ESA clears path for LISA gravitational wave mission

The Laser Interferometer Space Antenna (LISA) mission, aimed at detecting gravitational waves in space, has been approved by the European Space Agency at a meeting of its Science Programme Committee. After many years of development and delays, the mission is now scheduled to go ahead in 2034.

Gravitational waves are ripples in space-time caused by the movement of very massive objects, such as black holes. Originally predicted in the early 20th century by Albert Einstein, they were not detected until 2015, when the Laser Interferometer Gravitational-wave Observatory (LIGO) in the US identified a signal caused by two black holes spiralling towards each other and merging; it has since detected two other similar events.

The LISA mission will create a space-based observatory many times larger than LIGO. It will send three identical spacecraft into an orbit following the Earth's path around the sun; the craft will fly in an equilateral triangle formation, with each side 2. 5 million km long and measured by lasers. The craft will be kept on station using thrusters which control the position extremely precisely using a neutral gas as fuel; this will ensure that their position relative to each other does not change unless a gravitational wave passes through their location. This would only move them by a very small amount of the order of picometres, but measurement equipment whose precision was proven by the LISA Pathfinder mission which is soon to come to an end will detect their movement. Because of the immense distance between the three craft, LISA will be much more sensitive than LIGO, and ESA hopes it will be able to detect the merging of supermassive black holes millions of times larger, but much further away than the events detected by LIGO.