View source for Atacama Large Millimeter Array

{{Short description|66-telescope radio observatory in Chile}}
{{Infobox telescope
| built = {{start date and age|2013|03}}
}}

The '''Atacama Large Millimeter/submillimeter Array''' ('''ALMA''') is an [[astronomical interferometer]] of 66 [[radio telescope]]s in the [[Atacama Desert]] of northern [[Chile]], which observe [[electromagnetic radiation]] at millimeter and [[submillimeter]] [[wavelength]]s. The array has been constructed on the {{cvt|5000|m|ft}} elevation Chajnantor plateau – near the [[Llano de Chajnantor Observatory]] and the [[Atacama Pathfinder Experiment]]. This location was chosen for its high elevation and low [[humidity]], factors which are crucial to reduce noise and decrease signal attenuation due to Earth's atmosphere.<ref name="PARQUE">{{cite journal |doi=10.1086/679330 |title=Parque Astronómico de Atacama: An Ideal Site for Millimeter, Submillimeter, and Mid-Infrared Astronomy |date=2014 |last1=Bustos |first1=R. |last2=Rubio |first2=M. |last3=Otárola |first3=A. |last4=Nagar |first4=N. |journal=Publications of the Astronomical Society of the Pacific |volume=126 |issue=946 |pages=1126 |arxiv = 1410.2451 |bibcode = 2014PASP..126.1126B |s2cid=118539242 |display-authors=3 }}</ref> ALMA provides insight on star birth during the early [[Chronology of the universe#Earliest structures and stars emerge|Stelliferous era]] and detailed imaging of [[List of nearest stars and brown dwarfs|local]] star and planet formation.<ref name="AstroJour">{{cite journal |last1=Bae |first1=Jaehan |last2=Teague |first2=Richard |last3=Andrews |first3=Sean M. |last4=Benisty |first4=Myriam |last5=Facchini |first5=Stefano |last6=Galloway-Sprietsma |first6=Maria |last7=Loomis |first7=Ryan A. |last8=Aikawa |first8=Yuri |last9=Alarcón |first9=Felipe |last10=Bergin |first10=Edwin |last11=Bergner |first11=Jennifer B. |last12=Booth |first12=Alice S. |last13=Cataldi |first13=Gianni |last14=Cleeves |first14=L. Ilsedore |last15=Czekala |first15=Ian |last16=Guzmán |first16=Viviana V. |last17=Huang |first17=Jane |last18=Ilee |first18=John D. |last19=Kurtovic |first19=Nicolas T. |last20=Law |first20=Charles J. |last21=Gal |first21=Romane Le |last22=Liu |first22=Yao |last23=Long |first23=Feng |last24=Ménard |first24=François |last25=Öberg |first25=Karin I. |last26=Pérez |first26=Laura M. |last27=Qi |first27=Chunhua |last28=Schwarz |first28=Kamber R. |last29=Sierra |first29=Anibal |last30=Walsh |first30=Catherine |last31=Wilner |first31=David J. |last32=Zhang |first32=Ke |title=Molecules with ALMA at Planet-forming Scales (MAPS): A Circumplanetary Disk Candidate in Molecular-line Emission in the AS 209 Disk |journal=The Astrophysical Journal Letters |date=1 August 2022 |volume=934 |issue=2 |pages=L20 |doi=10.3847/2041-8213/ac7fa3|arxiv=2207.05923 |bibcode=2022ApJ...934L..20B |s2cid=250492936 |doi-access=free }}</ref><ref name="Plait">{{cite web |last1=Plait |first1=Phil |title=A still-forming exoplanet predicted to exist is found in exactly the right spot |url=https://www.syfy.com/syfy-wire/bad-astronomy-exoplanet-around-as-209-is-carving-gaps-in-its-disk |website=SYFY Official Site |date=8 September 2022}}</ref>

ALMA is an international partnership amongst [[Europe]], the [[United States]], [[Canada]], [[Japan]], [[South Korea]], [[Taiwan]], and [[Chile]].<ref name="bbc-2016-05-29">{{cite news
 | title= Alma telescope peers into space from Chile's mountains
 | first = Gideon | last = Long
 | work = BBC News
 | url = https://www.bbc.com/news/world-latin-america-36357501
 | date = 29 May 2016
 | access-date = 29 May 2016
}}</ref> Costing about US$1.4&nbsp;billion, it is the most expensive ground-based telescope in operation.<ref name="eso-alma-inauguration">{{cite web
 | title = ALMA Inauguration Heralds New Era of Discovery
 | publisher = ESO - European Southern Observatory
 | date = 13 March 2013
 | url = http://www.eso.org/public/news/eso1312/
 | access-date = 29 April 2014}}</ref><ref>{{cite web
 | last = Romero
 | first = Simon
 | title = At the End of the Earth, Seeking Clues to the Universe
 | work =The New York Times | date = 7 April 2012
 | url = https://www.nytimes.com/2012/04/08/world/americas/high-in-chilean-desert-a-huge-astronomy-project.html
 | access-date = 8 April 2012}}</ref> ALMA began scientific observations in the second half of 2011 and the first images were released to the press on 3 October 2011. The array has been fully operational since March 2013.<ref>{{cite news|title=Alma telescope: Ribbon cut on astronomical giant|url=https://www.bbc.co.uk/news/science-environment-21774448|publisher=BBC|access-date=13 March 2013|work=BBC News|date=2013-03-13|last1=Hernandez|first1=Vladimir}}</ref><ref>{{Cite journal | doi = 10.1117/2.3201407.14| title = Pierre Cox plenary: ALMA Update| journal = SPIE Newsroom| year = 2014| last1 = Spie}}</ref>

