View source for Gaia (spacecraft)

{{Short description|European optical space observatory for astrometry}}
{{Italic title}}
{{Use dmy dates|date=March 2019}}
{{Infobox spaceflight
| name               = ''Gaia''

<!--image of the spacecraft/mission-->| image              = File:Gaia observes the Milky Way ESA24305955.jpeg
| image_caption      = Artist's impression of the ''Gaia'' spacecraft
| image_alt          = 3D image of ''Gaia'' spacraft

<!--Basic details-->| mission_type       = [[Astrometric]] [[Space observatory|observatory]]
| operator           = [[European Space Agency|ESA]]
| website            = {{URL|https://www.esa.int/Science_Exploration/Space_Science/Gaia}}
| COSPAR_ID          = 2013-074A
| SATCAT             = 39479
| mission_duration   = {{time interval|19 Dec 2013|27 Mar 2025}}

<!--Spacecraft properties-->| manufacturer       = {{plainlist|
*[[EADS Astrium]]
*[[e2v|e2v Technologies]]}}
| dry_mass           = {{cvt|1392|kg}}
| launch_mass        = {{cvt|2029|kg}}<ref name="eoPortal">{{cite web |url=https://directory.eoportal.org/web/eoportal/satellite-missions/g/gaia |title=GAIA (Global Astrometric Interferometer for Astrophysics) Mission |publisher=[[ESA]] eoPortal|access-date=2014-03-28 }}</ref>
| BOL_mass           = <!--spacecraft mass in orbit at beginning of operational life, after LEOP phase-->
| payload_mass       = {{cvt|710|kg}}<ref name="esa-faq">{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Gaia/Frequently_Asked_Questions_about_Gaia |title=Frequently Asked Questions about Gaia |date=14 November 2013 |publisher=[[ESA]] }}</ref>
| dimensions         = {{cvt|4.6|x|2.3|m}}
| power              = 1,910&nbsp;watts

<!--Launch details-->| launch_date        = {{start date text|19 December 2013, 09:12:14 UTC|timezone=yes}}<ref name="gaiaLiftoff">{{cite web |url=http://blogs.esa.int/gaia/2013/12/19/gaia-liftoff/ |title=Gaia Liftoff |publisher=[[ESA]] |date=19 December 2013 }}</ref>
| launch_rocket      = [[Soyuz at the Guiana Space Centre|Soyuz ST-B]]/[[Fregat|Fregat-MT]]
| launch_site        = [[Guiana Space Centre|Kourou]] [[Ensemble de Lancement Soyouz|ELS]]
| launch_contractor  = [[Arianespace]]
| entered_service    = <!--date on which the spacecraft entered service, if it did not do so immediately after launch-->
| disposal_type      = 
| deactivated        = 27 March 2025
| last_contact       = 27 March 2025

<!--orbit parameters-->| orbit_epoch        = 2014
| orbit_reference    = [[Lagrangian point#L2|Sun–Earth L<sub>2</sub>]]
| orbit_regime       = [[Lissajous orbit]]
| orbit_periapsis    = {{cvt|263000|km}}<ref name="esaenter"/>
| orbit_apoapsis     = {{cvt|707000|km}}<ref name="esaenter"/>
| orbit_inclination  = 
| orbit_period       = 180 days
| apsis              = apsis
| instruments        = {{plainlist|
*'''ASTRO''': Astrometric instrument
*'''BP/RP''': Photometric instrument
*'''RVS''': Radial velocity spectrometer }}

<!--Telescope parameters-->| telescope_name     = <!--name, if different to the satellite-->
| telescope_type     = [[Three-mirror anastigmat]]<ref name="eoPortal"/>
| telescope_diameter = {{cvt|1.45|x|0.5|m}}
| telescope_focal_length = <!--focal length of telescope-->
| telescope_area     = 0.7&nbsp;m<sup>2</sup>
| telescope_wavelength = <!--wavelengths at which the telescope operates-->
| instrument_type    = telescope

<!--transponder parameters-->| trans_band         = {{plainlist|
*[[S band]] ([[TT&C]] support)
*[[X band]] (data acquisition)}}
| trans_bandwidth    = {{plainlist|
*a few kbit/s down & up (S band)
*3–8 Mbit/s download (X band)}}

<!--mission insignia or patch-->| insignia           = Gaia mission insignia.png
| insignia_alt       = Gaia mission insignia
| insignia_caption   = ESA insignia for ''Gaia''
| insignia_size      = 180x180px
| programme          = '''[[European Space Agency Science Programme#Horizon 2000 Plus|Horizon 2000 Plus]]'''
| previous_mission   = ''[[Planck (spacecraft)|Planck]]''
| next_mission       = [[LISA Pathfinder]]
}}

'''''Gaia''''' was a [[space observatory]] of the [[European Space Agency]] (ESA) that was launched in 2013 and operated until March 2025. The spacecraft was designed for [[astrometry]]: measuring the positions, distances and motions of stars with unprecedented precision,<ref name="ESA-Gaia">{{cite web |url=http://www.esa.int/gaia/ |title=ESA Gaia home |publisher=[[ESA]] |access-date=2013-10-23 }}</ref><ref>{{Cite journal | doi = 10.1117/2.3201407.13| title = Timo Prusti plenary: Gaia: Scientific In-orbit Performance| journal = SPIE Newsroom| year = 2014| last1 = Spie}}</ref> and the positions of exoplanets by measuring attributes about the stars they orbit such as their [[apparent magnitude]] and [[color]].<ref name=":022">{{Cite book |last1=Bohan |first1=Elise |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |pages=77 |oclc=940282526 |author-link6=Rebecca Wragg Sykes |author-link7=Peter Chrisp}}</ref> {{As of|May 2025}}, the mission data processing continues, aiming to construct the largest and most precise 3D space catalog ever made, totalling approximately 1 billion [[astronomical object]]s, mainly stars, but also planets, comets, asteroids and [[quasar]]s, among others.<ref name="NYT-20180501"/>

To study the precise position and motion of its target objects, the spacecraft monitored each of them about 70 times<ref name="ESA2011"/> over the five years of the nominal mission (2014&ndash;2019), and about as many during its extension.<ref name="BBC2011">{{cite news |url=https://www.bbc.co.uk/news/science-environment-15242383 |work=BBC Science and Environment |title=A billion pixels for a billion stars |publisher=BBC |date=10 October 2011 }}</ref><ref name="SK2011">{{cite web |url=http://www.scienceknowledge.org/2011/07/14/we-have-already-installed-the-eye-of-gaia-with-a-billion-pixels-to-study-the-milky-way/ |archive-url=https://web.archive.org/web/20160406192842/http://www.scienceknowledge.org/2011/07/14/we-have-already-installed-the-eye-of-gaia-with-a-billion-pixels-to-study-the-milky-way/ |url-status=dead |archive-date=6 April 2016 |title=We have already installed the eye of 'Gaia' with a billion pixels to study the Milky Way |publisher=Science Knowledge |date=14 July 2011 }}</ref> Due to its detectors degrading slower than initially expected, the mission was given an extension,<ref name="esa-factsheet">{{cite web |date=24 June 2013 |title=Gaia: fact sheet |url=http://sci.esa.int/gaia/47354-fact-sheet/ |publisher=[[ESA]]}}</ref> lasting until March 27, 2025, when scientists at the ESA switched off Gaia after more than a decade of service.<ref>{{Cite news |last=Miller |first=Katrina |date=2025-03-27 |title=Farewell to Gaia, the Milky Way's Cartographer |url=https://www.nytimes.com/2025/03/27/science/gaia-milky-way-spacecraft-retires.html |access-date=2025-03-29 |work=The New York Times |language=en-US |issn=0362-4331}}</ref> ''Gaia'' targeted objects brighter than [[magnitude (astronomy)|magnitude]] 20 in a broad photometric band that covered the extended visual range between near-UV and near infrared;<ref name="Science Performance">{{cite web |url=https://www.cosmos.esa.int/web/gaia/science-performance |title=Expected Nominal Mission Science Performance |publisher=European Space Agency | access-date = 20 November 2019}}</ref> such objects represent approximately 1% of the Milky Way population.<ref name="ESA2011">{{cite web |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=28820 |title=ESA Gaia spacecraft summary |date=20 May 2011 | publisher=ESA }}</ref> Additionally, ''Gaia'' was expected to detect thousands to tens of thousands of Jupiter-sized [[exoplanet]]s beyond the Solar System by using the astrometry method,<ref name="Wenz">{{cite journal |last1=Wenz |first1=John |title=Lessons from scorching hot weirdo-planets |journal=Knowable Magazine |publisher= Annual Reviews |date=10 October 2019 |doi=10.1146/knowable-101019-2|doi-access=free |url=https://knowablemagazine.org/article/physical-world/2019/hot-jupiter-formation-theories |access-date=4 April 2022 |language=en}}</ref><ref name="Space Science Gaia">{{cite web |title=Gaia Science Objectives |url=http://www.esa.int/Our_Activities/Space_Science/Gaia/Science_objectives |date=14 June 2013 |publisher=[[European Space Agency]] }}</ref> 500,000 quasars outside this galaxy and tens of thousands of known and new asteroids and comets within the Solar System.<ref name="cam-ac-uk">{{cite web |title=Gaia's mission: solving the celestial puzzle |work=University of Cambridge |url=http://www.cam.ac.uk/research/features/gaias-mission-solving-the-celestial-puzzle |date=21 October 2013 |publisher=[[University of Cambridge]] }}</ref><ref name="Gaia launch">{{cite web |title= ESA's Gaia... Launches With A Billion Pixel Camera |url=http://www.satnews.com/story.php?number=155387954 |date=19 December 2013 |publisher=Satnews.com }}</ref><ref name="Gaia asteroid collision warning">{{cite web|title=Gaia space telescope to detect killer asteroids |url=http://www.thehindubusinessline.com/news/science/gaia-space-telescope-to-detect-killer-asteroids/article5257693.com |archive-url=https://archive.today/20140603094733/http://www.thehindubusinessline.com/news/science/gaia-space-telescope-to-detect-killer-asteroids/article5257693.com |url-status=dead |archive-date=3 June 2014 |date=19 December 2013 |publisher=thehindubusinessline.com }}</ref>

The ''Gaia'' mission continues to create a precise three-dimensional map of astronomical objects throughout the Milky Way and map their motions, which encode the origin and subsequent evolution of the Milky Way. The [[Spectrophotometry|spectrophotometric]] measurements provide detailed physical properties of all stars observed, characterizing their [[luminosity]], [[effective temperature]], [[gravitation|gravity]] and [[chemical element|elemental]] composition. This massive stellar census is providing the basic observational data to analyze a wide range of important questions related to the origin, structure and evolutionary history of the Milky Way galaxy.

