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== Introduction ==
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{{DISPLAYTITLE:Introduction}}
  
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Planck is a space telescope of the European Space Agency designed to answer key cosmological
 
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questions.
 
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Its main goal is to determine the geometry and content of the Universe, and which theories describing the birth and evolution of the Universe are correct. To achieve this ambitious objective, it observed the Cosmic Microwave Background radiation (CMB), emitted about 14
 
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billion years ago, just over 300,000 years after the Big Bang. Today the CMB permeates
 
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the Universe and is observed to have an average temperature of 2.7 K. Small deviations from
 
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this average value (the so-called anisotropies), observable at angular scales larger than ∼5
 
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arcminutes, encode a wealth of information on the properties of the Universe in its infancy. The
 
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objective of Planck is to measure these properties with an unprecedented accuracy and level of
 
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detail.
 
  
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[[file:Planck_Logos.jpg|thumb|300px|The Planck collaboration institutes.]]
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== The Planck mission ==
  
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As with all ESA scientific missions, Planck was developed in a partnership with the
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[http://www.esa.int/Planck Planck] is a mission of the European
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European scientific community. [[Planck Collaboration|Two consortia of scientific institutes]], each led by a Principal
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Space Agency - ESA. The Planck satellite carried instruments provided by two scientific Consortia funded by ESA member
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Investigator, developed and delivered to ESA two instruments designed specifically for
+
states (in particular the lead countries: France and Italy) with contributions from [https://www.nasa.gov/ NASA] (USA), and
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Planck. Each of these instruments targets a specific number of wavelength bands within the
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telescope reflectors provided in a collaboration between ESA and a scientific Consortium led and
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range in which the CMB is observable. Together, the two instruments are capable of collecting
+
funded by Denmark.
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data of a quality adequate to measure the CMB signal and distinguish it from other confusing
 
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sources. A large telescope collects the light from the sky and deliver it to the instruments
 
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for measurement and analysis. The reflectors of the Planck telescope were developed and
 
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delivered to ESA by a Danish consortium of institutes.
 
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ESA retains overall management of the project, develops and procures the spacecraft, integrates
 
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the instruments into the spacecraft, and launches and operates it. Planck was launched on May 14th 2009 on an Ariane 5 rocket together with the Herschel
 
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Space Observatory. After launch, they were both
 
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placed into orbits around the L2 Lagrange of the Sun-Earth system, located about 1.5 million km from the Earth. From that far
 
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vantage point, Planck sweeped the sky regularly in large swaths, and covered it fully
 
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about six times.
 
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Each of the two instrument consortia operated their respective instrument and processed
 
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all the data into usable scientific products. At the end of the mission the consortia delivered the final products to ESA, which archives them
 
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and distributes them to the community.
 
  
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[[file:PlanckMissionTimeline.JPG|thumb|480px|A timeline of the Planck operations and archiving.]]
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Planck was conceived in 1992, in the wake of the release of the results from the
 +
Cosmic Background Explorer ([https://science.nasa.gov/missions/cobe COBE]) satellite, notably its measurement of the shape of the spectrum of the
 +
[http://pdg.lbl.gov/2017/reviews/rpp2016-rev-cosmic-microwave-background.pdf cosmic microwave background]
 +
(CMB), and its
 +
detection of the spatial anisotropies of the temperature of the CMB. The
 +
latter result in particular led to an explosion in the number of ground-based and suborbital
 +
experiments dedicated to mapping of the anisotropies, and to proposals for space experiments both in
 +
Europe and the USA.
  
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== Early operations and transfer to orbit ==
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The main objective of Planck was to measure the spatial anisotropies of the temperature of the CMB, with an accuracy set by fundamental astrophysical limits. Its level of performance enabled Planck to extract essentially all the information in the CMB temperature anisotropies. Planck also measured to high accuracy the polarization of the CMB anisotropies, which encodes not only a wealth of cosmological information, but also provides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. In addition, the Planck sky surveys produced a wealth of information on the properties of extragalactic sources and on the dust and gas in our own Galaxy. The scientific objectives of Planck as conceived in 2005 (4 years before launch) were described in detail in the {{PlanckPapers|Bluebook}}.
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Planck was launched from the Centre Spatial Guyanais in
 
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Kourou (French Guyana) on 14 May 2009 at its nominal lift-off
 
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time of 13:12 UT, on an Ariane 5 ECA rocket of Arianespace2.
 
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ESA’s Herschel observatory was launched on the same rocket.
 
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At 13:37:55 UT, Herschel was released from the rocket at an altitude
 
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of 1200 km; Planck followed suit at 13:40:25UT. The separation
 
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attitudes of both satellites were within 0.1 deg. of prediction.
 
