Laser Interferometer Space Antenna (LISA)

LISA is a space-based observatory dedicated to studying gravitational waves—minute distortions of spacetime produced by accelerating massive objects, including pairs of black holes as they orbit and merge. The mission is led by the European Space Agency (ESA), with NASA as a collaborative partner. Its three spacecraft will follow Earth around the Sun in a vast triangular formation. The mission is designed to observe low-frequency gravitational waves that are difficult or impossible to measure with ground-based detectors.

Laser beams exchanged between the spacecraft will measure changes in the distances between free-floating test masses carried inside them. Passing gravitational waves are expected to stretch and compress the triangle's arms by extremely small amounts. Combining measurements from all three spacecraft will allow researchers to identify signals and infer information about their sources. The mission's planned arm length is about 2.5 million kilometres. Its measurement approach builds on earlier space technology demonstrations, including ESA's LISA Pathfinder mission.

LISA is intended to study sources such as massive black-hole binaries and compact stellar remnants, including binary white dwarfs, neutron stars and black holes in the Milky Way. Gravitational waves provide information complementary to light: they can reveal the motion and properties of systems whose signals may be hidden or difficult to observe electromagnetically. The observations could help scientists investigate black-hole growth and evolution, test aspects of gravity, and search for signals from sources not yet known. These are research goals, not guaranteed discoveries.

ESA describes LISA as its first space-based observatory dedicated to gravitational-wave science. NASA's stated contributions include laser and telescope systems, charge-management devices for the test masses, data-analysis systems, and scientific and engineering expertise. ESA currently lists the launch as planned for 2035, from Europe's Spaceport in French Guiana on an Ariane 6 rocket. The date and mission plans are scheduled targets and may change as development continues.