==Overview==

{{multiple image
 |direction = vertical
 |align = right
 |width = 225
 |image1=ALMA first fringes at Chajnantor.jpg
 |image2=3-ALMA-antennas-interferometry.jpg
 |image3=Lights glowing on the ALMA correlator.jpg
 |caption1=The first two ALMA antennas linked together as an [[interferometer]]
 |caption2=Three ALMA antennas linked together as an interferometer for the first time
 |caption3=The ALMA [[Radio correlator|correlator]]
}}

The initial ALMA array is composed of 66 high-precision antennae, and operates at [[wavelength]]s of 3.6 to 0.32 millimeters (31 to 1000&nbsp;GHz).<ref>{{Cite web|url=https://www.eso.org/public/teles-instr/alma/?lang|title=ALMA - Atacama Large Millimeter/submillimeter Array|website=www.eso.org}}</ref> The array has much higher sensitivity and higher resolution than earlier [[submillimeter astronomy|submillimeter telescopes]] such as the single-dish [[James Clerk Maxwell Telescope]] or existing interferometer networks such as the [[Submillimeter Array]] or the ''[[Institut de Radio Astronomie Millimétrique]]'' (IRAM) [[Plateau de Bure Interferometer|Plateau de Bure]] facility.

The antennae can be moved across the desert plateau over distances from 150 m to 16&nbsp;km, which gives ALMA a powerful variable "zoom", similar in its concept to that employed at the centimeter-wavelength [[Very Large Array]] (VLA) site in [[New Mexico|New Mexico, United States]].

The high sensitivity is mainly achieved through the large numbers of antenna dishes that make up the array.

The telescopes were provided by the European, North American and East Asian partners of ALMA. The American and European partners each provided twenty-five 12-meter diameter antennae, for a subtotal of fifty antennae, that compose the main array. The participating East Asian countries are contributing 16 antennae (four 12-meter diameter and twelve 7-meter diameter antennae) in the form of the Atacama Compact Array (ACA), which is part of the enhanced ALMA.

By using smaller antennae than the main ALMA array, larger fields of view can be imaged at a given frequency using ACA. Placing the antennae closer together enables the imaging of sources of larger angular extent. The ACA works together with the main array in order to enhance the latter's wide-field imaging capability.

===History===
[[File:ALMA Site (artist's impression).jpg|thumb|left|An artist's impression of ALMA]]

ALMA has its conceptual roots in three astronomical projects: the Millimeter Array (MMA) of the United States, the Large Southern Array (LSA) of Europe, and the Large Millimeter Array (LMA) of Japan.

The first step toward the creation of what would become ALMA came in 1997, when the [[National Radio Astronomy Observatory]] (NRAO) and the [[European Southern Observatory]] (ESO) agreed to pursue a common project that merged the MMA and LSA. The merged array combined the sensitivity of the LSA with the frequency coverage and superior site of the MMA. ESO and NRAO worked together in technical, science, and management groups to define and organise a joint project between the two observatories with participation by Canada and Spain (the latter became a member of ESO later).

A series of resolutions and agreements led to the choice of "Atacama Large Millimeter Array", or ALMA, as the name of the new array in March 1999 and the signing of the ALMA Agreement on 25 February 2003, between the North American and European parties. ("Alma" means "soul" in Spanish and "learned" or "knowledgeable" in Arabic.) Following mutual discussions over several years, the ALMA Project received a proposal from the [[National Astronomical Observatory of Japan]] (NAOJ) whereby Japan would provide the ACA (Atacama Compact Array) and three additional receiver bands for the large array, to form Enhanced ALMA. Further discussions between ALMA and NAOJ led to the signing of a high-level agreement on 14 September 2004 that makes Japan an official participant in Enhanced ALMA, to be known as the Atacama Large Millimeter/submillimeter Array. A groundbreaking ceremony was held on November 6, 2003 and the ALMA logo was unveiled.<ref>{{cite web|url=http://www.almaobservatory.org/en/press-room/press-releases/121-ground-breaking-ceremony-for-the-atacama-large-millimeter-array-alma|title=Ground breaking ceremony for the Atacama Large Millimeter Array (ALMA)|author=Alejandro Peredo|access-date=15 November 2014|url-status=dead|archive-url=https://web.archive.org/web/20141111161008/http://www.almaobservatory.org/en/press-room/press-releases/121-ground-breaking-ceremony-for-the-atacama-large-millimeter-array-alma|archive-date=11 November 2014}}</ref>

During an early stage of the planning of ALMA, it was decided to employ ALMA antennae designed and constructed by known companies in North America, Europe, and Japan, rather than using one single design. This was mainly for political reasons. Although very different approaches have been chosen by the providers, each of the antenna designs appears to be able to meet ALMA's stringent requirements. The components designed and manufactured across Europe were transported by specialist aerospace and astrospace logistics company Route To Space Alliance,<ref>{{Cite web|url=http://www.route-to-space.eu/index.php/en/projects/atacama-large-millimeter-array|title=Route To Space Alliance|last=Grieves|first=Shell|website=www.route-to-space.eu|language=en-gb|access-date=2017-02-15|archive-date=2022-01-17|archive-url=https://web.archive.org/web/20220117012844/https://route-to-space.eu/index.php/en/projects/atacama-large-millimeter-array|url-status=dead}}</ref> 26 in total which were delivered to Antwerp for onward shipment to Chile.

