COBE — Cosmic Background Explorer (1989–1993)

The Cosmic Background Explorer (COBE) measured the cosmic microwave background's perfect blackbody spectrum at 2.725 K, detecting minute temperature anisotropies of just one part in 100,000. These pioneering observations earned John Mather and George Smoot the 2006 Nobel Prize in Physics, providing the foundation for precision cosmology. COBE's data was 30% more accurate than earlier balloon-borne experiments, establishing a baseline that Planck later refined.