Planck (spacecraft)

Planck was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013, which mapped the anisotropies of the cosmic microwave background (CMB) at microwave and infra-red frequencies, with high sensitivity and small angular resolution. The mission substantially improved upon observations made by the NASA Wilkinson Microwave Anisotropy Probe (WMAP). Planck provided a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early Universe and the origin of cosmic structure; as of 2013 it has provided the most accurate measurements of several key cosmological parameters, including the average density of ordinary matter and dark matter in the Universe.

The project was started around 1996 and was initially called COBRAS/SAMBA: the Cosmic Background Radiation Anisotropy Satellite/Satellite for Measurement of Background Anisotropies. It was later renamed in honour of the German physicist Max Planck (1858–1947), who derived the formula for black-body radiation.

Built at the Cannes Mandelieu Space Center by Thales Alenia Space, and created as a medium-sized mission for ESA's Horizon 2000 long-term scientific programme, Planck was launched in May 2009,^[2] reaching the Earth/Sun L₂ point by July, and by February 2010 had successfully started a second all-sky survey. On 21 March 2013, the mission's first all-sky map of the cosmic microwave background was released, with an expanded release including polarization data in February 2015; final data analysis will continue into 2016.

At the end of its mission Planck was put into a heliocentric orbit and passivated to prevent it from endangering any future missions. The final deactivation command was sent to Planck in October 2013.

Objectives

The mission had a wide variety of scientific aims, including:^[3]

• high resolution detections of both the total intensity and polarization of primordial CMB anisotropies,
• creation of a catalogue of galaxy clusters through the Sunyaev–Zel'dovich effect,
• observations of the gravitational lensing of the CMB, as well as the integrated Sachs–Wolfe effect,
• observations of bright extragalactic radio (active galactic nuclei) and infrared (dusty galaxy) sources,
• observations of the Milky Way, including the interstellar medium, distributed synchrotron emission and measurements of the Galactic magnetic field, and
• studies of the Solar System, including planets, asteroids, comets and the zodiacal light.

Planck has a higher resolution and sensitivity than WMAP, allowing it to probe the power spectrum of the CMB to much smaller scales (×3). It also observes in 9 frequency bands rather than WMAP's 5, with the goal of improving the astrophysical foreground models.

It is expected that most Planck measurements will be limited by how well foregrounds can be subtracted, rather than by the detector performance or length of the mission, a particularly important factor for the polarization measurements. The dominant foreground radiation depends on frequency, but could include synchrotron radiation from the Milky Way at low frequencies, and dust at high frequencies.

Instruments

The Planck 4K reference load qualification model.

Planck LFI 44GHz horn and front-end chassis.

LFI focal plane model.

The spacecraft carries two instruments: the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI).^[3] Both instruments can detect both the total intensity and polarization of photons, and together cover a frequency range of nearly 830 GHz (from 30 to 857 GHz). The cosmic microwave background spectrum peaks at a frequency of 160.2 GHz.

Planck's passive and active cooling systems allow its instruments to maintain a temperature of −273.05 °C (−459.49 °F), or 0.1 degrees Celsius above absolute zero. From August 2009, Planck was the coldest known object in space, until its active coolant supply was exhausted in January 2012.^[4]

NASA played a role in the development of the mission and contributes to the analysis of scientific data. Its Jet Propulsion Laboratory built components of the science instruments, including bolometers for the high-frequency instrument, a 20 kelvin cryocooler for both the low- and high-frequency instruments, and amplifier technology for the low-frequency instrument.^[5]

Low Frequency Instrument

The LFI has three frequency bands, covering the range of 30–70 GHz, covering the microwave to infra-red regions of the electromagnetic spectrum. The detectors use high-electron-mobility transistors.^[3]

High Frequency Instrument

The High Frequency Instrument qualification model.

