WMAP
Full Name: Wilkinson Microwave Anisotropy Probe
Phase: Operating
Launch Date: June 30, 2001
Mission Project Home Page: http://map.gsfc.nasa.gov/
Program(s): Astrophysics Explorers, Explorers
Analyses of a new high-resolution map of microwave light emitted only 380,000 years after the Big Bang appear to define our universe more precisely than ever before. The eagerly awaited results announced last year from the orbiting Wilkinson Microwave Anisotropy Probe resolve several long-standing disagreements in cosmology rooted in less precise data. Specifically, present analyses of above WMAP all-sky image indicate that the universe is 13.7 billion years old (accurate to 1 percent), composed of 73 percent dark energy, 23 percent cold dark matter, and only 4 percent atoms, is currently expanding at the rate of 71 km/sec/Mpc (accurate to 5 percent), underwent episodes of rapid expansion called inflation, and will expand forever. Astronomers will likely research the foundations and implications of these results for years to come.
Credit: WMAP Science Team, NASA
The WMAP mission addresses fundamental questions in cosmology: What is the geometry of the Universe? How did structures, such as galaxies and galaxy clusters, that we see in today’s sky come about? How old is the Universe, and what are its constituents?
Answers to these questions lie in the Cosmic Microwave Background (CMB), the remnant background radiation left over from the Big Bang, which is remarkably uniform over the entire sky, at an effective temperature of 2.7 degrees Kelvin. The CMB, smooth as it is, nevertheless contains tiny fluctuations in its temperature, on the level of one part in 100,000. From these fluctuations grew the structures in the Universe that we see today, and with a careful measurement of the properties of these fluctuations, much can be learned about the history and content of the Universe.
WMAP’s science goals demand 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 0.3°, a sensitivity of 20 µK per 0.3° square pixel, with systematic artifacts limited to 5 µK 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 Lagrange point, 1.5 million km from Earth. 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.
The Wilkinson Microwave Anisotropy Probe (WMAP) is named after Dr. David Wilkinson, a member of the science team and pioneer in the study of cosmic background radiation.