The European Space Agency (ESA) today gave the green light to two missions: one to find places just like home; the other to detect the biggest cataclysms in the history of the universe.
ESA’s Science Program Committee approved advancing Planetary Transits and Oscillations of stars (PLATO) to construction. In 2026, it will begin scouring the skies for alternative Earths, terrestrial planets at a distance from sunlike stars that are comfortable for life.
At the same time, the committee placed the Laser Interferometer Space Antenna (LISA) onto ESA’s roster of missions, and planners can now begin its detailed design. In 2034, LISA is scheduled to begin detecting gravitational waves in space; ripples that originate in the universe-shaking explosions produced when galaxies collide and the supermassive black holes at their cores spiral together and merge.
“We feel good,” says Karsten Danzmann of the Max Planck Institute for Gravitational Physics in Hanover, Germany, and head of the LISA consortium. “We know we’re going to fly, so we just have to work.”
LISA has had a long and difficult gestation. The idea for such a mission originated in the 1980s and was first proposed to ESA in the early 1990s: Fly three spacecraft in formation and, using lasers, measure the distance between them with exquisite precision to detect the fleeting squeeze and stretch of space when a gravitational wave passes by. Originally planned as a joint ESA-NASA mission, the U.S. agency pulled out in 2011 because of budget problems. ESA scaled back the design but LISA missed out on two earlier launch slots in ESA’s science mission program.
The first detection of gravitational waves by the U.S. ground-based detector Laser Interferometer Gravitational Observatory (LIGO) in 2015 gave LISA a boost followed by the success last year of ESA’s LISA Pathfinder mission, a demonstrator of the technology that would be needed for the full-scale detector. “LIGO and LISA Pathfinder both helped. It’s real astronomy now; [LIGO has found] four black holes and it will find many more. LISA Pathfinder showed that it will work, we just need to add longer arms and more laser power,” Danzmann says.
The success of LIGO has also given new impetus for U.S. involvement in LISA; NASA is now expected to contribute up to 20% of the roughly €1 billion cost of the mission, probably by contributing lasers and the telescopes to pick up their light.
The major frustration for the LISA team is the long wait until launch in 2034. It could fly much sooner but ESA can only afford to launch such large missions occasionally and there are two others already in the queue. It’s possible that ESA member states might pony up more money or one of the other large missions might stumble, so the LISA team is not sitting back. “The will is there to fly,” Danzmann says. “We will work as fast as possible to be ready to launch.”
The PLATO consortium, gathered today for a regular meeting in Stockholm, is now gearing up to move into construction. PLATO is a medium-sized ESA mission, with a budget below €500 million. The aim of the mission is to make a list of genuine Earth analogs: planets up to about 1.5 times Earth’s mass in the habitable zone around bright, sunlike stars. To find them, the spacecraft will be equipped with 26 telescopes, each 12 centimeters in diameter, which can continuously monitor about 50% of the sky.
Isabella Pagano of the Catania Astrophysical Observatory in Italy, a member of the PLATO consortium board, says its wide view is like looking up at the sky with the naked eye, but with eyes that can accurately measure the brightness of stars. Those measurements will detect the dips in stellar brightness when a planet passes in front of a star, revealing the planet’s size. Follow-up observations from the ground will add the planets’ masses to the catalog. PLATO will also closely monitor the stars themselves in search of “starquakes” that can reveal the age of the star and its planets. “The catalog will open up the possibility of studying the evolution of planetary systems,” Pagano says.