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The Ariane rocket placed Planck with excellent accuracy (semimajor
 
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axis within 1.6 % of prediction), on a trajectory towards
 
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the second Lagrangian point of the Earth-Sun system (L2)
 
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. The orbit describes a Lissajous trajectory
 
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around L2 with a ∼6 month period that avoids crossing
 
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the Earth penumbra for at least 4 years.
 
  
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[[file:HerschelPlanckLaunch.jpg|thumb|200px|The Herschel and Planck spacecrafts in the launch vehicle configuration.]]
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The development of Planck began with two proposals presented to the
 +
European Space Agency (ESA) in May of 1993, for the [https://dms.cosmos.esa.int/cs/livelink/Open/3557509 Cosmic Background Radiation Anisotropy Satellite] (COBRAS)
 +
and the [https://dms.cosmos.esa.int/cs/livelink/Open/3557510 Satellite for Measurement of Background Anisotropies] (SAMBA). Each of these proposed a payload formed by an offset
 +
Gregorian telescope focussing light from the sky onto an array of
 +
detectors (based on high-electron-mobility transistor [HEMT] low
 +
noise amplifiers for COBRAS and very low temperature bolometers for
 +
SAMBA) fed by corrugated horns. The two proposals were used by an
 +
ESA-led team to design a payload where a single COBRAS-like
 +
telescope fed two instruments, a COBRAS-like Low Frequency
 +
Instrument (LFI), and a SAMBA-like High Frequency Instrument (HFI),
 +
sharing a common focal plane. A period of study of this concept
 +
culminated in the selection by ESA in 1996 of the COBRAS/SAMBA
 +
satellite (described in the so-called {{PlanckPapers|Redbook}})
 +
into its programme of scientific satellites. At the time of
 +
selection the launch of COBRAS/SAMBA was expected to be in 2003.
 +
Shortly after the mission was approved, it was renamed in honour of
 +
the German scientist [https://www.cosmos.esa.int/web/planck/max-planck Max Planck] (1858-1947), winner of the Nobel
 +
Prize for Physics in 1918.
  
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[[file:PLANCK_HERSCHEL_LAUNCH.jpg|thumb|200px|The Herschel and Planck launch by an Ariane 5 ECA rocket.]]
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Shortly after its selection, the  development of Planck was joined
 +
with that of ESA's [https://www.cosmos.esa.int/web/herschel Herschel Space Telescope], based on a number of
 +
potential commonalities, the most important of which was that both
 +
missions targeted orbits around the second Lagrangian point of the
 +
Sun-Earth system and could therefore share a single heavy launcher.
 +
In practice the joint development meant that a single ESA
 +
engineering team led the development of both satellites by a
 +
single industrial prime contractor, leading to the use of many
 +
identical hardware and software subsystems in both satellites, and a
 +
synergistic sharing of engineering skills and manpower. The
 +
industrial prime contractor, Thales Alenia Space France, was
 +
competitively selected in early 2001. Thales Alenia Space France was
 +
supported by two major subcontractors: Thales Alenia Space Italy for
 +
the Service Module of both Planck and Herschel; and EADS Astrium
 +
GmbH for the Herschel Payload Module.  There were also contributions from many other industrial
 +
subcontractors from all ESA member states (the industrial team is described [http://sci.esa.int/planck/34787-industrial-team/  here] ).
  
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After release from the rocket, three large manoeuvres were
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In early 1999, ESA selected two Consortia of scientific institutes to provide the two Planck
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carried out to place Planck in its intended final orbit.
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instruments that were part of the payload described in the {{PlanckPapers|Redbook}}: the Low Frequency Instrument
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Once in its final orbit, very small manoeuvres are required at approximately
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was developed by a consortium led by N. Mandolesi of the [http://www.iasfbo.inaf.it/en/ Istituto di Astrofisica Spaziale e Fisica
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monthly intervals (1 ms−1 per year) to keep Planck
+
Cosmica] (CNR) in Bologna (Italy); and the High Frequency Instrument by a consortium led by J.-L.
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from drifting away from its intended path around L2. The attitude
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Puget of the [https://www.ias.u-psud.fr/ Institut d'Astrophysique Spatiale] (CNRS) in Orsay (France).  
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manoeuvres required to followthe scanning strategy require
 
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about 2.6 ms−1 per year. Overall, the excellent performance
 
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of launch and orbit manoeuvres will lead to a large amount
 
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(∼160 kg, or ∼40% of initial tank loading) of fuel remaining
 
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on board at end of mission operations.
 
