Wilkinson Microwave Anisotropy Probe
186468
225737652
2008-07-15T04:11:25Z
Headbomb
1461430
/* Five-year data release */ c-e table
{{redirect-acronym |WMAP| the radio station [[WMAP (AM)]]}}
{{Infobox Space Telescope
|name = Wilkinson Microwave Anisotropy Probe
|image = [[Image:WMAP collage.jpg|230px]]
|caption =
|organization = [[NASA]]
|major_contractors =
|alt_names = MAP; Explorer 80
|nssdc_id =
|location = [[Lagrangian point|Lagrange]] 2
|orbit_type = [[Lissajous orbit]]
|accel_gravity =
|launch_date = [[30 June]] [[2001]], 19:46 [[GMT]]
|launch_location = [[Cape Canaveral Air Force Station]]
|launch_vehicle = [[Delta II]] rocket
|mission_length =
|deorbit_date =
|wavelength =
|mass = 840 kg
|style =
|diameter =
|area =
|focal_length =
|instrument_1_name = K-band 23 GHz
|instrument_1_characteristics = 52.8 arcminute beam
|instrument_2_name = Ka-band 33 GHz
|instrument_2_characteristics = 39.6 arcminute beam
|instrument_3_name = Q-band 41 GHz
|instrument_3_characteristics = 30.6 arcminute beam
|instrument_4_name = V-band 61 GHz
|instrument_4_characteristics = 21 arcminute beam
|instrument_5_name = W-band 94 GHz
|instrument_5_characteristics = 13.2 arcminute beam
|website = http://map.gsfc.nasa.gov
|as_of =
|stats_ref = <ref name="2003Bennett" /><ref name="2008Limon" /><ref name="news_facts" />
}}
The '''Wilkinson Microwave Anisotropy Probe''' ('''WMAP'''; also known as the '''[[Microwave]] [[Anisotropy]] [[Probe]]''' or '''MAP''' and '''Explorer 80''') is a [[satellite]] mission to survey the sky and measure the [[cosmic microwave background radiation|temperature]] of the radiant heat left over from the [[Big Bang]]. The mission is led by Professor [[Charles L. Bennett]] of Johns Hopkins University, and is a joint project between [[NASA]] [[Goddard Space Flight Center]] and [[Princeton University]].<ref name="2003PressRelease" /> The satellite was launched by a [[Delta II]] rocket on [[June 30]], [[2001]], at 19:46:46 GDT from the [[Kennedy Space Center]] in [[Florida]]. It is the successor to [[COBE]] and one of the series of medium-class ([[MIDEX]]) satellites in the NASA [[Explorer program]]. It is named after [[David Todd Wilkinson|Dr. David Wilkinson]], a member of the science team and pioneer in the study of cosmic background radiation, who died in September 2002.<ref name="2003PressRelease" />
WMAP has provided much higher accuracy measurements of many cosmological parameters than had been available from previous instruments. According to the [[Lambda-CDM model]] of the universe, WMAP data shows that the [[age of the universe|age of the observable universe]] is 13.73 ± 0.12 billion years old, with a [[Hubble's law|Hubble constant]] of 70.1 ± 1.3 km·s<sup>-1</sup>·Mpc<sup>-1</sup>. It also shows that the universe is composed of 4.6% "ordinary" [[Baryonic#Baryonic matter|baryonic matter]], of 23% unknown type of [[dark matter]], which does not emit or absorb light, 72% [[dark energy]], which acts to accelerate expansion and of less than 1% neutrinos. The data is consistent with a [[Shape of the universe|flat geometry]], with the ratio of energy density to the [[critical density]] Ω = 1.02 ± 0.02. Its results support the [[Lambda-CDM model]], as well as the [[physical cosmology|cosmological]] scenarios of [[cosmic inflation]]. It has also provided independent evidence for [[cosmic neutrino background]] radiation.<ref name="2008Hinshaw">Hinshaw et al. (2008)</ref>.
There are several unexplained features within the WMAP data, including an anomaly at the largest angular measurements of the [[quadrupole moment]], dubbed the "Axis of Evil", and a large [[WMAP cold spot|cold spot]]. WMAP was the ''Breakthrough of the Year for 2003'' according to [[Science (journal)|Science]] magazine.<ref name="2003Seife">Seife (2003)</ref> Mission results papers were #1 and #2 on the list of "Super Hot Papers in Science Since 2003".<ref name="incites">{{cite web | url=http://www.in-cites.com/hotpapers/shp/1-50.html | title="Super Hot" Papers in Science | publisher=in-cites | month=October | year=2005 | accessdate=2008-04-26}}</ref> As of 2008 the probe is continuing to take measurements, and is due to complete observations in September 2009.
