LISA will search for low-frequency gravitational waves that will never be detectable by any terrestrial detectors, existing or planned. These low-frequency gravitational waves cannot be detected on Earth because Earth's gravitational field is constantly changing (due to atmospheric effects and ground motions). These changes cause motion of proof masses in a way which is indistinguishable from the motion caused by gravitational waves. Ground-based detectors like the Laser Interferometer Gravitational-Wave Observatory (LIGO) will view the high-frequency waves from transient phenomena, like supernovae and the final minutes of inspiraling neutron-star binaries. LISA will observe the lower frequency waves from quasi-periodic sources, like compact star binaries long before coalescence, and supermassive black-hole binaries in the final months of coalescence.

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