  
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Planck started cooling down radiatively shortly after launch.
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In early 2000, ESA and the [http://www.space.dtu.dk/english Danish National Space Institute] (DNSI) signed a Letter of Agreement for
−
Heaters were activated to hold the focal plane at 250 K, which
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the provision of the two reflectors that are used in the Planck telescope. DNSI led a Consortium of
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was reached around 5 h after launch. The valve opening the exhaust
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Danish institutes, which together with ESA subcontracted the development of the Planck reflectors to
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piping of the dilution cooler was activated at 03:30 UT,
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EADS Astrium GmbH (Friedrichshafen, D), now part of the Airbus group, who have manufactured the reflectors using state-of-the-art
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and the 4He-JT cooler compressors were turned on at low stroke
+
carbon-fibre technology.
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at 05:20 UT. After these essential operations were completed,
 
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on the second day after launch, the focal plane temperature was allowed to descend to 170 K for out-gassing and decontamination
 
−
of the telescope and focal plane.
 
  
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== Commissioning and initial science operations ==
+
In total, more than 40 European
 +
institutes, and some from the USA and Canada joined forces to constitute the [https://www.cosmos.esa.int/web/planck/planck-collaboration Planck Collaboration], and carry out the development, testing, and in-flight operations of these
 +
instruments, as well as the ensuing data analysis
 +
and initial scientific exploitation.
  
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=== Commissioning ===
+
[[file:Planck_Logos.jpg|thumb|center|500px|The Planck Collaboration's institutes and agencies.]]
  
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The first period of operations focussed on commissioning activities,
 
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i.e., functional check-out procedures of all sub-systems and
 
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instruments of the Planck spacecraft in preparation for running
 
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science operations related to calibration and performance verification
 
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of the payload. Planning for commissioning operations
 
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was driven by the telescope decontamination period of 2 weeks
 
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and the subsequent cryogenic cool-down of the payload and instruments.
 
−
The overall duration of the cool-down was approximately
 
−
2 months, including the decontamination period.
 
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The commissioning activities were executed very smoothly and
 
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all sub-systems were found to be in good health.
 
−
The commissioning activities were formally completed at the
 
−
time when the HFI bolometer stage reached its target temperature
 
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of 100 mK, on 3 July 2009 at 01:00 UT. At this time all the
 
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critical resource budgets (power, fuel, lifetime, etc.) were found
 
−
to contain very significant margins with respect to the original
 
−
specification.
 
  
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[[file:Cooldown.jpg|thumb|400px|Schematics of the cool-down sequence, from Planck Coll. 2011, A&A 536, A1.]]
+
The development history of the Planck satellite is summarised [https://www.cosmos.esa.int/web/planck/mission-history here].
 +
It culminated with the successful launch of Planck and Herschel on 14
 +
May 2009.
 +
After a period dedicated to Commissioning and Performance Verification, Planck started its planned survey observations on 12 August 2009.  
 +
It carried on observing for a period of about 30 months, around twice the span originally required, and completed five full-sky surveys with both instruments. The Low Frequency Instrument (LFI), which was able to work at higher temperatures than HFI,  continued to survey the sky for a large part of 2013, providing even more data to improve the final Planck results.  
 +
The last command to the Planck satellite was sent on the 23 October 2013, marking the end of operations.
  
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=== Calibration and performance verification ===
+
<!-- [[file:PlanckMissionTimelineV2.png|thumb|480px|Timeline of the Planck operations and archiving.]]  -->
  
−
Calibration and performance verification (CPV) activities
+
== The Planck data products and papers ==
−
started during the cool-down period and continued until the end
 
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of August 2009.
 
−
On completion of all the
 
−
planned activities, it was concluded that the two instruments were fully tuned and ready for routine
 
−
operations. No further parameter tuning was expected
 
−
to be needed, except for the sorption cooler, which requires
 
−
a weekly change in operational parameters.
 
−
The scientific performance parameters of both instruments
 
−
was in most respects as had been measured on the ground before
 
−
launch. The only significant exception was that, due to
 
−
the high level of Galactic cosmic rays, the bolometers of HFI
 
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were detecting a higher number of glitches than expected,
 
−
causing a modest (∼10%) level of systematic effects on
 
−
their noise properties. The satellite did not introduce any major systematic effects
 
−
into the science data. In particular, the telemetry transponder
 
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did not result in radio-frequency interference, which implies
 
−
that the data acquired during visibility periods is useable for
 
−
science.
 
  
−
=== First-Light Survey ===
+
The Data Products of Planck have been released in four different stages of increasing scope and quality.
  