The successor to the ''[[Hipparcos]]'' mission (operational 1989–1993), ''Gaia'' is part of ESA's [[Horizon 2000|Horizon 2000+]] long-term scientific program. ''Gaia'' was launched on 19 December 2013 by [[Arianespace]] using a [[Soyuz at the Guiana Space Centre|Soyuz ST-B]]/[[Fregat|Fregat-MT]] rocket flying from [[Guiana Space Centre|Kourou]] in French Guiana.<ref name="ESA-20121119">{{cite web |title=Announcement of Opportunity for the Gaia Data Processing Archive Access Co-Ordination Unit |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51116 |date=19 November 2012 |publisher=[[ESA]] }}</ref><ref>{{cite web|url=http://www.arianespace.com/news-press-release/2009/12-16-09-gaia-launch-contract.asp |title=Arianespace to launch Gaia; ESA mission will observe a billion stars in our galaxy |work=Press releases |publisher=Arianespace |date=16 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100918044022/http://arianespace.com/news-press-release/2009/12-16-09-gaia-launch-contract.asp |archive-date=18 September 2010}}</ref> The spacecraft currently operates in a [[Lissajous orbit]] around the [[Sun]]–[[Earth]] [[Lagrangian point#L2|L<sub>2</sub> Lagrangian point]]. The science observation officially ended on 15 January 2025.{{r|esa-20250115}}

== History ==

The ''Gaia'' space telescope had its roots in ESA's ''[[Hipparcos]]'' mission (1989–1993). Its mission was proposed in October 1993 by [[Lennart Lindegren]] ([[Lund Observatory]], [[Lund University]], Sweden) and [[Michael Perryman]] (ESA) in response to a call for proposals for ESA's Horizon Plus long-term scientific programme. It was adopted by ESA's Science Programme Committee as cornerstone mission number 6 on 13 October 2000, and the B2 phase of the project was authorised on 9 February 2006, with [[EADS Astrium]] taking responsibility for the hardware. The name "Gaia" was originally derived as an acronym for '''Global Astrometric Interferometer for Astrophysics'''. This reflected the optical technique of [[interferometry]] that was originally planned for use on the spacecraft. While the working method evolved during studies and the acronym is no longer applicable, the name ''Gaia'' remained to provide continuity with the project.<ref name="ESA-GO">{{cite web |url=http://www.esa.int/esaSC/120377_index_0_m.html |title=ESA Gaia overview |publisher=ESA}}</ref>

The total cost of the mission is around €740 million (~ $1 billion), including the manufacture, launch and ground operations.<ref name="theguardian">{{cite web |url=https://www.theguardian.com/science/2013/dec/13/gaia-spacecraft-set-launch-mission-3d-map-stars |publisher=Theguardian |title=Gaia spacecraft set for launch on mission to map a billion stars |date=13 December 2013 }}</ref> ''Gaia'' was completed two years behind schedule and 16% above its initial budget, mostly due to the difficulties encountered in polishing ''Gaia''{{'s}} ten [[silicon carbide]] mirrors and assembling and testing the focal plane camera system.<ref>{{cite web |title=Frequently Asked Questions about Gaia |url=https://www.esa.int/Science_Exploration/Space_Science/Gaia/Frequently_Asked_Questions_about_Gaia |website=www.esa.int |access-date=23 April 2023 |language=en}}</ref>

== Objectives ==

The ''Gaia'' space mission has the following objectives:<ref>{{cite web |title=Gaia Mission Science Objectives – Gaia – Cosmos |url=https://www.cosmos.esa.int/web/gaia/science-objectives |website=www.cosmos.esa.int |access-date=23 April 2023}}</ref><ref>{{cite web |title=Science objectives |url=https://www.esa.int/Science_Exploration/Space_Science/Gaia/Science_objectives |website=www.esa.int |access-date=23 April 2023 |language=en}}</ref>

* To determine the intrinsic luminosity of a star requires knowledge of its distance. One of the few ways to achieve this without physical assumptions is through the star's [[Stellar parallax|parallax]], but atmospheric effects and instrumental biases degrade the precision of parallax measurements. For instance, [[Cepheid variable]]s are used as [[standard candle]]s to measure distances to galaxies, but their own distances are poorly known. Thus, quantities depending on them, such as the [[Hubble constant|speed of expansion]] of the universe, remain inaccurate.
* Observations of the faintest objects will provide a more complete view of the stellar luminosity function. ''Gaia'' will observe 1 billion stars and other bodies, representing 1% of such bodies in the [[Milky Way]] galaxy. All objects up to a certain magnitude must be measured in order to have unbiased samples.
* To permit a better understanding of the more rapid stages of stellar evolution (such as the classification, frequency, correlations and directly observed attributes of rare fundamental changes and of cyclical changes). This has to be achieved by detailed examination and re-examination of a great number of objects over a long period of operation. Observing a large number of objects in the galaxy is also important to understand the dynamics of this galaxy.
* Measuring the astrometric and kinematic properties of a star is necessary in order to understand the various stellar populations, especially the most distant.

== Spacecraft ==
[[File:Maquette de Gaia salon du Bourget 2013 DSC 0191.JPG|thumb|Model of ''Gaia'' at Paris Air Show 2013]]
[[File:GAIA (14050944939).jpg|thumb|''Gaia'' from different angle]]
[[File:Gaia construcción de la sonda espacial en la Agencia Especial Europea.jpg|thumb|''Gaia'' at its final phase of construction, 2013]]

''Gaia'' was launched by [[Arianespace]], using a [[Soyuz at the Guiana Space Centre|Soyuz ST-B]] rocket with a [[Fregat|Fregat-MT]] upper stage, from the ''[[Ensemble de Lancement Soyouz]]'' at [[Guiana Space Centre|Kourou]] in [[French Guiana]] on 19 December 2013 at 09:12 UTC (06:12 local time). The satellite separated from the rocket's upper stage 43 minutes after launch at 09:54 UTC.<ref>{{cite web |url=http://www.spaceflightnow.com/soyuz/vs06/status.html |title=Mission Status Center |first=Stephen |last=Clark |work=Soyuz Launch Report |publisher=Spaceflight Now |date=19 December 2013 }}</ref><ref name="BBCLaunch">{{cite web |url=https://www.bbc.co.uk/news/science-environment-25426424 |title=BBC News – Gaia 'billion star surveyor' lifts off |date=19 December 2013 |last=Amos |first=Jonathan |publisher=[[BBC]]}}</ref>

The craft headed towards the Sun–Earth [[Lagrangian point#L2|Lagrange point L2]] located approximately 1.5 million kilometres from Earth, arriving there 8 January 2014.<ref>{{cite web |url=http://blogs.esa.int/gaia/2014/04/24/commissioning-update/ |title=Commissioning update |author=Gaia project team |publisher=esa |date=24 April 2014 }}</ref> The L2 point provides the spacecraft with a very stable gravitational and thermal environment. There, it uses a [[Lissajous orbit]] that avoids blockage of the Sun by the Earth, which would limit the amount of solar energy the satellite could produce through its [[solar panels]], as well as disturb the spacecraft's thermal equilibrium. After launch, a 10-metre-diameter sunshade was deployed. The sunshade always maintains a fixed 45 degree angle to the Sun, while precessing to scan the sky, thus keeping all telescope components cool and powering ''Gaia'' using solar panels on its surface. These factors and the materials used in its creation allow ''Gaia'' to function in conditions between -170'''°'''C and 70'''°'''C.<ref name=":0223">{{Cite book |last1=Bohan |first1=Elise |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |pages=76 |oclc=940282526 |author-link6=Rebecca Wragg Sykes |author-link7=Peter Chrisp}}</ref>

=== Scientific instruments ===

The ''Gaia'' payload consists of three main instruments:

# The astrometry instrument '''(Astro)''' precisely determines the positions of all stars brighter than magnitude 20 by measuring their angular position.<ref name="Science Performance"/> By combining the measurements of any given star over the duration of the mission, it will be possible to determine its [[parallax]], and therefore its distance, and its [[proper motion]]—the velocity of the star projected on the plane of the sky.
# The photometric instrument '''(BP/RP)''' allows the acquisition of luminosity measurements of stars over the 320–1000&nbsp;nm spectral band, of all stars brighter than magnitude 20.<ref name="Science Performance"/> The blue and red photometers (BP/RP) are used to determine stellar properties such as temperature, mass, age and elemental composition.<ref name="ESA-GO"/><ref>{{cite journal |title=The expected performance of stellar parametrization from Gaia spectrophotometry |journal= Monthly Notices of the Royal Astronomical Society|volume= 426|issue= 3|pages= 2463–2482|arxiv=1207.6005 |bibcode = 2012MNRAS.426.2463L |doi = 10.1111/j.1365-2966.2012.21797.x |date= 2012|last1= Liu|first1= C.|last2= Bailer-Jones|first2= C. A. L.|last3= Sordo|first3= R.|last4= Vallenari|first4= A.|last5= Borrachero|first5= R.|last6= Luri|first6= X.|last7= Sartoretti|first7= P.|doi-access= free|s2cid= 1841271}}</ref> Multi-colour photometry is provided by two low-resolution fused-silica [[Prism (optics)|prism]]s dispersing all the light entering the field of view in the along-scan direction prior to detection. The Blue Photometer (BP) operates in the wavelength range 330–680&nbsp;nm; the Red Photometer (RP) covers the wavelength range 640–1050&nbsp;nm.<ref name="Jordan2008">{{cite journal |arxiv=0811.2345 |title=The Gaia Project – technique, performance and status |doi=10.1002/asna.200811065 |year=2008 |last=Jordan |first=S. |journal=Astronomische Nachrichten |volume=329 |issue=9–10 |pages=875–880 |bibcode = 2008AN....329..875J |s2cid=551015 }}</ref>
# The Radial-Velocity Spectrometer '''(RVS)''' is used to determine the velocity of celestial objects along the line of sight by acquiring high-resolution spectra in the spectral band 847–874&nbsp;nm (field lines of calcium ion) for objects up to magnitude 17. Radial velocities are measured with a precision between 1&nbsp;km/s (V=11.5) and 30&nbsp;km/s (V=17.5). The measurements of radial velocities are important "to correct for perspective acceleration which is induced by the motion along the line of sight".<ref name="Jordan2008"/> The RVS reveals the velocity of the star along the line of sight of ''Gaia'' by measuring the [[Doppler shift]] of absorption lines in a high-resolution spectrum.

In order to maintain the fine pointing to focus on stars many light years away, the only moving parts are actuators to align the mirrors and the valves to fire the thrusters. It has no reaction wheels or gyroscopes. The spacecraft subsystems are mounted on a rigid [[silicon carbide]]<ref name=":022" /> frame, which provides a stable structure that will not expand or contract due to temperature. Attitude control is provided by small [[cold gas thruster]]s that can output 1.5 micrograms of nitrogen per second.

The telemetric link with the satellite is about 3 [[Mbit/s]] on average, while the total content of the focal plane represents several [[Gbit/s]].<ref>{{cite book|author=Neil English|title=Space Telescopes: Capturing the Rays of the Electromagnetic Spectrum|location=Germany|publisher=Springer International Publishing|date=November 8, 2016|url=https://books.google.com/books?id=1tF2DQAAQBAJ|access-date=March 21, 2023|page=256|isbn=9783319278148 }}</ref> Therefore, only a few dozen pixels around each object can be downlinked.