== Objectives ==
[[Image:CMB Timeline75.jpg|thumb|A timeline of the universe, from inflation to WMAP]]
The goal of WMAP is to measure the minute temperature differences in the [[Cosmic microwave background radiation|Cosmic Microwave Background (CMB) radiation]]. Measurements of these anisotropies can be used to measure the [[geometry]], content and evolution of the [[universe]], and can be used to test the [[Big Bang]] model of the formation of the universe and the theory of [[cosmic inflation]].<ref name="2003Bennett" />
In order to do this, the mission aimed to create a full-sky map of the CMB with a resolution of 13 [[arcminute]]s using observations at multiple frequencies. The map was required to have the least amount of [[systematic error]]s possible in it, with no correlated noise on the pixels and accurate calibration, so that it was accurate on all angular scales greater than its resolution.<ref name="2003Bennett">Bennett et al. (2003a)</ref> The created map contains 3,145,728 pixels, and uses the [[HEALPix]] scheme for the pixelization of a sphere.<ref name="2003Bennettb" />
The philosophy behind the design of the telescope was to minimize the systematic errors, and control those that could not be minimized. The philosophy was adhered to even if it meant sacrificing some sensitivity or simplicity, or increasing the cost of the instrument.<ref name="2008Limon" />
The instrument can also measure the E-mode polarization of the CMB,<ref name="2003Bennett" /> as well as the polarization of the foregrounds, although it was not designed to be a true [[polarimeter]].<ref name="2008Hinshaw" /> The telescope had a design lifetime of 27 months, which consisted of 3 months getting to the L2 position, followed by 2 years of observing.<ref name="2003Bennett" />
== Development ==
[[Image:BigBangNoise.jpg|thumb|A comparison of the sensitivity of WMAP with COBE and Penzias and Wilson's telescope. Simulated data.]]
Prior to WMAP, there had been two space-based missions to observe the CMB. [[RELIKT-1]] provided upper limits on the CMB anisotropies before [[COBE]] measured the very large scale fluctuations. There were also a series of ground- and balloon-based experiments which looked at the small-scale fluctuations in small patches of sky; these included [[BOOMERanG experiment|Boomerang]], the [[Cosmic Background Imager]] and the [[Very Small Array]].
The MAP mission was proposed to NASA in 1995, and was selected in April 1996<ref name="news_facts">{{cite web | url=http://map.gsfc.nasa.gov/news/facts.html | title=WMAP News: Facts | publisher=NASA | date=[[22 April]] [[2008]] | accessdate=2008-04-27}}</ref> for a definition study. It was approved for development in 1997.<ref name="news_events">{{cite web | url=http://map.gsfc.nasa.gov/news/events.html | title=WMAP News: Events | publisher=NASA | date=[[17 April]] [[2008]] | accessdate=2008-04-27}}</ref>
WMAP has 45 times the sensitivity, and 33 times the angular resolution of its predecessor, the [[COBE]] satellite.<ref name="2008Limon">Limon et al. (2008)</ref>
== Description ==
[[Image:WMAP spacecraft diagram.jpg|thumb|WMAP spacecraft diagram]]
The primary reflectors on the telescope are a pair of nearly identical [[Gregorian]] 1.4 m by 1.6 m dishes, which look in opposite directions. These focus the signal onto a pair of nearly identical 0.9 m by 1.0 m secondary reflectors. The mirrors are shaped to optimize their performance, and are constructed from a [[carbon fibre]] shell on a [[Korex]] core, and are coated by thin layers of [[aluminium]] and [[silicon oxide]]. The signal is reflected from the secondary reflectors onto the corrugated feedhorns, which sit in a [[focal plane]] array box beneath the primary mirrors.<ref name="2003Bennett" />
[[Image:WMAP receivers.png|thumb|Illustration of WMAP's receivers]]