−
The First Light Survey (FLS) was the last major activity planned
+
* The first set of scientific data, the Early Release Compact Source Catalogue (ERCSC; {{PlanckPapers|planck2011-1-10}}), was published in January 2011. At the same time, a set of 26 papers related to astrophysical foregrounds was published in a special issue of Astronomy and Astrophysics (Vol. 536, 2011), among which there is an overview paper ({{PlanckPapers|planck2011-1-1}}).
−
before the start of routine surveying of the sky. It was conceived
+
* The second set of data products (sometimes referred to as Planck Release 1 or “PR1,” because it was the first release of cosmologically useful data) was based on data acquired during the so-called nominal mission, i.e. from start of routine operations to 28 November 2010. These products were based on temperature analysis of the whole sky, and were released in March of 2013. The data and associated scientific results are described in a set of 32 papers in another special issue of A&A (Vol. 571, 2014), among which there is another overview ({{PlanckPapers|planck2013-p01}}).  
−
as a two-week period during which Planck would be fully tuned
+
* The third set of data products (and second set of cosmological data, hence “PR2”) and scientific results released by Planck, was based on the data acquired during the complete Planck mission from 12 August 2009 to 23 October 2013, and hereafter referred to as the “2015 products.” They are based on both temperature and polarization analysis of the entire sky, and were released between February and July 2015. The data and associated scientific results are described in a set of 28 papers published in a third special issue of A&A (Vol. 594, 2016). Again there is an overview paper paper ({{PlanckPapers|planck2014-a01}}).
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up and operated as if it was in its routine phase. This stable
+
* The fourth set of scientific data (and third set of cosmological data, hence "PR3") was based on the full mission, focussing on inclusion of the polarization data.  The data and associated scientific results are described in a series of 11 papers, including a final "Legacy" which also includes an overview of this release ({{PlanckPapers|planck2016-l01}}.
−
period could have resulted in the identification of further tuning
 
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activities required to optimise the performance of Planck in
 
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the long-duration surveys to come. The FLS was conducted between
 
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13 and 27 August, and in fact led to the conclusion that
 
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the Planck payload was operating stably and optimally, and required
 
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no further tuning of its instruments. Therefore the period
 
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of the FLS was accepted as a valid part of the first Planck survey.
 
  
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== Routine operations phase ==
+
In addition to the above listed four groups of data-release-related papers, the Planck Collaboration has published more than 50 “Intermediate” papers containing further astrophysical investigations. These papers are usually based on data products that are either already public or about to become public at the time of publication.  
−
The routine operations phase of Planck is characterised by continuous
 
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and stable scanning of the sky and data acquisition by
 
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LFI and HFI. It started with the FLS on 13 August of 2009, at
 
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14:15 UT.
 
  
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The Planck satellite generates (and stores on-board) data
+
All of the Planck Collaboration papers are listed in and can be downloaded from [https://www.cosmos.esa.int/web/planck/publications]. At the current time, we encourage people interested in an overview on Planck to start with the latest overview paper ({{PlanckPapers|planck2016-l01}}), and follow references to more specific areas of interest.
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continuously at the following typical rates: 21 kilobit s−1 (kbps)
 
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of house-keeping (HK) data from all on-board sources, 44 kbps
 
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of LFI science data and 72 kbps of HFI science data. The data
 
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are brought to ground in a daily pass of approximately 3 h duration.
 
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Besides the data downloads, the passes also acquire realtime
 
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HK and a 20 min period of real-time science (used to monitor
 
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instrument performance during the pass). Planck utilises the
 
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two ESA deep-space ground stations in New Norcia (Australia)
 
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and Cebreros (Spain), usually the former. Scheduling of the daily
 
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telecommunication period is quite stable, with small perturbations
 
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due to the need to coordinate the use of the antenna with
 
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other ESA satellites (in particular Herschel).
 
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At the ground station the telemetry is received by redundant
 
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chains of front-end/back-end equipment. The data flows to the
 
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mission operations control centre (MOC) located at ESOC in
 
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Darmstadt (Germany), where it is processed by redundant mission
 
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control software (MCS) installations and made available to
 
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the science ground segment. To reduce bandwidth requirements
 
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between the station and ESOC only one set of science telemetry
 
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is usually transferred. Software is run post-pass to check the
 
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completeness of the data. This software check is also used to
 
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build a catalogue of data completeness, which is used by the science
 
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ground segment to control its own data transfer process.
 
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Where gaps are detected, attempts to fill them are made as an
 
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offline activity (normally next working day), the first step being
 
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to attempt to reflow the relevant data from station. Early in
 
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the mission these gaps were more frequent, with some hundreds
 
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of packets affected per week (impact on data return of order
 
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50 ppm) due principally to a combination of software problems
 
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with the data ingestion and distribution in the MCS, and imperfect
 
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behaviour of the software gap check. Software updates implemented
 
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during the mission have improved the situation such
 
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that gaps are much rarer, with a total impact on data return well
 
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below 1 ppm.
 
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Redump of data from the spacecraft is attempted when there
 
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have been losses in the space link. This has only been necessary
 
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on three occasions. In each case the spacecraft redump has
 
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successfully recovered all the data.
 
  
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All the data downloaded from the satellite, and processed
+
== The Planck Legacy Archive ==
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products such as filtered attitude information, are made available
 
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each day for retrieval from the MOC by the LFI and HFI
 
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Data Processing Centres (DPCs).
 