==Funding==
ALMA was initially a 50-50 collaboration between the [[National Radio Astronomy Observatory]] and [[European Southern Observatory]] (ESO) and later extended with the help of the other Japanese, Taiwanese, and Chilean partners.<ref>{{cite web|url=http://www.alma.nrao.edu/partners/|title=National Radio Astronomy Observatory - Legacy Content - ALMA (CV)|work=nrao.edu}}</ref> ALMA is the largest and most expensive ground-based astronomical project, costing between US$1.4 and 1.5&nbsp;billion.<ref name="eso-alma-inauguration" /><ref>[http://bigstory.ap.org/article/chiles-alma-probes-origins-universe Chile's ALMA probes for origins of universe] {{webarchive |url=https://web.archive.org/web/20140310045535/http://bigstory.ap.org/article/chiles-alma-probes-origins-universe |date=March 10, 2014 }}, [[Associated Press]]</ref> (However, various space astronomy projects including the [[Hubble Space Telescope]], the [[James Webb Space Telescope]], and several major planet probes have cost considerably more).

;Partners
* [[European Southern Observatory]] and the European Regional Support Centre
* [[National Science Foundation]] via the [[National Radio Astronomy Observatory]] and the North American ALMA Science Center
* [[National Research Council of Canada]]
* [[National Astronomical Observatory of Japan]] (NAOJ) under the National Institutes of Natural Sciences (NINS)
* ALMA-[[Taiwan]] at the [[Academia Sinica]] Institute of Astronomy & Astrophysics (ASIAA)
* Republic of Chile

== Construction ==
[[File:Atacama-52_(25876789334).jpg|thumb|Finished antenna.]]

The complex was built primarily by European, U.S., Japanese, and Canadian companies and [[universities]]. Three prototype antennae have undergone evaluation at the [[Karl G. Jansky Very Large Array|Very Large Array]] since 2002.

[[General Dynamics C4 Systems]] and its SATCOM Technologies division was contracted by Associated Universities, Inc. to provide twenty-five of the 12&nbsp;m antennae,<ref>{{cite web|url=http://www.gdsatcom.com/Communicator/7-26-05.htm|title=General Dynamics Receives $169 Million to Build 12-Meter Antennae for Advanced Radio Telescope|work=gdsatcom.com}}</ref> while European manufacturer [[Thales Alenia Space]] provided the other twenty-five principal antennae<ref>{{Cite web|url=http://www.eso.org/outreach/press-rel/pr-2005/pr-31-05.html|archive-url=https://web.archive.org/web/20060207152851/http://www.eso.org/outreach/press-rel/pr-2005/pr-31-05.html|url-status=dead|title=ESO – 2005|archive-date=February 7, 2006}}</ref> (in the largest-ever European industrial contract in ground-based astronomy). Japan's [[Mitsubishi Electric]] was contracted to assemble NAOJ's 16 antennae.<ref>{{cite web|url=https://www.nao.ac.jp/en/research/telescope/alma.html|title=ALMA|work=[[National Astronomical Observatory of Japan]]|access-date=8 March 2021}}
</ref><ref>{{Cite web |url=https://www.almaobservatory.org/en/announcement/result-of-the-initial-testing-of-the-japanese-aca-12-m-antenna-to-be-delivered-to-alma-2/ |title=Result of the initial testing of the Japanese ACA 12-m antenna to be delivered to ALMA |date=March 18, 2008 |website=ALMA |archive-url=https://web.archive.org/web/20200225154548/https://www.almaobservatory.org/en/announcement/result-of-the-initial-testing-of-the-japanese-aca-12-m-antenna-to-be-delivered-to-alma-2/ |archive-date=February 25, 2020 |url-status=dead}}</ref> The antennae were delivered to the site from December 2008 to September 2013.<ref>{{Cite press release |url=https://www.almaobservatory.org/en/press-release/alma-observatory-equipped-with-its-first-antenna/ |title=ALMA observatory equipped with its first antenna |date=December 19, 2008 |website=ALMA |archive-url=https://web.archive.org/web/20191220214024/https://www.almaobservatory.org/en/press-release/alma-observatory-equipped-with-its-first-antenna/ |archive-date=December 20, 2019 |url-status=dead}}</ref>

=== Transporting the antennae ===
[[File:Alma antenna in transit.jpg|thumb|Alma antenna in transit on board of the transporter.]]

Transporting the 115&nbsp;[[tonne]] antennae from the Operations Support Facility at 2900&nbsp;m altitude to the site at 5000&nbsp;m, or moving antennae around the site to change the array size, presents enormous challenges; as portrayed in the television documentary ''Monster Moves: Mountain Mission''.<ref>{{Cite web |url=http://www.windfallfilms.com/show/1759/Monster-Moves-Episode-6-Mountain-Mission.aspx |title=Monster Moves, Season 5, Episode 6: Mountain Mission |access-date=17 March 2012}}</ref> The solution chosen is to use two custom 28-wheel self-loading [[heavy hauler]]s. The vehicles were made by {{Interlanguage link multi|Scheuerle Fahrzeugfabrik|de}}<ref>[http://www.scheuerle.de/en/products/new-vehicles/special-transporters/antenna-transporter.html Scheuerle Fahrzeugfabrik]</ref> in Germany and are 10&nbsp;m wide, 20&nbsp;m long and 6&nbsp;m high, weighing 130&nbsp;tonnes. They are powered by twin [[Turbocharger|turbocharged]] 500&nbsp;kW [[diesel engine]]s.

The transporters, which feature a driver's seat designed to accommodate an [[oxygen]] tank to aid breathing the thin high-altitude air, place the antennae precisely on the pads. The first vehicle was completed and tested in July 2007.<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/science/nature/6922967.stm |title=Giant truck set for sky-high task |work=BBC News |date=30 July 2007 |access-date=31 July 2007}}</ref> Both transporters were delivered to the ALMA Operations Support Facility (OSF) in Chile on 15 February 2008.