The receivers are differential [[radiometer]]s, meaning that the difference between a pair of telescope beams is measured. They are [[polarization]] sensitive. The signal is amplified by [[HEMT]] [[low-noise amplifier]]s. There are 20 feeds in total, 10 looking in each direction. Each radiometer uses one feed from each direction, meaning that the signal measured is the difference in the sky signal from opposite directions. The directions are separated in azimuth by around 180 degrees, and in total angle by around 141 degrees.<ref name="2003Bennett" />
To facilitate rejection of foreground signals from our own Galaxy, WMAP uses five separate frequency bands from 23 to 94 [[GHz]].<ref name="2003Bennett" />
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 90%;"
|- bgcolor="#B0C4DE" align="center"
|+ Properties of WMAP at different frequencies<ref name="2003Bennett" />
! Property !! K-band !! Ka-band !! Q-band !! V-band !! W-band
|-
| Central [[wavelength]] (mm) || 13 || 9.1 || 7.3 || 4.9 || 3.2
|-
| Central [[frequency]] ([[GHz]]) || 23 || 33 || 41 || 61 || 94
|-
| [[Bandwidth (signal processing)|Bandwidth]] (GHz) || 5.5 || 7.0 || 8.3 || 14.0 || 20.5
|-
| Beam size (arcminutes) || 52.8 || 39.6 || 30.6 || 21 || 13.2
|-
| Number of [[radiometer]]s || 2 || 2 || 4 || 4 || 8
|-
| System temperature ([[Kelvin|K]]) || 29 || 39 || 59 || 92 || 145
|-
| Sensitivity (mK s<math>^{1/2}</math>) || 0.8 || 0.8 || 1.0 || 1.2 || 1.6
|}
The base of the instrument is a 5 m diameter solar array. In addition to hosting [[solar panel]]s, the solar array also constantly keeps the instrument in shadow, and it is constantly angled at just over 22 degrees with respect to the sun during observations of the CMB. Upon this sits a bottom deck supporting the warm instrument's electronics and a top deck. The cold components of the telescope, namely the focal plane array and the mirrors, are separated from the warm components by a 33 cm long cylindrical, thermally isolating shell that sits on the top deck.<ref name="2003Bennett" />
The instrument is cooled to around 90 K using passive thermal radiators, which are connected directly to the low noise amplifiers. The telescope uses a total of 419 [[watt|W]] of power. The only heaters on the telescope are survival heaters for emergencies, and a heater located adjacent to the transmitters that is turned on when the transmitters are off to keep the thermal load constant. The temperature of the spacecraft is monitored using a series of [[platinum resistance thermometer]]s.<ref name="2003Bennett" />
Calibration is done using the dipole of the CMB and measurements of [[Jupiter]], with the beam patterns measured using Jupiter. Data is relayed daily from the telescope via a 2 GHz [[transponder]] providing a 667 [[kbs]] downlink to a 70 m [[Deep Space Network]] telescope. There are two transponders, one of which is redundant. They are turned on for the minimum possible time—around 40 minutes per day—to keep [[radio frequency interference]] to a minimum. The telescope is kept in position in all three axes using three [[reaction wheel]]s, [[gyroscope]]s, a pair of [[star tracker]]s and sun sensors, and is steered using 8 [[hydrazine]] [[thruster]]s.<ref name="2003Bennett" />
== Launch, trajectory and orbit ==
[[Image:WMAP trajectory and orbit.jpg|thumb|The trajectory and orbit of WMAP]]
The instrument arrived at the [[Kennedy Space Center]] on [[20 April]], [[2001]]; the following two months were spent testing the instrument and integrating it with the launch vehicle, a [[Boeing]] [[Delta II]] 7425 rocket. The telescope was launched from [[launch pad]] 17B of the [[Cape Canaveral Air Force Station]] on [[June 30]], [[2001]], at 19:46:46 [[GMT]], and was the 286th Delta launch. The observatory was exposed to space for the first time 5 minutes later, when the first-stage engine cut off and was ejected.<ref name="2008Limon" /><ref name="news_facts" />
The observatory switched to internal power five minutes before launch, and relied on its internal batteries until the solar array was deployed at 21:03 GMT. The instrument was turned on at 21:43 GMT, and it was monitored while it cooled down. It started observing two days later, at 19:18 GMT on [[2 July]], [[2001]], with in-flight testing running from the instruments launch until [[17 August]], [[2001]], when the instrument began to constantly observe.<ref name="2008Limon" />