The HFI is sensitive between 100 and 857 GHz, using 48 bolometric detectors, manufactured by JPL/Caltech,^[6] optically coupled to the telescope through cold optics, manufactured by Cardiff University's School of Physics and Astronomy,^[7] consisting of a triple horn configuration and optical filters, a similar concept to that used in the Archeops balloon-borne experiment. These detection assemblies are divided into 6 frequency bands (centred at 100, 143, 217, 353, 545 and 857 GHz), each with a bandwidth of 33%. Of these six bands, only the lower four have the capability to measure the polarisation of incoming radiation; the two higher bands do not.^[3]

On 13 January 2012, it was reported that the on-board supply of helium-3 used in Planck's dilution refrigerator had been exhausted, and that the HFI would become unusable within a few days.^[8] By this date, Planck had completed five full scans of the CMB, exceeding its target of two. The LFI (cooled by helium-4) was expected to remain operational for another six to nine months.^[8]

Service Module

Some of the Herschel-Planck team, from left to right: Jean-Jacques Juillet, director of scientific programmes, Thales Alenia Space; Marc Sauvage, project scientist for Herschel PACS experiment, CEA; François Bouchet, Planck operations manager, IAP; and Jean-Michel Reix, Herschel & Planck operations manager, Thales Alenia Space. During presentations of the first results for the missions, Cannes, October 2009

A common service module (SVM) was designed and built by Thales Alenia Space in its Turin plant, for both the Herschel Space Observatory and Planck missions, combined into one single program.^[3]

The overall cost is estimated to be €700 million for the Planck^[9] and €1,100 million for the Herschel mission.^[10] Both figures include their mission's spacecraft and payload, (shared) launch and mission expenses, and science operations.

Structurally, the Herschel and Planck SVMs are very similar. Both SVMs are octagonal in shape and each panel is dedicated to accommodate a designated set of warm units, while taking into account the dissipation requirements of the different warm units, of the instruments, as well as the spacecraft. On both spacecraft, a common design was used for the avionics, attitude control and measurement (ACMS), command and data management (CDMS), power, and tracking, telemetry and command (TT&C) subsystems. All units on the SVM are redundant.

Power Subsystem

On each spacecraft, the power subsystem consists of a solar array, employing triple-junction solar cells, a battery and the power control unit (PCU). The PCU is designed to interface with the 30 sections of each solar array, to provide a regulated 28 volt bus, to distribute this power via protected outputs, and to handle the battery charging and discharging.

For Planck, the circular solar array is fixed on the bottom of the satellite, always facing the Sun as the satellite rotates on its vertical axis.

Attitude and Orbit Control

This function is performed by the attitude control computer (ACC), which is the platform for the attitude control and measurement subsystem (ACMS). It was designed to fulfil the pointing and slewing requirements of the Herschel and Planck payloads.

The Planck satellite rotates at one revolution per minute, with an aim of an absolute pointing error less than 37 arc-minutes. As Planck is also a survey platform, there is the additional requirement for pointing reproducibility error less than 2.5 arc-minutes over 20 days.

The main line-of-sight sensor in both Herschel and Planck is the star tracker.

Launch and orbit

The satellite was successfully launched, along with the Herschel Space Observatory, at 13:12:02 UTC on 14 May 2009 aboard an Ariane 5 ECA heavy launch vehicle from the Guiana Space Centre. The launch placed the craft into a very elliptical orbit (perigee: 270 km [170 mi], apogee: more than 1,120,000 km [700,000 mi]), bringing it near the L₂ Lagrangian point of the Earth-Sun system, 1,500,000 kilometres (930,000 mi) from the Earth.

The manoeuvre to inject Planck into its final orbit around L₂ was successfully completed on 3 July 2009, when it entered a Lissajous orbit with a 400,000 km (250,000 mi) radius around the L₂ Lagrangian point.^[11] The temperature of the High Frequency Instrument reached just a tenth of a degree above absolute zero (0.1 K) on 3 July 2009, placing both the Low Frequency and High Frequency Instruments within their cryogenic operational parameters, making Planck fully operational.^[12]