  
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The scanning strategy is the following: the spin axis follows a cycloidal path on the sky by step-wise displacements of 2 arcmin
+
The [http://pla.esac.esa.int/ Planck Legacy Archive] (PLA) contains all public products originating from the Planck mission, and provides an online interface to select and retrieve them. The majority of the scientific data products from Planck have been produced by the LFI and HFI Data Processing Centres on behalf of the [[Planck Collaboration|Planck Collaboration]].  
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approximately every 50 min. The dwell time (i.e., the duration of
 
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stable data acquisition at each pointing) has varied sinusoidally
 
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by a factor of ∼2.
 
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Planck’s scanning strategy results
 
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in significantly inhomogeneous depth of integration time
 
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across the sky; the areas near the ecliptic poles are observed
 
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with greater depth than all others.
 
  
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The scanning strategy for the second year of Routine
+
The data products distributed by PLA are classified into the following categories.
−
Operations (i.e., Surveys 3 and 4) is exactly the same as for the
+
* "Timelines" contain time series of data acquired. The types of data provided are:
−
first year, except that all pointings are shifted by 1 arcmin along
+
** "semi-raw timelines" containing data samples per detector, which have been very minimally processed after retrieval from the satellite;
−
the cross-scanning direction, in order to provide finer sky sampling
+
** "calibrated timelines" containing data samples per detector after cleaning and calibration.
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for the highest frequency detectors when combining two
+
* "Rings" are timelines that have been binned into individual periods of fixed spin axis pointing. Each ring traces a quasi-large circle on the sky.
−
years of observations.
+
* "Maps" are generally all-sky maps in HEALPix format. There are two major types of Planck maps:
 +
** "frequency maps" are maps as observed at one of the nine frequency channels of Planck, containing at least temperature, and in the later versions also polarization, and existing in many varieties of maps, depending on which detectors and/or time coverage is included in their production;
 +
** "component maps" are maps of diffuse emission of specific physical components, including the CMB, Galactic, and extragalactic foregrounds, which are constructed from Planck observations using different methods.
 +
* The "Likelihood code" is the software used by the Planck Collaboration to extract the values of cosmological parameters from the Planck data. The code is bundled with the data set (from Planck and other experiments) that it needs to run.
 +
* "Catalogues" contain lists of compact or point-like sources extracted from the Planck maps. The basic Planck catalogues have been extracted without regard to the type of source, but some specialized lists of specific source types are also available.
 +
* "Cosmological data" contain results of some of the cosmological analyses that formed the main objective of Planck, i.e. CMB angular power spectra, cosmological model parameters, etc.
  
−
Orbit maintenance manoeuvres were carried out at approximately
+
In addition to the above, the PLA also includes a wide variety of additional products:
−
monthly intervals6. Although the manoeuvres only
+
* external scientific data that were used in the generation of Planck products;
−
required a few minutes, preparations, post-manoeuvre massproperty
+
* data characterizing the Planck payload;
−
calibration, and re-entry into scientific slewing mode
+
* operational data.
−
increased the overhead to several hours. The manoeuvres were
 
−
carried out without disturbing the path of the spin axis from its nominal scanning law. The dwell times of pointings before and
 
−
after the execution of the manoeuvre were reduced to allow all
 
−
pre-planned pointings to be carried out.
 
  
−
While the Planck detectors are scanning the sky, they also naturally
+
All of the Planck products are labelled according to their release: ERCSC-A 2012; PR1 2013; PR2 2015; and PR3 2018. In addition, the product most recommended for use is labelled as the "Legacy" product. The PLA interface allows the user to search the Archive using a wide variety of parameters. It also provides the possibility to extract parts of the products, e.g. a section of the sky, and in some cases to modify them. The PLA also makes it easy to transfer products to generic data analysis tools for further analysis, e.g. Aladin for maps, and Topcat for catalogues.
−
observe celestial calibrators. The main objects used for this
 
−
purpose are the Crab Nebula, and the bright planets Mars, Jupiter and Saturn.
 
  
−
== Payload performance ==
+
Finally, the PLA also contains some selected data products that are based on Planck data, but have not been produced by the Planck Collaboration. These data are labelled as "Community" products.
−
The main achievements in terms of payload performance are the following:
 
  
−
* the angular resolution measured on planets is within a few per cent of that predicted on the ground
+
All the PLA products can be accessed via its [http://pla.esac.esa.int/pla/#home graphical interface]. Some of the products can also be extracted via a [http://pla.esac.esa.int/pla/#aio machine interface].
  
