NASA’s LISA Mission to Detect Exoplanets via Gravitational Waves in Double White Dwarf Systems

NASA’s Laser Interferometer Space Antenna (LISA), scheduled for launch in the mid-2030s, will detect gravitational waves emitted by massive orbiting objects. Two recent papers led by NASA astrophysicist Casey McGrath detail how LISA can also identify exoplanets orbiting double white dwarf binaries by detecting subtle modulations in the gravitational wave signals.

Double white dwarfs are compact star remnants orbiting each other closely, producing nearly continuous gravitational waves. When an exoplanet orbits such a binary, its gravitational pull induces a reflex motion, imprinting periodic Doppler-like sidebands onto the gravitational wave frequency detected by LISA.

This detection method is conceptually analogous to radial velocity techniques used in optical astronomy, where starlight oscillations caused by orbiting planets reveal planet presence. Here, gravitational wave sidebands act as carriers of information about the orbiting exoplanet’s mass and orbital period, offering a unique approach to identifying planets not easily observable by conventional methods.

Astronomers estimate about 10 million double white dwarf systems exist in the Milky Way with suitable orbital periods for LISA detection, with roughly 10,000 expected to be resolvable individually. Discovering exoplanets in these systems would establish a new category of planetary bodies beyond those found around single stars or isolated white dwarfs.

To confirm planets detected by LISA, researchers propose using the James Webb Space Telescope’s sensitive infrared instruments. Planets in these binaries emit distinct infrared excess light beyond that of the white dwarfs alone, enabling confirmation of planets several times Jupiter’s mass within approximately 500 light-years.

The LISA mission involves three spacecraft positioning in a triangular formation with sides 2.5 million kilometers apart, precisely measuring minuscule distance changes caused by passing gravitational waves. NASA contributes critical hardware and scientific expertise to this ESA-led initiative, advancing gravitational wave astronomy into new realms.

While gravitational waves provide an innovative channel for exoplanet discovery, the technique’s sensitivity depends on planet mass and orbit characteristics, with smaller planets or more complex system arrangements posing detection challenges. Cross-validation with infrared observations will be crucial to rule out false positives and verify discoveries.