Decommissioning

In January 2012 the HFI exhausted its supply of liquid helium, causing the detector temperature to rise and rendering the HFI unusable. The LFI continued to be used until science operations ended on 3 October 2013. The spacecraft performed a manoeuvre on 9 October to move it away from Earth and its L₂ point, placing it into a heliocentric orbit, while payload deactivation occurred on 19 October. Planck was commanded on 21 October to exhaust its remaining fuel supply; passivation activities were conducted later, including battery disconnection and the disabling of protection mechanisms.^[13] The final deactivation command, which switched off the spacecraft's transmitter, was sent to Planck on 23 October 2013 at 12:10:27 UTC.^[14]

Results

Comparison of CMB results from COBE, WMAP and Planck

Planck started its First All-Sky Survey on 13 August 2009.^[15] In September 2009, the European Space Agency announced the preliminary results from the Planck First Light Survey, which was performed to demonstrate the stability of the instruments and the ability to calibrate them over long periods. The results indicated that the data quality is excellent.^[16]

On 15 January 2010 the mission was extended by 12 months, with observation continuing until at least the end of 2011. After the successful conclusion of the First Survey, the spacecraft started its Second All Sky Survey on 14 February 2010, with more than 95% of the sky observed already and 100% sky coverage being expected by mid-June 2010.^[11]

Some planned pointing list data from 2009 have been released publicly, along with a video visualization of the surveyed sky.^[15]

On 17 March 2010, the first Planck photos were published, showing dust concentration within 500 light years from the Sun.^[17][18]

On 5 July 2010, the Planck mission delivered its first all-sky image.^[19]

The first public scientific result of Planck is the Early-Release Compact-Source Catalogue, released during the January 2011 Planck conference in Paris.^[20][21]

On 5 May 2014 a map of the galaxy's magnetic field created using Planck was published.^[22]

2013 data release

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background.^[23][24] This map suggests the Universe is slightly older than thought: according to the map, subtle fluctuations in temperature were imprinted on the deep sky when the Universe was about 370,000 years old. The imprint reflects ripples that arose as early in the existence of the Universe as the first nonillionth (10⁻³⁰) of a second. It is currently theorised that these ripples gave rise to the present vast cosmic web of galactic clusters and dark matter. According to the team, the Universe is 7001137980000000000♠13.798±0.037 billion years old, and contains 7000482000000000000♠4.82±0.05% ordinary matter, 7001258000000000000♠25.8±0.4% dark matter and 7001690000000000000♠69±1% dark energy.^[25][26][27] The Hubble constant was also measured to be 7001678000000000000♠67.80±0.77 (km/s)/Mpc.^{[23][25][28][29][30]}

Cosmological parameters from 2013 Planck results^[31][25]