{{multiple image
| direction = horizontal
| align = center
| width1 = 294
| width2 = 409
| image1 = Schéma-gaia.png
| image2 = M4-au-plan-focal.png
| caption1 = <div style="background-color: #f2f2f2; text-align: center; padding: 6px 0; font-weight: bold;">Diagram of ''Gaia''</div> 
; Mirrors (M)
* '''M'''irrors of telescope 1 (M1, M2 and M3)
* '''M'''irrors of telescope 2 (M'1, M'2 and M'3)
* mirrors M4, M'4, M5, M6 are not shown
;Other components (1–9)
# [[Optical table|Optical bench]] ([[silicon carbide]] torus)
# Focal plane cooling radiator
# Focal plane electronics<ref name="focalplane"/>
# Nitrogen tanks
# [[Diffraction grating]] [[spectroscope]]
# Liquid propellant tanks
# Star trackers
# Telecommunication panel and batteries
# Main propulsion subsystem
; (A) Light path of telescope 1
| caption2 = <div style="background-color: #f2f2f2; text-align: center; padding: 6px 0; font-weight: bold;">Design of the focal plane and instruments</div>
The design of the ''Gaia'' focal plane and instruments. Due to the spacecraft's rotation, images cross the focal plane array right-to-left at 60 arcseconds per second.<ref name="focalplane">{{cite web |url=http://sci.esa.int/gaia/40129-payload-module/?fbodylongid=1907 |publisher=ESA Science and Technology |title=Gaia Focal Plane}}</ref>
# Incoming light from mirror M3
# Incoming light from mirror M'3
# Focal plane, containing the detector for the Astrometric instrument in light blue, Blue Photometer in dark blue, Red Photometer in red, and Radial Velocity Spectrometer in pink
# Mirrors M4 and M'4, which combine the two incoming beams of light
# Mirror M5
# Mirror M6, which illuminates the focal plane
# Optics and diffraction grating for the Radial Velocity Spectrometer (RVS)
# Prisms for the Blue Photometer and Red Photometer (BP and RP)
}}

===Measurement principles===
{{comparison_optical_telescope_primary_mirrors.svg}}
[[File:Gaia Scan.svg|thumb|Scanning method]]

Similar to its predecessor ''Hipparcos'', but with a precision one hundred times greater, ''Gaia'' consists of two telescopes providing two observing directions with a fixed, wide angle of 106.5° between them.<ref>{{cite web |url=http://sci.esa.int/gaia/53198-astrometry-in-space/ |work=ESA Science and Technology |title=Astrometry in Space |publisher=ESA}}</ref> The spacecraft rotates continuously around an axis perpendicular to the two telescopes' lines of sight, with a spin period of 6 hours. Thus, every 6 hours the spacecraft scans a great circle stripe approximately 0.7 degrees wide. The spin axis in turn has a slower [[precession]] across the sky: it maintains a fixed 45 degree angle to the Sun, but follows a cone around the Sun every 63 days, giving a cycloid-like path relative to the stars.  Over the course of the mission, each star is scanned many times at various scan directions, providing interlocking measurements over the full sky.

The two key telescope properties are:
* 1.45 × 0.5 m [[primary mirror]] for each telescope
* 1.0 × 0.5 m [[focal plane]] array on which light from both telescopes is projected. This in turn consists of 106 [[Charge-coupled device|CCDs]] of 4500 × 1966 pixels each, for a total of 937.8 megapixels (commonly depicted as a [[gigapixel]]-class imaging device).<ref name="techcrunch">{{cite news |url=https://techcrunch.com/2011/07/06/europe-launches-gigapixel-probe-to-map-milky-way/ |work= Techcrunch science update |title=Europe Launching Gigapixel Probe To Map Milky Way |publisher=Techcrunch |date=6 July 2011 }}</ref><ref name="gigapixel">{{cite news |url=http://lostintransits.wordpress.com/tag/gigapixel/ |work=lostintransits |title=Gaia: Planets and Parallax |date=19 December 2013 }}</ref><ref name="petapixel">{{cite news |url=http://petapixel.com/2013/12/19/esas-gigapixel-camera-now-space-will-map-milky-way-unprecedented-detail/ |work=petapixel reviews |title=ESA's Gigapixel Camera Now In Space, Will Map the Milky Way in Unprecedented Detail |publisher=Petapixel |date=19 December 2013 }}</ref><ref name=":0223" />

Each celestial object was observed on average about 70 times during the five years of the nominal mission, which has been extended to approximately ten years and will thus obtain twice as many observations.<ref>{{cite web |title=Events forecast and areas of the sky ''Gaia'' has observed |url=https://gaia.esac.esa.int/gost/ |publisher=[[ESA]] |date=28 April 2022 }}</ref> These measurements will help determine the astrometric parameters of stars: two corresponding to the angular position of a given star on the sky, two for the derivatives of the star's position over time (motion) and lastly, the star's [[parallax]] from which distance can be calculated. The radial velocity of the brighter stars is measured by an integrated [[spectrometer]] observing the [[Doppler effect]]. Because of the physical constraints imposed by the Soyuz spacecraft, ''Gaia''{{'s}} focal arrays could not be equipped with optimal radiation shielding, and ESA expected their performance to suffer somewhat toward the end of the initial five-year mission. Ground tests of the CCDs while they were subjected to radiation provided reassurance that the primary mission's objectives can be met.<ref>{{cite book |arxiv=1608.01476|doi=10.1117/12.2232078|chapter=Radiation effects on the ''Gaia'' CCDS after 30 months at L2|title=High Energy, Optical, and Infrared Detectors for Astronomy VII|volume=9915|pages=99150K|year=2016|last1=Crowley|first1=Cian|last2=Abreu|first2=Asier|last3=Kohley|first3=Ralf|last4=Prod'Homme|first4=Thibaut|last5=Beaufort|first5=Thierry|last6=Berihuete|first6=A.|last7=Bijaoui|first7=A.|last8=Carrión|first8=C.|last9=Dafonte|first9=C.|last10=Damerdji|first10=Y.|last11=Dapergolas|first11=A.|last12=de Laverny|first12=P.|last13=Delchambre|first13=L.|last14=Drazinos|first14=P.|last15=Drimmel|first15=R.|last16=Frémat|first16=Y.|last17=Fustes|first17=D.|last18=García-Torres|first18=M.|last19=Guédé|first19=C.|last20=Heiter|first20=U.|last21=Janotto|first21=A. -M.|last22=Karampelas|first22=A.|last23=Kim|first23=D. -W.|last24=Knude|first24=J.|last25=Kolka|first25=I.|last26=Kontizas|first26=E.|last27=Kontizas|first27=M.|last28=Korn|first28=A. J.|last29=Lanzafame|first29=A. C.|last30=Lebreton|first30=Y.|s2cid=118633229|editor2-first=James|editor2-last=Beletic|editor1-first=Andrew D|editor1-last=Holland|display-authors=29}}</ref>

An atomic clock on board ''Gaia'' plays a crucial role in achieving the mission's primary objectives. ''Gaia'' rotates with angular velocity of 60"/sec or 0.6 microarcseconds in 10 nanoseconds. Therefore, in order to meet its positioning goals, ''Gaia'' must be able to record the exact time of observation to within nanoseconds. Furthermore, no systematic positioning errors over the rotational period of 6 hours should be introduced by the clock performance. For the timing error to be below 10 nanoseconds over each rotational period, the frequency stability of the on-board clock needs to be better than 10<sup>−12</sup>. The rubidium atomic clock aboard the ''Gaia'' spacecraft has a stability reaching ~ 10<sup>−13</sup> over each rotational period of 21600 seconds.<ref name="Klioner_2015">{{cite journal |last1=Klioner |first1=S. |title=High-accuracy timing for Gaia data from one-way time synchronization |journal=Proc. J. 2014 |date=2015 |volume=1 |issue=55–60 |page=55 |bibcode=2015jsrs.conf...55K |url=https://syrte.obspm.fr/jsr/journees2014/pdf/Klioner.pdf |access-date=10 September 2023}}</ref>

''Gaia'''s measurements contribute to the creation and maintenance of a high-precision celestial reference frame, the [[Barycentric and geocentric celestial reference systems|Barycentric Celestial Reference System (BCRS)]], which is essential for both astronomy and navigation. This reference frame serves as a fundamental grid for positioning celestial objects in the sky, aiding astronomers in various research endeavors. All observations, regardless of the actual positioning of the spacecraft, must be expressed in terms of this reference system. As a fully relativistic model, the influence of the gravitational field of the solar-system must be taken into account, including such factors as the gravitational light-bending due to the Sun, the major planets and the Moon.<ref name="Klioner">{{cite web |last1=Klioner |first1=Sergei |title=3.1.5 Relativistic model |url=https://gea.esac.esa.int/archive/documentation/GDR2/Data_processing/chap_cu3ast/sec_cu3ast_intro/ssec_cu3ast_intro_relativity.html |website=Gaia Data Release 2 Documentation release 1.2 |publisher=European Space Agency |access-date=10 September 2023}}</ref>

The expected accuracies of the final catalogue data have been calculated following in-orbit testing, taking into account the issues of stray light, degradation of the optics, and the basic angle instability. The best accuracies for parallax, position and proper motion are obtained for the brighter observed stars, apparent magnitudes 3–12. The standard deviation for these stars is expected to be 6.7 micro-arcseconds or better. For fainter stars, error levels increase, reaching 26.6 micro-arcseconds error in the parallax for 15th-magnitude stars, and several hundred micro-arcseconds for 20th-magnitude stars.<ref>{{cite journal|bibcode=2014EAS....67...23D|title=Gaia astrometric science performance – post-launch predictions|volume=1502|pages=23–29|last1=De Bruijne|first1=J. H. J.|last2=Rygl|first2=K. L. J.|last3=Antoja|first3=T.|year=2015 |arxiv=1502.00791 |doi=10.1051/eas/1567004|journal=EAS Publications Series|s2cid=118112059}}</ref> For comparison, the best parallax error levels from the new Hipparcos reduction are no better than 100 micro-arcseconds, with typical levels several times larger.<ref name=hipparcos>{{cite journal |bibcode=2007A&A...474..653V |title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics |volume=474 |issue=2 |pages=653–664 |last1=Van Leeuwen|first1=F. |year=2007 |doi=10.1051/0004-6361:20078357 |arxiv= 0708.1752 |s2cid=18759600}}</ref>

== Launch and orbit ==
{{multiple image|perrow = 1|total_width=
| header = Animation of Gaia's trajectory
| image1 = Animation of Gaia trajectory - Polar view.gif
| caption1 = Polar view
| image2 = Animation of Gaia trajectory - Equatorial view.gif
| caption2 = Equatorial view
| image3 = Animation of Gaia's trajectory - viewed from Sun.gif 
| caption3 = Viewed from the Sun
| footer = {{legend2|magenta|[[Gaia]]}}{{·}}{{legend2|RoyalBlue|[[Earth]]}}
}}
[[File:Gaia observatory trajectory.svg|thumb|Simplified illustration of ''Gaia''{{'s}} trajectory and orbit (not to scale)]]

