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== Introduction ==
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{{DISPLAYTITLE:Introduction}}
  
Planck is a space telescope of the European Space Agency designed to answer key cosmological
 
questions.
 
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
 
billion years ago, just over 300,000 years after the Big Bang. Today the CMB permeates
 
the Universe and is observed to have an average temperature of 2.7 K. Small deviations from
 
this average value (the so-called anisotropies), observable at angular scales larger than ∼5
 
arcminutes, encode a wealth of information on the properties of the Universe in its infancy. The
 
objective of Planck is to measure these properties with an unprecedented accuracy and level of
 
detail.
 
  
[[file:Planck_Logos.jpg|thumb|300px|The Planck collaboration institutes.]]
+
== The Planck mission ==
  
As with all ESA scientific missions, Planck was developed in a partnership with the
+
[http://www.esa.int/Planck Planck] is a mission of the European
European scientific community. [[Planck Collaboration|Two consortia of scientific institutes]], each led by a Principal
+
Space Agency - ESA. The Planck satellite carried instruments provided by two scientific Consortia funded by ESA member
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
Planck. Each of these instruments targets a specific number of wavelength bands within the
+
telescope reflectors provided in a collaboration between ESA and a scientific Consortium led and
range in which the CMB is observable. Together, the two instruments are capable of collecting
+
funded by Denmark.
data of a quality adequate to measure the CMB signal and distinguish it from other confusing
 
sources. A large telescope collects the light from the sky and deliver it to the instruments
 
for measurement and analysis. The reflectors of the Planck telescope were developed and
 
delivered to ESA by a Danish consortium of institutes.
 
ESA retains overall management of the project, develops and procures the spacecraft, integrates
 
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
 
Space Observatory. After launch, they were both
 
placed into orbits around the L2 Lagrange of the Sun-Earth system, located about 1.5 million km from the Earth. From that far
 
vantage point, Planck sweeped the sky regularly in large swaths, and covered it fully
 
about six times.
 
Each of the two instrument consortia operated their respective instrument and processed
 
all the data into usable scientific products. At the end of the mission the consortia delivered the final products to ESA, which archives them
 
and distributes them to the community.
 
  
[[file:PlanckMissionTimeline.JPG|thumb|480px|A timeline of the Planck operations and archiving.]]
+
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.
  
== Early operations and transfer to orbit ==
+
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}}.
Planck was launched from the Centre Spatial Guyanais in
 
Kourou (French Guyana) on 14 May 2009 at its nominal lift-off
 
time of 13:12 UT, on an Ariane 5 ECA rocket of Arianespace2.
 
ESA’s Herschel observatory was launched on the same rocket.
 
At 13:37:55 UT, Herschel was released from the rocket at an altitude
 
of 1200 km; Planck followed suit at 13:40:25UT. The separation
 
attitudes of both satellites were within 0.1 deg. of prediction.
 
The Ariane rocket placed Planck with excellent accuracy (semimajor
 
axis within 1.6 % of prediction), on a trajectory towards
 
the second Lagrangian point of the Earth-Sun system (L2)
 
. The orbit describes a Lissajous trajectory
 
around L2 with a ∼6 month period that avoids crossing
 
the Earth penumbra for at least 4 years.
 
  
[[file:HerschelPlanckLaunch.jpg|thumb|200px|The Herschel and Planck spacecrafts in the launch vehicle configuration.]]
+
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.
  
[[file:PLANCK_HERSCHEL_LAUNCH.jpg|thumb|200px|The Herschel and Planck launch by an Ariane 5 ECA rocket.]]
+
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] ).
  
After release from the rocket, three large manoeuvres were
+
In early 1999, ESA selected two Consortia of scientific institutes to provide the two Planck
carried out to place Planck in its intended final orbit.
+
instruments that were part of the payload described in the {{PlanckPapers|Redbook}}: the Low Frequency Instrument
Once in its final orbit, very small manoeuvres are required at approximately
+
was developed by a consortium led by N. Mandolesi of the [http://www.iasfbo.inaf.it/en/ Istituto di Astrofisica Spaziale e Fisica
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.
from drifting away from its intended path around L2. The attitude
+
Puget of the [https://www.ias.u-psud.fr/ Institut d'Astrophysique Spatiale] (CNRS) in Orsay (France).  
manoeuvres required to followthe scanning strategy require
 
about 2.6 ms−1 per year. Overall, the excellent performance
 
of launch and orbit manoeuvres will lead to a large amount
 
(∼160 kg, or ∼40% of initial tank loading) of fuel remaining
 
on board at end of mission operations.
 