Parameter	Symbol	Planck Best fit	Planck 68% limits	Planck+lensing Best fit	Planck+lensing 68% limits	Planck+WP Best fit	Planck+WP 68% limits	Planck+WP +HighL Best fit	Planck+WP +HighL 68% limits	Planck+lensing +WP+highL Best fit	Planck+lensing +WP+highL 68% limits	Planck+WP +highL+BAO Best fit	Planck+WP +highL+BAO 68% limits
Baryon density		0.022068	6998220700000000000♠0.02207±0.00033	0.022242	6998221700000000000♠0.02217±0.00033	0.022032	6998220500000000000♠0.02205±0.00028	0.022069	6998220700000000000♠0.02207±0.00027	0.022199	6998221799999999999♠0.02218±0.00026	0.022161	6998221400000000000♠0.02214±0.00024
Cold dark matter density		0.12029	6999119600000000000♠0.1196±0.0031	0.11805	6999118600000000000♠0.1186±0.0031	0.12038	6999119900000000000♠0.1199±0.0027	0.12025	6999119800000000000♠0.1198±0.0026	0.11847	6999118600000000000♠0.1186±0.0022	0.11889	6999118700000000000♠0.1187±0.0017
100x approximation to rs = DA (CosmoMC)		1.04122	7000104132000000000♠1.04132±0.00068	1.04150	7000104141000000000♠1.04141±0.00067	1.04119	7000104131000000000♠1.04131±0.00063	1.04130	7000104132000000000♠1.04132±0.00063	1.04146	7000104143999999999♠1.04144±0.00061	1.04148	7000104146999999999♠1.04147±0.00056
Thomson scattering optical depth due to reionization		0.0925	6998970000000000000♠0.097±0.038	0.0949	6998890000000000000♠0.089±0.032	0.0925	6998890000000000000♠0.089+0.012 −0.014	0.0927	6998910000000000000♠0.091+0.013 −0.014	0.0943	6998900000000000000♠0.090+0.013 −0.014	0.0952	6998920000000000000♠0.092±0.013
Power spectrum of curvature perturbations		3.098	7000310300000000000♠3.103±0.072	3.098	7000308500000000000♠3.085±0.057	3.0980	7000308900000000000♠3.089+0.024 −0.027	3.0959	7000309000000000000♠3.090±0.025	3.0947	7000308700000000000♠3.087±0.024	3.0973	7000309100000000000♠3.091±0.025
Scalar spectral index		0.9624	6999961600000000000♠0.9616±0.0094	0.9675	6999963500000000000♠0.9635±0.0094	0.9619	6999960300000000000♠0.9603±0.0073	0.9582	6999958500000000000♠0.9585±0.0070	0.9624	6999961400000000000♠0.9614±0.0063	0.9611	6999960800000000000♠0.9608±0.0054
Hubble's constant (km Mpc-1 s-1)		67.11	7001674000000000000♠67.4±1.4	68.14	7001679000000000000♠67.9±1.5	67.04	7001673000000000000♠67.3±1.2	67.15	7001673000000000000♠67.3±1.2	67.94	7001679000000000000♠67.9±1.0	67.77	7001678000000000000♠67.80±0.77
Dark energy density		0.6825	6999686000000000000♠0.686±0.020	0.6964	6999693000000000000♠0.693±0.019	0.6817	6999685000000000000♠0.685+0.018 −0.016	0.6830	6999685000000000000♠0.685+0.017 −0.016	0.6939	6999693000000000000♠0.693±0.013	0.6914	6999692000000000000♠0.692±0.010
Density fluctuations at 8h−1 Mpc		0.8344	6999834000000000000♠0.834±0.027	0.8285	6999823000000000000♠0.823±0.018	0.8347	6999829000000000000♠0.829±0.012	0.8322	6999828000000000000♠0.828±0.012	0.8271	6999823300000000000♠0.8233±0.0097	0.8288	6999826000000000000♠0.826±0.012
Redshift of reionization		11.35	7001114000000000000♠11.4+4.0 −2.8	11.45	7001108000000000000♠10.8+3.1 −2.5	11.37	7001111000000000000♠11.1±1.1	11.38	7001111000000000000♠11.1±1.1	11.42	7001111000000000000♠11.1±1.1	11.52	7001113000000000000♠11.3±1.1
Age of the Universe (Gy)		13.819	7001138130000000000♠13.813±0.058	13.784	7001137960000000000♠13.796±0.058	13.8242	7001138170000000000♠13.817±0.048	13.8170	7001138130000000000♠13.813±0.047	13.7914	7001137940000000000♠13.794±0.044	13.7965	7001137980000000000♠13.798±0.037
100× angular scale of sound horizon at last-scattering		1.04139	7000104148000000000♠1.04148±0.00066	1.04164	7000104156000000000♠1.04156±0.00066	1.04136	7000104146999999999♠1.04147±0.00062	1.04146	7000104148000000000♠1.04148±0.00062	1.04161	7000104159000000000♠1.04159±0.00060	1.04163	7000104162000000000♠1.04162±0.00056
Comoving size of the sound horizon at z = zdrag		147.34	7002147530000000000♠147.53±0.64	147.74	7002147700000000000♠147.70±0.63	147.36	7002147490000000000♠147.49±0.59	147.35	7002147470000000000♠147.47±0.59	147.68	7002147670000000000♠147.67±0.50	147.611	7002147680000000000♠147.68±0.45