In October 2013 [[ESA]] had to postpone ''Gaia''{{'s}} original launch date, due to a precautionary replacement of two of ''Gaia''{{'s}} transponders. These are used to generate timing signals for the downlink of science data. A problem with an identical transponder on a satellite already in orbit motivated their replacement and reverification once incorporated into ''Gaia''. The rescheduled launch window was from 17 December 2013 to 5 January 2014, with ''Gaia'' slated for launch on 19 December.<ref name="Postponement">{{cite web |title=Gaia launch postponement update |url=http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_launch_postponement_update |publisher=[[ESA]] |date=23 October 2013 }}</ref>

''Gaia'' was successfully launched on 19 December 2013 at 09:12 [[Coordinated Universal Time|UTC]].<ref name="Launched">{{cite web |title=Soyuz ST-B successfully launches Gaia space observatory |url=http://www.nasaspaceflight.com/2013/12/soyuz-stb-launch-gaia-space-observatory/ |publisher=nasaspaceflight.com |date=19 December 2013 }}</ref>
About three weeks after launch, on 8 January 2014, it reached its designated orbit around the Sun-Earth [[Lagrangian point#L2|L2 Lagrange point]] (SEL2),<ref name="esaenter">{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_enters_its_operational_orbit |title=Gaia enters its operational orbit |publisher=[[ESA]] |date=8 January 2014 }}</ref><ref>{{cite news |url=http://www.spaceflight101.com/gaia-mission-and-orbit-design.html |title=Gaia Mission & Orbit Design Gaia Mission Section |publisher=Spaceflight101 |access-date=2013-12-19 |archive-url=https://web.archive.org/web/20190328192127/http://spaceflight101.com/gaia/gaia-mission-orbit-design/ |archive-date=2019-03-28}}</ref> about 1.5 million kilometers from Earth.

In 2015, the [[Pan-STARRS]] observatory discovered an object orbiting the Earth, which the [[Minor Planet Center]] catalogued as object {{mp|2015 HP|116}}. It was soon found to be an accidental rediscovery of the Gaia spacecraft and the designation was promptly retracted.<ref>{{cite web |url=http://www.minorplanetcenter.net/mpec/K15/K15HC5.html |title=MPEC 2015-H125: DELETION OF 2015 HP116 |website=Minor Planet Center |access-date=2019-11-21}}</ref>

==Issues==
=== Stray light problem ===
Shortly after launch, ESA revealed that ''Gaia'' suffers from a [[stray light]] problem. The problem was initially thought to be due to ice deposits reflecting some of the light diffracted around the edges of the sunshield into the telescope apertures and on towards the focal plane.<ref>{{cite news |url=http://blogs.esa.int/gaia/2014/04/24/commissioning-update/ |title=GAIA – Commissioning Update |work=[[European Space Agency]] |date=24 April 2014 |access-date=2014-06-03 }}</ref> The actual source of the stray light was later identified as the fibers of the sunshield, protruding beyond the edges of the shield.<ref>{{cite news| title=STATUS OF THE GAIA STRAYLIGHT ANALYSIS AND MITIGATION ACTIONS| url=http://www.cosmos.esa.int/web/gaia/news_20141217| publisher=ESA |access-date=1 January 2015| date=2014-12-17}}</ref> This results in a "degradation in science performance [which] will be relatively modest and mostly restricted to the faintest of ''Gaia''{{'s}} one billion stars." Mitigation schemes were implemented<ref>{{Cite journal|last1=Mora|first1=A.|last2=Biermann|first2=M.|last3=Bombrun|first3=A.|last4=Boyadjian|first4=J.|last5=Chassat|first5=F.|last6=Corberand|first6=P.|last7=Davidson|first7=M.|last8=Doyle|first8=D.|last9=Escolar|first9=D.|last10=Gielesen|first10=W. L. M.|last11=Guilpain|first11=T.|editor6-first=Edward C|editor6-last=Tong|editor5-first=Nicholas|editor5-last=Siegler|editor4-first=Natalie|editor4-last=Batalha|editor3-first=Makenzie|editor3-last=Lystrup|editor2-first=Giovanni G|editor2-last=Fazio|editor1-first=Howard A|editor1-last=MacEwen|date=2016-07-01|title=Gaia: focus, straylight and basic angle|journal=Space Telescopes and Instrumentation 2016: Optical|volume=9904|pages=99042D|doi=10.1117/12.2230763|bibcode=2016SPIE.9904E..2DM|arxiv=1608.00045|series=Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave|s2cid=119260855}}</ref> to improve performance. The degradation is more severe for the RVS spectrograph than for the astrometry measurements, because it spreads the light of the star onto a much larger number of detector pixels, each of which collects scattered light.

This kind of problem has some historical background. In 1985 on [[STS-51-F]], the Space Shuttle [[Spacelab]]-2 mission, another astronomical mission hampered by stray debris was the [[Spacelab Infrared Telescope|Infrared Telescope]] (IRT), in which a piece of [[mylar]] insulation broke loose and floated into the line-of-sight of the telescope causing corrupted data.<ref name=kent>{{cite journal |bibcode=1992ApJS...78..403K|title=Galactic Structure from the Spacelab Infrared Telescope. I. 2.4 Micron Map|journal=The Astrophysical Journal Supplement Series|volume=78|pages=403|last1=Kent|first1=S. M.|last2=Mink|first2=D.|last3=Fazio|first3=G.|last4=Koch|first4=D.|last5=Melnick|first5=G.|last6=Tardiff|first6=A.|last7=Maxson|first7=C.|year=1992|doi=10.1086/191633}}</ref> The testing of stray-light and baffles is a noted part of space imaging instruments.<ref>{{cite book |bibcode=2017SPIE10562E..4VH|volume=10562|pages=105624V|last1=Hellin|first1=M. -L|last2=Mazy|first2=E.|last3=Marcotte|first3=S.|last4=Stockman|first4=Y.|last5=Korendyke|first5=C.|last6=Thernisien|first6=A.|title=International Conference on Space Optics — ICSO 2016 |chapter=Stray light testing of WISPR baffle development model |editor-first1=Zoran |editor-first2=Bruno |editor-first3=Nikos |editor-last1=Sodnik |editor-last2=Cugny |editor-last3=Karafolas |year=2017|doi=10.1117/12.2296104 |isbn=9781510616134 |s2cid=125498560 }}</ref>

=== Micrometeoroid hit ===
In April 2024, a [[micrometeoroid]] hit and damaged Gaia's protective cover, creating "a little gap that allowed stray sunlight – around one billionth of the intensity of direct sunlight felt on Earth – to occasionally disrupt ''Gaia''’s very sensitive sensors". In May, the electronics of one of the CCDs failed, which caused a high rate of false detections. After that, the engineers refocused ''Gaia'''s optics "for the final time".<ref>{{cite web |title=Double trouble: Gaia hit by micrometeoroid and solar storm |url=https://www.esa.int/Enabling_Support/Operations/Double_trouble_Gaia_hit_by_micrometeoroid_and_solar_storm |website=www.esa.int |access-date=19 July 2024 |language=en}}</ref>

== Mission progress ==

[[File:The_colour_of_the_sky_from_Gaia%E2%80%99s_Early_Data_Release_3_ESA22358060.png|upright=1.5|thumb|''Gaia'' map of the sky by star density]]
The testing and calibration phase, which started while ''Gaia'' was en route to SEL2 point, continued until the end of July 2014,<ref name="firstscience">{{cite news |url=http://blogs.esa.int/gaia/2014/06/05/gaia-takes-science-measurements |title=Gaia takes science measurements |publisher=ESA |access-date=2014-07-28}}</ref> three months behind schedule due to unforeseen issues with stray light entering the detector. After the six-month commissioning period, the satellite started its nominal five-year period of scientific operations on 25 July 2014 using a special scanning mode that intensively scanned the region near the [[ecliptic pole]]s; on 21 August 2014 ''Gaia'' began using its normal scanning mode which provides more uniform coverage.<ref>{{ Cite web | date = 16 August 2016 | title = Gaia's second anniversary marked by successes and challenges | publisher = [[ESA]] | url = http://sci.esa.int/gaia/58135-gaia-s-second-anniversary-marked-by-successes-and-challenges/ | access-date = 19 September 2016 }}</ref>

Although it was originally planned to limit ''Gaia''{{'}}s observations to stars fainter than magnitude 5.7, tests carried out during the commissioning phase indicated that ''Gaia'' could autonomously identify stars as bright as magnitude 3. When ''Gaia'' entered regular scientific operations in July 2014, it was configured to routinely process stars in the magnitude range 3 – 20.<ref>{{cite conference | last1 = Martín-Fleitas | first1 = J. | last2 = Mora | first2 = A. | last3 = Sahlmann | first3 = J. | last4 = Kohley | first4 = R. | last5 = Massart | first5 = B. | display-authors = etal | editor-last = Oschmann | editor-first = Jacobus M. | editor2-last = Clampin | editor2-first = Mark | editor3-last = Fazio | editor3-first = Giovanni G. | editor4-last = MacEwen | editor4-first = Howard A. | book-title = Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave | series = Proc. SPIE | volume = 9143 | date = 2 August 2014 | pages = 91430Y |arxiv = 1408.3039v1 | doi = 10.1117/12.2056325 | chapter = Enabling Gaia observations of naked-eye stars | title = Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave }}</ref> On the bright side of that limit, special operational procedures download raw scanning data for the remaining 230 stars brighter than magnitude 3; methods to reduce and analyse these data are being developed; and it is expected that there will be "complete sky coverage at the bright end" with standard errors of "a few dozen μas".<ref>{{ Cite journal | author = T. Prusti | collaboration = GAIA Collaboration | date = 2016 | title = The ''Gaia'' mission | type = forthcoming article | journal = Astronomy and Astrophysics | doi = 10.1051/0004-6361/201629272 | bibcode=2016A&A...595A...1G | volume=595 | pages=A1|arxiv = 1609.04153 | s2cid = 9271090 }}</ref>

On 30 August 2014, ''Gaia'' discovered its first [[supernova]] in another galaxy.<ref>{{cite web |url=http://sci.esa.int/gaia/54630-gaia-discovers-its-first-supernova/ |title=GAIA DISCOVERS ITS FIRST SUPERNOVA |website=ESA |access-date=2019-11-21}}</ref> On 3 July 2015, a map of the Milky Way by star density was released, based on data from the spacecraft.<ref name=stardensitymap>{{cite web| title=Counting stars with Gaia| url=http://sci.esa.int/gaia/56125-counting-stars-with-gaia/| website=sci.esa.int/gaia| publisher=European Space Agency| access-date=16 July 2015}}</ref> As of August 2016, "more than 50 billion focal plane transits, 110 billion photometric observations and 9.4 billion spectroscopic observations have been successfully processed."<ref name=jansen>{{cite web| url=http://sci.esa.int/gaia/58135-gaia-s-second-anniversary-marked-by-successes-and-challenges/ |title=Gaia's second anniversary marked by successes and challenges| website=ESA |access-date = 17 August 2016}}</ref>