After launch, the probe went through three Earth-Moon phasing loops, during which 7 burns fine-tuned its trajectory. The loops were also used to measure the instrument's [[sidelobe]]s. The probe then underwent a [[fly-by]] of the Moon at 16:37 on [[30 July]], [[2001]], which put it on a course for the L2 Sun-Earth [[Lagrangian point]]. Two corrections to the trajectory were made<ref name="2008Limon" /> during the 3 months it took for the probe to reach L2.<ref name="2003Bennett" /> It arrived at L2 on [[1 October]], [[2001]].<ref name="news_events" /> It is the first mission that uses L2 as a permanent observing station.<ref name="news_facts" />
[[Image:WMAP orbit.jpg|thumb|WMAP's orbit and sky scan strategy]]
The spacecraft's orbit at Lagrange 2, 1.5 million kilometers from Earth, was chosen in order to minimize the amount of contaminating emission from the Sun, Earth and Moon, and to help thermally stabilize the spacecraft. In order to view all of the sky without looking towards the sun, WMAP orbits around L2 in a [[Lissajous orbit]] of between 1 and 10 degrees,<ref name="2003Bennett" /> with a period of 6 months.<ref name="news_facts" /> Between the start of 2002 and mid-2006, a total of 12 station keeping burns were made to keep it in this orbit.<ref name="2008Limon" /> The telescope also spins once every 2 minutes and 9 seconds (0.464*nbsp;[[rpm]]) and precesses at a rate of 1 revolution per hour.<ref name="2003Bennett" /> WMAP measures all of the sky every 6 months,<ref name="news_facts" /> and completed its first full sky observation in April 2002.<ref name="news_events" />
== Foreground subtraction ==
WMAP observes in five frequency bands so that the foreground contamination of the CMB from our own galaxy (and also from extragalactic sources) can be measured and subtracted. The main emission mechanisms are [[synchrotron radiation]] and [[free-free emission]] dominant at the lower frequencies, with emission from [[astrophysical dust]] dominant at the higher frequencies. Due to the spectral properties of these emission mechanisms, they contribute in different amounts to the five frequencies, allowing for their identification and removal.<ref name="2003Bennett" />
There are a variety of methods to remove the foreground contamination. One method is to subtract existing maps of the emission from the WMAP measurements; another is to use known values for the spectra of the different components to identify them, and a third approach is to fit the data simultaneously for both the position and spectra of the foreground emission, optionally also using extra data sets. Foreground contamination can also be reduced by only using the parts of the full-sky map that have the least foreground contamination, whilst masking the rest.<ref name="2003Bennett" />
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 90%;"
|+ The five-year models of foreground emission at different frequencies. Synchrotron is red, free-free is green and thermal dust is blue.
|-
| [[Image:WMAP 2008 23GHz foregrounds.png|150px|23 GHz]] || [[Image:WMAP 2008 33GHz foregrounds.png|150px|33 GHz]] || [[Image:WMAP 2008 41GHz foregrounds.png|150px|41 GHz]] || [[Image:WMAP 2008 61GHz foregrounds.png|150px|61 GHz]] || [[Image:WMAP 2008 94GHz foregrounds.png|150px|94 GHz]]
|-
| 23 GHz || 33 GHz || 41 GHz || 61 GHz || 94 GHz
|}
== Measurements and discoveries ==
=== One-year data release ===
[[Image:Baby Universe.jpg|thumb|The first year map of the CMB]]
On [[11 February]] [[2003]], based on the one-year WMAP data, [[NASA]] issued a press release regarding the age and composition of the [[universe]]. This release included the "best baby picture" of the universe taken up to that point. According to NASA, this picture "contains such stunning detail that it may be one of the most important scientific results of recent years". The new data far exceeded previous CMB measurements in both accuracy and precision.<ref name="2003PressRelease">{{cite web | url=http://www.gsfc.nasa.gov/topstory/2003/0206mapresults.html | title=New image of infant universe reveals era of first stars, age of cosmos, and more | publisher=NASA / WMAP team | date=[[11 February]] [[2003]] | accessdate=2008-04-27}}</ref>
