A Cosmic Cartographer; January 2001; Scientific American Magazine; by Charles L. Bennett, Gary F. Hinshaw and Lyman Page; 2 Page(s)

This summer the National Aeronautics and Space Administration is planning to launch a Delta 2 rocket carrying an 830-kilogram, four-meter-high spacecraft. Over the next three months the Microwave Anisotropy Probe (MAP) will maneuver into its target orbit around the sun, 1.5 million kilometers beyond Earth's orbit. Then the probe will begin its two-year mission, observing the cosmic microwave background (CMB) radiation in exquisite detail over the entire sky. Because this radiation was emitted nearly 15 billion years ago and has not interacted significantly with anything since then, getting a clear picture of the CMB is equivalent to drawing a map of the early universe. By studying this map, scientists can learn the composition, geometry and history of the cosmos.

As its name suggests, MAP is designed to measure the anisotropy of the CMB-the minuscule variations in the temperature of the radiation coming from different parts of the sky. MAP will be able to record differences of only 20 millionths of a kelvin from the radiation's average temperature of 2.73 kelvins. What is more, the probe can detect hot and cold spots that subtend less than 0.23 degree across the sky, yielding a total of about one million measurements. Thus, MAP's observations of the CMB will be far more detailed than the previous full-sky map, produced in the early 1990s by the Cosmic Background Explorer (COBE), which was limited to a seven-degree angular resolution.