In 2018 the ''Gaia'' mission was extended to 2020, and in 2020 it was further extended through 2022, with an additional "indicative extension" extending through 2025.<ref name="extension">{{ Cite web | date = 14 November 2018 | title = Extended life for ESA's science missions | url = http://sci.esa.int/director-desk/60943-extended-life-for-esas-science-missions/ |publisher=ESA | access-date = 14 November 2018 }}</ref><ref name="extension2">{{ Cite web | date = 13 October 2020 | title = Extended operations confirmed for science missions | url = https://sci.esa.int/s/8OJDymW |publisher=ESA | access-date = 15 October 2020 }}</ref> The limiting factor to further mission extensions is the supply of nitrogen for the cold gas thrusters of the micro-propulsion system.<ref name="Brown2018">{{ Cite conference | last = Brown | first = Anthony | date = 29 August 2018 | title = 21st Century Astrometry: crossing the Dark and Habitable frontiers | series = IAU Symposium 348 | contribution = The Gaia Mission and its Extension | contribution-url = https://www.cosmos.esa.int/documents/29201/295769/IAU2018_Brown_IAUS348_GaiaMissionExtension.pdf/73237457-2836-101d-eaa1-0625a739b0bf | access-date = 14 November 2018 }}</ref> The amount of [[dinitrogen tetroxide]] (NTO) and [[monomethylhydrazine]] (MMH) for the chemical propulsion subsystem on board might have been enough to stabilize the spacecraft at L2 for several decades. Without the cold gas, though, the space craft could no longer be pointed on a microarcsecond scale.

In March 2023, the ''Gaia'' mission was extended through the second quarter of 2025, when the spacecraft was expected to run out of cold gas propellant.<ref name="esa-20230307">{{cite web |url=https://sci.esa.int/web/director-desk/-/extended-life-for-esa-s-science-missions |title=Extended life for ESA's science missions |work=[[ESA]] |date=7 March 2023 |access-date=20 March 2023}}</ref>

=== End of mission ===
''Gaia'''s last targeted observation was done on 10 January 2025.<ref name=jan2025>{{Cite web|url=https://www.esa.int/Science_Exploration/Space_Science/Gaia/Last_starlight_for_ground-breaking_Gaia|title=Last starlight for ground-breaking Gaia|website=www.esa.int}}</ref> After several weeks of onboard technology tests, ''Gaia'' left its orbit near {{L2}} and was put into a [[heliocentric orbit]] away from Earth's [[Sphere of influence (astrodynamics)|sphere of influence]].<ref name="gaia-eom">{{cite web |url=https://www.cosmos.esa.int/web/gaia/end-of-observations |title=Gaia spacecraft end of operations |work=[[ESA]] |date=October 2024 |access-date=16 December 2024}}</ref> After downlinking all remaining data to Earth, ''Gaia'' was decommissioned and [[Passivation (spacecraft)|passivated]] on 27 March 2025.<ref name=jan2025/><ref>{{Cite web |title=Farewell, Gaia! Spacecraft operations come to an end |url=https://www.esa.int/Enabling_Support/Operations/Farewell_Gaia!_Spacecraft_operations_come_to_an_end |access-date=2025-03-27 |website=www.esa.int |language=en}}</ref> The mission has since entered a post-operations phase to complete and publish the final Gaia Data Release, DR5, by the end of 2030.<ref name="esa-20230307" />

== Data releases ==
{{main|Gaia catalogues}}
Several [[Gaia catalogues]] are released over the years each time with increasing amounts of information and better astrometry; the early releases also miss some stars, especially fainter stars located in dense star fields and members of close binary pairs.<ref name=releasescenario/> The first data release, Gaia DR1, based on 14 months of observation was on 14 September 2016.<ref>{{cite news |url=https://www.bbc.com/news/science-environment-37355154 |title=Gaia space telescope plots a billion stars |author=Jonathan Amos |publisher=BBC |date=14 July 2016}}</ref><ref>{{cite web |url=http://sci.esa.int/gaia/58272-gaia-s-billion-star-map-hints-at-treasures-to-come/ |title=Gaia's billion-star map hints at treasures to come, ESA press release |date=13 September 2016 |website=ESA |access-date=2019-11-21}}</ref><ref>{{cite web |url=https://www.aanda.org/component/toc/?task=topic&id=641 |publisher=Astronomy & Astrophysics |title=Gaia Data Release 1 |access-date=2019-11-21}}</ref> The data release includes "positions and ... magnitudes for 1.1 billion stars using only ''Gaia'' data; positions, parallaxes and proper motions for more than 2 million stars" based on a combination of ''Gaia'' and [[Tycho-2 Catalogue|Tycho-2]] data for those objects in both catalogues; "light curves and characteristics for about 3,000 variable stars; and positions and magnitudes for more than 2000 ... extragalactic sources used to define the [[celestial reference frame]]".<ref name=releasescenario>{{cite web |url=https://www.cosmos.esa.int/web/gaia/release |title=Gaia Data Release Scenario |work=[[ESA]] |access-date=8 August 2024}}</ref><ref>{{ Cite web | date = 14 September 2016 | title = Gaia Data Release 1 (Gaia DR1) | url=http://www.cosmos.esa.int/web/gaia/dr1 | website=ESA |access-date = 16 September 2016 }}</ref><ref>{{ Cite web | website=ESA |date = 15 September 2016 | title = Data Release 1 | url = http://sci.esa.int/gaia/58275-data-release-1/ | access-date = 15 September 2016 }}</ref>

The second data release (DR2), which occurred on 25 April 2018,<ref name="NYT-20180501">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Gaia's Map of 1.3 Billion Stars Makes for a Milky Way in a Bottle |url=https://www.nytimes.com/2018/05/01/science/gaia-map-milky-way.html |date=1 May 2018 |work=[[The New York Times]] |access-date=1 May 2018 }}</ref><ref>{{cite web |last1=Greenfieldboyce |first1=Nell |url=https://www.npr.org/sections/thetwo-way/2018/04/25/605622779/you-are-here-scientists-unveil-precise-map-of-more-than-a-billion-stars |title=You Are Here: Scientists Unveil Precise Map Of More Than A Billion Stars |website=NPR |date=25 April 2018 |access-date=2019-11-21}}</ref> is based on 22 months of observations made between 25 July 2014 and 23 May 2016. It includes positions, parallaxes and proper motions for about 1.3 billion stars and positions of an additional 300 million stars in the magnitude range g = 3–20,<ref name="DR2 primer">{{ Citation | author = Gaia Helpdesk | date = 9 December 2019 | title = Gaia DR2 primer: Everything you wish you had known before you started working with Gaia Data Release 2 | volume = 1 | url = https://www.cosmos.esa.int/documents/29201/1773953/Gaia+DR2+primer.pdf/a4459741-6732-7a98-1406-a1bea243df79?t=1575906638431 | access-date = 10 December 2019 | format = pdf }}</ref> red and blue photometric data for about 1.1 billion stars and single colour photometry for an additional 400 million stars, and median radial velocities for about 7 million stars between magnitude 4 and 13. It also contains data for over 14,000 selected Solar System objects.<ref>{{ Cite web | date = 25 April 2018 | title = Gaia Data Release 2 (Gaia DR2) | website=ESA |url = https://www.cosmos.esa.int/web/gaia/dr2 | access-date = 26 April 2018 }}</ref><ref name=SelectedAsteroids>{{cite web | url=http://sci.esa.int/gaia/59821-selected-asteroids-detected-by-gaia-between-august-2014-and-may-2016/ | website=ESA |access-date=2 December 2017 | title=Selected asteroids detected by Gaia between August 2014 and May 2016}}</ref>

[[File:Gaia%E2%80%99s_Early_Data_Release_3_in_numbers_ESA22359174.jpeg|upright=1.5|thumb|Stars and other objects in ''Gaia'' Early Data Release 3]]

Due to uncertainties in the data pipeline, the third data release, based on 34 months of observations, was split into two parts so that data that was ready first, was released first. The first part, EDR3 ("Early Data Release 3"), consisting of improved positions, parallaxes and proper motions, was released on 3 December 2020.<ref name="EDR3">{{ Cite web |website = ESA | title = Gaia Early Data Release 3 (Gaia EDR3) | url = https://www.cosmos.esa.int/web/gaia/earlydr3 | access-date = 12 December 2020 }}</ref> The coordinates in EDR3 use a new version of the ''Gaia'' celestial reference frame (''Gaia''–CRF3), based on observations of 1,614,173 extragalactic sources,<ref name="EDR3"/> 2,269 of which were common to radio sources in the third revision of the [[International Celestial Reference Frame#ICRF3|International Celestial Reference Frame (ICRF3)]].<ref>{{ Cite journal | last1 = Lindegren | first1 = L. | last2 = Klioner | first2 = S. | last3 = Hernandez | first3 = J. | last4 = Bombrun | first4 = A. | display-authors = et al | year = 2021 | title = ''Gaia'' Early Data Release 3 – The astrometric solution | journal = Astronomy & Astrophysics | volume = A2 | page = 649 | doi = 10.1051/0004-6361/202039709 | arxiv = 2012.03380 | bibcode = 2021A&A...649A...2L | s2cid = 227342958 }}</ref> Included is the Gaia Catalogue of Nearby Stars (GCNS), containing 331,312 stars within (nominally) {{Convert|100|pc|ly|abbr=off}}.<ref>{{Cite web|url=https://www.cosmos.esa.int/web/gaia/edr3-gcns|title=Gaia EDR3 - Gaia Catalogue of Nearby Stars - Gaia - Cosmos|website=Gaia}}</ref><ref>{{Cite journal |author1=Richard Smart|author2=L. M. Sarro|author3=J. Rybizki|author4=C. Reyle|author5=A. C. Robin |title=Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars |journal=Astronomy & Astrophysics |year=2021|volume=A6 |page=649 |issn=0004-6361 |doi=10.1051/0004-6361/202039498| arxiv=2012.02061 |bibcode=2021A&A...649A...6G |s2cid=227255512 |url=https://www.aanda.org/articles/aa/abs/forth/aa39498-20/aa39498-20.html}}</ref>

The full DR3, published on 13 June 2022, includes the EDR3 data plus Solar System data; variability information; results for non-single stars, for quasars, and for extended objects; astrophysical parameters; and a special data set, the Gaia Andromeda Photometric Survey (GAPS).<ref>{{ Cite web | date = 29 January 2019 | title = Gaia Data Release 3 split into two parts | url = https://www.cosmos.esa.int/web/gaia/news-2019#GaiaDR3Announcement |website=ESA |access-date = 29 January 2019 }}</ref>

Between DR3 and DR4 there was a Focused Product Release, publishing among other things new data on the [[Omega Centauri]] cluster using a novel observation technique; the technique will be extended to all globular clusters and other dense fields in future full Data Releases.

