Wilkinson Microwave Anisotropy Probe (WMAP)

Introduction

The Wilkinson Microwave Anisotropy Probe (WMAP) was a NASA mission that operated from 2001 to 2010. Its primary objective was to measure the temperature differences across the sky in the cosmic microwave background radiation (CMB), which is the afterglow of the Big Bang. WMAP provided a detailed picture of the early universe, leading to significant advancements in cosmology.

Mission Overview

WMAP was launched on June 30, 2001, and was named in honor of cosmologist David Wilkinson. The spacecraft was positioned at the second Lagrange point (L2), approximately 1.5 million kilometers from Earth. This location provided a stable environment with minimal interference from Earth's radiation.

Scientific Objectives

The primary scientific objectives of WMAP included:

Measuring the temperature fluctuations in the CMB.
Determining the geometry of the universe.
Constraining the parameters of the ΛCDM model.
Investigating the inflationary period of the early universe.
Studying the reionization epoch.

Instrumentation

WMAP was equipped with a set of five differential microwave radiometers that operated at frequencies of 23, 33, 41, 61, and 94 GHz. These instruments were designed to measure the temperature differences in the CMB with high precision. The radiometers were cooled to minimize thermal noise, and the spacecraft's spin-stabilized design allowed for continuous scanning of the sky.

Data Collection and Analysis

WMAP collected data by continuously scanning the sky in a pre-determined pattern. The data was then transmitted to Earth, where it underwent extensive processing and analysis. The mission's data analysis involved several steps:

Calibration of the radiometers.
Removal of foreground emissions from the Milky Way and other sources.
Construction of temperature maps of the CMB.
Statistical analysis to extract cosmological parameters.

Key Findings

WMAP's observations led to several groundbreaking discoveries:

The universe is approximately 13.8 billion years old.
The geometry of the universe is flat.
The universe is composed of approximately 4.6% ordinary matter, 24% dark matter, and 71.4% dark energy.
The first stars formed about 400 million years after the Big Bang.
The data provided strong evidence for the inflationary model of the early universe.

Legacy and Impact

WMAP's findings have had a profound impact on the field of cosmology. The mission's data has been used to refine models of the universe's evolution and to constrain theories of fundamental physics. WMAP's success paved the way for subsequent missions, such as the Planck spacecraft, which provided even higher resolution measurements of the CMB.

References