The WMAP team produced a number of sets of constraints on cosmological parameters from the WMAP first year results, based on the [[Lambda-CDM model]], using various combinations of data sets. Three of these sets are given below. The first set given is from the WMAP data alone, as is the second: the difference is the addition of another parameter: the running of the spectral indices, which is a prediction of some inflationary models. The third combines the constraints from WMAP with those from some other CMB experiments ([[ACBAR]] and [[CBI]]), as well as with constraints from the [[2dF Galaxy Redshift Survey]] and [[Lyman alpha forest]] measurements. Note that there are degeneracies between the different parameters, the most significant of which is between <math>n_s</math> and <math>\tau</math>. The errors given are at 68% confidence.<ref name="2003spergel" />
<center>
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; text-align:center;"
|- bgcolor="#B0C4DE" align="center"
|+ Best-fit [[Lambda-CDM model|cosmological parameters]] from WMAP one-year results<ref name="2003spergel">Spergel et al. (2003)</ref>
! Parameter !! Symbol !! Best fit (WMAP only) !! Best fit (WMAP, extra parameter) !! Best fit (all data)
|-
| [[Hubble's constant]] ( {{frac|km|[[parsec|Mpc]]·s}} ) || <math>H_0</math> || 0.72 ± 0.05 || 0.70 ± 0.05 || <math>0.71^{+0.04}_{-0.03}</math>
|-
| [[Baryon]]ic content || <math>\Omega_b h^2</math> || 0.024 ± 0.001 || 0.023 ± 0.002 || 0.0224 ± 0.0009
|-
| Matter content || <math>\Omega_m h^2</math> || 0.14 ± 0.02 || 0.14 ± 0.02 || <math>0.135^{+0.008}_{-0.009}</math>
|-
| [[Optical depth]] to [[reionization]] || <math>\tau</math> || <math>0.166^{+0.076}_{-0.071}</math> || 0.20 ± 0.07 || 0.17 ± 0.06
|-
| Amplitude || <math>A</math> || 0.9 ± 0.1 || 0.92 ± 0.12 || <math>0.83^{+0.09}_{-0.08}</math>
|-
| Scalar spectral index || <math>n_s</math> || 0.99 ± 0.04 || <math>0.93^{+0.07}_{-0.07}</math> || 0.93 ± 0.03
|-
| Running of spectral index || <math>dn_s / dk</math> ||—||-0.047 ± 0.04 || <math>-0.031^{+0.016}_{-0.017}</math>
|-
| Fluctuation amplitude at 8h<sup>−1</sup> Mpc|| <math>\sigma_8</math> || 0.9 ± 0.1 ||—|| 0.84 ± 0.04
|-
| [[Age of the universe]] ([[Annum|Ga]]) || <math>t_0</math> || 13.4 ± 0.3|| — || 13.7 ± 0.2
|-
| Total density of the universe || <math>\Omega_{tot}</math> || — || — || 1.02 ± 0.02
|}
</center>
Using the best fit to all data, and theoretical models, the WMAP team put constraints on the times that various important events happened within our universe. These include the redshift of [[reionization]], 17 ± 4, the redshift of [[decoupling]], 1089 ± 1 (as well as age of universe at decoupling, <math>379^{+8}_{-7}</math> kyr) and the redshift of matter/radiation equality, <math>3233^{+194}_{-210}</math>. They determined the thickness of the [[surface of last scattering]] to be 195 ± 2 in redshift, or <math>118^{+3}_{-2}</math> kyr. They were also able to determine the current density of baryons, <math>(2.5 \pm 0.1) \times 10^{-7} cm^{-1}</math>, and the ratio of the number of baryons to the number of photons, <math>(6.1^{+0.3}_{-0.2}) \times 10^{-10}</math>. WMAP's detection of an early reionization ruled out [[warm dark matter]].<ref name="2003spergel" />
The team also examined the emission from our galaxy at the WMAP frequencies, and produced a catalogue of 208 [[point source]]s. They also observed the [[Sunyaev-Zel'dovich effect]] at <math>2.5 \sigma</math> with the strongest source being the [[Coma cluster]].<ref name="2003Bennettb">Bennett et al. (2003b)</ref>
=== Three-year data release ===
[[Image:Microwave Sky polarization.png|thumb|A map of the polarization from the 3rd year results]]
The three-year WMAP data were released on [[March 17]], [[2006]]. The data included temperature and [[polarization]] measurements of the CMB, which provided further confirmation of the standard flat [[Lambda-CDM model]] and new evidence in support of inflation.