===Future releases===
The full data release for the five-year nominal mission, DR4, will include full astrometric, photometric and radial-velocity catalogues, variable-star and non-single-star solutions, source classifications plus multiple astrophysical parameters for stars, unresolved binaries, galaxies and quasars, an exo-planet list and epoch and transit data for all sources.<ref name=brown2025>{{cite arXiv |last1=Brown |first1=Anthony G. A. |eprint=2503.01533v1 |title=Gaia: Ten Years of Surveying the Milky Way and Beyond |date=2025 |class=astro-ph.GA }}</ref> Additional release(s) will take place depending on mission extensions.<ref name=releasescenario/> Most measurements in DR4 are expected to be 1.7 times more precise than DR2; proper motions will be 4.5 times more precise.<ref name="Brown_Future">{{cite conference | first = Anthony G.A. | last = Brown | title = The Future of the Gaia Universe | conference = 53rd ESLAB symposium "the Gaia universe" | date = 12 April 2019 | url = https://zenodo.org/record/2637972 | doi = 10.5281/zenodo.2637971 }}</ref> DR4 is expected to be released no earlier than December 2026.<ref name=releasescenario />

The final Gaia catalogue, DR5, will consist of all data collected during the lifespan of the mission. It will be 1.4 times more precise than DR4, while proper motions will be 2.8 times more precise than DR4.<ref name="Brown_Future"/> It will be published no earlier than the end of 2030.<ref name=releasescenario /> All data of all catalogues will be available in an online data base that is free to use.

An outreach application, ''[[Gaia Sky]]'', has been developed to explore the galaxy in three dimensions using ''Gaia'' data.<ref>{{ Cite web | last = Sagristà Sellés | first = Toni | date = 2016 | title = Gaia Sky | publisher = Astronomisches Rechen-Institut (ZAH), Universität Heidelberg | place = Heidelberg | url = https://zah.uni-heidelberg.de/gaia/outreach/gaiasky/ |access-date=2019-11-21}}</ref>

=== Data processing ===
[[File:VST Snaps Gaia en Route to a Billion Stars.jpg|thumb|[[VLT Survey Telescope|VST]] snaps ''Gaia'' en route to a billion stars<ref>{{cite news |title=VST Snaps Gaia en Route to a Billion Stars |url=http://www.eso.org/public/images/potw1407a/ |access-date=2014-03-12 |work=ESO }}</ref>]]

The overall data volume that was retrieved from the spacecraft during the nominal five-year mission at a compressed data rate of 1&nbsp;Mbit/s is approximately 60&nbsp;[[Terabyte|TB]], amounting to about 200&nbsp;TB of usable uncompressed data on the ground, stored in an [[InterSystems Caché]] database. The responsibility of the data processing, partly funded by ESA, is entrusted to a European consortium, the [[Data Processing and Analysis Consortium]] (DPAC), which was selected after its proposal to the ESA Announcement of Opportunity released in November 2006. DPAC's funding is provided by the participating countries and has been secured until the production of ''Gaia''{{'s}} final catalogue.<ref>{{cite web|url=http://sci.esa.int/gaia/58274-the-role-of-dpac/|title=Making sense of it all – the role of the Gaia Data Processing and Analysis Consortium|access-date=2017-04-08|website=ESA}}</ref>

''Gaia'' sends back data for about eight hours every day at about 5&nbsp;Mbit/s. ESA's three 35-metre-diameter radio dishes of the [[ESTRACK]] network in [[Cebreros Station|Cebreros]], Spain, [[Malargüe Station|Malargüe]], Argentina and [[New Norcia Station|New Norcia]], Australia, receive the data.<ref name="ESA-GO"/>

== Significant results ==
In July 2017, the Gaia–ESO Survey reported using Gaia data to find double-, triple-, and quadruple- stars. Using advanced techniques they identified 342 binary candidates, 11 triple candidates, and 1 quadruple candidate. Nine of these had been identified by other means, thus confirming that the technique can correctly identify multiple star systems.<ref name="GIAISURVEY">{{cite journal |last1=Gilmore |first1=Gerry |last2=Randich |first2=Sofia |title=The Gaia-ESO Public Spectroscopic Survey |journal=The Messenger |date=March 2012 |volume=147 |issue=147 |pages=25–31 |publisher=European Southern Observatory |location=Garching, Germany |language=en |bibcode=2012Msngr.147...25G}}</ref> The possible quadruple star system is [[HD 74438]], which was, in a paper published in 2022, identified as a possible progenitor of a [[Supernova#Non-standard type Ia|sub-Chandrasekhar Type Ia supernovae]].<ref name="supernova">{{cite journal |last1=Merle |first1=Thibault |last2=Hamers |first2=Adrian S. |last3=Van Eck |first3=Sophie |last4=Jorissen |first4=Alain |last5=Van der Swaelmen |first5=Mathieu |last6=Pollard |first6=Karen |last7=Smiljanic |first7=Rodolfo |last8=Pourbaix |first8=Dimitri |last9=Zwitter |first9=Tomaž |last10=Traven |first10=Gregor |last11=Gilmore |first11=Gerry |last12=Randich |first12=Sofia |last13=Gonneau |first13=Anaïs |last14=Hourihane |first14=Anna |last15=Sacco |first15=Germano |last16=Worley |first16=C. Clare |title=A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae |journal=Nature Astronomy |date=12 May 2022 |volume=6 |issue=6 |pages=681–688 |doi=10.1038/s41550-022-01664-5|arxiv=2205.05045 |bibcode=2022NatAs...6..681M |s2cid=248665714 }}</ref>

In November 2017, scientists led by [[Davide Massari]] of the [[Kapteyn Astronomical Institute]], [[University of Groningen]], Netherlands released a paper<ref>{{cite journal |url=http://www.spacetelescope.org/static/archives/releases/science_papers/heic1719/heic1719a.pdf |bibcode=2018NatAs...2..156M |title=Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era |journal=Nature Astronomy |volume=2 |issue=2 |pages=156–161 |last1=Massari |first1=D. |last2=Breddels |first2=M. A. |last3=Helmi |first3=A. |last4=Posti |first4=L. |last5=Brown |first5=A. G. A. |last6=Tolstoy |first6=E. |year=2018 |doi=10.1038/s41550-017-0322-y |arxiv=1711.08945 |hdl=1887/71679 |s2cid=54512272 }}</ref> describing the characterization of [[proper motion]] (3D) within the [[Sculptor Dwarf Galaxy|Sculptor dwarf galaxy]], and of that galaxy's trajectory through space and with respect to the [[Milky Way]], using data from ''Gaia'' and the [[Hubble Space Telescope]]. Massari said, "With the precision achieved we can measure the yearly motion of a star on the sky which corresponds to less than the size of a pinhead on the Moon as seen from Earth." The data showed that Sculptor orbits the Milky Way in a highly elliptical orbit; it is currently near its closest approach at a distance of about {{convert|83.4|kpc|ly}}, but the orbit can take it out to around {{convert|222|kpc|ly}} distant.

In October 2018, [[Leiden University]] astronomers were able to determine the orbits of 20  hyperrunaway star candidates from the DR2 dataset. Expecting to find a single star exiting the [[Milky Way]], they instead found seven. More surprisingly, the team found that 13 hyperrunaway stars were instead approaching the Milky Way, possibly originating from as-of-yet unknown extragalactic sources. Alternatively, they could be halo stars to this galaxy, and further spectroscopic studies will help determine which scenario is more likely.<ref>{{cite web|website=phys.org|url=https://phys.org/news/2018-10-gaia-stars-galaxies.html|title= Gaia spots stars flying between galaxies|date=2018-10-02|access-date=2018-10-03}}</ref><ref>{{ Cite journal | last1 = Marchetti | first1 = T | last2 = Rossi | first2 = E M | last3 = Brown | first3 = A G A | date = 20 September 2018 | title = Gaia DR2 in 6D: Searching for the fastest stars in the Galaxy | journal = Monthly Notices of the Royal Astronomical Society | volume = 490 | pages = 157–171 | doi = 10.1093/mnras/sty2592 | doi-access = free | arxiv = 1804.10607 | s2cid = 73571958 }}</ref> Independent measurements have demonstrated that the greatest ''Gaia'' radial velocity among the hyperrunaway stars is contaminated by light from nearby bright stars in a crowded field and cast doubt on the high ''Gaia'' radial velocities of other hypervelocity stars.<ref>{{Cite journal | last = Boubert | first = Douglas |display-authors=etal | date = 2019 | title = Lessons from the curious case of the 'fastest' star in Gaia DR2 | journal = Monthly Notices of the Royal Astronomical Society | volume = 486 | issue = 2 | pages = 2618–2630 | doi = 10.1093/mnras/stz253 | doi-access = free | arxiv = 1901.10460 | bibcode = 2019MNRAS.486.2618B | s2cid = 119213165 }}</ref>

In late October 2018, the galactic population [[Gaia-Enceladus]], the remains of a major merger with the defunct Enceladus dwarf, was discovered.<ref name="Skibba">{{cite journal |last1=Skibba |first1=Ramin |title=A galactic archaeologist digs into the Milky Way's history |journal=Knowable Magazine |date=10 June 2021 |doi=10.1146/knowable-060921-1 |s2cid=236290725 |url=https://knowablemagazine.org/article/physical-world/2021/a-galactic-archaeologist-digs-milky-ways-history |access-date=4 August 2022|doi-access=free }}</ref> This system is associated with at least 13 globular clusters, and the creation of the Thick Disk of the Milky Way. It represents a significant merger about 10 billion years ago in the Milky Way Galaxy.<ref>{{cite web |url= https://sci.esa.int/web/gaia/-/60892-galactic-ghosts-gaia-uncovers-major-event-in-the-formation-of-the-milky-way |title= Galactic Ghosts: Gaia Uncovers Major Event in the Formation of the Milky Way Galaxy |date= 31 October 2018 |work= Gaia |publisher= ESA }}</ref>

[[File:Gaia’s Hertzsprung-Russell diagram ESA393151.jpg|thumb|Gaia's [[HR Diagram]]]]
In November 2018, the galaxy [[Antlia 2]] was discovered. It is similar in size to the [[Large Magellanic Cloud]], despite being 10,000 times fainter. Antlia 2 has the lowest surface brightness of any galaxy discovered.<ref>{{cite web
|url=https://www.forbes.com/sites/brucedorminey/2018/11/18/esas-gaia-spacecraft-spots-ghost-galaxy-lurking-in-milky-ways-outskirts/#1ba2340c3652 |title=ESA's Gaia Spacecraft Spots Ghost Galaxy Lurking In Milky Way's Outskirts |access-date=20 November 2018 |work=[[Forbes]] }}</ref>

