Wilkinson Microwave Anisotropy Probe

Wilkinson Microwave Anisotropy Probe

Wilkinson Microwave Anisotropy Probe (WMAP) satellite
Names	Explorer 80 MAP Microwave Anisotropy Probe MIDEX-2 WMAP
Mission type	Cosmic microwave background Astronomy
Operator	NASA
COSPAR ID	2001-027A
SATCAT no.	26859
Website	http://map.gsfc.nasa.gov/
Mission duration	27 months (planned) 9 years (achieved)[1]
Spacecraft properties
Spacecraft	Explorer LXXX
Spacecraft type	Wilkinson Microwave Anisotropy Probe
Bus	WMAP
Manufacturer	NRAO
Launch mass	840 kg (1,850 lb)[2]
Dry mass	763 kg (1,682 lb)
Dimensions	3.6 × 5.1 m (12 × 17 ft)
Power	419 watts
Start of mission
Launch date	30 June 2001, 19:46:46 UTC[3]
Rocket	Delta II 7425-10 (Delta 246)
Launch site	Cape Canaveral, SLC-17B
Contractor	Boeing Launch Services
Entered service	1 October 2001
End of mission
Disposal	Graveyard orbit
Deactivated	20 October 2010[4]
Last contact	19 August 2010
Orbital parameters
Reference system	Sun-Earth L2 orbit
Regime	Lissajous orbit
Main telescope
Type	Gregorian
Diameter	1.4 × 1.6 m (4 ft 7 in × 5 ft 3 in)
Wavelengths	23 GHz to 94 GHz
Instruments
Pseudo-Correlation Radiometer
Wilkinson Microwave Anisotropy Probe mission patch Explorer program ← HETE-2 (Explorer 79) RHESSI (Explorer 81) →

The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP and Explorer 80), was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang.^[5][6] Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University.^[7] The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002),^[7] who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by European Space Agency (ESA) in 2009.

WMAP's measurements played a key role in establishing the current Standard Model of Cosmology: the Lambda-CDM model. The WMAP data are very well fit by a universe that is dominated by dark energy in the form of a cosmological constant. Other cosmological data are also consistent, and together tightly constrain the Model. In the Lambda-CDM model of the universe, the age of the universe is 13.772±0.059 billion years. The WMAP mission's determination of the age of the universe is to better than 1% precision.^[8] The current expansion rate of the universe is (see Hubble constant) 69.32±0.80 km·s⁻¹·Mpc⁻¹. The content of the universe currently consists of 4.628%±0.093% ordinary baryonic matter; 24.02%+0.88%
−0.87% cold dark matter (CDM) that neither emits nor absorbs light; and 71.35%+0.95%
−0.96% of dark energy in the form of a cosmological constant that accelerates the expansion of the universe.^[9] Less than 1% of the current content of the universe is in neutrinos, but WMAP's measurements have found, for the first time in 2008, that the data prefer the existence of a cosmic neutrino background^[10] with an effective number of neutrino species of 3.26±0.35. The contents point to a Euclidean flat geometry, with curvature (${\displaystyle \Omega _{k}}$) of −0.0027+0.0039
−0.0038. The WMAP measurements also support the cosmic inflation paradigm in several ways, including the flatness measurement.

The mission has won various awards: according to Science magazine, the WMAP was the Breakthrough of the Year for 2003.^[11] This mission's results papers were first and second in the "Super Hot Papers in Science Since 2003" list.^[12] Of the all-time most referenced papers in physics and astronomy in the INSPIRE-HEP database, only three have been published since 2000, and all three are WMAP publications. Bennett, Lyman A. Page Jr., and David N. Spergel, the latter both of Princeton University, shared the 2010 Shaw Prize in astronomy for their work on WMAP.^[13] Bennett and the WMAP science team were awarded the 2012 Gruber Prize in cosmology. The 2018 Breakthrough Prize in Fundamental Physics was awarded to Bennett, Gary Hinshaw, Norman Jarosik, Page, Spergel, and the WMAP science team.

In October 2010, the WMAP spacecraft was derelict in a heliocentric graveyard orbit after completing nine years of operations.^[14] All WMAP data are released to the public and have been subject to careful scrutiny. The final official data release was the nine-year release in 2012.^[15][16]

Some aspects of the data are statistically unusual for the Standard Model of Cosmology. For example, the largest angular-scale measurement, the quadrupole moment, is somewhat smaller than the Model would predict, but this discrepancy is not highly significant.^[17] A large cold spot and other features of the data are more statistically significant, and research continues into these.