Farewell, then, to NASA's Wilkinson Microwave Anisotropy Probe (WMAP): the little satellite that could. Last month, the spacecraft fired its boosters for the final time and fell into a graveyard orbit around the Sun, where it will remain as a permanent fixture in the Universe it helped to decode.

Launched in June 2001, the WMAP makes a strong case to be considered one of the greatest scientific experiments of all time. It turned cosmology from informed guesswork into a precision science, and brought our fuzzy understanding of the nature of the Universe into breathtaking focus. Along the way, its findings yielded some of the most highly cited papers in physics — as well as bewitching images that introduced millions of people to the truths and enduring mysteries of the cosmos.

The WMAP studied the remnants of heat that lingered after the Big Bang, a pattern frozen in time when the Universe was only about 380,000 years old and which has since stretched to microwave wavelengths. Subtle differences seen in the texture of this 'cosmic microwave background' by the WMAP have revealed the geometry, composition and age of the Universe. The probe showed that the Universe is flat and probably endless, and produced the first fine-resolution, full-sky map of the cosmic microwave background. It also revealed how this original light is polarized — the blueprint for the first galaxy formation. Physicists have yet to encounter dark matter or dark energy, but the WMAP has already audited the expected contribution of these components to the Universe: 23.3% and 72.1%, respectively. And it has determined that ordinary matter makes up just 4.6% of the Universe, to within 0.1%.

The probe's discoveries have resonated far beyond the scientific sphere. When singer–songwriter Katie Melua sang, “We are 12 billion light years from the edge/That's a guess/No one can ever say it's true” in her 2005 hit Nine Million Bicycles, science writer Simon Singh complained that the lyrics did not reflect current scientific knowledge. The WMAP, after all, had recently determined the age of the Universe with great accuracy. Melua agreed to re-record the song using Singh's revision: “We are 13.7 billion light years from the edge of the observable Universe/That's a good estimate with well-defined error bars/And with the available information.” (See http://go.nature.com/ONJSQG.)

Science marches on, and a replacement for the WMAP is already in orbit: the European Space Agency's Planck satellite. Whatever this latest spacecraft may discover, the legacy of the Wilkinson Microwave Anisotropy Probe is assured.