On 7 July 2008, an ALMA transporter moved an antenna for the first time, from inside the antenna assembly building (Site Erection Facility) to a pad outside the building for testing (holographic surface measurements).<ref>July 2008 NRAO ALMA newsletter article by Dr. Al Wootten</ref>

[[File:ALMA transporter known as Otto.jpg|left|thumb|ALMA transporter known as Otto.<ref>{{cite web|title=Beauty and a Beast|url=https://www.eso.org/public/images/potw1703a/|website=www.eso.org|access-date=23 January 2017}}</ref>]]

During Autumn 2009, the first three antennae were transported one-by-one to the Array Operations Site. At the end of 2009, a team of ALMA astronomers and engineers successfully linked three antennae at the {{convert|5000|m|adj=on}} elevation observing site thus finishing the first stage of assembly and integration of the fledgling array. Linking three antennae allows corrections of errors that can arise when only two antennae are used, thus paving the way for precise, high-resolution imaging. With this key step, commissioning of the instrument began 22 January 2010.

On 28 July 2011, the first European antenna for ALMA arrived at the Chajnantor plateau, 5,000 meters above sea level, to join 15 antennae already in place from the other international partners. This was the number of antennae specified for ALMA to begin its first science observations, and was therefore an important milestone for the project.<ref>{{cite news|title=European ALMA antenna brings total on Chajnantor to 16|url=http://www.eso.org/public/news/eso1127/|access-date=29 July 2011|newspaper=ESO Organisation Release|date=28 July 2011}}</ref> In October 2012, 43 of the 66 antennae had been set up.

==Scientific results==

===Images from initial testing===
[[Image:Antennae Galaxies composite of ALMA and Hubble observations.jpg|thumb|[[Antennae Galaxies]] composite of ALMA and [[Hubble Space Telescope|Hubble]] observations]]
[[File:HL_Tau_protoplanetary_disk.jpg|thumb|[[HL Tauri]] protoplanetary disk.<ref>{{cite web|url=https://public.nrao.edu/news/pressreleases/planet-formation-alma|title=Birth of Planets Revealed in Astonishing Detail in ALMA's 'Best Image Ever' - NRAO: Revealing the Hidden Universe|work=nrao.edu}}</ref>]]

By the summer of 2011, sufficient telescopes were operational during the extensive program of testing prior to the Early Science phase for the first images to be captured.<ref>{{cite news|title=ALMA Opens its Eyes|url=http://www.almaobservatory.org/en/press-room/press-releases/297-alma-opens-its-eyes|access-date=4 October 2011|newspaper=ALMA Press Release|date=3 October 2011|url-status=dead|archive-url=https://web.archive.org/web/20111005042527/http://www.almaobservatory.org/en/press-room/press-releases/297-alma-opens-its-eyes|archive-date=5 October 2011}}</ref> These early images gave a first glimpse of the potential of the new array that will produce much better quality images in the future as the scale of the array continues to increase.

The target of the observation was a pair of colliding galaxies with dramatically distorted shapes, known as the [[Antennae Galaxies]]. Although ALMA did not observe the entire galaxy merger, the result is the best submillimeter-wavelength image ever made of the Antennae Galaxies, showing the clouds of dense cold gas from which new stars form, which cannot be seen using visible light.

===Comet studies===
On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/submillimeter Array (ALMA) for the first time, that detailed the distribution of [[Hydrogen cyanide|HCN]], [[Hydrogen isocyanide|HNC]], [[Formaldehyde|H<sub>2</sub>CO]], and [[dust]] inside the [[Coma (cometary)|comae]] of [[comet]]s [[C/2012 F6 (Lemmon)]] and [[Comet ISON|C/2012 S1 (ISON)]].<ref name="NASA-20140811">{{cite web |last1=Zubritsky |first1=Elizabeth |last2=Neal-Jones |first2=Nancy |title=RELEASE 14-038 - NASA's 3-D Study of Comets Reveals Chemical Factory at Work |url=http://www.nasa.gov/press/2014/august/goddard/nasa-s-3-d-study-of-comets-reveals-chemical-factory-at-work |date=11 August 2014 |work=[[NASA]] |access-date=12 August 2014 }}</ref><ref name="AJL-20140811">{{cite journal |author=Cordiner, M.A. |title=Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/submillimeter Array |date=11 August 2014 |journal=[[The Astrophysical Journal]] |volume=792 |number=1 |doi=10.1088/2041-8205/792/1/L2 |display-authors=etal|arxiv = 1408.2458 |bibcode = 2014ApJ...792L...2C |page=L2|s2cid=26277035 }}</ref>

===Planetary formation===
An image of the protoplanetary disc surrounding [[HL Tauri]] (a very young [[T Tauri star]]<ref>{{cite journal |title=In Search of HL Tauri |journal=The Astrophysical Journal Letters |first1=David A. |last1=Weintraub |first2=Joel H. |last2=Kastner |first3=Barbara A. |last3=Whitney |volume=452 |issue=2 |pages=L141–L145 |date=October 1995 |bibcode=1995ApJ...452L.141W |doi=10.1086/309720|doi-access= }}</ref> in the constellation [[Taurus (constellation)|Taurus]]) was made public in 2014, showing a series of concentric bright rings separated by gaps, indicating protoplanet formation. {{As of|2014}}, most theories did not expect planetary formation in such a young (100,000-1,000,000-year-old) system, so the new data spurred renewed theories of protoplanetary development. One theory suggests that the faster accretion rate might be due to the complex magnetic field of the protoplanetary disc.<ref>{{cite journal |title=Spatially resolved magnetic field structure in the disc of a T Tauri star |journal=[[Nature (journal)|Nature]] |first1=Ian W. |last1=Stephens |first2=Leslie W. |last2=Looney |first3=Woojin |last3=Kwon |first4=Manuel |last4=Fernández-López |first5=A. Meredith |last5=Hughes |first6=Lee G. |last6=Mundy |first7=Richard M. |last7=Crutcher |first8=Zhi-Yun |last8=Li |first9=Ramprasad |last9=Rao |display-authors=5 |volume=514 |issue=7524 |pages=597–599 |date=October 2014 |arxiv=1409.2878 |bibcode=2014Natur.514..597S |doi=10.1038/nature13850 |pmid=25337883|s2cid=4396150 }}</ref>

