higashimura |first28=Frank |last28=Kiwy |first29=Elijah J. |last29=Marchese |first30=Nikolaj Stevnbak |last30=Andersen |first31=Christopher |last31=Tanner |first32=Jim |last32=Walla |first33=Zbigniew |last33=Wedracki |last34=The Backyard Worlds Collaboration|volume=967 |issue=2 |page=147 |doi=10.3847/1538-4357/ad3f1d |doi-access=free |bibcode=2024ApJ...967..147M }}</ref> In December 2024 a team published a list of 51 ultracool dwarfs that are co-moving with white dwarfs. Some of these were also discovered by backyard worlds citizen scientists.<ref name="Bravo2024">{{Cite journal |arxiv=2412.04597 |last1=Bravo |first1=Alexia |title=New Ultracool Companions to Nearby White Dwarfs |date=2024-12-05 |last2=Schneider |first2=Adam C. |last3=Casewell |first3=Sarah |last4=Rothermich |first4=Austin |last5=Faherty |first5=Jacqueline K. |last6=French |first6=Jenni R. |last7=Bickle |first7=Thomas P. |last8=Meisner |first8=Aaron M. |last9=Kirkpatrick |first9=J. Davy|journal=The Astronomical Journal |volume=169 |issue=2 |page=100 |doi=10.3847/1538-3881/ad9b9b |doi-access=free |bibcode=2025AJ....169..100B }}</ref>

=== Additional discoveries ===
This list contains additional notable discoveries by the Backyard Worlds: Planet 9 project.
{| class="sortable wikitable" style="width: 100%; text-align: center;"
|-
! Name
! [[Stellar distance|Distance]]<br /> <small>([[light year|ly]])</small>
! [[Stellar classification|Spectral<br />type]]
! [[Mass]]<br /><small>({{Jupiter mass|link=y}})</small>
!Temperature<br /><small>[[Kelvin|K]] ([[Celsius|°C]])</small>
! note
! Ref
|-
|[[WISEA 1930−2059]]
|{{Val|30.7|1.5|1.4}}
|>[[Y dwarf|Y1]]
|
|{{Val|367|79}} (94)
|Cold and nearby Y-dwarf candidate
|<ref name="spitzer" /><ref name=":1">{{Cite journal |last1=Kirkpatrick |first1=J. Davy |last2=Gelino |first2=Christopher R. |last3=Faherty |first3=Jacqueline K. |last4=Meisner |first4=Aaron M. |last5=Caselden |first5=Dan |last6=Schneider |first6=Adam C. |last7=Marocco |first7=Federico |last8=Cayago |first8=Alfred J. |last9=Smart |first9=R. L. |last10=Eisenhardt |first10=Peter R. |last11=Kuchner |first11=Marc J. |date=2021-03-01 |title=The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs |journal=The Astrophysical Journal Supplement Series |volume=253 |issue=1 |pages=7 |arxiv=2011.11616 |bibcode=2021ApJS..253....7K |doi=10.3847/1538-4365/abd107 |issn=0067-0049 |s2cid=227126954 |doi-access=free}}</ref>
|-
|[[WISEU 0503−5648]]
|{{Val|33.2|1.4|1.3}}
|>Y1
|
|{{Val|367|79}} (94)
|Target for [[James Webb Space Telescope|JWST]] follow-up observations
|<ref name="spitzer" /><ref>{{Cite web|title=Program Information JWST GO 2124|url=https://www.stsci.edu/jwst/science-execution/program-information.html?id=2124|access-date=2021-08-12|website=STScI.edu|language=en}}</ref><ref name=":1" />
|-
|CWISE J2035–4936
|{{Val|265.8|4.9}}
|[[Brown dwarf#Spectral class M|M8pec]]
|
|
|Companion to a [[red dwarf]], underluminous and peculiar spectrum
|<ref>{{Cite journal|last1=Rothermich|first1=Austin|last2=Schneider|first2=Adam C.|last3=Faherty|first3=Jacqueline K.|last4=Allers|first4=Katelyn|last5=Bardalez-Gagliuffi|first5=Daniella|last6=Meisner|first6=Aaron M.|last7=Kuchner|first7=Marc|last8=Kirkpatrick|first8=J. Davy|last9=Caselden|first9=Dan|last10=Beaulieu|first10=Paul|date=Jan 2021|title=Backyard Worlds: Planet 9 Discovery of an Unusual Low-mass Companion to an M Dwarf at 80 pc|journal=Research Notes of the AAS|language=en|volume=5|issue=1|pages=18|doi=10.3847/2515-5172/abdf46|arxiv=2102.02815|bibcode=2021RNAAS...5...18R|s2cid=231839609|issn=2515-5172 |doi-access=free }}</ref>
|-
|2MASS J13173072+4833343
|{{Val|127.2|0.3}}
|M8.5
|{{Val|80.2|0.5|1.8}}
|
|Orbits a white dwarf at 79 [[Astronomical unit|au]]. 