In December 2019 the star cluster [[Price-Whelan 1]] was discovered.<ref>{{Cite journal|last1=Price-Whelan|first1=Adrian M.|last2=Nidever|first2=David L.|last3=Choi|first3=Yumi|last4=Schlafly|first4=Edward F.|last5=Morton|first5=Timothy|last6=Koposov|first6=Sergey E.|last7=Belokurov|first7=Vasily|date=2019-12-05|title=Discovery of a disrupting open cluster far into the Milky Way halo: a recent star formation event in the leading arm of the Magellanic stream?|journal=The Astrophysical Journal|volume=887|issue=1|pages=19|doi=10.3847/1538-4357/ab4bdd|arxiv=1811.05991|bibcode=2019ApJ...887...19P|s2cid=119489013|issn=1538-4357 |doi-access=free }}</ref> The cluster belongs to the [[Magellanic Clouds]] and is located in the leading arm of these [[Dwarf galaxy|Dwarf Galaxies]]. The discovery suggests that the stream of gas extending from the Magellanic Clouds to the Milky Way is about half as far from the Milky Way as previously thought.<ref>{{Cite web|url=https://www.cosmos.esa.int/web/gaia/iow_20200109|title=IoW_20200109 – Gaia – Cosmos|website=www.cosmos.esa.int|access-date=2020-01-09}}</ref>

The [[Radcliffe wave]] was discovered in data measured by ''Gaia'', published in January 2020.<ref name="theguardian-sample">{{cite news|first1=Ian |last1= Sample |access-date=2020-01-07|title=Astronomers discover huge gaseous wave holding Milky Way's newest stars|url=https://www.theguardian.com/science/2020/jan/07/astronomers-discover-huge-gaseous-wave-holding-milky-ways-newest-stars|newspaper=The Guardian|date=7 January 2020|issn=0261-3077|via=www.theguardian.com}}</ref><ref>{{cite news|first1=Paul|last1=Rincon|access-date=2020-01-07|title=Vast 'star nursery' region found in our galaxy|work=BBC News |url=https://www.bbc.com/news/science-environment-51021704|date=7 January 2020}}</ref>

In November 2020, Gaia measured the acceleration of the solar system towards the galactic center as 0.23 nanometers/s<sup>2</sup>.<ref>{{cite web | date = 3 December 2020 | title = Gaia's measurement of the solar system acceleration with respect to the distant universe | url = https://www.cosmos.esa.int/web/gaia/edr3-acceleration-solar-system | accessdate = 14 September 2022 | website = esa.int | publisher = [[European Space Agency]] }}</ref><ref>{{cite journal | author = Gaia Collaboration  | last2 = Klioner | first2 = S. A. | display-authors = etal | date = 2021 | title = Gaia Early Data Release 3: Acceleration of the Solar System from Gaia astrometry | journal = Astronomy & Astrophysics  | volume = 649 | issue = | page = A9 | doi = 10.1051/0004-6361/202039734 | arxiv = 2012.02036 | bibcode = 2021A&A...649A...9G | s2cid = 234687035 }}</ref>

In March 2021, the European Space Agency announced that ''Gaia'' had identified a transiting exoplanet for the first time. The planet was discovered orbiting solar-type star Gaia EDR3 3026325426682637824. Following its initial discovery, the PEPSI spectrograph from the [[Large Binocular Telescope]] (LBT) in Arizona was used to confirm the discovery and categorise it as a Jovian planet, a gas planet composed of hydrogen and helium gas.<ref>{{cite web |url=https://rocketrundown.com/esas-gaia-observatory-has-found-its-first-transiting-exoplanet/ |title=ESA's Gaia observatory has found its first transiting exoplanet |date=30 March 2021 |access-date=31 March 2021 |archive-date=19 January 2023 |archive-url=https://web.archive.org/web/20230119114421/https://rocketrundown.com/esas-gaia-observatory-has-found-its-first-transiting-exoplanet/ |url-status=dead }}</ref><ref name="IOW20210330">{{cite web |url=https://www.cosmos.esa.int/web/gaia/iow_20210330 |title=Image of the Week: First Transiting Exoplanet by Gaia |date=30 March 2021 |website=cosmos.esa.int |publisher=[[ESA]]/Gaia/DPAC/CU7/TAU+INAF |access-date=19 September 2022}}</ref> In May 2022, the confirmation of this exoplanet, designated [[Gaia-1b]], was formally published, along with a second planet, [[Gaia-2b]].<ref name=Panahi2022>{{cite journal |arxiv=2205.10197|doi=10.1051/0004-6361/202243497 |title=The detection of transiting exoplanets by Gaia |year=2022 |last1=Panahi |first1=Aviad |last2=Zucker |first2=Shay |last3=Clementini |first3=Gisella |last4=Audard |first4=Marc |last5=Binnenfeld |first5=Avraham |last6=Cusano |first6=Felice |last7=Evans |first7=Dafydd Wyn |last8=Gomel |first8=Roy |last9=Holl |first9=Berry |last10=Ilyin |first10=Ilya |last11=De Fombelle |first11=Grégory Jevardat |last12=Mazeh |first12=Tsevi |last13=Mowlavi |first13=Nami |last14=Nienartowicz |first14=Krzysztof |last15=Rimoldini |first15=Lorenzo |last16=Shahaf |first16=Sahar |last17=Eyer |first17=Laurent |journal=Astronomy & Astrophysics |volume=663 |pages=A101 |bibcode=2022A&A...663A.101P |s2cid=248965147 }}</ref>

Based on its data, Gaia's [[Hertzsprung–Russell diagram]] (HR diagram) is one of the most accurate ones ever produced of the Milky Way Galaxy.<ref name="GAIA'S HERTZSPRUNG-RUSSELL DIAGRAM">{{ Cite web |website = ESA | title = GAIA'S HERTZSPRUNG-RUSSELL DIAGRAM | url = https://sci.esa.int/web/gaia/-/60198-gaia-hertzsprung-russell-diagram | access-date = 13 June 2022 }}</ref>

Analysis of Gaia DR3 data in 2022 revealed a Sun-like star with the identifier Gaia DR3 4373465352415301632 orbiting a [[black hole]], dubbed [[Gaia BH1]]. At a distance of roughly {{convert|1600|ly|pc}}, it is the closest known black hole to Earth.<ref name="NOIRLab2227">{{cite web |url=https://noirlab.edu/public/news/noirlab2227/ |title=Astronomers Discover Closest Black Hole to Earth |date=4 November 2022 |website=noirlab.edu |publisher=[[NOIRLab]] |access-date=4 November 2022}}</ref><ref name="El-Badry2022">{{cite journal |last1=El-Badry |first1=Kareem |last2=Rix |first2=Hans-Walter |last3=Quataert |first3=Eliot |last4=Howard |first4=Andrew W. |last5=Isaacson |first5=Howard |last6=Fuller |first6=Jim |last7=Hawkins |first7=Keith |last8=Breivik |first8=Katelyn |last9=Wong |first9=Kaze W. K. |last10=Rodriguez |first10=Antonio C. |last11=Conroy |first11=Charlie |last12=Shahaf |first12=Sahar |last13=Mazeh |first13=Tsevi |last14=Arenou |first14=Frédéric |last15=Burdge |first15=Kevin B. |display-authors=2 |date=2 November 2022 |title=A Sun-like star orbiting a black hole |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=518 |issue=1 |pages=1057–1085 |arxiv=2209.06833 |doi=10.1093/mnras/stac3140 |doi-access=free |bibcode=2023MNRAS.518.1057E}}</ref> Another system with a [[red giant]] orbiting a black hole, [[Gaia BH2]], was also discovered.<ref name="El-Badry2023">{{Cite journal |last1=El-Badry |first1=Kareem |last2=Rix |first2=Hans-Walter |last3=Cendes |first3=Yvette |last4=Rodriguez |first4=Antonio C. |last5=Conroy |first5=Charlie |last6=Quataert |first6=Eliot |last7=Hawkins |first7=Keith |last8=Zari |first8=Eleonora |last9=Hobson |first9=Melissa |last10=Breivik |first10=Katelyn |last11=Rau |first11=Arne |last12=Berger |first12=Edo |last13=Shahaf |first13=Sahar |last14=Seeburger |first14=Rhys |last15=Burdge |first15=Kevin B. |display-authors=2 |date=2023-02-01 |title=A red giant orbiting a black hole |journal=Monthly Notices of the Royal Astronomical Society |volume=521 |issue=3 |pages=4323–4348 |doi=10.1093/mnras/stad799 |doi-access=free |arxiv=2302.07880 |bibcode=2023MNRAS.521.4323E}}</ref>

In September 2023, [[Doppler spectroscopy|radial velocity]] observations were used to confirm an exoplanet orbiting the star [[HIP 66074]] that was first detected in Gaia DR3 [[astrometry]] data. This planet, known as HIP 66074 b or Gaia-3b, is the third Gaia exoplanet discovery to be confirmed and the first such discovery made using astrometry.<ref name="Sozzetti2023">{{cite journal |last1=Sozzetti |first1=A. |last2=Pinamonti |first2=M. |display-authors=etal |date=September 2023 |title=The GAPS Programme at TNG. XLVII. A conundrum resolved: HIP 66074b/Gaia-3b characterised as a massive giant planet on a quasi-face-on and extremely elongated orbit |journal=[[Astronomy & Astrophysics]] |volume=677 |issue= |pages=L15 |doi=10.1051/0004-6361/202347329 |arxiv=2307.08653 |doi-access=free |bibcode=2023A&A...677L..15S|hdl=2108/347124 |hdl-access=free }}</ref> In addition, another exoplanet was discovered from a [[gravitational microlensing]] event observed by Gaia, [[Gaia22dkv]]. The host star is brighter than that of any exoplanet previously detected by microlensing, potentially making the planet detectable by radial velocity as well.<ref name="Wu2023">{{cite journal |last1=Wu |first1=Zexuan |last2=Dong |first2=Subo |display-authors=etal |date=September 2023 |title=Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-Velocity Characterization |journal=The Astronomical Journal |volume=168 |issue=2 |page=62 |doi=10.3847/1538-3881/ad5203 |doi-access=free |arxiv=2309.03944 |bibcode=2024AJ....168...62W }}</ref>

In March 2024, ''Gaia'' discovered two streams of stars, named by researchers Shakti and Shiva, that formed more than 12 billion years ago.<ref>{{cite web |title=Gaia unravels the ancient threads of the Milky Way |url=https://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_unravels_the_ancient_threads_of_the_Milky_Way |website=www.esa.int |access-date=30 March 2024 |language=en}}</ref>

In 2025 a detailed 3D map of dust distribution within the Milky Way was constructed using data from ''Gaia'' and [[LAMOST]] spectral survey and machine learning.<ref>{{Cite journal |last1=Zhang |first1=Xiangyu |last2=Green |first2=Gregory M. |date=2025-03-14 |title=Three-dimensional maps of the interstellar dust extinction curve within the Milky Way galaxy |url=https://www.science.org/doi/10.1126/science.ado9787 |journal=Science |volume=387 |issue=6739 |pages=1209–1214 |doi=10.1126/science.ado9787 |pmid=40080581 |arxiv=2407.14594 |bibcode=2025Sci...387.1209Z }}</ref>

