The X-ray Maximum Mission (XMM-Newton) satellite is a major European X-ray space telescope observatory, and was the largest orbiting scientific payload ever built in Europe. It was launched on December 10, 1999, and is operated by the European Space Agency. In addition to its main X-ray telescope—the most sensitive ever built—it also carries a smaller monitor telescope that works in ultraviolet and visible light. That co-aligned telescope points at the same location in space as the X-ray telescope and allows astronomers to locate the X-ray sources immediately in a detailed visible light image.