The white dwarf has an estimated age of about 5.5 Billion years.
|<ref>{{Cite journal|last1=Jalowiczor|first1=Peter A.|last2=Casewell|first2=Sarah|last3=Schneider|first3=Adam C.|last4=Gagné|first4=Jonathan|last5=Faherty|first5=Jacqueline K.|last6=Kuchner|first6=Marc J.|last7=Meisner|first7=Aaron M.|last8=Burgasser|first8=Adam J.|date=Apr 2021|title=Identification of a Low-mass Companion to the White Dwarf SDSS J131730.84$\mathplus$483332.7|journal=Research Notes of the AAS|language=en|volume=5|issue=4|pages=76|doi=10.3847/2515-5172/abf49a|issn=2515-5172|doi-access=free}}</ref>
|-
|CWISE 0738−6643
|{{Val|142.2|33.9|27.4}}
|esd(?)[[T dwarf|T5]]±1.2
|
|
|candidate extreme [[subdwarf]] of spectral type T
|<ref name=":0">{{cite journal|last1=Meisner|first1=Aaron M.|last2=Schneider|first2=Adam C.|last3=Burgasser|first3=Adam J.|last4=Marocco|first4=Federico|last5=Line|first5=Michael R.|last6=Faherty|first6=Jacqueline K.|last7=Kirkpatrick|first7=J. Davy|last8=Caselden|first8=Dan|last9=Kuchner|first9=Marc J.|last10=Gelino|first10=Christopher R.|last11=Gagne|first11=Jonathan|date=2021-06-02|title=New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project|journal=The Astrophysical Journal |volume=915 |issue=2 |page=120 |doi=10.3847/1538-4357/ac013c |arxiv=2106.01387|bibcode=2021ApJ...915..120M |s2cid=235313911 |doi-access=free }}</ref>
|-
|CW2335+0142{{Br}}([[Gliese 900]] b)
|67.97{{+-|0.03}}
|T9
|10.5
|
|Very long orbital separation from its host star (actually a three-star system), 12,000 [[Astronomical unit|astronomical units]]
|<ref>{{Cite journal |last1=Rothermich |first1=Austin |last2=Faherty |first2=Jacqueline K. |last3=Bardalez-Gagliuffi |first3=Daniella |last4=Schneider |first4=Adam C. |last5=Kirkpatrick |first5=J. Davy |last6=Meisner |first6=Aaron M. |last7=Burgasser |first7=Adam J. |last8=Kuchner |first8=Marc |last9=Allers |first9=Katelyn |last10=Gagné |first10=Jonathan |last11=Caselden |first11=Dan |last12=Calamari |first12=Emily |last13=Popinchalk |first13=Mark |last14=Suárez |first14=Genaro |last15=Gerasimov |first15=Roman |date=2024-06-01 |title=89 New Ultracool Dwarf Comoving Companions Identified with the Backyard Worlds: Planet 9 Citizen Science Project |journal=The Astronomical Journal |volume=167 |issue=6 |pages=253 |doi=10.3847/1538-3881/ad324e |doi-access=free |arxiv=2403.04592 |bibcode=2024AJ....167..253R |issn=0004-6256}}</ref>
|-
|WISEA 1553+6933
|{{Val|125.9|15.0|13.7}}
|sdT4±0.5
|
|{{Val|1076|89}} (803)
|confirmed subdwarf of spectral type T, might be kinematically extreme
|<ref name=":0" />
|-
|CWISE
2217−1454
|{{Val|128.5|31.0|24.8}}
|esd(?)T5.5±1.2
|
|
|candidate extreme subdwarf of spectral type T
|<ref name=":0" />
|-
|[[WISE 1534–1043|WISE 1534−1043]]
|{{Val|53.2|4.6|3.9}}
|sdY?