The 3-year WMAP data alone shows that the universe must have dark matter. Results were computed both only using WMAP data, and also with a mix of parameter constraints from other instruments, including other CMB experiments ([[ACBAR]], [[CBI]] and [[BOOMERANG]]), [[SDSS]], the [[2dF Galaxy Redshift Survey]], the [[Supernova Legacy Survey]] and constraints on the Hubble constant from the [[Hubble Space Telescope]].<ref name="2007Spergel" />
<center>
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; text-align:center;"
|- bgcolor="#B0C4DE" align="center"
|+ Best-fit [[Lambda-CDM model|cosmological parameters]] from WMAP three-year results<ref name="2007Spergel">Spergel et al. (2007)</ref>
! Parameter !! Symbol !! Best fit (WMAP only)
|-
| [[Hubble's constant]] ( {{frac|km|Mpc·s}} ) || <math>H_0</math> || <math>0.732^{+0.031}_{-0.032}</math>
|-
| [[Baryon]]ic content || <math>\Omega_b h^2</math> || 0.0229 ± 0.00073
|-
| Matter content || <math>\Omega_m h^2</math> || <math>0.1277^{+0.0080}_{-0.0079}</math>
|-
| [[Optical depth]] to [[reionization]] <sup>{{ref|a|[a]}}</sup> || <math>\tau</math> || 0.089 ± 0.030
|-
| Scalar spectral index ||<math>n_s</math> || 0.958 ± 0.016
|-
| Fluctuation amplitude at 8h<sup>−1</sup> Mpc ||<math>\sigma_8</math> || <math>0.761^{+0.049}_{-0.048}</math>
|-
| [[Age of the universe]] ([[Annum|Ga]]) || <math>t_0</math> || <math>13.73^{+0.16}_{-0.15}</math>
|-
| Tensor-to-scalar ratio <sup>{{ref|b|[b]}}</sup> || <math>r</math> || <0.65
|}
</center>
[a] {{note|a}} Optical depth to reionization improved due to polarization measurements.<ref name="2007Hinshaw">Hinshaw et al. (2007)</ref> <br>
[b] {{note|b}} < 0.30 when combined with [[SDSS]] data. No indication of non-gaussianity.<ref name="2007Spergel" /> <br>
=== Five-year data release ===
[[Image:WMAP 2008.png|thumb|5 year WMAP image of background cosmic radiation (2008)]]
The five-year WMAP data were released on [[February 28]], [[2008]]. The data included new evidence for the [[cosmic neutrino background]], evidence that it took over half a billion years for the first stars to reionize the universe, and new constraints on [[cosmic inflation]]. <ref name="2008PressRelease">{{cite web | url=http://map.gsfc.nasa.gov/news/ | title=WMAP Press Release — WMAP reveals neutrinos, end of dark ages, first second of universe | publisher=NASA / WMAP team | date=[[7 March]] [[2008]] | accessdate=2008-04-27}}</ref>
The improvement in the results came from both having an extra 2 years of measurements (the data set runs between midnight on [[10 August]] [[2001]] to midnight of the [[9 August]] [[2006]]), as well as using improved data processing techniques and a better characterization of the instrument, most notably of the beam shapes. They also make use of the 33GHz observations for estimating cosmological parameters; previously only the 41 and 61GHz channels had been used. Finally, improved masks were used to remove foregrounds.<ref name="2008Hinshaw" />
[[Image:WMAP 2008 TT and TE spectra.png|thumb|The five-year total-intensity and polarization spectra from WMAP]]
Improvements to the spectra were in the 3rd acoustic peak, and the polarization spectra.<ref name="2008Hinshaw" />
The measurements put constraints on the content of the universe at the time that the CMB was emitted; at the time 10% of the universe was made up of neutrinos, 12% of atoms, 15% of photons and 63% dark matter. The contribution of dark energy at the time was negligible.<ref name="2008PressRelease" />
The WMAP five-year data was combined with measurements from [[Type Ia supernova]] (SNe) and [[Baryon acoustic oscillations]] (BAO).<ref name="2008Hinshaw" />
[[Image:WMAP 2008 universe content.png|thumb|Matter content in the current universe]]
<center>
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 90%;"