In 2022 ALMA initiated a program called exoALMA, a very detailed survey of 15 protoplanetary disk systems with the aim of finding still forming exoplanets.<ref>{{Cite web |title=exoALMA |url=https://www.exoalma.com/home |access-date=2025-05-15 |website=www.exoalma.com |language=en-US}}</ref><ref>{{Cite web |title=Workshops |url=https://www.exoalma.com/workshops |access-date=2025-05-15 |website=www.exoalma.com |language=en-US}}</ref> 

=== Event Horizon Telescope ===
{{Main|Event Horizon Telescope}}
ALMA participated in the Event Horizon Telescope project, which produced the first direct image of a [[black hole]], published in 2019.<ref>{{Cite web|url=http://www.sci-news.com/astronomy/first-image-black-hole-07079.html|title=Event Horizon Telescope Captures First Image of Black Hole {{!}} Astronomy {{!}} Sci-News.com|website=Breaking Science News {{!}} Sci-News.com|language=en-US|access-date=2019-04-10}}</ref>

===Phosphine in the atmosphere of Venus===
ALMA participated in the claimed [[Life on Venus#Phosphine|detection of phosphine]], a biomarker, in the air of Venus. As no known non-biological source of phosphine on Venus could produce phosphine in the concentrations detected, this would have indicated the presence of biological organisms in the atmosphere of Venus.<ref name="Greaves et al">{{cite journal |last1=Greaves |first1=Jane S. |last2=Richards |first2=A.M.S. |last3=Bains |first3=W |title=Phosphine gas in the cloud decks of Venus |journal=Nature Astronomy |date=14 September 2020 |volume=5 |issue=7 |pages=655–664 |doi=10.1038/s41550-020-1174-4 |arxiv=2009.06593 |bibcode=2021NatAs...5..655G |s2cid=221655755 |url=https://www.nature.com/articles/s41550-020-1174-4#citeas |access-date=16 September 2020}}</ref><ref>{{cite news |last1=Sample |first1=Ian |title=Scientists find gas linked to life in atmosphere of Venus |url=https://www.theguardian.com/science/2020/sep/14/scientists-find-gas-linked-to-life-in-atmosphere-of-venus |access-date=16 September 2020 |work=The Guardian |date=14 September 2020}}</ref> Later reanalyses cast doubt on the detection,<ref>{{cite journal|last1=Villanueva|first1=Geronimo|last2=Cordiner|first2=Martin|last3=Irwin|first3=Patrick|last4=de Pater|first4=Imke|last5=Butler|first5=Bryan|last6=Gurwell|first6=Mark|last7=Milam|first7=Stefanie|last8=Nixon|first8=Conor|last9=Luszcz-Cook|first9=Statia|last10=Wilson|first10=Colin|last11=Kofman|first11=Vincent|year=2021|title=No phosphine in the atmosphere of Venus|journal=Nature Astronomy|volume=5|pages=631–635|doi=10.1038/s41550-021-01422-z|arxiv=2010.14305|s2cid=236090264}}</ref> although later analyses confirmed the results.<ref>{{cite journal|last1=Clements |first1=David L. |date=12 January 2023 |title=Venus, Phosphine and the Possibility of Life |journal=Contemporary Physics |volume=63 |issue=3 |page=180 |doi=10.1080/00107514.2023.2184932 |arxiv=2301.05160 |bibcode=2022ConPh..63..180C }}</ref> The detection remains controversial, and is awaiting [[Life_on_Venus#Planned_measurements_of_phosphine_levels|additional measurements]].<ref>{{cite news |last1=Sansom |first1=Clare |title=The hellish chemistry of Venus' atmosphere |url=https://www.chemistryworld.com/features/the-hellish-chemistry-of-venus-atmosphere/4013145.article |work=Chemistry World |language=en}}</ref><ref>{{cite journal |last1=Cleland |first1=Carol E. |last2=Rimmer |first2=Paul B. |title=Ammonia and Phosphine in the Clouds of Venus as Potentially Biological Anomalies |journal=Aerospace |date=26 November 2022 |volume=9 |issue=12 |pages=752 |doi=10.3390/aerospace9120752|arxiv=2211.07786 |bibcode=2022Aeros...9..752C |doi-access=free }}</ref>

==Global collaboration==
[[File:ALMA Greater than the Sum of its Parts (cropped).jpg|thumb|Several ALMA dishes]]
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the [[European Southern Observatory]] (ESO), in North America by the U.S. [[National Science Foundation]] (NSF) in cooperation with the [[National Research Council (Canada)|National Research Council]] of Canada (NRC) and the [[National Science Council]] of Taiwan (NSC) and in East Asia by the [[National Institutes of Natural Sciences, Japan|National Institutes of Natural Sciences]] of Japan (NINS) in cooperation with the [[Academia Sinica]] (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the [[National Radio Astronomy Observatory]] (NRAO), which is managed by [[Associated Universities, Inc]] (AUI) and on behalf of East Asia by the [[National Astronomical Observatory of Japan]] (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.<ref>{{cite web |title=First Light for Band 5 at ALMA - New receivers improve ALMA's ability to search for water in the Universe |url=https://www.eso.org/public/news/eso1645/ |publisher=European Southern Observatory |access-date=9 June 2018 |date=21 December 2016}} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Its current director since February 2018 is [[Sean Dougherty]].<ref>[https://www.almaobservatory.org/en/announcement/alma-selects-new-director/ ALMA Observatory: ALMA Selects New Director]</ref>