2015 data release

Results from an analysis of Planck's full mission were made public on 1 December 2014 at a conference in Ferrara, Italy.^[32] A full set of papers detailing the mission results were released in February 2015.^[33] Some of the results include:

• More agreement with previous WMAP results on parameters such as the density and distribution of matter in the Universe, as well as more exact results with less margin of error.
• Confirmation of the Universe having a 26% content of dark matter. These results also raise related questions about the positron excess over electrons detected by the Alpha Magnetic Spectrometer, an experiment on the International Space Station. Previous research suggested that positrons could be created by the collision of dark matter particles, which could only occur if the probability of dark matter collisions is significantly higher now than in the early Universe. Planck data suggests that the probability of such collisions must remain constant over time to account for the structure of the Universe, negating the previous theory.
• Validation of the simplest models of inflation, thus giving the Lambda-CDM model stronger support.
• That there are likely only three types of neutrinos, with a proposed sterile neutrino flavour unlikely to exist.

Project scientists worked too with BICEP2 scientists to release joint research in 2015 answering whether a signal detected by BICEP2 was evidence of primordial gravitational waves, or was simple background noise from dust in the Milky Way galaxy.^[32] Their results suggest the latter.^[34]

Cosmological parameters from 2015 Planck results^[33][35]

Parameter	Symbol	TT+lowP 68% limits	TT+lowP +lensing 68% limits	TT+lowP +lensing+ext 68% limits	TT,TE,EE+lowP 68% limits	TT,TE,EE+lowP +lensing 68% limits	TT,TE,EE+lowP +lensing+ext 68% limits
Baryon density		6998222200000000000♠0.02222±0.00023	6998222600000000000♠0.02226±0.00023	6998222700000000000♠0.02227±0.00020	6998222500000000000♠0.02225±0.00016	6998222600000000000♠0.02226±0.00016	6998223000000000000♠0.02230±0.00014
Cold dark matter density		6999119700000000000♠0.1197±0.0022	6999118600000000000♠0.1186±0.0020	6999118400000000000♠0.1184±0.0012	6999119800000000000♠0.1198±0.0015	6999119300000000000♠0.1193±0.0014	6999118800000000000♠0.1188±0.0010
100x approximation to rs / DA (CosmoMC)		7000104085000000000♠1.04085±0.00047	7000104102999999999♠1.04103±0.00046	7000104106000000000♠1.04106±0.00041	7000104077000000000♠1.04077±0.00032	7000104087000000000♠1.04087±0.00032	7000104092999999999♠1.04093±0.00030
Thomson scattering optical depth due to reionization		6998780000000000000♠0.078±0.019	6998660000000000000♠0.066±0.016	6998670000000000000♠0.067±0.013	6998790000000000000♠0.079±0.017	6998630000000000000♠0.063±0.014	6998660000000000000♠0.066±0.012
Power spectrum of curvature perturbations		7000308900000000000♠3.089±0.036	7000306200000000000♠3.062±0.029	7000306400000000000♠3.064±0.024	7000309400000000000♠3.094±0.034	7000305900000000000♠3.059±0.025	7000306400000000000♠3.064±0.023
Scalar spectral index		6999965500000000000♠0.9655±0.0062	6999967700000000000♠0.9677±0.0060	6999968100000000000♠0.9681±0.0044	6999964500000000000♠0.9645±0.0049	6999965300000000000♠0.9653±0.0048	6999966700000000000♠0.9667±0.0040
Hubble's constant (km Mpc-1 s-1)		7001673100000000000♠67.31±0.96	7001678100000000000♠67.81±0.92	7001679000000000000♠67.90±0.55	7001672700000000000♠67.27±0.66	7001675100000000000♠67.51±0.64	7001677400000000000♠67.74±0.46