|- bgcolor="#B0C4DE" align="center"
|+ Best-fit [[Lambda-CDM model|cosmological parameters]] from WMAP five-year results<ref name="2008Hinshaw" />
! Parameter !! Symbol !! Best fit (WMAP only) !! Best fit (WMAP + SNe + BAO)
|-
| [[Hubble's constant]] ( {{frac|km|Mpc·s}} ) || <math>H_0</math> || <math>0.719^{+0.026}_{-0.027}</math> || 0.701 ± 0.013
|-
| [[Baryon]]ic content || <math>\Omega_b h^2</math> || 0.02273 ± 0.00062 || 0.02265 ± 0.00059
|-
| Cold dark matter content || <math>\Omega_c h^2</math> || 0.1099 ± 0.0062 || 0.1143 ± 0.0034
|-
| [[Dark energy]] content || <math>\Omega_\Lambda</math> || 0.742 ± 0.030 || 0.721 ± 0.015
|-
| [[Optical depth]] to [[reionization]] || <math>\tau</math> || 0.087 ± 0.017 || 0.084 ± 0.016
|-
| Scalar spectral index || <math>n_s</math> || <math>0.963^{+0.014}_{-0.015}</math>|| <math>0.960^{+0.014}_{-0.013}</math>
|-
| Running of spectral index || <math>dn_s / dk</math> || −0.037 ± 0.028 || <math>-0.032^{+0.021}_{-0.020}</math>
|-
| Fluctuation amplitude at 8h<sup>−1</sup> Mpc || <math>\sigma_8</math> || 0.796 ± 0.036 || 0.817 ± 0.026
|-
| [[Age of the universe]] (Ga) || <math>t_0</math> || 13.69 ± 0.13 || 13.73 ± 0.12
|-
| Total density of the universe || <math>\Omega_{tot}</math> || <math>1.099^{+0.100}_{-0.085}</math> || 1.0052 ± 0.0064
|-
| Tensor-to-scalar ration || <math>r</math> || <0.20 || —
|}
</center>
The data puts a limits on the value of the tensor-to-scalar ratio, r < 0.20 (95% certainty), which determines the level at which gravitational waves affect the polarization of the CMB, and also puts limits on the amount of primordial [[non-gaussianity]]. Improved constraints were put on the redshift of reionization, which is 10.8 ± 1.4, the redshift of [[decoupling]], <math>1091.00^{+0.72}_{-0.73}</math> (as well as age of universe at decoupling, <math>375,938^{+3148}_{-3115}</math> years) and the redshift of matter/radiation equality, <math>3280^{+88}_{-89}</math>. <ref name="2008Hinshaw" />
The [[extragalactic]] source catalogue was expanded to include 390 sources, and variability was detected in the emission from [[Mars]] and [[Saturn]].<ref name="2008Hinshaw" />
{| border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 90%;"
|- bgcolor="#B0C4DE" align="center"
|+ The five-year maps at different frequencies from WMAP with foregrounds (the red band)
|-
| [[Image:WMAP 2008 23GHz.png|150px|23 GHz]] || [[Image:WMAP 2008 33GHz.png|150px|33 GHz]] || [[Image:WMAP 2008 41GHz.png|150px|41 GHz]] || [[Image:WMAP 2008 61GHz.png|150px|61 GHz]] || [[Image:WMAP 2008 94GHz.png|150px|94 GHz]]
|-
| 23 GHz || 33 GHz || 41 GHz || 61 GHz || 94 GHz
|}
== Future measurements ==
[[Image:Planck satellite.jpg|thumb|upright|Artist's impression of the [[Planck satellite]]]]
The original timeline for WMAP gave it two years of observations; these were completed by September 2003. Mission extensions were granted in both 2002 and 2004, giving the spacecraft a total of 8 observing years (the originally proposed duration), which end in September 2009.<ref name="news_facts" />
WMAP's results will be built upon by several other instruments that are currently under construction. These will either be focusing on higher sensitivity total intensity measurements or measuring the polarization more accurately in the search of [[B-mode polarization]] indicative of primordial [[gravitational wave]]s.
The next space-based instrument will be the [[Planck satellite]], which is currently being built and will launch towards the end of 2008. This instrument aims to measure the CMB more accurately than WMAP at all angular scales, both in total intensity and polarization. Various ground- and balloon-based instruments are being constructed to look for B-mode polarization, including [[Clover (telescope)|Clover]] and [[The E and B Experiment|EBEX]].