==ALMA regional centre (ARC)==
The ALMA regional centre (ARC) has been designed as an interface between user communities of the major contributors of the ALMA project and the JAO. Activates for operating the ARC have also divided into the three main regions involved (Europe, North America and East Asia). The European ARC (led by [[European Southern Observatory|ESO]]) has been further subdivided into ARC-nodes<ref>{{cite web|url=http://www.eso.org/sci/facilities/alma/arc/nodes|title=ARC-nodes|author=webteam@eso.org|access-date=15 November 2014}}</ref> located across Europe in Bonn-Bochum-Cologne, Bologna, Ondřejov, [[Onsala Space Observatory|Onsala]], [[Institut de Radio Astronomie Millimétrique|IRAM]] (Grenoble), Leiden and [[Jodrell Bank Centre for Astrophysics|JBCA]] (Manchester).

The core purpose of the ARC is to assist the user community with the preparation of observing proposals, ensure observing programs meet their scientific goals efficiently, run a help-desk for submitting proposals and observing programs, delivering the data to principal investigators, maintenance of the ALMA data archive, assistance with the calibration of data and providing user feedback.<ref>{{cite web|url=http://www.eso.org/sci/facilities/alma/arc|title=ALMA regional centre|author=webteam@eso.org|access-date=15 November 2014}}</ref>

== Project detail ==
[[File:Counting sheep on the Chajnantor plateau (potw2328a).jpg|thumb|ALMA site from above]]

* At least 50 [[antenna (electronics)|antennae]] of 12&nbsp;m diameter located at an elevation of 5,000&nbsp;m at [[Llano de Chajnantor Observatory]], enhanced by a compact array of {{nowrap|4&nbsp;m × 12&nbsp;m}} and {{nowrap|12&nbsp;m × 7&nbsp;m}} [[antenna (electronics)|antennae]] (in 2006, consortium considered whether to build 50 or 64 of the 12&nbsp;m ones. [http://www.sciencemag.org/cgi/content/full/312/5776/990 After a Tough Year, ALMA's Star Begins to Rise at Last] [http://www.nature.com/nature/journal/v439/n7076/full/439526a.html High and dry])
* [[Digital imaging|Imaging]] instrument in all [[Radio window|atmospheric windows]] between 350&nbsp;μm and 10&nbsp;mm
* Array configurations from approximately 150&nbsp;m to 14&nbsp;km
* [[Spatial resolution]] of 10&nbsp;[[arcsecond|milliarcsecond]]s (10<sup>−7</sup>&nbsp;radians), 10 times better than the [[Very Large Array]] (VLA) and 5 times better than the [[Hubble Space Telescope]], but still considerably lower than the resolution achieved with [[Astronomical interferometer|optical and infrared interferometers]].
* The ability to image sources [[arcminute]]s to degrees across at one arcsecond resolution
* Velocity resolution under 50&nbsp;m/s
* Faster and more flexible imaging instrument than the Very Large Array
* Largest and most sensitive instrument in the world at millimeter and submillimeter wavelengths
* Point source detection sensitivity 20 times better than the Very Large Array
* Data reduction system will be CASA (Common Astronomy Software Applications) which is a new software package based on [[AIPS++]]

=== Atacama Compact Array ===
[[File:The Atacama Compact Array.jpg|thumb|The Atacama Compact Array]]
The Atacama Compact Array, ACA, is a subset of 16 closely separated antennae that will greatly improve ALMA's ability to study celestial objects with a large angular size, such as molecular clouds and nearby galaxies. The antennae forming the Atacama Compact Array, four 12-meter antennae and twelve 7-meter antennae, were produced and delivered by Japan. In 2013, the Atacama Compact Array was named the Morita Array after Professor Koh-ichiro Morita, a member of the Japanese ALMA team and designer of the ACA, who died on 7 May 2012 in Santiago.<ref>{{cite news|title=ALMA Compact Array Completed and Named After Japanese Astronomer|url=http://www.eso.org/public/announcements/ann13040/|access-date=8 May 2013|newspaper=ESO Announcement}}</ref>

