Two studies described by NASA on November 10, 2026, examine how the Laser Interferometer Space Antenna, or LISA, could detect planets through their effect on gravitational waves. The modeled systems contain two white dwarfs orbiting closely together and a planet whose gravity changes the motion of the stellar pair.
In NASA’s account of the research, Casey McGrath’s first paper examines the detection method and the planet masses and orbital periods it could identify. A second paper by McGrath and coauthors examines complementary observations with the James Webb Space Telescope. Both appeared in The Astrophysical Journal.
A Planet Alters the Binary’s Signal
The close stellar pair emits gravitational waves at a nearly continuous frequency. A planet causes the pair to move around the system’s common center of mass, adding a Doppler modulation to the signal. That modulation produces additional frequencies called sidebands.
The effect is related to the principle used in radial-velocity planet searches. In that method, astronomers measure changes in the wavelength of light as a star moves toward and away from the observer. A planet’s gravitational pull contributes to that motion. The proposed LISA method examines corresponding changes in gravitational radiation from a binary source.
The signal being measured originates from the compact stellar pair. The planet affects the pair’s motion, leaving a recurring pattern in the received waves. Detecting that pattern connects the observed signal to the orbital behavior of the larger system.
Three Spacecraft Form the Observatory
The Albert Einstein Institute’s description of LISA explains the planned instrument. Three spacecraft will form a triangle with sides measuring 2.5 million kilometers. They will follow Earth around the Sun and exchange laser light to measure changes in the distances between freely falling test masses inside the spacecraft.
Laser interferometry compares light signals to measure extremely small changes in distance. The test masses provide the reference points for the measurement. The surrounding spacecraft carry the telescopes and other equipment that allow the separated instruments to operate together as one observatory.
The institute identifies a target frequency band from 0.1 millihertz to 0.1 hertz. This band contains signals from compact stellar binaries and other sources with periods longer than those typically measured by ground-based gravitational-wave detectors. Placing the observatory in space permits the very long separation between its measuring points.
LISA Pathfinder tested technologies used for free-fall measurements and precision control. The full LISA mission applies these principles across three separate spacecraft rather than within a single technology-demonstration vehicle. The planned constellation turns the distance between spacecraft into part of the measuring instrument.
Extracting Sources From the Data
The Caltech, IPAC, and JPL team describes work on a global fit of LISA’s time-series data to create a catalog of sources. A time series records how the measured signal changes over successive observations. The global analysis accounts for signals from multiple objects contributing to the data.
The team’s modeling work includes compact binaries, massive black-hole mergers, and smaller black holes moving around much larger ones. These sources have different patterns of motion and radiation. Mathematical descriptions of those patterns connect the recorded measurements to physical properties of the emitting systems.
For a planet-bearing binary, the additional orbital motion is part of that physical description. The model contains the stellar binary’s signal together with the changes associated with the planet. A planet search uses the structure of the signal over time, rather than an image of the planetary surface.
Infrared Observations Provide a Second Measurement
The companion study examines infrared excess from planets around double white dwarfs. A planet can add infrared light beyond the amount expected from the stars. For a modeled system 500 light-years away, the researchers found that Webb could detect a planet about five times Jupiter’s mass, with ideal LISA observations sensitive to a sub-Jupiter planet.
These measurements concern different physical effects. LISA would measure changes associated with the system’s motion through gravitational waves. Webb would measure infrared radiation. The studies describe how those two observations could be combined for nearby systems as part of the science program of the planned space observatory.