== References ==
{{Reflist|2}}
=== Technical pages ===
{{refbegin}}
* {{cite journal | title=The Microwave Anisotropy Probe (MAP) Mission | first=C. | last=Bennett | coauthors=et al. | journal=[[Astrophysical Journal]] | volume=583 | pages=1–23 | year=2003a | url=http://adsabs.harvard.edu/abs/2003ApJ...583....1B | doi=10.1086/345346}}
* {{cite journal | title=First-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Foreground Emission | last=Bennett | first=C. | coauthors=et al. | journal=Astrophysical Journal Supplement | volume=148 | pages=97–117 | year=2003b | doi=10.1086/377252}}
* {{cite journal | doi= 10.1086/513698 | title=Three-Year Wilkinson Microwave Anisotropy Probe (WMAP1) Observations: Temperature Analysis | first=G. | last=Hinshaw | coauthors=et al. | journal=Astrophysical Journal Supplement | volume=170 | pages=288–334 | year=2007}}
* {{cite journal | title=Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results | first=G. | last=Hinshaw | coauthors=et al. | journal=[[Astrophysical Journal]] Supplement (submitted) | year=2008 | url=http://lambda.gsfc.nasa.gov/product/map/dr3/pub_papers/fiveyear/basic_results/wmap5basic.pdf | id={{arxiv|0803.0732}}}}
* {{cite web | title=Wilkinson Microwave Anisotropy Probe (WMAP): Five–Year Explanatory Supplement |
first=M. | last=Limon | coauthors=et al. | date=[[20 March]] [[2008]] | url=http://lambda.gsfc.nasa.gov/product/map/dr3/pub_papers/fiveyear/supplement/WMAP_supplement.pdf | format=[[PDF]]}}
* {{cite journal | authorlink=Charles Seife | last=Seife | first= Charles | title=Breakthrough of the Year: Illuminating the Dark Universe | url=http://www.sciencemag.org/cgi/content/full/302/5653/2038 | journal=Science | year=2003 | volume=302 | pages=2038–2039 | doi=10.1126/science.302.5653.2038 | pmid=14684787}}
* {{cite journal | title=First-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters | last=Spergel | first=D. N. | coauthors=et al. | journal=Astrophysical Journal Supplement | volume=148 | pages=175–194 | year=2003 | url=http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:astro-ph/0302209 | doi=10.1086/377226}}
* {{cite journal | title=Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Implications for Cosmology | last=Sergel | first=D. N. | coauthors=et al. | journal=Astrophysical Journal Supplement | volume=170 | pages=377–408 | year=2007 | url=http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:astro-ph/0603449 | doi=10.1086/513700}}
{{refend}}
== External links ==
{{commonscat|WMAP}}
* [http://www.bioedonline.org/news/news.cfm?art=977 Sizing up the universe]
* [http://www.space.com/scienceastronomy/map_mission_basics_030211.html About WMAP and the Cosmic Microwave Background] - Article at Space.com
* [http://www.newscientist.com/article.ns?id=dn4879 Big Bang glow hints at funnel-shaped Universe], [[NewScientist]], [[2004-04-15]]
* [http://www.nasa.gov/home/hqnews/2006/mar/HQ_06097_first_trillionth_WMAP.html NASA [[March 16]], [[2006]] WMAP inflation related press release]
* {{cite journal | last = Seife | first = Charles |authorlink=Charles Seife | title=With Its Ingredients MAPped, Universe's Recipe Beckons | journal=Science | year=2003 | volume=300 | issue=5620 |
pages=730–731 | url=http://adsabs.harvard.edu/abs/1998RPPh...61...77K | doi=10.1126/science.300.5620.730 | pmid=12730575 }}
{{CMB_experiments}}
{{Explorer program}}
{{Space telescopes}}
[[Category:NASA probes]]
[[Category:Space telescopes]]
[[Category:Radio telescopes]]
[[Category:Artificial satellites currently in Lagrange points around the Earth]]
[[Category:Explorer program]]
[[Category:Current spaceflights]]
[[bn:উইলকিনসন মাইক্রোওয়েভ এনিসোট্রপি প্রোব]]
[[ca:WMAP]]
[[de:Wilkinson Microwave Anisotropy Probe]]
[[et:WMAP]]
[[es:WMAP]]
[[fr:Wilkinson Microwave Anisotropy Probe]]
[[it:WMAP]]
[[he:לוויין המחקר WMAP]]
[[hu:Wilkinson Microwave Anisotropy Probe]]
[[nl:Wilkinson Microwave Anisotropy Probe]]
[[ja:WMAP]]
[[pl:WMAP]]
[[pt:WMAP]]
[[ru:WMAP]]
[[fi:WMAP]]
[[sv:WMAP]]
[[zh:威尔金森微波各向异性探测器]]