==Work stoppage==
In August 2013, workers at the telescope went on strike to demand better pay and working conditions. This is one of the first strikes to affect an astronomical observatory. The work stoppage began after the observatory failed to reach an agreement with the workers' union.<ref>{{cite web|url=http://almaobservatory.org/en/component/content/article/634|title=ALMA Observatory Statement|author=Alejandro Peredo|access-date=15 November 2014|url-status=dead|archive-url=https://web.archive.org/web/20141129014233/http://almaobservatory.org/en/component/content/article/634|archive-date=29 November 2014}}</ref><ref>{{cite news|url=https://www.washingtonpost.com/world/the_americas/workers-at-earths-largest-radio-telescope-in-chile-strike-over-pay-working-conditions/2013/08/22/05eb11d6-0b6e-11e3-89fe-abb4a5067014_story.html|archive-url=https://web.archive.org/web/20130823191323/http://www.washingtonpost.com/world/the_americas/workers-at-earths-largest-radio-telescope-in-chile-strike-over-pay-working-conditions/2013/08/22/05eb11d6-0b6e-11e3-89fe-abb4a5067014_story.html|url-status=dead|archive-date=23 August 2013|title=Workers at Earth's largest radio telescope in Chile strike over pay, working conditions|date=22 August 2013|newspaper=[[The Washington Post]]}}</ref><ref>{{cite news|url=https://www.bbc.com/news/av/world-latin-america-23807459/alma-telescope-crew-go-on-strike|title=Alma telescope crew go on strike|work=[[BBC News]]|access-date=15 November 2014}}</ref><ref>{{cite web|url=https://www.huffingtonpost.com/huff-wires/20130822/lt-chile-alma-observatory-strike/|title=Workers strike at world's largest radio telescope|publisher=[[Huffington Post]]|access-date=15 November 2014|archive-url=https://archive.today/20130825013249/http://www.huffingtonpost.com/huff-wires/20130822/lt-chile-alma-observatory-strike/|archive-date=25 August 2013|url-status=live}}</ref> After 17 days an agreement was reached providing for reduced schedules and higher pay for work done at high altitude.<ref>{{cite web |title=ALMA resumes operations after end of workers' strike |url=http://www.almaobservatory.org/en/press-room/announcements-events/639-alma-resumes-operations-after-end-of-workers-strike |website=almaobservatory.org |access-date=11 May 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150518095236/http://www.almaobservatory.org/en/press-room/announcements-events/639-alma-resumes-operations-after-end-of-workers-strike |archive-date=18 May 2015 }}</ref><ref>{{cite news|title=17-Day ALMA Strike Ends in Resolution|url=http://www.skyandtelescope.com/astronomy-news/17-day-alma-strike-ends-in-resolution/|website=Sky & Telescope|access-date=11 May 2015|date=2013-09-06}}</ref>

In March 2020, ALMA was shut down due to the [[COVID-19 pandemic]]. It also delayed the cycle 8 proposal submission deadline and suspended public visits to the site.<ref>{{Cite web|url=https://www.almaobservatory.org/en/announcement/alma-precautionary-measures-against-coronavirus/|title=COVID-19 (coronavirus) Measures at ALMA|date=2020-03-19|website=ALMA|access-date=2020-03-23}}</ref>

On October 29, 2022, ALMA suspended observations due to a cyber attack.<ref>{{Cite web|url=https://almascience.eso.org/news/alma-update-on-the-recovery-from-october-29-cyberattack|title=ALMA Update on the Recovery from Cyberattack|date=2022-11-18|website=ALMA|access-date=2023-01-15}}</ref> Observations were restarted 48 days later, on December 16, 2022.<ref>{{Cite web|url=https://phys.org/news/2022-12-alma-successfully-restarts-cyberattack.html|title=ALMA successfully restarts observations after cyberattack|date=2022-12-20|website=phys.org|access-date=2023-01-16}}</ref>

==Project timeline==
[[File:The final ALMA antenna.jpg|thumb|The final ALMA antenna.<ref>{{cite news|title=Final Antenna Delivered to ALMA|url=http://www.eso.org/public/news/eso1342/|access-date=2 October 2013|newspaper=ESO Press Release}}</ref>]]
{| class="wikitable" style="line-height:1.3em; font-size:95%;"
|+ style="font-size:125%;"| Timeline
!style="width:10em;"| Date
! Activity
|-
|style="text-align:right;" | 1995
|style="padding-left:1.0em;"| ESO/NRAO/NAOJ joint site testing with Chile.
|-
|style="text-align:right;" | May 1998
|style="padding-left:1.0em;"| Start of phase 1 (design & development).
|-
|style="text-align:right;" | June 1999
|style="padding-left:1.0em;"| European/U.S. memorandum of understanding for design & development.
|-
|style="text-align:right;" | February 2003
|style="padding-left:1.0em;"| Final European / North American agreement, with 50% of funding from ESO, and 50% of funding shared between USA and Canada.
|-
|style="text-align:right;" | April 2003
|style="padding-left:1.0em;"| Testing of first prototype antenna begins at the ALMA Test Facility (ATF) site in Socorro, New Mexico.
|-
|style="text-align:right;" | November 2003
|style="padding-left:1.0em;"| Groundbreaking ceremony at ALMA site.
|-
|style="text-align:right;" | September 2004
|style="padding-left:1.0em;"| European, North American & Japanese draft agreement, with Japan providing new extensions to ALMA.
|-
|style="text-align:right;" | October 2004
|style="padding-left:1.0em;"| Opening of Joint ALMA office, Santiago, Chile.
|-
|style="text-align:right;" | September 2005
|style="padding-left:1.0em;"| Taiwan joins the ALMA Project through Japan.
|-
|style="text-align:right;" | July 2006
|style="padding-left:1.0em;"| European, North American & Japanese amend agreement on the Enhanced ALMA.
|-
|style="text-align:right;" | April 2007
|style="padding-left:1.0em;"| Arrival of first antenna in Chile.
|-
|style="text-align:right;" | February 2008
|style="padding-left:1.0em;"| Arrival of the two ALMA transporters in Chile.
|-
|style="text-align:right;" | July 2008
|style="padding-left:1.0em;"| First antenna movement with a transporter.
|-
|style="text-align:right;" | December 2008
|style="padding-left:1.0em;"| Acceptance of the first ALMA antenna.
|-
|style="text-align:right;" | May 2009
|style="padding-left:1.0em;"| First interferometry with two antennae at the Operations Support Facility (OSF).
|-
|style="text-align:right;" | September 2009
|style="padding-left:1.0em;"| First move of an ALMA antenna to Chajnantor.
|-
|style="text-align:right;" | November 2009
|style="padding-left:1.0em;"| Phase closure with three antennae at Chajnantor.
|-
|style="text-align:right;" | 2010
|style="padding-left:1.0em;"| Call for shared-risk Early Science proposals.
|-
|style="text-align:right;" | September 2011
|style="padding-left:1.0em;"| Start of Early Science Cycle 0. Sixteen 12-m antennae in the 12-m array.
|-
|style="text-align:right;" | February 2012
|style="padding-left:1.0em;"| First paper published with ALMA data<ref>{{cite journal |title=Pre-ALMA observations of GRBs in the mm/submm range |date=February 2012 |last1=de Ugarte Postigo |first1=A. |last2=Lundgren |first2=A. |last3=Martín |first3=S. |last4=García-Appadoo |first4=D. |journal=Astronomy and Astrophysics |volume=538 |pages=44 |arxiv = 1108.1797 |bibcode = 2012A&A...538A..44D |doi = 10.1051/0004-6361/201117848 |s2cid=59140684 |display-authors=3 }}</ref>
|-
|style="text-align:right;" | January 2013
|style="padding-left:1.0em;"| Start of Early Science Cycle 1. Thirty-two 12-m antennae in the 12-m array.
|-
|style="text-align:right;" | March 13, 2013
|style="padding-left:1.0em;"| ALMA Inauguration.
|-
|style="text-align:right;" | September 23, 2013
|style="padding-left:1.0em;"| 66th and final antenna arrived and accepted.
|-
|style="text-align:right;" | June 2014
|style="padding-left:1.0em;"| Start of Early Science Cycle 2. Thirty-four 12-m antennae in the 12-m array, nine 7-m antennae in the 7-m array, and two 12-m antennae in the TP array.
|-
|style="text-align:right;" | June 2018
|style="padding-left:1.0em;"| ALMA 1000th published paper<ref>{{cite journal |title=Spatial variations in Titan's atmospheric temperature: ALMA and Cassini comparisons from 2012 to 2015 |date=June 2018 |last1=Thelen |first1=A.E. |last2=Nixon |first2=C.A. |last3=Chanover |first3=N.J. |last4=Molter |first4=E.M. |journal=Icarus |volume=307 |pages=380–390 |bibcode = 2018Icar..307..380T |doi = 10.1016/j.icarus.2017.10.042 |display-authors=3 |arxiv=1809.10891 |s2cid=54641701 }}</ref>
|-
|style="text-align:right;" | March 2020
|style="padding-left:1.0em;"| ALMA shut down due to the [[COVID-19]] crisis
|}