|
|<500 (<227)
|Likely first subdwarf of spectral type Y, extreme blue color with [[Spitzer Space Telescope|Spitzer]] ch1-ch2, while very red in J-ch2
|<ref>{{cite journal|last1=Kirkpatrick|first1=J. Davy|last2=Marocco|first2=Federico|last3=Caselden|first3=Dan|last4=Meisner|first4=Aaron M.|last5=Faherty|first5=Jacqueline K.|last6=Schneider|first6=Adam C.|last7=Kuchner|first7=Marc J.|last8=Casewell|first8=S. L.|last9=Gelino|first9=Christopher R.|last10=Cushing|first10=Michael C.|last11=Eisenhardt|first11=Peter R.|date=2021-06-01|title= The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. "The Accident")|journal=The Astrophysical Journal Letters|volume=915|issue=1|pages=L6|doi=10.3847/2041-8213/ac0437|issn=2041-8205 |arxiv=2106.13408|bibcode=2021ApJ...915L...6K|s2cid=235651911 |doi-access=free }}</ref>
|-
|[[HP Draconis]] C
|{{Val|260.9|1.6}}
|
|471.3±31.4
|7087±205 (6814)
|White dwarf, separated by 1140 au from the [[eclipsing binary]] HP Draconis
|<ref>{{Cite journal|last1=Jalowiczor|first1=Peter A.|last2=Casewell|first2=Sarah|last3=Schneider|first3=Adam C.|last4=Faherty|first4=Jacqueline K.|last5=Kuchner|first5=Marc J.|date=Jul 2021|title=Identification of a White Dwarf Companion in the V\ast HP Dra System|journal=Research Notes of the AAS|language=en|volume=5|issue=7|pages=170|doi=10.3847/2515-5172/ac151f|issn=2515-5172|doi-access=free}}</ref>
|-
|[[Ross 19]] B
|56.9
|T9.5±1.5
|15 - 40
|{{Val|500|115|100}} (227)
|Orbits the [[Metallicity|metal-poor]] and old (~7.2 Billion years) red dwarf Ross 19 A with a projected distance of 9900 au. The pair has a very low [[gravitational binding energy]], between <math>4.8\times 10^{39}</math> and <math>3.0\times 10^{40}</math> [[erg]]s, near the theoretical minimum of 10<sup>40</sup> ergs for substellar binaries.
|<ref>{{cite journal|last1=Schneider|first1=Adam C.|last2=Meisner|first2=Aaron M.|last3=Gagne|first3=Jonathan|last4=Faherty|first4=Jacqueline K.|last5=Marocco|first5=Federico|last6=Burgasser|first6=Adam J.|last7=Kirkpatrick|first7=J. Davy|last8=Kuchner|first8=Marc J.|last9=Gramaize|first9=Leopold|last10=Rothermich|first10=Austin|last11=Brooks|first11=Hunter|date=2021-08-11|title=Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project|journal=The Astrophysical Journal|volume=921|issue=2|page=140|doi=10.3847/1538-4357/ac1c75|arxiv=2108.05321|bibcode=2021ApJ...921..140S|s2cid=236976119 |doi-access=free }}</ref>
|-
|[[CWISE 0617+1945 AB]]
|{{Val|28.2|5.7}}
|L2+L4
|
|{{Val|1853|40|52}} (1580)
|nearby brown dwarf binary co-discovered by Backyard Worlds volunteers
|<ref name=":1" /><ref>{{Cite journal |last1=Humphreys |first1=Austin |last2=Meisner |first2=Aaron M. |last3=Burgasser |first3=Adam J. |last4=Hsu |first4=Chih-Chun |last5=Schneider |first5=Adam C. |last6=Theissen |first6=Christopher A. |last7=Aganze |first7=Christian |last8=Gerasimov |first8=Roman |last9=Schapera |first9=Noah |last10=Kirkpatrick |first10=J. Davy |last11=Marocco |first11=Federico |last12=Faherty |first12=Jacqueline K. |last13=Caselden |first13=Dan |last14=Kuchner |first14=Marc J. |last15=Cushing |first15=Michael C. |date=August 2023 |title=Spectroscopic Confirmation of the Nearby, Wide-separation L Dwarf Pair CWISE J061741.79+194512.8AB |journal=Research Notes of the AAS |language=en |volume=7 |issue=8 |pages=184 |doi=10.3847/2515-5172/acf4a0 |issn=2515-5172 |doi-access=free |bibcode=2023RNAAS...7..184H }}</ref>
|-
|2MASS J22410186-4500298
|{{Val|189.2|6.5}}
|L2
|
|
|Forms with LEHPM 5005 a co-moving system. LEHPM is reported in the discovery as a possible M-dwarf binary.