== GaiaNIR ==
GaiaNIR (Gaia Near Infra-Red) is a proposed successor of Gaia in the [[Infrared#Commonly used sub-division scheme|near-infrared]].<ref name=":1">{{Cite journal|url=https://doi.org/10.1007/s10686-021-09705-z|title=All-sky visible and near infrared space astrometry|journal=Experimental Astronomy|date=2021 |doi=10.1007/s10686-021-09705-z |language=en-GB|access-date=2023-06-29 |last1=Hobbs |first1=David |last2=Brown |first2=Anthony |last3=Høg |first3=Erik |last4=Jordi |first4=Carme|author4-link=Carme Jordi |last5=Kawata |first5=Daisuke |last6=Tanga |first6=Paolo |last7=Klioner |first7=Sergei |last8=Sozzetti |first8=Alessandro |last9=Wyrzykowski |first9=Łukasz |last10=Walton |first10=Nicholas |last11=Vallenari |first11=Antonella |last12=Makarov |first12=Valeri |last13=Rybizki |first13=Jan |last14=Jiménez-Esteban |first14=Fran |last15=Caballero |first15=José A. |last16=McMillan |first16=Paul J. |last17=Secrest |first17=Nathan |last18=Mor |first18=Roger |last19=Andrews |first19=Jeff J. |last20=Zwitter |first20=Tomaž |last21=Chiappini |first21=Cristina |last22=Fynbo |first22=Johan P. U. |last23=Ting |first23=Yuan-Sen |last24=Hestroffer |first24=Daniel |last25=Lindegren |first25=Lennart |last26=McArthur |first26=Barbara |last27=Gouda |first27=Naoteru |last28=Moore |first28=Anna |last29=Gonzalez |first29=Oscar A. |last30=Vaccari |first30=Mattia |volume=51 |issue=3 |pages=783–843 |arxiv=1907.12535 |bibcode=2021ExA....51..783H |s2cid=260439407 }}</ref> The mission would enlarge the current catalog with sources that are only (or better) visible in the near-infrared, at the cost of less precise measurements than an equivalent visible-light mission due to the broader [[diffraction]] pattern at longer wavelengths. It would at the same time improve the star parallax and particularly proper motion accuracy by revisiting the sources of the Gaia catalog.<ref name=":0"/> One of the main challenges in building GaiaNIR is the low [[technology readiness level]] of near-infrared [[time delay and integration]] detectors but recent progress with [[Avalanche photodiode]] detectors (APDs) is overcoming this. In a 2017 ESA report two alternative concepts using conventional near-infrared detectors and de-spin mirrors were proposed but even without the development of NIR TDI detectors the technological challenge will likely increase the cost over an ESA M-class mission and might need shared cost with other space agencies.<ref name=":0">{{Cite web|url=http://sci.esa.int/future-missions-department/60028-cdf-study-report-gaianir/|title=CDF Study Report: GaiaNIR – Study to Enlarge the Achievements of Gaia with NIR Survey|website=sci.esa.int|language=en-GB|access-date=2019-03-05}}</ref> One possible partnership with US institutions was proposed.<ref>{{Cite journal|last1=McArthur|first1=Barbara|last2=Hobbs|first2=David|last3=Høg|first3=Erik|last4=Makarov|first4=Valeri|last5=Sozzetti|first5=Alessandro|last6=Brown|first6=Anthony|last7=Martins|first7=Alberto Krone|last8=Bartlett|first8=Jennifer Lynn|author8-link=Jennifer Bartlett (astronomer)|last9=Tomsick|first9=John|last10=Shao|first10=Mike|last11=Benedict|first11=Fritz|date=May 2019|title=All-Sky Near Infrared Space Astrometry|journal=BAAS|language=en|volume=51|issue=3|pages=118|arxiv=1904.08836|bibcode=2019BAAS...51c.118M}}</ref> Since then the [[European Space Agency Science Programme]] Voyage 2050 has selected the theme of "Galactic Ecosystem with Astrometry in the Near-infrared" as one of two potential L-class missions to be implemented in the coming years thus boosting the chances for GaiaNIR which proposes exactly this.

== Gallery ==
{{Gallery

|File:Gaia- Exploring the multi-dimensional Milky Way ESA24305488.jpeg|Four maps of the galaxy: [[radial velocity]] (top left), [[proper motion]] (bottom left); [[interstellar dust]] (top right); and [[metallicity]] (bottom right).<ref>{{Cite web |title=Gaia: Exploring the multi-dimensional Milky Way |url=https://www.esa.int/ESA_Multimedia/Images/2022/06/Gaia_Exploring_the_multi-dimensional_Milky_Way |access-date=2022-06-18 |website=www.esa.int |language=en}}</ref>

|File:GAIAscanning.gif|A visualisation of Gaia scanning the sky in [[Great-circle navigation|great circles]] lasting about 6 hours from July 2014 to September 2015.<ref>{{Cite web |title=ESA Science & Technology – Gaia's billion-star map hints at treasures to come |url=https://sci.esa.int/web/gaia/-/58272-gaia-s-billion-star-map-hints-at-treasures-to-come |access-date=2022-06-18 |website=sci.esa.int}}</ref>

|File:OortGAIA.gif|Illustration of [[Oort's formulae]] describing the curve obtained from plotting angular velocities against the [[galactic longitude]]<ref>{{Cite web |title=Where do the stars go or come from? – Gaia – Cosmos |url=https://www.cosmos.esa.int/web/gaia/dr3-where-do-the-stars-go-or-come-from |access-date=2022-06-18 |website=www.cosmos.esa.int}}</ref><ref>{{Cite journal |last1=Gaia Collaboration |last2=Drimmel |first2=R. |last3=Romero-Gomez |first3=M. |last4=Chemin |first4=L. |last5=Ramos |first5=P. |last6=Poggio |first6=E. |last7=Ripepi |first7=V. |last8=Andrae |first8=R. |last9=Blomme |first9=R. |last10=Cantat-Gaudin |first10=T. |last11=Castro-Ginard |first11=A. |date=2023 |title=''Gaia'' Data Release 3 |journal=Astronomy & Astrophysics |volume=674 |pages=A37 |doi=10.1051/0004-6361/202243797 |arxiv=2206.06207|s2cid=249626274 }}</ref>

|File:MicrolensingGAIA.gif|[[Gravitational microlensing|Microlensing]] events over the galactic map as observed by Gaia from 2014 to 2018<ref>{{Cite web |title=Do they go boom? – Gaia – Cosmos |url=https://www.cosmos.esa.int/web/gaia/dr3-do-they-go-boom |access-date=2022-06-18 |website=www.cosmos.esa.int}}</ref><ref>{{Cite journal |last1=Wyrzykowski |first1=Łukasz |last2=Kruszyńska |first2=K. |last3=Rybicki |first3=K. A. |last4=Holl |first4=B. |last5=ur-Taïbi |first5=I. Lecøe |last6=Mowlavi |first6=N. |last7=Nienartowicz |first7=K. |last8=de Fombelle |first8=G. Jevardat |last9=Rimoldini |first9=L. |last10=Audard |first10=M. |last11=Garcia-Lario |first11=P. |date=2023 |title=''Gaia'' Data Release 3 |journal=Astronomy & Astrophysics |volume=674 |pages=A23 |doi=10.1051/0004-6361/202243756 |arxiv=2206.06121|s2cid=249625849 }}</ref> (Timer on bottom left corner)

||12 [[Einstein Cross|Einstein crosses]] discovered by Gaia in 2021<ref>{{Cite web |title=ESA Science & Technology – 12 rare Einstein crosses discovered with Gaia |url=https://sci.esa.int/web/gaia/-/12-rare-einstein-crosses-discovered-with-gaia |access-date=2022-06-18 |website=sci.esa.int}}</ref><ref>{{Cite journal |last1=Stern |first1=D. |last2=Djorgovski |first2=S. G. |last3=Krone-Martins |first3=A. |last4=Sluse |first4=D. |last5=Delchambre |first5=L. |last6=Ducourant |first6=C. |last7=Teixeira |first7=R. |last8=Surdej |first8=J. |last9=Boehm |first9=C. |last10=den Brok |first10=J. |last11=Dobie |first11=D. |date=2021-10-28 |title=Gaia GraL: Gaia DR2 Gravitational Lens Systems. VI. Spectroscopic Confirmation and Modeling of Quadruply Imaged Lensed Quasars |journal=The Astrophysical Journal |language=en |volume=921 |issue=1 |pages=42 |doi=10.3847/1538-4357/ac0f04 |arxiv=2012.10051 |bibcode=2021ApJ...921...42S |s2cid=229331628 |issn=0004-637X |doi-access=free }}</ref>

|File:Gaia sky mapper image near the Galactic centre ESA382985.png|The image covers about 0.6 square degrees, making it conceivable that there are some 2.8 million stars captured in this image sequence alone. The image appears in strips, each representing a sky mapper CCD. The image was taken on 7 February 2017.<ref>{{cite web |title=Gaia sky mapper image near the Galactic centre |url=https://www.esa.int/ESA_Multimedia/Images/2017/08/Gaia_sky_mapper_image_near_the_Galactic_centre |website=www.esa.int |access-date=19 September 2022 |language=en}}</ref>
}}

== See also ==
*{{annotated link|Gaia catalogues}}
*{{annotated link|Cosmic distance ladder}}
*{{annotated link|Space Interferometry Mission}}

== References ==
{{Reflist|refs=

<ref name="esa-20250115">{{cite web
| title= Last starlight for ground-breaking Gaia
| url= https://www.esa.int/Science_Exploration/Space_Science/Gaia/Last_starlight_for_ground-breaking_Gaia
| website= esa.int
| publisher= [[European Space Agency]]
| date= 15 January 2025 }}
</ref>

}}

== External links ==
{{Commons category|Gaia (spacecraft)}}
* [https://cosmos.esa.int/web/gaia/ Gaia mission home]
* [https://www.esa.int/Science_Exploration/Space_Science/Gaia ESA Gaia mission]
* [http://archives.esac.esa.int/gaia ESA Gaia Archive]
* [https://www.esa.int/Enabling_Support/Operations/Gaia_operations ''Gaia'' page at ESA Spacecraft Operations]
* {{YouTube|5pAjvQ5uu7I|1st Data Release (''Gaia''; 14 September 2016)}}
* {{YouTube|VINs-JcNmKs|2nd Data Release (''Gaia''; 25 April 2018)}}
* {{YouTube|x6MGF0BhckE|3rd Data Release (''Gaia''; 13 June 2022)}}
* {{YouTube|bZfFdCknTQc|Video (01:25; 360° view) – Entire Sky (''Gaia''; 25 April 2018)}}
* [https://www.eoportal.org/satellite-missions/gaia GAIA article on eoPortal by ESA]

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