== Gallery ==
<gallery mode="packed">
File:Flying over the ALMA Site.jpg|ALMA construction site from above, 2011
File:Visualisation of ALMA as an interferometer.ogv|This artist's rendering of the ALMA array on the Chajnantor plateau shows how, as an interferometer, ALMA acts like a single telescope with a diameter as large as the distance between its individual antennae (represented by the blue circle).
File:ESOcast 51 All Systems Go for Highest Altitude Supercomputer.ogv|ESOcast 51: Video report about the ALMA [[Radio correlator|correlator]].
File:The movie ALMA — In Search of our Cosmic Origins.ogv|This 16-minute video presents the history of ALMA from the origins of the project several decades ago to the recent first science results.
File:Atacama Large Millimeter-submillimeter Array, Milky Way.jpg|ALMA dishes under the Milky Way
</gallery>

{{Wide image|The Moon and the Arc of the Milky Way01.jpg|1100|ALMA site under the arc of the Milky Way, photo by Stéphane Guisard, 2012}}

==See also==
* [[Atacama Pathfinder Experiment]] (APEX), single dish submillimeter telescope built on a modified ALMA prototype antenna
* [[Atacama Submillimeter Telescope Experiment]]
* [[Combined Array for Research in Millimeter-wave Astronomy]] (CARMA), a sensitive millimeter-wave array operated by a consortium of universities
* [[Cosmic Background Imager]], a 13 element interferometer operating in Llano de Chajnantor since 1999.
* [[IRAM - 30m|IRAM 30 Meter Telescope]], the largest millimetric telescope in the world
* [[ALESS 073.1]]

==Further reading==
* Vanden Bout, Paul A.; Dickman, Robert L.; Plunkett, Adele L. (2023). ''The ALMA Telescope: The Story of a Science Mega-Project''. Cambridge University Press. 

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Atacama Large Millimeter Array}}
* [http://www.almaobservatory.org/ Official ALMA site]
* [https://public.nrao.edu/telescopes/alma/ NRAO ALMA site]
* [https://nrc.canada.ca/en/research-development/research-collaboration/programs/atacama-large-millimetersubmillimeter-array-research-development National Research Council Canada ALMA site]
* [http://www.alma.ac.uk/ UK ALMA site]
* [http://www.eso.org/projects/alma/ ESO ALMA site]
* [https://web.archive.org/web/20120103095253/http://alma.mtk.nao.ac.jp/e/index.html ALMA site] by [[National Astronomical Observatory of Japan|NAOJ]]
* [http://www.space.com/20183-alma-radio-telescope-infographic.html How the Huge ALMA Radio Telescope Works (Infographic)], ''[[Space.com]]'', 12 March 2013.
* [http://www.kqed.org/tv/programs/index.jsp?pgmid=21063 ''Into Deep Space: The Birth of the Alma Observatory''] {{Webarchive|url=https://web.archive.org/web/20140408212001/http://www.kqed.org/tv/programs/index.jsp?pgmid=21063 |date=2014-04-08 }}
* [http://spie.org/x108587.xml An optical system design for the Atacama Large Millimeter Array] SPIE Newsroom, 5 June 2014.
* [https://www.cbsnews.com/news/alma-peering-into-the-universes-past/ CBS News' "60 Minutes" program], <small>original broadcast on 9 March 2014, rebroadcast on 27 July 2014. Bob Simon is the correspondent. Michael Gavshon and David Levine, producers.</small>

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