−
* the instantaneous sensitivity of the Planck LFI and HFI channels is estimated to be approximately 10% larger than that measured on the ground and extrapolated to launch conditions
+
== This Explanatory Supplement ==
  
−
* the photometric calibration uncertainty quoted is conservatively based on the current knowledge of systematic effects and data processing pipelines. There is no reason to believe that the mission goals (1% in CMB channels and 3% at the highest frequencies) will not be reached for all Planck channels in due time.
+
This Explanatory Supplement (ES) has been built by the Planck Collaboration and the Planck Science Office. It contains:
 +
* general technical information on the Planck satellite, its payload, and its operations;
 +
* specific information for each of the products being distributed by the PLA.
 +
 
 +
The ES can be accessed online independently or can be called directly from the PLA interface (in this case it will direct the user to the appropriate sections). In general, it will display descriptions appropriate to the "Legacy" products. However,  descriptions specific for each of the four Planck releases can be found at the end of each of the ES sections; the background colour of the ES page identifies the release it refers to.
 +
 
 +
We emphasize that the ES  contains a bare minimum of necessary information on the data products. We strongly recommend that users read the scientific papers by the Planck Collaboration that are closest to their own application. Those papers contain the most relevant and useful information on the quality and limitations of the Planck products, which has often not been fully captured in the ES.
  
 
==For more information==
 
==For more information==
  
−
A complete overview of the Planck mission and its science programme can be found in the Blue Book [[http://www.sciops.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf]].
+
A complete list of Planck publications can be found [http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers here].
 +
 
 +
Suggestions or questions should be sent to the [https://support.cosmos.esa.int/pla/ Helpdesk].
  
−
More details on the Planck mission performance can be found in <cite>#planck2011-1-1</cite>, {{PEarly|1}}.
+
==Acknowledgments==
 +
The development of Planck has been supported by: ESA; CNES and
 +
CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA);
 +
STFC and UKSA (UK); CSIC, MICINN, JA, and RES (Spain); Tekes, AoF, and CSC
 +
(Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO
 +
(Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE
 +
(EU). A description of the Planck Collaboration and a list of its members,
 +
including the technical or scientific activities in which they have been
 +
involved, can be found at  [http://www.cosmos.esa.int/web/planck/planck-collaboration this site].
  
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Latest revision as of 12:43, 17 July 2018


The Planck mission[edit]

Planck is a mission of the European Space Agency - ESA. The Planck satellite carried instruments provided by two scientific Consortia funded by ESA member states (in particular the lead countries: France and Italy) with contributions from NASA (USA), and telescope reflectors provided in a collaboration between ESA and a scientific Consortium led and funded by Denmark.

Planck was conceived in 1992, in the wake of the release of the results from the Cosmic Background Explorer (COBE) satellite, notably its measurement of the shape of the spectrum of the cosmic microwave background (CMB), and its detection of the spatial anisotropies of the temperature of the CMB. The latter result in particular led to an explosion in the number of ground-based and suborbital experiments dedicated to mapping of the anisotropies, and to proposals for space experiments both in Europe and the USA.

The main objective of Planck was to measure the spatial anisotropies of the temperature of the CMB, with an accuracy set by fundamental astrophysical limits. Its level of performance enabled Planck to extract essentially all the information in the CMB temperature anisotropies. Planck also measured to high accuracy the polarization of the CMB anisotropies, which encodes not only a wealth of cosmological information, but also provides a unique probe of the thermal history of the Universe during the time when the first stars and galaxies formed. In addition, the Planck sky surveys produced a wealth of information on the properties of extragalactic sources and on the dust and gas in our own Galaxy. The scientific objectives of Planck as conceived in 2005 (4 years before launch) were described in detail in the Bluebook[1].

The development of Planck began with two proposals presented to the European Space Agency (ESA) in May of 1993, for the Cosmic Background Radiation Anisotropy Satellite (COBRAS) and the Satellite for Measurement of Background Anisotropies (SAMBA). Each of these proposed a payload formed by an offset Gregorian telescope focussing light from the sky onto an array of detectors (based on high-electron-mobility transistor [HEMT] low noise amplifiers for COBRAS and very low temperature bolometers for SAMBA) fed by corrugated horns. The two proposals were used by an ESA-led team to design a payload where a single COBRAS-like telescope fed two instruments, a COBRAS-like Low Frequency Instrument (LFI), and a SAMBA-like High Frequency Instrument (HFI), sharing a common focal plane. A period of study of this concept culminated in the selection by ESA in 1996 of the COBRAS/SAMBA satellite (described in the so-called Redbook[2]) into its programme of scientific satellites. At the time of selection the launch of COBRAS/SAMBA was expected to be in 2003. Shortly after the mission was approved, it was renamed in honour of the German scientist Max Planck (1858-1947), winner of the Nobel Prize for Physics in 1918.

Shortly after its selection, the development of Planck was joined with that of ESA's Herschel Space Telescope, based on a number of potential commonalities, the most important of which was that both missions targeted orbits around the second Lagrangian point of the Sun-Earth system and could therefore share a single heavy launcher. In practice the joint development meant that a single ESA engineering team led the development of both satellites by a single industrial prime contractor, leading to the use of many identical hardware and software subsystems in both satellites, and a synergistic sharing of engineering skills and manpower. The industrial prime contractor, Thales Alenia Space France, was competitively selected in early 2001. Thales Alenia Space France was supported by two major subcontractors: Thales Alenia Space Italy for the Service Module of both Planck and Herschel; and EADS Astrium GmbH for the Herschel Payload Module. There were also contributions from many other industrial subcontractors from all ESA member states (the industrial team is described here ).

