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WMAP is a scientific mission to map the universe.

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WMAP is a NASA satellite mission led by Professor Charles L. Bennett of Johns Hopkins University. WMAP's mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. The WMAP satellite was launched by a Delta II rocket on June 30, 2001, at 3:46 p.m. EDT from Cape Canaveral Air Force Station, Florida, USA. WMAP is the acronym for Wilkinson Microwave Anisotropy Probe.

Artist depiction of the WMAP satellite at the L2 point.

WMAP was the Breakthrough of the Year for 2003 according to Science magazine. Mission results papers were #1 and #2 on the list of "Super Hot Papers in Science Since 2003."

The goal of WMAP is to map out minute differences in the Cosmic Microwave Background (CMB) radiation in order to help test theories of the nature of the universe. It is the successor to COBE and one of the series of medium-class explorer (MIDEX) satellites.

WMAP is named after Dr. David Wilkinson, a member of the science team and pioneer in the study of cosmic background radiation. The science goals of the WMAP broadly dictate that the relative CMB temperature be measured accurately over the full sky with high Angular resolution and sensitivity. The overriding priority in the design was the need to control systematic errors in the final maps. The specific goal of WMAP is to map the relative CMB temperature over the full sky with an angular resolution of at least 0.3º, a sensitivity of 20 K per 0.3º square pixel, with systematic artifacts limited to 5 K per pixel.

To achieve these goals, WMAP uses differential microwave radiometers that measure temperature differences between two points on the sky. WMAP observes the sky from an orbit about the L2 Sun-Earth Lagrangian point, 1.5 million km from Earth. This is on the line from the Sun to the Earth, but at a larger distance from the Sun than the Earth, where the sum of the (larger) Sun's gravity and the (smaller) Earth's gravity is equal to the centripetal force needed for an object to have the same Orbital period in its orbit around the Sun as the Earth, with the result that the object will stay in that relative position. Gravity from the Sun is 2% (118 m/s) less than at the Earth (5.9 mm/s), while the increase of required centripetal force is half of this (59 m/s). The sum of both effects is balanced by the gravity of the Earth, which is here also 177 m/s.

WMAP spacecraft.
WMAP spacecraft diagram.

This vantage point offers an exceptionally stable environment for observing, since the observatory can always point away from the Sun, Earth and Moon while maintaining an unobstructed view to deep space. WMAP scans the sky in such a way as to cover ~30% of the sky each day and as the L2 point follows the Earth around the Sun WMAP observes the full sky every six months. To facilitate rejection of foreground signals from our own Galaxy, WMAP uses five separate frequency bands from 22 to 90 GHz.

On February 11, 2003, 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 three-year WMAP data were released at noon on March 17, 2006. The data included temperature and Polarization measurements of the CMB, which provide stronger confirmation of the standard flat Lambda-CDM model and new evidence in support of inflation.

Findings so far from WMAP.

WMAP image.
WMAP image of background cosmic radiation.

WMAP provided higher accuracy measurements of many cosmological parameters than had been available from previous instruments. According to current models of the universe, WMAP data show:

  • The universe is 13.7 billion 200 million years old.
  • The universe is composed of:
    • 4% ordinary baryonic matter.
    • 22% of an unknown type of Dark matter, which does not emit or absorb light.
    • 74% of a mysterious Dark energy, which acts to accelerate expansion.
  • The cosmological scenarios of cosmic inflation are in better agreement with the three-year data, although there is still an unexplained anomaly on the largest angular measurement of the quadrupole moment.
  • The Hubble constant is 70 (km/s)/Mpc, +2.4/-3.2.
  • The data are consistent with a flat geometry.
  • CMB polarization results provide experimental confirmation of cosmic inflation favoring the simplest versions of the theory.

Instruments which also measured fluctuations in the Cosmic Microwave Background

Cosmic microwave background experiments

Earlier missions before WMAP.

Before WMAP, there were several incremental improvements in our maps of the Cosmic Microwave Background:

  • COBE - measured the very large scale fluctuations.
  • Cosmic Anisotropy Telescope - measured the very small scale fluctuations in small regions of the sky.
  • BOOMERanG - measured fluctuations with improved precision.
  • Maxima - measured fluctuations with improved precision.
  • Cosmic Background Imager - measured the very small scale fluctuations with improved precision in small regions of the sky.
  • Very Small Array - measured fluctuations with improved precision in small regions of the sky.


Future instruments are expected to build upon WMAP's results. These include:

  • Clover - improved precision and B-mode polarization measurements.
  • Planck Surveyor - improved precision.

Past and current WMAP science team members are:

  • Charles L. Bennett (PI) , Johns Hopkins University .
  • Mark Halpern , University of British Columbia .
  • Gary Hinshaw , NASA Goddard Space Flight Center .
  • Norman Jarosik , Princeton University .
  • Al Kogut , NASA Goddard Space Flight Center .
  • Michele Limon , NASA Goddard Space Flight Center/SSAI .
  • Stephan Meyer , University of Chicago .
  • Lyman Page , Princeton University .
  • David Spergel , Princeton University .
  • Greg Tucker , Brown University .
  • David Wilkinson , Princeton University .
  • Ed Wollack , NASA Goddard Space Flight Center .
  • Edward L. (Ned) Wright , University of California- Los Angeles .
  • Rachel Bean , Cornell University .
  • Olivier Dore , University of Toronto .
  • Michael Nolta , University of Toronto .
  • Eiichiro Komatsu , Univ. of Texas, Austin .
  • Hiranya Peiris, University of Chicago .
  • Licia Verde , Univ. of Pennsylvania .
  • Chris Barnes , Princeton University .
  • Michael Greason , NASA Goddard Space Flight Center .
  • Robert Hill , NASA Goddard Space Flight Center .
  • Alan Kogut , NASA Goddard Space Flight Center .
  • Michele Limon, NASA Goddard Space Flight Center .
  • Nils Odegard , NASA Goddard Space Flight Center .
  • Greg Tucker , Brown University .
  • Janet Weiland , NASA Goddard Space Flight Center .

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