|<ref>{{cite journal|last1=Kiwy|first1=Frank|last2=Faherty|first2=Jacqueline|last3=Meisner|first3=Aaron|last4=Schneider|first4=Adam C.|last5=Kuchner|first5=Marc|last6=Kirkpatrick|first6=J. Davy|last7=Worlds|first7=The Backyard|last8=Collaboration|first8=Planet 9|date=2021-08-23|title=Discovery of a low-mass comoving system using NOIRLab Source Catalog DR2|journal=Research Notes of the AAS|volume=5|issue=8|page=196|arxiv=2108.10308|doi=10.3847/2515-5172/ac1f9c|bibcode=2021RNAAS...5..196K|s2cid=237266467 |doi-access=free }}</ref>
|-
|[[BD+60 1417b]]
|{{Val|144|13}}
|L8γ
|10-20
|{{Val|1303|74}}
|Confirmed [[exoplanet]]<ref>{{Cite web |title=BD+60 1417 {{!}} NASA Exoplanet Archive |url=https://exoplanetarchive.ipac.caltech.edu/overview/BD+60%201417%20b |access-date=2022-06-28 |website=exoplanetarchive.ipac.caltech.edu}}</ref> orbiting around a young K0 star, with a projected separation of 1662 [[Astronomical unit|astronomical units]].
|<ref>{{Cite journal |last1=Faherty |first1=Jacqueline K. |last2=Gagné |first2=Jonathan |last3=Popinchalk |first3=Mark |last4=Vos |first4=Johanna M. |last5=Burgasser |first5=Adam J. |last6=Schümann |first6=Jörg |last7=Schneider |first7=Adam C. |last8=Kirkpatrick |first8=J. Davy |last9=Meisner |first9=Aaron M. |last10=Kuchner |first10=Marc J. |last11=Bardalez Gagliuffi |first11=Daniella C. |date=2021-12-01 |title=A Wide Planetary Mass Companion Discovered through the Citizen Science Project Backyard Worlds: Planet 9 |journal=The Astrophysical Journal |volume=923 |issue=1 |pages=48 |doi=10.3847/1538-4357/ac2499 |arxiv=2112.04678 |bibcode=2021ApJ...923...48F |s2cid=245005964 |issn=0004-637X |doi-access=free }}</ref>
|-
|CWISE J052306.42-015355.4
|≤222
|esdT(?)
|
|
|extreme T subdwarf candidate
|<ref>{{Cite journal |last1=Brooks |first1=Hunter |last2=Kirkpatrick |first2=J. Davy |last3=Caselden |first3=Dan |last4=Schneider |first4=Adam C. |last5=Meisner |first5=Aaron M. |last6=Faherty |first6=Jacqueline K. |last7=Casewell |first7=S. L. |last8=Kuchner |first8=Marc J. |last9=Kuchner |first9=Marc J. |last10=Backyard Worlds: Planet 9 Collaboration |date=2022-02-01 |title=Discovery of CWISE J052306.42-015355.4, an Extreme T Subdwarf Candidate |journal=The Astronomical Journal |volume=163 |issue=2 |pages=47 |doi=10.3847/1538-3881/ac3a0a |arxiv=2111.08182 |bibcode=2022AJ....163...47B |s2cid=244129989 |issn=0004-6256 |doi-access=free }}</ref>
|-
|[[CWISE J0146-0508AB]]
|~130
|L4+L8(blue)
|{{Val|72|6}}; {{Val|66|10}}
|{{Val|1720|150}}; {{Val|1340|140}}
|The widest known (as of Feb 2022) brown dwarf binary not in a star cluster or [[stellar association]]. The pair has a projected separation of 129 astronomical units.