In early 1999, ESA selected two Consortia of scientific institutes to provide the two Planck instruments that were part of the payload described in the Redbook[2]: the Low Frequency Instrument was developed by a consortium led by N. Mandolesi of the [http://www.iasfbo.inaf.it/en/ Istituto di Astrofisica Spaziale e Fisica Cosmica] (CNR) in Bologna (Italy); and the High Frequency Instrument by a consortium led by J.-L. Puget of the Institut d'Astrophysique Spatiale (CNRS) in Orsay (France).

In early 2000, ESA and the Danish National Space Institute (DNSI) signed a Letter of Agreement for the provision of the two reflectors that are used in the Planck telescope. DNSI led a Consortium of Danish institutes, which together with ESA subcontracted the development of the Planck reflectors to EADS Astrium GmbH (Friedrichshafen, D), now part of the Airbus group, who have manufactured the reflectors using state-of-the-art carbon-fibre technology.

In total, more than 40 European institutes, and some from the USA and Canada joined forces to constitute the Planck Collaboration, and carry out the development, testing, and in-flight operations of these instruments, as well as the ensuing data analysis and initial scientific exploitation.

The Planck Collaboration's institutes and agencies.


The development history of the Planck satellite is summarised here. It culminated with the successful launch of Planck and Herschel on 14 May 2009. After a period dedicated to Commissioning and Performance Verification, Planck started its planned survey observations on 12 August 2009. It carried on observing for a period of about 30 months, around twice the span originally required, and completed five full-sky surveys with both instruments. The Low Frequency Instrument (LFI), which was able to work at higher temperatures than HFI, continued to survey the sky for a large part of 2013, providing even more data to improve the final Planck results. The last command to the Planck satellite was sent on the 23 October 2013, marking the end of operations.


The Planck data products and papers[edit]

The Data Products of Planck have been released in four different stages of increasing scope and quality.

  • The first set of scientific data, the Early Release Compact Source Catalogue (ERCSC; Planck-Early-VII[3]), was published in January 2011. At the same time, a set of 26 papers related to astrophysical foregrounds was published in a special issue of Astronomy and Astrophysics (Vol. 536, 2011), among which there is an overview paper (Planck-Early-I[4]).
  • The second set of data products (sometimes referred to as Planck Release 1 or “PR1,” because it was the first release of cosmologically useful data) was based on data acquired during the so-called nominal mission, i.e. from start of routine operations to 28 November 2010. These products were based on temperature analysis of the whole sky, and were released in March of 2013. The data and associated scientific results are described in a set of 32 papers in another special issue of A&A (Vol. 571, 2014), among which there is another overview (Planck-2013-I[5]).
  • The third set of data products (and second set of cosmological data, hence “PR2”) and scientific results released by Planck, was based on the data acquired during the complete Planck mission from 12 August 2009 to 23 October 2013, and hereafter referred to as the “2015 products.” They are based on both temperature and polarization analysis of the entire sky, and were released between February and July 2015. The data and associated scientific results are described in a set of 28 papers published in a third special issue of A&A (Vol. 594, 2016). Again there is an overview paper paper (Planck-2015-A01[6]).
  • The fourth set of scientific data (and third set of cosmological data, hence "PR3") was based on the full mission, focussing on inclusion of the polarization data. The data and associated scientific results are described in a series of 11 papers, including a final "Legacy" which also includes an overview of this release (Planck-2020-A1[7].

In addition to the above listed four groups of data-release-related papers, the Planck Collaboration has published more than 50 “Intermediate” papers containing further astrophysical investigations. These papers are usually based on data products that are either already public or about to become public at the time of publication.

All of the Planck Collaboration papers are listed in and can be downloaded from [1]. At the current time, we encourage people interested in an overview on Planck to start with the latest overview paper (Planck-2020-A1[7]), and follow references to more specific areas of interest.

The Planck Legacy Archive[edit]

The Planck Legacy Archive (PLA) contains all public products originating from the Planck mission, and provides an online interface to select and retrieve them. The majority of the scientific data products from Planck have been produced by the LFI and HFI Data Processing Centres on behalf of the Planck Collaboration.

The data products distributed by PLA are classified into the following categories.