  
Planck started cooling down radiatively shortly after launch.
+
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
+
the provision of the two reflectors that are used in the Planck telescope. DNSI led a Consortium of
was reached around 5 h after launch. The valve opening the exhaust
+
Danish institutes, which together with ESA subcontracted the development of the Planck reflectors to
piping of the dilution cooler was activated at 03:30 UT,
+
EADS Astrium GmbH (Friedrichshafen, D), now part of the Airbus group, who have manufactured the reflectors using state-of-the-art
and the 4He-JT cooler compressors were turned on at low stroke
+
carbon-fibre technology.
at 05:20 UT. After these essential operations were completed,
 
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.
 
  
== 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.
  
=== Commissioning ===
+
[[file:Planck_Logos.jpg|thumb|center|500px|The Planck Collaboration's institutes and agencies.]]
  
The first period of operations focussed on commissioning activities,
 
i.e., functional check-out procedures of all sub-systems and
 
instruments of the Planck spacecraft in preparation for running
 
science operations related to calibration and performance verification
 
of the payload. Planning for commissioning operations
 
was driven by the telescope decontamination period of 2 weeks
 
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.
 
The commissioning activities were executed very smoothly and
 
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
 
of 100 mK, on 3 July 2009 at 01:00 UT. At this time all the
 
critical resource budgets (power, fuel, lifetime, etc.) were found
 
to contain very significant margins with respect to the original
 
specification.
 
  
[[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.
  
=== 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
 
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
 
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
 
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}}).
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
 
activities required to optimise the performance of Planck in
 
the long-duration surveys to come. The FLS was conducted between
 
13 and 27 August, and in fact led to the conclusion that
 
the Planck payload was operating stably and optimally, and required
 
no further tuning of its instruments. Therefore the period
 
of the FLS was accepted as a valid part of the first Planck survey.
 
  
== 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
 
and stable scanning of the sky and data acquisition by
 
LFI and HFI. It started with the FLS on 13 August of 2009, at
 
14:15 UT.
 
  
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.
continuously at the following typical rates: 21 kilobit s−1 (kbps)
 
of house-keeping (HK) data from all on-board sources, 44 kbps
 
of LFI science data and 72 kbps of HFI science data. The data
 
are brought to ground in a daily pass of approximately 3 h duration.
 
Besides the data downloads, the passes also acquire realtime
 
HK and a 20 min period of real-time science (used to monitor
 
instrument performance during the pass). Planck utilises the
 
two ESA deep-space ground stations in New Norcia (Australia)
 
and Cebreros (Spain), usually the former. Scheduling of the daily
 
telecommunication period is quite stable, with small perturbations
 
due to the need to coordinate the use of the antenna with
 
other ESA satellites (in particular Herschel).
 
At the ground station the telemetry is received by redundant
 
chains of front-end/back-end equipment. The data flows to the
 
mission operations control centre (MOC) located at ESOC in
 
Darmstadt (Germany), where it is processed by redundant mission
 
control software (MCS) installations and made available to
 
the science ground segment. To reduce bandwidth requirements
 
between the station and ESOC only one set of science telemetry
 
is usually transferred. Software is run post-pass to check the
 
completeness of the data. This software check is also used to
 
build a catalogue of data completeness, which is used by the science
 
ground segment to control its own data transfer process.
 
Where gaps are detected, attempts to fill them are made as an
 
offline activity (normally next working day), the first step being
 
to attempt to reflow the relevant data from station. Early in
 
the mission these gaps were more frequent, with some hundreds
 
of packets affected per week (impact on data return of order
 
50 ppm) due principally to a combination of software problems
 
with the data ingestion and distribution in the MCS, and imperfect
 
behaviour of the software gap check. Software updates implemented
 
during the mission have improved the situation such
 
that gaps are much rarer, with a total impact on data return well
 
below 1 ppm.
 
Redump of data from the spacecraft is attempted when there
 
have been losses in the space link. This has only been necessary
 
on three occasions. In each case the spacecraft redump has
 
successfully recovered all the data.
 
  
All the data downloaded from the satellite, and processed
+
== The Planck Legacy Archive ==
products such as filtered attitude information, are made available
 
each day for retrieval from the MOC by the LFI and HFI
 
Data Processing Centres (DPCs).
 
  
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]].  
approximately every 50 min. The dwell time (i.e., the duration of
 
stable data acquisition at each pointing) has varied sinusoidally
 
by a factor of ∼2.
 
Planck’s scanning strategy results
 
in significantly inhomogeneous depth of integration time
 
across the sky; the areas near the ecliptic poles are observed
 
with greater depth than all others.
 
  
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.
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].
  
A complete list of Planck publications can be found here [http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers].
 
  
 
==References==
 
==References==
<biblio force=false>
+
<References />
#[[References]]
+
</biblio>
 
  
[[Category:The Planck mission|000]]
 
 
[[Category:PSOBook]]
 
[[Category:PSOBook]]

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