The Rossi X-ray Timing Explorer was a NASA mission that was used to investigate bright cosmic X-ray sources by observing how their X-ray intensities change over a broad range of timescales from milliseconds to years. Three instruments designed to perform the observations were carried into space on a spacecraft that was launched in December, 1995, and that operated until January, 2012.

A nearby star is pummeling a companion planet with a barrage of X-rays a hundred thousand times more than the Earth receives from the Sun. Credit: NASA/CXC/NSF/IPAC/2MASS (see the 