  • "Timelines" contain time series of data acquired. The types of data provided are:
    • "semi-raw timelines" containing data samples per detector, which have been very minimally processed after retrieval from the satellite;
    • "calibrated timelines" containing data samples per detector after cleaning and calibration.
  • "Rings" are timelines that have been binned into individual periods of fixed spin axis pointing. Each ring traces a quasi-large circle on the sky.
  • "Maps" are generally all-sky maps in HEALPix format. There are two major types of Planck maps:
    • "frequency maps" are maps as observed at one of the nine frequency channels of Planck, containing at least temperature, and in the later versions also polarization, and existing in many varieties of maps, depending on which detectors and/or time coverage is included in their production;
    • "component maps" are maps of diffuse emission of specific physical components, including the CMB, Galactic, and extragalactic foregrounds, which are constructed from Planck observations using different methods.
  • The "Likelihood code" is the software used by the Planck Collaboration to extract the values of cosmological parameters from the Planck data. The code is bundled with the data set (from Planck and other experiments) that it needs to run.
  • "Catalogues" contain lists of compact or point-like sources extracted from the Planck maps. The basic Planck catalogues have been extracted without regard to the type of source, but some specialized lists of specific source types are also available.
  • "Cosmological data" contain results of some of the cosmological analyses that formed the main objective of Planck, i.e. CMB angular power spectra, cosmological model parameters, etc.

In addition to the above, the PLA also includes a wide variety of additional products:

  • external scientific data that were used in the generation of Planck products;
  • data characterizing the Planck payload;
  • operational data.

All of the Planck products are labelled according to their release: ERCSC-A 2012; PR1 2013; PR2 2015; and PR3 2018. In addition, the product most recommended for use is labelled as the "Legacy" product. The PLA interface allows the user to search the Archive using a wide variety of parameters. It also provides the possibility to extract parts of the products, e.g. a section of the sky, and in some cases to modify them. The PLA also makes it easy to transfer products to generic data analysis tools for further analysis, e.g. Aladin for maps, and Topcat for catalogues.

Finally, the PLA also contains some selected data products that are based on Planck data, but have not been produced by the Planck Collaboration. These data are labelled as "Community" products.

All the PLA products can be accessed via its graphical interface. Some of the products can also be extracted via a machine interface.

This Explanatory Supplement[edit]

This Explanatory Supplement (ES) has been built by the Planck Collaboration and the Planck Science Office. It contains:

  • general technical information on the Planck satellite, its payload, and its operations;
  • specific information for each of the products being distributed by the PLA.

The ES can be accessed online independently or can be called directly from the PLA interface (in this case it will direct the user to the appropriate sections). In general, it will display descriptions appropriate to the "Legacy" products. However, descriptions specific for each of the four Planck releases can be found at the end of each of the ES sections; the background colour of the ES page identifies the release it refers to.

We emphasize that the ES contains a bare minimum of necessary information on the data products. We strongly recommend that users read the scientific papers by the Planck Collaboration that are closest to their own application. Those papers contain the most relevant and useful information on the quality and limitations of the Planck products, which has often not been fully captured in the ES.

For more information[edit]

A complete list of Planck publications can be found here.

Suggestions or questions should be sent to the Helpdesk.

Acknowledgments[edit]

The development of Planck has been supported by: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN, JA, and RES (Spain); Tekes, AoF, and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE (EU). A description of the Planck Collaboration and a list of its members, including the technical or scientific activities in which they have been involved, can be found at this site.


References[edit]

  1. ↑ The Planck Bluebook, The Scientific Programme of Planck, Planck Collaboration, 2005, ESA Publication ESA-SCI(2005)01
  2. ↑ 2.02.1 The Planck Redbook, Report on the Phase A Study of COBRAS/SAMBA, 1996, ESA Publication D-SCI(96)3
  3. ↑ Planck early results. VII. The Early Release Compact Source Catalogue, Planck Collaboration VII, A&A, 536, A7, (2011).
  4. ↑ Planck early results. I. The Planck mission, Planck Collaboration I, A&A, 536, A1, (2011).
  5. ↑ Planck 2013 results. I. Overview of Products and Results, Planck Collaboration, 2014, A&A, 571, A1.
  6. ↑ Planck 2015 results. I. Overview of products and results, Planck Collaboration, 2016, A&A, 594, A1.
  7. ↑ 7.07.1 Planck 2018 results. I. Overview, and the cosmological legacy of Planck, Planck Collaboration, 2020, A&A, 641, A1.

European Space Agency

Cosmic Microwave background

High Electron Mobility Transistor

(Planck) Low Frequency Instrument

(Planck) High Frequency Instrument

Early Release Compact Source Catalog

Planck Legacy Archive

(Hierarchical Equal Area isoLatitude Pixelation of a sphere, <ref name="Template:Gorski2005">HEALPix: A Framework for High-Resolution Discretization and Fast Analysis of Data Distributed on the Sphere, K. M. Górski, E. Hivon, A. J. Banday, B. D. Wandelt, F. K. Hansen, M. Reinecke, M. Bartelmann, ApJ, 622, 759-771, (2005).

Explanatory Supplement

Solar System Object

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