Dark energy density		6999685000000000000♠0.685±0.013	6999692000000000000♠0.692±0.012	6999693500000000000♠0.6935±0.0072	6999684400000000000♠0.6844±0.0091	6999687900000000000♠0.6879±0.0087	6999691100000000000♠0.6911±0.0062
Matter density		6999315000000000000♠0.315±0.013	6999308000000000000♠0.308±0.012	6999306500000000000♠0.3065±0.0072	6999315600000000000♠0.3156±0.0091	6999312100000000000♠0.3121±0.0087	6999308900000000000♠0.3089±0.0062
Density fluctuations at 8h−1 Mpc		6999829000000000000♠0.829±0.014	6999814900000000000♠0.8149±0.0093	6999815400000000000♠0.8154±0.0090	6999831000000000000♠0.831±0.013	6999815000000000000♠0.8150±0.0087	6999815900000000000♠0.8159±0.0086
Redshift of reionization		7000990000000000000♠9.9+1.8 −1.6	7000880000000000000♠8.8+1.7 −1.4	7000890000000000000♠8.9+1.3 −1.2	7001100000000000000♠10.0+1.7 −1.5	7000850000000000000♠8.5+1.4 −1.2	7000880000000000000♠8.8+1.2 −1.1
Age of the Universe (Gy)		7001138130000000000♠13.813±0.038	7001137990000000000♠13.799±0.038	7001137960000000000♠13.796±0.029	7001138130000000000♠13.813±0.026	7001138070000000000♠13.807±0.026	7001137990000000000♠13.799±0.021
Redshift at decoupling		7003109008999999999♠1090.09±0.42	7003108994000000000♠1089.94±0.42	7003108990000000000♠1089.90±0.30	7003109006000000000♠1090.06±0.30	7003109000000000000♠1090.00±0.29	7003108990000000000♠1089.90±0.23
Comoving size of the sound horizon at z = z*		7002144610000000000♠144.61±0.49	7002144890000000000♠144.89±0.44	7002144930000000000♠144.93±0.30	7002144570000000000♠144.57±0.32	7002144710000000000♠144.71±0.31	7002144810000000000♠144.81±0.24
100× angular scale of sound horizon at last-scattering		7000104105000000000♠1.04105±0.00046	7000104122000000000♠1.04122±0.00045	7000104126000000000♠1.04126±0.00041	7000104096000000000♠1.04096±0.00032	7000104106000000000♠1.04106±0.00031	7000104112000000000♠1.04112±0.00029
Redshift with baryon-drag optical depth = 1		7003105957000000000♠1059.57±0.46	7003105957000000000♠1059.57±0.47	7003105959999999999♠1059.60±0.44	7003105965000000000♠1059.65±0.31	7003105961999999999♠1059.62±0.31	7003105968000000000♠1059.68±0.29
Comoving size of the sound horizon at z = zdrag		7002147330000000000♠147.33±0.49	7002147600000000000♠147.60±0.43	7002147630000000000♠147.63±0.32	7002147270000000000♠147.27±0.31	7002147410000000000♠147.41±0.30	7002147500000000000♠147.50±0.24
Legend	68% limits: Parameter 68% confidence limits for the base ΛCDM model TT, TE, EE: Planck Cosmic microwave background (CMB) power spectra; here TT represents temperature power spectrum, TE is temperature-polarization cross spectrum, and EE is polarisation power spectrum. lowP: Planck polarization data in the low-ℓ likelihood lensing: CMB lensing reconstruction ext: External data (BAO+JLA+H0). BAO: Baryon acoustic oscillations, JLA: Joint Light-curve Analysis (of supernovae), H0: Hubble constant

See also

• Lambda-CDM model
• List of cosmological computation software
• Observational cosmology
• Physical cosmology

References

Further reading

• Dambeck, Thorsten (May 2009). "Planck Readies to Dissect the Big Bang". Sky & Telescope 117 (5): 24–28. OCLC 318973848. 

External links

Wikimedia Commons has media related to Planck (spacecraft).

Wikinews has related news: ESA launches Herschel Space Observatory and Planck Satellite

• ESA
  • Planck mission website
  • Planck science website
  • Planck operations website
  • Planck science results website
• NASA
  • Planck mission website
  • NASA/IPAC Planck archive

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