|<ref>{{Cite journal |last1=Softich |first1=Emma |last2=Schneider |first2=Adam C. |last3=Patience |first3=Jennifer |last4=Burgasser |first4=Adam J. |last5=Shkolnik |first5=Evgenya |last6=Faherty |first6=Jacqueline K. |last7=Caselden |first7=Dan |last8=Meisner |first8=Aaron M. |last9=Kirkpatrick |first9=J. Davy |last10=Kuchner |first10=Marc J. |last11=Gagné |first11=Jonathan |date=2022-02-01 |title=CWISE J014611.20-050850.0AB: The Widest Known Brown Dwarf Binary in the Field |journal=The Astrophysical Journal |volume=926 |issue=2 |pages=L12 |doi=10.3847/2041-8213/ac51d8 |arxiv=2202.02315 |bibcode=2022ApJ...926L..12S |s2cid=246608034 |issn=0004-637X |doi-access=free }}</ref>
|-
|[[CWISE J0506+0738]]
|104
|L8γ-T0γ
|7 ± 2
|1140 ± 80
|Candidate of the [[Beta Pictoris moving group|Beta Pictoris Moving Group]]. Very red near-infrared colors.
|<ref>{{Cite journal |last1=Schneider |first1=Adam C. |last2=Burgasser |first2=Adam J. |last3=Bruursema |first3=Justice |last4=Munn |first4=Jeffrey A. |last5=Vrba |first5=Frederick J. |last6=Caselden |first6=Dan |last7=Kabatnik |first7=Martin |last8=Rothermich |first8=Austin |last9=Sainio |first9=Arttu |last10=Bickle |first10=Thomas P. |last11=Dahm |first11=Scott E. |last12=Meisner |first12=Aaron M. |last13=Kirkpatrick |first13=J. Davy |last14=Suárez |first14=Genaro |last15=Gagné |first15=Jonathan |date=2023-02-01 |title=Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf |journal=The Astrophysical Journal |volume=943 |issue=2 |pages=L16 |doi=10.3847/2041-8213/acb0cd |issn=0004-637X|arxiv=2301.02322 |bibcode=2023ApJ...943L..16S |doi-access=free }}</ref>
|-
|[[W0727−3607]]
|111
|L7+T4
|
|
|Candidate spectroscopic binary, or a single highly variable object
|<ref name=":2">{{Cite journal |last1=Bravo |first1=Alexia |last2=Schneider |first2=Adam C. |last3=Bardalez-Gagliuffi |first3=Daniella |last4=Burgasser |first4=Adam J. |last5=Meisner |first5=Aaron M. |last6=Kirkpatrick |first6=J. Davy |last7=Faherty |first7=Jacqueline K. |last8=Kuchner |first8=Marc J. |last9=Caselden |first9=Dan |last10=Sainio |first10=Arttu |last11=Hamlet |first11=Les |last12=The Backyard Worlds: Planet 9 Collaboration |date=10 Oct 2023 |title=An Investigation of New Brown Dwarf Spectral Binary Candidates From the Backyard Worlds: Planet 9 Citizen Science Initiative |journal=Astronomical Journal |volume=166 |issue=6 |page=226 |doi=10.3847/1538-3881/acffc1 |doi-access=free |arxiv=2310.06957 |bibcode=2023AJ....166..226B}}</ref>
|-
|[[W1036−5144]]
|88
|L7+T4
|
|
|Candidate spectroscopic binary
|<ref name=":2" />
|-
|[[W1344−7320]]
|65
|L7+T7
|
|
|Candidate spectroscopic binary
|<ref name=":2" />
|-
|[[CWISE J1055+5443|W1055+5443]]
|19.5-26
|Y0pec
|
|500±150
|Bluest Spitzer colors among spectroscopically confirmed Y-dwarfs. Discovered by Caselden (BYW, CatWISE), Goodman (BYW) and [[J. Davy Kirkpatrick|Kirkpatrick]] (CatWISE)<ref name=":1" />
|<ref>{{Cite journal |last1=Robbins |first1=Grady |last2=Meisner |first2=Aaron M. |last3=Schneider |first3=Adam C. |last4=Burgasser |first4=Adam J. |last5=Kirkpatrick |first5=J. Davy |last6=Gagné |first6=Jonathan |last7=Hsu |first7=Chih-Chun |last8=Moranta |first8=Leslie |last9=Casewell |first9=Sarah |last10=Marocco |first10=Federico |last11=Gerasimov |first11=Roman |last12=Faherty |first12=Jacqueline K. |last13=Kuchner |first13=Marc J. |last14=Caselden |first14=Dan |last15=Cushing |first15=Michael C.|last16=Alejandro |first16=Sherelyn |last17=The Backyard Worlds: Planet 9 Collaboration |last18=The Backyard Worlds: Cool Neighbors Collaboration |date=14 Oct 2023 |title=CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES |journal=The Astrophysical Journal |volume=958 |issue=1 |page=94 |doi=10.3847/1538-4357/ad0043 |doi-access=free |arxiv=2310.09524 |bibcode=2023ApJ...958...94R}}</ref>
|-
|[[CWISE J1249+3621|J1249+36]]
|
|sdL
|
|
|[[Stellar kinematics#Hypervelocity stars|hypervelocity star]] with a low mass, moving at a high speed (initially estimated to be 600 km/s)
|<ref>{{Cite web |date=June 10, 2024 |title=Lone Star State: Tracking a Low-Mass Star as it Speeds Across the Milky Way |url=https://today.ucsd.edu/story/speedy-star |access-date=2024-06-11 |website=UC San Diego Today |language=en}}</ref>
|-
|[[CWISE J1848−8757]]
|29
|young L?
|
|
|CatWISE team discovery, but also independently discovered by two BYW citizen scientists. Red J-W2 color, possibly young L-dwarf
|<ref>{{Cite journal |last1=Kota |first1=Tarun |last2=Kirkpatrick |first2=J. Davy |last3=Caselden |first3=Dan |last4=Marocco |first4=Federico |last5=Schneider |first5=Adam C. |last6=Gagné |first6=Jonathan |last7=Faherty |first7=Jacqueline K. |last8=Meisner |first8=Aaron M. |last9=Kuchner |first9=Marc J. |last10=Casewell |first10=Sarah |last11=Kacholia |first11=Kanishk |last12=Bickle |first12=Tom |last13=Beaulieu |first13=Paul |last14=Colin |first14=Guillaume |last15=Hamlet |first15=Leslie K. |date=2022-03-01 |title=Discovery of 16 New Members of the Solar Neighborhood Using Proper Motions from CatWISE2020 |journal=The Astronomical Journal |volume=163 |issue=3 |pages=116 |arxiv=2112.11314 |bibcode=2022AJ....163..116K |doi=10.3847/1538-3881/ac4713 |doi-access=free |issn=0004-6256}}</ref>
|}

==See also==
{{Portal|Astronomy}}
*[[Amateur astronomy]]
*[[Citizen science]]

[[Zooniverse]] projects:
{{columns-list|colwidth=15em|style=width: 600px; font-style: italic;|
*[[Asteroid Zoo]]
*[[Disk Detective]]
*[[Galaxy Zoo]]
*[[Old Weather]]
*[[Planet Hunters]]
*[[SETILive]]
*[[The Milky Way Project]]
*[[Radio Galaxy Zoo]]
}}

==References==
{{Reflist}}

==External links==
*{{Official website|http://www.backyardworlds.org}}

[[Category:Astronomy websites]]
[[Category:Astronomy projects]]
[[Category:Human-based computation]]
[[Category:Citizen science]]
[[Category:Internet properties established in 2017]]
[[Category:Exoplanet search projects]]